VAPOR INTRUSION FROM REGULATORY, TECHNICAL,

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1 VAPOR INTRUSION FROM REGULATORY, TECHNICAL, AND LEGAL PERSPECTIVES Presented by the American Bar Association Section of Environment, Energy, and Resources, Section of State and Local Government Law and Center for Professional Development

2 American Bar Association Center for Professional Development 321 North Clark Street, Suite 1900 Chicago, IL Submit a Question Visit to submit a question on the content of this course to program faculty. We ll route your question to a faculty member or qualified commentator in 2 business days. The materials contained herein represent the opinions of the authors and editors and should not be construed to be the action of the American Bar Association Section of Environment, Energy, and Resources, Section of State and Local Government Law or Center for Professional Development unless adopted pursuant to the bylaws of the Association. Nothing contained in this book is to be considered as the rendering of legal advice for specific cases, and readers are responsible for obtaining such advice from their own legal counsel. This book and any forms and agreements herein are intended for educational and informational purposes only American Bar Association. All rights reserved. This publication accompanies the audio program entitled Vapor Intrusion from Regulatory, Technical, and Legal Perspectives broadcast on June 7, 2016 (event code: CE1606TLP).

3 TABLE OF CONTENTS 1. Presentation Slides 2. Vapor Intrusion: Regulatory, Technical, and Legal Perspectives (Presentation Slides) Ravi Arulanantham 3. OSWER Technical Guide for (June 2015) 4. Memo from OSWER to Superfund National Policy Managers, Regions 1-10, Subject: Transmittal of OSWER Directive , Assessing Protectiveness at Sites for Vapor Intrusion. Supplement to the Comprehensive Five-Year Review Guidance (December 3, 2012) 5. Memo from OSWER to Region 9 Superfund Division Staff and Management, Subject: EPA Region 9 Response Action Levels and Recommendations to Address Near-Term Inhalation Exposure to TCE in Air from Subsurface Vapor Intrusion (July 9, 2014) 6. Memo from OSWER to Superfund Division Directors, EPA Regions 1-10, Subject: Compilation of Information Relating to Early/Interim Actions at Superfund Sites and the TCE IRIS Assessment (August 27, 2014) 7. Federal Register Vol. 81, No. 39, Part II: Environmental Protection Agency (February 29, 2016)

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5 Vapor Intrusion from Regulatory, Technical, and Legal Perspectives Tuesday, June 7, :00 PM Eastern Sponsored by the Section of Environment, Energy, and Resources, Section of State and Local Government Law, and the ABA Center for Professional Development Faculty Ravi Arulanantham, Ph.D. Senior Principal Geosyntec Consultants. Inc. Walnut Creek, CA

6 Presentation Overview Overview of VI Pathway (5 min) Why is VI so Challenging? (5 min) State VI Guidance (4 min) Assessment Challenges and Solutions (8 min) Mitigation Options (8 min) Overview What is Vapor Intrusion? What is Vapor Intrusion? Human receptors Vapor intrusion is the migration of subsurface chemicals into indoor air of overlying structures Volatile chemicals in soil and groundwater can migrate through soil, cracks, sewers, utilities into indoor air.

7 General Conceptual Site Model Overview Conceptual Preferential Pathway Model Utility conduits or the bedding material around them are thought to potentially facilitate transport of vapors from sources to buildings, i.e., serve as preferential pathway. Overview VOC VOC

8 Overview of VI Pathway Vapor intrusion assessment & decision making is technically complicated, challenging and can be expensive. Overview of VI Pathway Vapor intrusion has now become an important Exposure Pathway (current and future) that has to be evaluated: In cleanup of contaminated sites In human health risk assessments For remedy selection For site closure/nfa letters In site assessments in real estate transactions ASTM E / E (includes VI evaluation) In toxic tort and property damage litigation

9 Presentation Overview Overview of VI Pathway Why is VI so Challenging? State VI Guidance Assessment Challenges and Solutions Mitigation Options Why is VI so Challenging? Not practicable to provide alternative air. Volatile organic chemicals (VOCs) of concern are common and can be found in indoor air > risk-based screening levels o Household cleaners, pesticides o Air fresheners o Household solvents o Gun cleaners o Natural gas o Tobacco smoke o Gasoline in mowers, gas cans o Some plastics and plastic toys o Paints and architectural coatings o Glues and Adhesives o Dry-cleaned clothes, mothballs o Carpets and furniture o Plywood and building materials

10 Why is VI so Challenging? Very low screening levels for indoor air Background levels in outdoor air can exceed RBSLs for some VOCs in many urban areas Evaluation of background contributions to indoor air is challenging EPA/State empirical attenuation factors are very conservative hence low concentrations of VOCs in soil and groundwater can be an issue Temporal and spatial variability in indoor air Temperature, air pressure, rainfall, soil moisture & building ventilation can affect indoor air measurements Influence of preferential pathways Why is VI so Challenging? Petroleum vs Chlorinated Solvents A morass of new and changing regulatory guidance Increasing data needs for MLE assessments Need to consider long term & short term exposures o Rapid assessment and prompt response required o Potential evacuation scenarios Understanding uncertainties associated w/ VI modeling VI mitigation standard practice not well defined o Lack of VI certification programs and standards o Current standards based on radon technology Need innovative tools to improve confidence in risk management decisions for both short & long time frames

11 Why is VI so Challenging? Typical Benzene Background Concentrations (µg/m 3 ) Source Media Median 90 %ile CARB LA Station USEPA IA Review Outdoor Indoor ND MT DEQ Indoor Batterman Garage Compared to residential risk-based screening level of µg/m Ambient background o VOCs in urban air Indoor sources o VOCs emitted from consumer products and building materials VOCs from background sources can appear in sub-slab Degreasers, Gun cleaners Background Sources If you sample indoor air, you will detect these Toluene ( ) m/p-xylene ( ) Benzene ( ) o-xylene ( ) Ethylbenzene ( ) Methylene chloride ( ) Chloroform ( ) Tetrachloroethylene ( ) Carbon tetrachloride ( ) 1,1,1-Trichloroethane ( ) Trichloroethylene ( ) 1,2-Dichloroethane ( ) 1,1-Dichloroethylene ( ) Vinyl chloride ( ) cis 1,2-Dichloroethylene ( ) 1,1-Dichloroethane ( ) Total Percent Detections Values in parentheses are reporting limits in µg/m 3 Source: Dawson and McAlary,

12 Background Sources How to distinguish background from VI sources? Typical Ranges of VOC Concentrations Background vs Vapor Intrusion PCE 111TCA TCE 11DCE Source = vapor intrusion Source = background Concentration (ug/m3) Max 95th % 50th % Background Database Background Database Background Database Background Database USEPA Empirical Attenuation Factors 1 Sampling Medium Groundwater Groundwater (fine-grained soil) Sub-slab soil gas Near-source soil gas Crawl Space Attenuation Factor Residential Buildings (1000 fold attenuation) (2000 fold attenuation) 0.03 (33 fold attenuation) 0.03 (33 fold attenuation) 1.0 (no attenuation) 1 U.S. EPA, 2015 Indoor air concentration Attenuation Factor = Soil-gas concentration

13 TCE: Changing Screening Levels 16 Indoor Air 600 Groundwater Concentration (µg/m 3 ) Concentration (µg/l) Year Year TCE: Short-Term Action Levels US EPA Regions and several states have adopted different short-term action levels for TCE. Region or State US EPA Region 9 (Accelerated Response Action Level) Residential (µg/m 3 ) Commercial (µg/m 3 ) 2 8 US EPA Region 10 (Removal Action Level) 2 9 Massachusetts (Imminent Hazard) 6 24 New Hampshire (Action Level) 2 9 New Jersey (Rapid Action Level) 4 18 Indiana (Action Level) 20 New York (Immediate Action Level)

14 Multiple Lines of Evidence Chemistry Weather Geology Hydrology Building Biology Vapor Intrusion More Likely High Source Conc., Lower IA RBCs Heating Season, Strong Winds Coarse- Grained Soils, Vertically Fractured Media, Shallow Water Table, Large Water Table Fluctuations No Slab, Sumps, Low AER, Colder Climates No Biodegrad ation Vapor Intrusion Less Likely Low Source Conc., Higher IA RBCs Moderate Climate, Minimal Wind, Laterally Extensive Fine- Grained Layers with High Moisture Content Thick Capillary Fringe, Deep Water Table Positive Bldg Pressure, High AER, Intact Slab Degradable COCs Conditions These factors can be addressed qualitatively or quantitatively Increase VI Pathway Sampling Indoor air o Multiple sampling rounds Sub-slab o Multiple samples per building Soil vapor o Multiple locations and depths How many samples? How many rounds? How long to sample? How to find the maximum? Do these extra samples improve risk management decisions?

15 Petroleum VI Guidance (PVIG) PVI is different than VI for chlorinated compounds { Atmosphere Oxygen and Indoor Air PVI frequently assessed, but rarely shown to be a complete pathway { Vadose Zone Soil Gas Methane Natural biodegradation in soil mitigates Production? VI of (this occurs frequently when the vapor source zone is anaerobic) petroleum compounds PVIG focuses on identifying site conditions where PVI is not of concern (exclusion criteria) o Presence/absence of NAPL o Depth of source (e.g., contaminated groundwater) Vapor Migration Advective Soil Gas Flow Soil Source (residual or NAPL) basement Aerobic Biodegradation Hydrocarbon Vapor Migration Oxygen Vapor Migration Groundwater Source From API, 2004 Aerobic Zone Anaerobic Zone PVI Exclusion Criteria EPA Office of Underground Storage Tanks has developed a database focused on petroleum hydrocarbon sites Data analysis used to identify source-receptor distance where PVI is not of concern Source Vertical Exclusion Criteria Dissolved Plume NAPL Plume USEPA OUST (2015) 6 feet 15 feet ITRC (2014) 5 feet feet NJDEP (2013) 5 10 feet 30 feet Cal/EPA SWRCB (2012) 5 10 feet 30 feet

16 California Low Threat Closure Policy Adopted August 2012, by State Water Resources Control Board Provides exclusion criteria for vapor intrusion pathway investigation at petroleum UST sites 1000x bioattenuation factor when sufficient vadose zone oxygen demonstrated 5 to 10 feet bioattenuation zone for dissolved plume sites 30 feet bioattenuation zone for sites with LNAPL Overview Overview of VI Pathway Why is VI so Challenging? State Vapor Intrusion Guidance Assessment Challenges and Solutions Mitigation Options ` `

17 The Morass of Vapor Intrusion Guidance Many different agencies have issued vapor intrusion guidance, and those guidance documents and the associated standards have changed over time. It is important to understand what the purpose of the vapor intrusion analysis is, what agency will oversee the analysis, and what guidance documents apply. Many states have their own guidance documents for vapor intrusion. Geosyntec link provides helpful and relevant guidance documents State VI Guidance/Rule Originally published (C) Laurent C. Levy Courtesy of Gradient, as prepared for the National Ground Water Association, April

18 California VI Guidance Summary Final Vapor Intrusion Guidance (Oct. 2011) Requires an eleven step approach Greater focus on multiple lines of evidence evaluation More conservative default sub-slab soil gas screening evaluation (0.05 vs in USEPA 2012) Expectation for multiple sampling events and recommends permanent soil vapor sampling probes for site investigation Guidance on use of passive samplers for indoor air sampling Detailed guidance on mitigation and public outreach in separate documents CHHSLs do not apply to VI (October 2015 HHRA Note 3) Adopted EPA Region 9 Response Action Levels (Note 5) Other Guidance Interstate Technology & Regulatory Council (ITRC) o Coalition of personnel from federal and state agencies, tribes and public and industry stakeholders o 2007 Guidance documents o cid=28&subtopicid=39 ASTM Phase I standard: ASTM E o Requires a vapor intrusion screening o ASTM E : Standard Guide for Vapor o Encroachment screening on property involved in real estate transactions

19 Overview Overview of VI Pathway Why is VI so Challenging? State VI Guidance Assessment Challenges and Solutions Indoor Air Sampling Challenges Mitigation Options Indoor Air Sampling Challenges & Solutions Background Sources Comparison to Typical Indoor Air Data Compound-Ratio Analysis (sub-slab vs indoor) Portable Mass Spectrometers Building Pressure Cycling Stable Isotope Analysis Spatial Variability High Volume Sampling (ESTCP ER 13-22) Multi-Increment Sampling (AFCEE BAA) Temporal Variability Long-Term Passive Sampling (ESTCP ER 08-30) Mass Flux Monitoring (ESTCP ER 15-03) Preferential Pathways Pneumatic Testing and Tracer Testing

20 Indoor Air Sampling Challenges & Solutions Building Pressure Cycling o To clarify background sources & identify acute risks Stable Isotope Analysis o To fingerprint VOCs High Volume Samples o To manage spatial variability Passive Sampling o To manage temporal variability Mass Flux Monitoring o To reduce temporal variability Pneumatic Testing and Tracer Testing o To evaluate preferential pathways and optimize mitigation

21 Indoor Air Sampling Challenges & Solutions Deflate Building Inflate Building Change in indoor concentration indicates contribution from subsurface (Berry-Spark et al, 2004 and McHugh et al, ESTCP ER-0707) Indoor Air Sampling Challenges & Solutions Atom Carbon Hydrogen Chlorine Oxygen Ratio 13 C/ 12 C 2 H/ 1 H 37 Cl/ 35 Cl 18 O/ 16 O and 17 O/ 16 O C ( ) δ 13 C Biodegradation Adsorption, Dilution Progressive vaporization Fraction of Contaminant Remaining δ 37 Cl Indoor Air Manufactured Products Range δ 13 C Soil Vapor or Groundwater igure 7. Illustration of the potential to use compound specific isotope nalysis to distinguish between physical processes and biodegradation in he field.

22 Indoor Air Sampling Challenges & Solutions Fan or Vacuum Summa canister Lung Box Discharge Sample Port Vacuum Gauge Essentially the same kit as an SVE pilot test Typical flows of scfm at inches W.C. Indoor Air Sampling Challenges & Solutions Developed by the University of Waterloo (Ontario, Canada) Commercialized since 2010 Strong correlation with Summa canister results Patent pending for use in quantitative soil vapor sampling Passive Waterloo Membrane Sampler

23 Real Time Monitoring with Portable GC/MS Building survey to sub-ppbv levels Use to identify preferential pathways or indoor sources HAPSITE GC/MS o Analyze for target VOCs in SIM mode o ~10 minute sample time o Can also be run in scan mode Overview Overview of VI Pathway Why is VI so Challenging? State VI Guidance Assessment Challenges and Solutions Mitigation Options

24 The VI mitigation consist of following general concepts Mitigation Concept Cut-off VI pathways Reverse VI pathways Direct treatment Building material/design management Material Reverse VI Pathway Direct Treatment Cut-off VI Pathway Mitigation Options Cut-off VI Pathways o Sub-Slab Depressurization (Active or Passive) o Aerated Flooring (new construction) o Membrane Barrier (new construction) o Slab surface and conduit sealing Reverse VI Pathways o Building Pressurization Direct Mitigation o Indoor Air Filtration o Building Ventilation Safe Design o Intrinsically Safe Building Design (new construction)

25 Sub-Slab Depressurization SSD System: Low Vacuum, High Flow rate, no treatment Passive SSD SSD System: High Vacuum, Low Flow rate, with Treatment Active SSD Aerated Flooring A plastic form is used to create a continuous void below concrete slabs and concrete is poured over the forms.

26 Membrane Barrier Manufactured Geomembrane Barrier Geo-membrane Barrier Fluid-applied Geomembrane Barrier Slab Surface and Conduits Sealing Sealants & Caulks Slab Surface Coating Photo: Land Sciences TM Conduit Sealing

27 Building Pressurization HVAC system modified to pressurize the building. ΔP of 0.01 to 0.08 in-h2o Vapor pathway changed Building Pressurization Air Filtration and Building Ventilation Air Purifiers Building Ventilation (Natural or Forced)

28 Typical Installation Cost Existing Buildings Sub-slab depressurization No exhaust air treatment Cost $/SF* Building Conditions $1-3 Single family residential $2-4 Single story commercial/warehouse $4-10 Multi-story residential/commercial $10+ Complex buildings/codes * Mitigated area Note: does not include cost of investigation, design, permits, regulatory reporting Typical Installation Cost New Buildings Cost $/SF* System Type $1-3 Conventional radon (liner/gravel) $3-7 Spray-on asphaltic liner $1-3 Aerated floor system Courtesy of Land Sciences Technologies Note: does not include cost of investigation, design, permits, regulatory reporting

29 Is Mitigation Working? Indoor air tests o Often required by agency; requires good background forensic skills o Can provide line of evidence for background source o Costly and inefficient way to show performance Radon tests o Qualitative indicator of performance o Not always a direct correspondence with VOCs Sub-slab concentration o Below SS action level? o Typically decreases after system start-up Mass flux measurements o Exhaust gas concentration and flow rate o Compare to theoretical maximum flux from source Vacuum (active systems) o Physical evidence of downward air flow o Easily measured, easily monitored Rapid Response - What to Do Ventilation o Increase air exchange rate by factor of 2 to 4 (higher for initially tight building) o Opening upper windows could exacerbate vapor flux into building HVAC Modifications o Work with mechanical contractor to evaluate whether building HVAC can be modified to create positive pressure o 100% reductions are feasible Indoor air treatment o 200 HealthMate TM 450 portable units installed at a building in NH o TCE concentrations reduced ~42 to 87% in performance tests Sealing cracks o May work well if major vapor entry points are identified o Multiple/hidden entry points can limit effectiveness o 0 to 50% reduction might be expected (EPA, 1993)

30 Key Takeaways Typical Approach Groundwater sampling Soil gas sampling Sub-slab sampling Indoor air sampling Compare to screening levels Better Approach Develop a conceptual site model Select appropriate lines of evidence Develop site-specific screening levels Negotiate regulatory approval Implement response (rapid) options Provide robust documentation Thank You

31 Faculty Bethany Dreyfus Assistant Regional Counsel U.S. EPA Region IX Objectives Taking a look at: How Vapor Intrusion has impacted EPA work at area-wide Superfund sites Impact of TCE health risk assessment on Vapor Intrusion investigations and mitigation strategies at these sites Opinions expressed in this presentation are that of the presenter and not necessarily those of the US EPA.

32 EPA Vapor Intrusion Guidance 2002 EPA Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils 2015 OSWER Final Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Sources to Indoor Air [OSWER Publication ; June 2015] VI Guidance - Key Components Risk management decision-making framework based on multiple lines of evidence Flexible framework for planning and conducting VI investigations to evaluate sites and buildings Includes assessment approach for nonresidential buildings

33 2015 EPA VI Guidance Institutional Controls Need to layer multiple types of ICs Governmental, proprietary, enforcement instruments, notice Land use is not necessarily limited Unique non-interference issues operation of remedial components, including HVAC use of informational mechanisms EPA Region 9 VI Site Evaluation Reliance on multiple lines of evidence and multiple sampling rounds to increase confidence in decision-making, consistent with OSWER Guidance Assessing sites on building-by-building basis Consideration of pre-emptive mitigation

34 Vapor Intrusion and TCE More than 850 Superfund sites have TCE contamination TCE History on EPA s IRIS database Draft Health Assessment posted on IRIS in 1987 Draft withdrawn in 1989 (in interim, EPA R9 used Cal/EPA number) Final TCE Health Assessment posted on IRIS in September IRIS TCE Health Assessment September 2011, EPA finalized TCE Health Assessment (see Toxicological Review of TCE Established TCE as known human carcinogen Kidney Liver Non-hodgkins lymphoma Identified TCE non-cancer effects Immune system, central nervous system, endocrine system Fetal cardiac development

35 TCE Health Protective Risk Range Chronic cancer toxicity risk range ( ) for 30 year residential exposure lowered to: μg/m 3 Non-cancer toxicity expressed as a Hazard Quotient (HQ) established at: 2 μg/m 3 Using both cancer risk range and non-cancer HQ truncates TCE health protective risk range: µg/m 3 for residential exposures 3 8 µg/m 3 for commercial/industrial exposures (8-hour work day) Impact of Less-than-Lifetime Exposure IRIS generally established for impacts from chronic, long term exposure TCE health risk assessment found fetal cardiac malformations, i.e. developmental impacts Developmental impacts by definition are not chronic, so appropriate to look at less-than-lifetime exposure scenario (Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions, EPA 1991)

36 EPA Region IX Accelerated RALs July 9, 2014 Region 9 TCE Accelerated Response Action Level Recommendations Memorandum Establishes Response Action Levels (RALs) to be protective of sensitive populations Considerations for expedited sampling analysis turnaround Provides for implementation of interim response actions to lower levels above RALs Provides tiered response actions for RALs at which to take Accelerated Responses (>HQ) and Urgent Responses (>HQx3) R9 Interim TCE Accelerated and Urgent Response Action Levels

37 EPA HQ 2014 TCE Memorandum August 27, 2014 EPA OSWER TCE Memorandum Affirms IRIS non-cancer toxicity evaluation Encourages use of Interim and Early Response Actions to ensure protectiveness of sensitive populations Others Using EPA s IRIS Assessment ATSDR: Rescinded of 540 μg/m 3 as intermediate-duration (< year) Minimum Risk Level and found IRIS RfC of 2 μg/m 3 as protective of developmental effects States adopting RfCs: NH-DES (2013), Mass-DEP (2014), California DTSC (2014), Connecticut DPH and DEEP (2015), New York DOH (2015), Indiana DEM (2016) Alliance for Risk Assessment (ARA): Recommended applying IRIS assessment for TCE to less-than-lifetime exposures Ontario Ministry of the Environment (2013)

38 State of Vapor Intrusion and TCE EPA structuring investigation, sampling, and monitoring to account for potential accelerated response Using Interim Actions to address elevated TCE in indoor air Encouraging use of pre-emptive mitigation and accelerated source cleanups Faculty Kathleen B. Campbell, Esq. Partner Manko, Gold, Katcher & Fox, LLP

39 Presentation Overview Key Takeaways from 2015 EPA Guidance Implications for Site Owners Investigation and Remediation Real Estate Transactions Toxic Tort and Property Damage Litigation Observations & Strategy Considerations Photo 2008 Peter Craven Key Takeaways: 2015 EPA Guidance Multiple lines of evidence for vapor intrusion assessment Role of preferential pathways (vapors follow the path of least resistance) Vapor intrusion in the workplace EPA v. OSHA

40 Key Takeaways: 2015 EPA Guidance (cont d) Vapor intrusion in the workplace (cont d) OSHA permissible exposure limits (PELs) can be orders of magnitude greater than EPA VI screening levels (VISLs) EPA previously did not regulate workplace exposure if the contaminant was used in the workplace Photo Yen Hung Lin Dreamstime.com Key Takeaways: 2015 EPA Guidance (cont d) Vapor intrusion in the workplace (cont d) In 2015 guidance, EPA claims broad authority and distinct responsibilities to address VI in both residential and non-residential settings Specifically recommends that EPA VISLs apply in lieu of OSHA PELs (Sec ) PELs described as outdated and inadequate

41 Implications for Site Owners Investigation and Remediation Real Estate Transactions Toxic Tort and Property Damage Litigation Photo Tony Tremblay istockphoto.com Implications for Site Owners Investigation and Remediation Old sites may come back to life CERCLA 5-year reviews Assessing Protectiveness at Sites for Vapor Intrusion: Supplement to the Comprehensive Five-Year Review Guidance, OSWER (Dec. 3, 2012) Potential for reopeners under state cleanup programs-- formal process in some states; ad hoc in others Photo Robert Keenan Dreamstime.com

42 Implications for Site Owners Investigation and Remediation (cont d) EPA proposed rulemaking to use VI in Hazard Ranking System under CERCLA Sites previously not eligible for the Superfund National Priorities List (NPL) may become eligible Public comment period closed on April 29, 2016 See 81 Fed. Reg (Feb. 29, 2016) Implications for Site Owners Real Estate Transactions Due diligence considerations ASTM E Standard Practice for Phase I Environmental Site Assessments VI as a component of All Appropriate Inquiry under CERCLA Requires investigation of VI risk is VI a recognized environmental condition? Consider vapor migration from off-site source

43 Implications for Site Owners Real Estate Transactions (cont d) Due diligence considerations (cont d) May be difficult to reconcile EPA guidance recommendations with time constraints of a deal Cost Factor Breeze393 Dreamstime Stock Photos & Stock Free Images Implications for Site Owners Real Estate Transactions (cont d) Understanding Risk and Managing Potential Liabilities Possible exposure points Site reopeners Potential continuing obligations to maintain CERCLA liability protection Impact of development/future changes in use Third-party tort claims by tenants, future residents, adjacent property owners

44 Implications for Site Owners Real Estate Transactions (cont d) Understanding Risk and Managing Potential Liabilities (cont d) How to manage risk? Mitigation measures Contracting Environmental insurance Photo Ivelinr Dreamstime.com Implications for Site Owners Toxic Tort and Property Damage Litigation Based on Traditional Legal Theories, Seeking (Mostly) Traditional Remedies Complaints may include statutory (CERCLA, RCRA, etc.), contractual, and common law claims (nuisance, negligence, trespass, etc.) Potential relief includes personal injury, medical monitoring, diminution in property value, remediation/restoration, punitive damages

45 Implications for Site Owners Toxic Tort and Property Damage Litigation (cont d) But Unique Defense Issues Do Arise Statute of Limitations -- When did the plaintiff know of the injury? Is it a continuing tort? Medical monitoring -- Cost of monitoring for a latent disease caused by exposure to hazardous substances in the indoor air Implications for Site Owners Toxic Tort and Property Damage Litigation (cont d) Unique Defense Issues (cont d) Differing Scientific Risk Levels and Role of EPA Screening Levels ** Remember: Exceedance of a screening level does not equate with risk! Class Actions developing case law here; see Ebert, et al. v General Mills, Inc., 2016 U.S. App. LEXIS 9233 (8 th Cir. May 20, 2016)

46 Implications for Site Owners Toxic Tort and Property Damage Litigation (cont d) Unique Defense Issues (cont d) Developing a case around what was knowable and when groundwater pathway v. VI pathway Role of background concentrations Settlement future claims; Medicare compliance Aminemhammdi Dreamstime Stock Photos & Stock Free Images Observations & Strategy Considerations Closed sites may come back to life. At sites that have not yet been cleaned up, VI assessment is now often a critical element of investigation and remediation.

47 Observations & Strategy Considerations (cont d) Planning is key! Assemble the right team Understand how sampling results may be used before you sample Consider role of background concentrations Develop communication plan if there is potential current exposure Take into account timing and cost of multiple lines of evidence approach Consider early mitigation as a tool to manage risk

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49 VAPOR INTRUSION Regulatory, Technical, and Legal Perspectives Ravi Arulanantham, Ph.D Tuesday, June 7, :00 PM Eastern Sponsored by the ABA Center for Professional Development Faculty Ravi Arulanantham, Ph.D. Senior Principal Geosyntec Consultants. Inc. Walnut Creek, CA

50 Presentation Overview Overview of VI Pathway (5 min) Why is VI so Challenging? (5 min) State/other VI Guidance (3 min) Assessment Challenges and Solutions (8 min) Mitigation Options (5 min) Overview What is Vapor Intrusion? What is Vapor Intrusion? Human receptors Vapor intrusion is the migration of subsurface chemicals into indoor air of overlying structures Volatile chemicals in soil and groundwater can migrate through soil, cracks, sewers, utilities, etc. into indoor air

51 General Conceptual Site Model Overview Conceptual Preferential Pathway Model Utility conduits or the bedding material around them are thought to potentially facilitate transport of vapors from sources to buildings, i.e., serve as preferential pathway. Overview VOC VOC

52 Overview of VI Pathway Vapor intrusion assessment & decision making is technically complicated, challenging and can be expensive Overview of VI Pathway Vapor intrusion has now become an important Exposure Pathway (current and future) that has to be evaluated: In cleanup of contaminated sites In human health risk assessments For remedy selection For site closure/nfa letters In site assessments in real estate transactions ASTM E / ASTM E (includes VI evaluation) In toxic tort and property damage litigation

53 Overview of VI Pathway Potential Impacts to Projects are Significant Sensitive subject for many stakeholders PRP s, homeowners, employees, building owners & occupants, regulators, adverse litigants, public & media The subject of new and changing regulatory guidance and litigation Timeframe for assessment and response can be very short Re-opening of Closed Sites VI ROD Amendments Difficult Risk Communication Potential evacuation scenarios Overview of VI Pathway Vapor Intrusion may be of concern for range of chemical release Vapor sites Intrusion Sites Dry cleaners Manufacturing locations with degreasers Gasoline retail / refineries Landfills Hazardous waste management facilities Under a wide range of regulatory programs CERCLA RCRA NCP Compliance EPA s brownfields grantees/prospective purchaser State Lead

54 EPA VI Screening Levels for >100 Chemicals Overview of VI Pathway Most Common VI Chemicals VI Chemicals of of Potential Concern Chlorinated Solvents Trichloroethylene (TCE) Perchloroethylene (PCE) Trichloroethane (TCA) Petroleum Hydrocarbons Benzene Methane Radon Presentation Overview Overview of VI Pathway Why is VI so Challenging? State Vapor Intrusion Guidance Assessment Challenges and Solutions Mitigation Options

55 Why is VI so Challenging? Not practicable to provide alternative air. Volatile organic chemicals (VOCs) of concern are common and can be found in indoor air > risk-based screening levels Household cleaners, pesticides Air fresheners Household solvents and gun cleaners Natural gas Tobacco smoke Gasoline in cars, mowers, gas cans Some plastics and plastic toys Paints and architectural coatings Glues and Adhesives Dry-cleaned clothes, mothballs Carpets and furniture Plywood and building materials Why is VI so Challenging? Very low screening levels for indoor air Background levels in outdoor air can exceed RBSLs for some VOCs in many urban areas Evaluation of background contributions to indoor air is challenging EPA/State empirical attenuation factors are very conservative hence low concentrations of VOCs in soil and groundwater can be an issue Temporal and spatial variability in indoor air measurements Temperature, air pressure, rainfall & soil moisture and building ventilation among others can all affect indoor air measurements Influence of preferential pathways

56 Why is VI so Challenging? Petroleum VI Versus Chlorinated solvents VI A morass of new and changing regulatory guidance. Increasing data needs and interpretation for MLE assessments Need to consider both long term as well as short term exposures Rapid assessment and prompt response required Potential evacuation scenarios Understanding uncertainties associated with vapor intrusion modeling VI mitigation standard practice not well defined Lack of VI certification programs and standards Current standards based on radon mitigation technology Need innovative tools to improve confidence in risk management decisions for both short and long time frames Why is VI so Challenging? Why are VI Screening Levels So Low? MCL for TCE = 5 µg/liter of water Average adult drinks 2 liters per day MCL dose = 5 µg/l x 2 L/day = 10 µg/day Equivalent MCL for TCE in indoor air Average adult breathes 20 cubic meters per day 20 m 3 /day = 20,000 L/day If MCL dose for indoor air = 10 µg/day 10 µg/day / 20,000 L/day = µg/l of air = 0.5 µg /m 3 = EPA residential RSL based on cancer risk over 30 years

57 Why is VI so Challenging? Typical Benzene Background Concentrations (µg/m 3 ) Source Media Median 90 %ile CARB LA Station USEPA IA Review Outdoor Indoor ND MT DEQ Indoor Batterman Garage Compare to residential risk-based screening level of µg/m Background Sources Ambient background VOCs in urban air Indoor sources VOCs emitted from consumer products and building materials VOCs from background sources can appear in sub-slab Degreasers, Gun cleaners If you sample indoor air, you will detect these Toluene ( ) m/p-xylene ( ) Benzene ( ) o-xylene ( ) Ethylbenzene ( ) Methylene chloride ( ) Chloroform ( ) Tetrachloroethylene ( ) Carbon tetrachloride ( ) 1,1,1-Trichloroethane ( ) Trichloroethylene ( ) 1,2-Dichloroethane ( ) 1,1-Dichloroethylene ( ) Vinyl chloride ( ) cis 1,2-Dichloroethylene ( ) 1,1-Dichloroethane ( ) Total Percent Detections Values in parentheses are reporting limits in µg/m 3 Source: Dawson and McAlary,

58 Background Sources How to distinguish background from VI sources? Typical Ranges of VOC Concentrations Background vs Vapor Intrusion PCE 111TCA TCE 11DCE Source = vapor intrusion Source = background Concentration (ug/m3) Max 95th % 50th % Background Database Background Database Background Database Background Database Vapor Intrusion Timeline MA DEP Hillside School Investigation Air-Superfund Guidance J&E Model Published ASTM RBCA Guidance CDOT Redfields Sites RCRA EI Supplemental VI Guidance RCRA Guidance OSWER Draft VI Guidance ITRC VI Guidance OSWER Draft Final VI Guidance Public Comment Release Low Threat Closure Policy > 10 Years ASTM VI Standard E2600 TCE Toxicity Reassess. New EPA Region 9 TCE Policy South Bay DTSC Sites Letter HHRA Note 5 OSWER Tech Guide

59 US EPA Guidance In June, 2015, US EPA s Office of Solid Waste and Emergency Response (OSWER) issued two key guidance documents 1. OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from (Applies to all volatile organic compounds, including chlorinated solvents) 2. Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (Applies to petroleum hydrocarbons and LUST sites) These 2015 OSWER guidance documents replace the 2002 vapor intrusion guidance US EPA Guidance Key Components / Changes in Direction Increased reliance on multiple lines of evidence MLE assessments to address spatial and temporal variability More cautious screening evaluation / requirements may vary from site to site, depending upon site conditions and uses Less reliance on vapor intrusion modeling / greater use of indoor air sampling Consideration of short-term (TCE) action levels Alternate lines of evidence (in particular to evaluate indoor air background sources) Consider preferential pathways Increased emphasis on engineering controls and pre-emptive mitigation Companion petroleum vapor intrusion guidance

60 Trichloroethylene (TCE) Changes in TCE Toxicity 1985 EPA posts TCE health assessment in IRIS 1989 Withdrawn from IRIS 2001 Draft EPA TCE health assessment for review 2006 NRC review report 2009 Revised draft EPA TCE toxicity review Trichloroethylene (TCE) 2011 EPA Identified non-cancer effects based on three studies: Decreased thymus weights (immune system) Toxic nephropathy (kidney) Fetal cardiac defects (developmental) Each of these studies had some flaws but EPA SAB believed the body of evidence supported their use. EPA 2015 VI Guide recommends considering potential for adverse non-cancer effects from short duration exposures (e.g., to TCE)

61 TCE - Changing Screening Levels 16 Indoor Air 600 Groundwater Concentration (ug/m3) Concentration (ug/l) Year Year Trichloroethylene (TCE) EPA (R9) internal memo dated 9 July 2014 Recommends Region-wide use of Interim Accelerated and Urgent Action Levels for TCE Accelerated or Urgent Mitigation Options Temporarily relocating occupants Treating indoor air (carbon filtration, air purifiers) Increasing building pressure Sealing conduits

62 TCE Action Levels US EPA Regions and several states have adopted different short-term action levels for TCE. Region or State Residential (mg/m3) Commercial (mg/m3) US EPA Region 9 (Accelerated Response Action Level) 2 8 US EPA Region 10 (Removal Action Level) 2 9 Massachusetts (Imminent Hazard) 6 24 New Hampshire (Action Level) 2 9 New Jersey (Rapid Action Level) 4 18 Indiana (Action Level) 20 New York (Immediate Action Level) Confusion: TCE Regulatory Levels for Commercial/Industrial Workers 1,000, ,000 TCE Concentration (ug/m 3 100,000 10,000 1, ,000 11, Great deal of variability and uncertainty regarding regulatory levels No clear guidance on appropriate action levels

63 Multiple Lines of Evidence Chemistry Weather Geology Hydrology Building Biology Vapor Intrusion More Likely High Source Conc., Lower IA RBCs Heating Season, Strong Winds Coarse- Grained Soils, Vertically Fractured Media, Shallow Water Table, Large Water Table Fluctuations No Slab, Sumps, Low AER, Colder Climates No Biodegrad ation Vapor Intrusion Less Likely Low Source Conc., Higher IA RBCs Moderate Climate, Minimal Wind, Laterally Extensive Fine- Grained Layers with High Moisture Content Thick Capillary Fringe, Deep Water Table Positive Bldg Pressure, High AER, Intact Slab Degradable COCs Conditions These factors can be addressed qualitatively or quantitatively Increase VI Pathway Sampling Indoor air Multiple sampling rounds Sub-slab Multiple samples per building Soil vapor Multiple locations and depths How many samples? How many rounds? How long to sample? How to find the maximum? Do these extra samples improve risk management decisions?

64 USEPA Empirical Attenuation Factors Empirical data from over 900 buildings at over 40 sites from across the country Data are predominantly from residential buildings Majority of data from few sites Used paired data (indoor air and subsurface data) to calculate empirical attenuation factors Filtered data to screen out poor data quality and results impacted by background sources USEPA Empirical Attenuation Factors 1 Sampling Medium Groundwater Groundwater (fine-grained soil) Sub-slab soil gas Near-source soil gas Crawl Space Attenuation Factor Residential Buildings (1000 fold attenuation) (2000 fold attenuation) 0.03 (33 fold attenuation) 0.03 (33 fold attenuation) 1.0 (no attenuation) 1 U.S. EPA, 2015 Indoor air concentration Attenuation Factor = Soil-gas concentration

65 Petroleum VI Guidance (PVIG) PVI is different than VI for chlorinated compounds Atmosphere and Indoor Air PVI frequently assessed, but rarely Vadose Zone shown to be a complete pathway Methane Natural biodegradation in soil mitigates VI Production? of (this occurs frequently when the vapor source zone is anaerobic) petroleum compounds PVIG focuses on identifying site conditions where PVI is not of concern (exclusion criteria) Presence/absence of NAPL Depth of source (e.g., contaminated groundwater) { Oxygen { Soil Gas Vapor Migration Advective Soil Gas Flow Soil Source (residual or NAPL) basement Aerobic Biodegradation Hydrocarbon Vapor Migration Oxygen Vapor Migration Groundwater Source From API, 2004 Aerobic Zone Anaerobic Zone PVI Exclusion Criteria EPA Office of Underground Storage Tanks has developed a database focused on petroleum hydrocarbon sites Data analysis used to identify source-receptor distance where PVI is not of concern Investigators Vertical Exclusion Criteria Dissolved Plume NAPL Plume USEPA OUST (2015) 6 ft 15 ft ITRC (2014) 5 ft ft NJDEP (2013) 5 10 ft 30 ft Cal/EPA SWRCB (2012) 5 10 ft 30 ft

66 Status of State VI Guidance/Rule THE MORASS OF VAPOR INTRUSION GUIDANCE Many different agencies have issued vapor intrusion guidance, and those guidance documents and the associated standards have changed over time It is important to understand what the purpose of the vapor intrusion analysis is, what agency will oversee the analysis, and what guidance documents apply Many states have their own guidance documents for vapor intrusion Geosyntec link provides helpful and relevant guidance documents

67 CA VI Guidance / DTSC Status 2011 VI Guidance Requires an eleven step approach Steps 1, 2 and 3: Identification, Characterization and Evaluation Step 4: Identification of any imminent hazard Step 5: Performance of preliminary screening evaluation Steps 6 and 7: Collection of additional site data and performance of site-specific vapor intrusion evaluation Steps 8, 9 and 10: Conduct of building surveys, collection of indoor air samples and determination if they are acceptable Step 11: Mitigation of indoor air exposure and conduct of long term monitoring California VI Guidance Summary Final Vapor Intrusion Guidance (Oct. 2011) Requires an eleven step approach Greater focus on multiple lines of evidence evaluation More conservative default sub-slab soil gas screening evaluation (0.05 vs in US EPA 2012) Expectation for multiple sampling events and recommends permanent soil vapor sampling probes for site investigation Guidance on use of passive samplers for indoor air sampling Detailed guidance on mitigation and public outreach in separate documents Other CHHSLs do not apply to VI (October 2015 HHRA Note 3) Adopted EPA Region 9 Response Action Levels (HHRA Note 5)

68 California Low Threat Closure Policy Adopted August 2012, by State Water Resources Control Board Provides exclusion criteria for vapor intrusion pathway investigation at petroleum UST sites 1000x bioattenuation factor when sufficient vadose zone oxygen demonstrated 5 to 10 ft bioattenuation zone for dissolved plume sites 30 ft bioattenuation zone for sites with LNAPL Other Guidance Interstate Technology & Regulatory Council (ITRC) Coalition of personnel from federal and state agencies, tribes and public and industry stakeholders 2007 Guidance documents D=39 ASTM Phase I standard: ASTM E Requires a vapor intrusion screening ASTM E : Standard Guide for Vapor Encroachment screening on property involved in real estate transactions

69 Overview Overview of VI Pathway Why is VI so Challenging? State Vapor Intrusion Guidance Assessment Challenges and Solutions Indoor Air Sampling Challenges Mitigation Options Indoor air sampling challenges and solutions Background Sources Comparison to Typical Indoor Air Data Compound-Ratio Analysis (sub-slab vs indoor) Portable Mass Spectrometers Building Pressure Cycling Stable Isotope Analysis Spatial Variability High Volume Sampling (ESTCP ER 13-22) Multi-Increment Sampling (AFCEE BAA) Temporal Variability Long-Term Passive Sampling (ESTCP ER 08-30) Mass Flux Monitoring (ESTCP ER 15-03) Preferential Pathways Pneumatic Testing and Tracer Testing

70 Example Background Indoor Air Concentrations From Dawson and McAlary, 2009 Consider background range as well as typical values

71 Observed Temporal Variability in Indoor Air Continuous Monitoring Monitoring results (24-hour average) for house over a TCE Plume. Hill AFB, Utah (Johnson et al, 2012) How many samples do we need to estimate the long term mean? How long a sample duration do we need Do we need to minimize risk of missing peaks that continuous dominate average exposure? monitoring? Indoor air sampling challenges and solutions Building Pressure Cycling To clarify background sources and identify acute risks Stable Isotope Analysis To fingerprint VOCs High Volume Samples To manage spatial variability Passive Sampling To manage temporal variability Mass Flux Monitoring To reduce temporal variability Pneumatic Testing and Tracer Testing To evaluate preferential pathways and optimize mitigation

72 Indoor air sampling challenges and solutions Deflate Building Inflate Building Change in indoor concentration indicates contribution from subsurface (Berry-Spark et al, 2004 and McHugh et al, ESTCP ER-0707) Indoor air sampling challenges and solutions TCE Outdoor Air Predicted IA IA Pre- IA Post- -8Pa +8Pa Mitigation Mitigation 10 Benzene -8Pa +8Pa Outdoor Air Predicted IA IA Pre-Mitigation IA Post-Mitigation maximum 1 Concentration(ug/m 3 ) th median 25th minimum Concentration (ug/m 3 ) 0.1 maximum th median th minimum (Berry-Spark et al., 2004) Indoor Air concentrations were initially similar to predictions from soil gas data >10X drop after building pressurized Indoor Air concentrations were initially similar to outdoor air concentrations No change when building pressurized

73 Indoor air sampling challenges and solutions Atom Carbon Hydrogen Chlorine Oxygen Ratio 13 C/ 12 C 2 H/ 1 H 37 Cl/ 35 Cl 18 O/ 16 O and 17 O/ 16 O C ( ) δ 13 C Biodegradation Adsorption, Dilution Progressive vaporization δ 37 Cl Indoor Air Manufacture d Products Range Soil Vapor or Groundwater Fraction of Contaminant Remaining δ 13 C Figure 7. Illustration of the potential to use compound specific isotope analysis to distinguish between physical processes and biodegradation in the field. Indoor air sampling challenges and solutions Fan or Vacuum Summa canister Lung Box Discharge Sample Port Vacuum Gauge Essentially the same kit as an SVE pilot test Typical flows of scfm at inches W.C.

74 Indoor air sampling challenges and solutions Developed by the University of Waterloo (Ontario, Canada) Commercialized since 2010 Strong correlation with Summa canister results Patent pending for use in quantitative soil vapor sampling Passive Waterloo Membrane Sampler Real Time Monitoring with Portable GC/MS Building survey to sub-ppbv levels Use to identify preferential pathways or indoor sources HAPSITE GC/MS Analyze for target VOCs in SIM mode ~10 minute sample time Can also be run in scan mode

75 Overview Overview of VI Pathway Why is VI so Challenging? State Vapor Intrusion Guidance Assessment Challenges and Solutions Mitigation Options The VI mitigation consist of following general concepts Mitigation Concept Cut-off VI pathways Reverse VI pathways Direct treatment Building material/design management Material Reverse VI Pathway Direct Treatment Cut-off VI Pathway

76 Mitigation Options Cut-off VI Pathways Sub-Slab Depressurization (Active or Passive) Aerated Flooring (new construction) Membrane Barrier (new construction) Slab surface and conduit sealing Reverse VI Pathways Building Pressurization Direct Mitigation Indoor Air Filtration Building Ventilation Safe Design Intrinsically Safe Building Design (new construction) Sub-Slab Depressurization SSD System: Low Vacuum, High Flow rate, no treatment Passive SSD SSD System: High Vacuum, Low Flow rate, with Treatment Active SSD

77 Aerated Flooring A plastic form is used to create a continuous void below concrete slabs and concrete is poured over the forms. Membrane Barrier Manufactured Geomembrane Barrier Geo-membrane Barrier Fluid-applied Geomembrane Barrier

78 Slab Surface and Conduits Sealing Sealants & Caulks Slab Surface Coating Photo: Land Sciences TM Conduit Sealing Building Pressurization HVAC system modified to pressurize the building. ΔP of 0.01 to 0.08 in-h2o Vapor pathway changed Building Pressurization

79 Air Filtration and Building Ventilation Air Purifiers Building Ventilation (Natural or Forced) Intrinsically Safe Building Design Little or no O&M or monitoring Moderate incremental construction cost

80 Typical Installation Costs Existing Buildings Sub-slab depressurization No exhaust air treatment Cost $/SF* Building Conditions $1-3 Single family residential $2-4 Single story commercial/warehouse $4-10 Multi-story residential/commercial $10+ Complex buildings/codes * Mitigated area Note: does not include cost of investigation, design, permits, regulatory reporting Typical Installation Cost New Buildings Cost $/SF* System Type $1-3 Conventional radon (liner/gravel) $3-7 Spray-on asphaltic liner $1-3 Aerated floor system Courtesy of Land Sciences Technologies Note: does not include cost of investigation, design, permits, regulatory reporting

81 Is Mitigation Working? Indoor air tests Often required by agency Requires good background forensic skills Can provide line of evidence for background source Costly and inefficient way to show performance Radon tests Qualitative indicator of performance Not always a direct correspondence with VOCs Sub-slab concentration Below SS action level? Typically decreases after system start-up Mass flux measurements Exhaust gas concentration and flow rate Compare to theoretical maximum flux from source Vacuum (active systems) Physical evidence of downward air flow Easily measured Easily monitored Rapid Response - What to Do Ventilation Increase air exchange rate by factor of 2 to 4 (higher for initially tight building) Opening upper windows could exacerbate vapor flux into building HVAC Modifications Work with mechanical contractor to evaluate whether building HVAC can be modified to create positive pressure 100% reductions are feasible Indoor air treatment 200 HealthMate TM 450 portable units installed at a building in NH TCE concentrations reduced ~42 to 87% in performance tests Sealing cracks May work well if major vapor entry points are identified Multiple/hidden entry points can limit effectiveness 0 to 50% reduction might be expected (EPA, 1993)

82 Key Takeaways Typical Approach Groundwater sampling Soil gas sampling Sub-slab sampling Indoor air sampling Compare to screening levels Better Approach Develop a conceptual site model Select appropriate lines of evidence Develop site-specific screening levels Negotiate regulatory approval Implement response (rapid) options Provide robust documentation Thank You

83 3

84 OSWER Publication OSWER TECHNICAL GUIDE FOR ASSESSING AND MITIGATING THE VAPOR INTRUSION PATHWAY FROM SUBSURFACE VAPOR SOURCES TO INDOOR AIR U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response June 2015

85 DISCLAIMER This document presents current technical recommendations of the U.S. Environmental Protection Agency (EPA) based on our current understanding of vapor intrusion into indoor air from subsurface vapor sources. This guidance document does not impose any requirements or obligations on the EPA, the states or tribal governments, or the regulated community. Rather, the sources of authority and requirements for addressing subsurface vapor intrusion are the relevant statutes and regulations. Decisions regarding a particular situation should be made based upon statutory and regulatory authority. EPA decision-makers retain the discretion to adopt or approve approaches on a case-by-case basis that differ from this guidance document, where appropriate, as long as the administrative record supporting its decision provides an adequate basis and reasoned explanation for doing so. i

86 TABLE OF CONTENTS DISCLAIMER... i TABLE OF CONTENTS... ii LIST OF FIGURES... vi LIST OF TABLES... vi LIST OF APPENDICES... vii ACRONYMS AND ABBREVIATIONS... viii 1.0 INTRODUCTION Definition of Vapor Intrusion Statutory Authorities Taking Action with Limited Data under CERCLA and the NCP Taking Action with Limited Data under RCRA Corrective Action Scope and Recommended Uses of this Technical Guide Petroleum Hydrocarbons Nonresidential Buildings Companion Documents and Technical Resources Vapor Intrusion Screening Level Calculator Technical Support Documents Historical Context Public Involvement in Developing Vapor Intrusion Technical Guide Organization CONCEPTUAL MODEL OF VAPOR INTRUSION Subsurface Vapor Sources Subsurface Vapor Migration Openings and Driving Forces for Soil Gas Entry into Buildings Air Exchange and Mixing Conceptual Model Scenarios Variability in Exposure Levels Consideration of Indoor and Outdoor Sources of VOCs OVERVIEW OF VAPOR INTRUSION TECHNICAL GUIDE Contaminants of Potential Concern ii

87 3.2 Vapor Intrusion Assessment Building Mitigation and Subsurface Remediation Community Outreach and Involvement CONSIDERATIONS FOR NONRESIDENTIAL BUILDINGS PRELIMINARY ANALYSIS OF VAPOR INTRUSION Assemble, Evaluate, and Review Available Information Identify and Respond to Conditions that Warrant Prompt Action Determine Presence of Structures and Vapor-forming Chemicals Develop Initial Conceptual Site Model Evaluating Pre-Existing and Readily Ascertainable Sampling Data Evaluate Sampling Data Reliability and Quality Evaluate Applicability of the VISLs and Adequacy of the Initial CSM Preliminary Risk-based Screening DETAILED INVESTIGATION OF VAPOR INTRUSION Common Vapor Intrusion Scenarios Planning and Scoping Vapor Intrusion Inclusion Zones Prioritizing Investigations with Multiple Buildings Planning for Community Involvement Characterize the Vapor Intrusion Pathway Characterize Nature and Extent of Subsurface Vapor Sources Characterize Vapor Migration in the Vadose Zone Assess Building Susceptibility to Soil Gas Entry Evaluate Presence and Concentration of Subsurface Contaminants in Indoor Air Identify and Evaluate Contributions from Indoor and Ambient Air Sources Select, Prioritize, and Sequence Investigation Objectives General Principles and Recommendations for Sampling Indoor Air Sampling Outdoor Air Sampling Sub-slab Soil Gas Sampling Soil Gas Sampling Groundwater Sampling iii

88 6.4.6 Planning for Building and Property Access Overview of Risk-Based Screening Objectives of Screening Scope and Basis for Health-based, Vapor Intrusion Screening Levels Recommended Attenuation Factors for Health-based Screening Comparing Sample Concentrations to Health-based Screening Levels Planning for Communication of Sampling Results General Principles and Recommendations for Mathematical Modeling RISK ASSESSMENT AND MANAGEMENT FRAMEWORK Collect Site-specific Lines of Evidence Weigh and Assess Concordance Among the Lines of Evidence Evaluate Whether the Vapor Intrusion Pathway is Complete or Incomplete Conduct and Interpret Human Health Risk Assessment Risk Management Benchmarks Accounting for Background Contributions Occupational Exposure Limits Concentration Levels Indicating Potential Need for Prompt Response Action Potential Explosion Hazards Considering Short-term and Acute Exposures Risk-based Cleanup Levels Options for Response Action Pre-emptive Mitigation/Early Action Rationale General Decision Framework Some General Scenarios Where Pre-emptive Mitigation May be Warranted Additional Considerations BUILDING MITIGATION AND SUBSURFACE REMEDIATION Subsurface Remediation for Vapor Source Control Building Mitigation for Vapor Intrusion Prompt Response Options for Existing Buildings Active Depressurization Technologies for Existing Buildings Approaches and Considerations for New Buildings Owner/Occupant Preferences and Building Access iv

89 8.3 Operation and Maintenance of Vapor Intrusion Mitigation Systems Monitoring of Vapor Intrusion Mitigation Systems Documentation of Engineered Exposure Controls for Vapor Intrusion Mitigation Use of Institutional Controls Evaluating ICs in the Overall Context of Response Selection Common Considerations and Scenarios Involving ICs Selecting the Right Instrument(s) Long-term Stewardship Community Involvement and ICs Termination/Exit Strategy Termination of Subsurface Remediation Activities Termination of Building Mitigation Termination of ICs Termination of Monitoring PLANNING FOR COMMUNITY INVOLVEMENT Developing a Community Involvement or Public Participation Plan Communication Strategies and Conducting Community Outreach Addressing Building Access for Sampling and Mitigation Communication of Indoor Sampling Efforts and Results Transmitting Messages Regarding Mitigation Systems Addressing Community Involvement at Legacy Sites Property Value Concerns for Current and Prospective Property Owners Additional Community Involvement Resources GLOSSARY CITATIONS AND REFERENCES APPENDIX A Recommended Subsurface-to-Indoor Air Attenuation Factors...A-1 APPENDIX B Data Quality Assurance Considerations... B-1 APPENDIX C Calculating Vapor Source Concentration from Groundwater Data... C-1 v

90 LIST OF FIGURES Figure 2-1 Figure 2-2 Figure 2-3 Figure 3-1 Figure 6-1 Figure 7-1 Figure 7-2 Figure 8-1 Figure 8-2 Figure 8-3 Figure 8-4 Illustration of Key Elements of the Conceptual Model of Soil Vapor Intrusion Illustration of Potential Openings in Various Building Types Some Factors That Affect Vapor Intrusion Overview of Recommended Framework for Vapor Intrusion Assessment and Response Action Overview of Planning, Scoping, and Conducting Vapor Intrusion Investigations Sample Depiction of Subsurface Vapor Source and Data to Support Pre-emptive Mitigation/Early Action for Multiple Buildings, Each with Limited Data Sample Depiction of Subsurface Vapor Source and Data to Support Pre-emptive Mitigation/Early Action for Multiple Buildings, Some with Only Limited or No Data Illustration of Sub-slab Depressurization (SSD) System Illustration of Drain-tile Depressurization (DTD) System Illustration of Block-wall Depressurization (BWD) System Illustration of Sub-membrane Depressurization (SMD) System LIST OF TABLES Table 1-1 Table 1-2 Table 1-3 Table 6-1 Table 7-1 Table 8-1 Directory to Updates in This Technical Guide Addressing Recommendations of EPA Office of Inspector General (EPA 2009) Directory to Additional Updates in This Technical Guide Publicly Identified by OSWER (EPA 2010A) Vapor Intrusion Topics Receiving Substantive Public Comment Recommended Vapor Attenuation Factors for Risk-based Screening of the Vapor Intrusion Pathway Matrix of Options to Respond to Human Health Risk Posed by the Vapor Intrusion Pathway Vapor Intrusion Mitigation Quick Guide for Existing Buildings vi

91 LIST OF APPENDICES Appendix A Appendix B Appendix C Recommended Subsurface-to-Indoor Air Attenuation Factors Data Quality Assurance Considerations Calculating Vapor Source Concentration from Groundwater Sampling Data vii

92 ACRONYMS AND ABBREVIATIONS ACH ADT AER ANSI ASQ ASTM ASTSWMO ATSDR BTEX BWD CalEPA CASRN CEI CERCLA CFR CHC CIC CIO CIP CMS CSM DCE DNAPL DoD DoN DQO DTD EI EPA ERT FR FS air changes per hour (air exchanges per hour) active depressurization technology air exchange rate American National Standards Institute American Society for Quality American Society for Testing and Materials Association of State and Territorial Solid Waste Management Officials Agency for Toxic Substances and Disease Registry benzene, toluene, ethylbenzene, xylenes block-wall depressurization California Environmental Protection Agency Chemical Abstracts Service Registry Number Community Engagement Initiative Comprehensive Environmental Response, Compensation, and Liability Act Code of Federal Regulations chlorinated hydrocarbon Community Involvement Coordinator Chief Information Officer community involvement plan corrective measures study conceptual site model dichloroethylene, or equivalently dichloroethene dense non-aqueous-phase liquid U.S. Department of Defense U.S. Department of Navy data quality objective drain-tile depressurization environmental indicator U.S. Environmental Protection Agency Environmental Response Team Federal Register feasibility study viii

93 FYR HI HQ HVAC IC ICIAP IDLH ITRC LCR LEL LEP LNAPL LTS MADEP NAPL NAS NCP NFA NIST NPL NRC NIOSH NYSDOH O&M OIG OSC OSHA OSWER OUST PAH PCB PCE PEM PID five-year review Hazard Index Hazard Quotient heating, ventilation and air conditioning institutional control Institutional Controls Implementation and Assurance Plan immediately dangerous to life or health Interstate Technology and Regulatory Council lifetime cancer risk lower explosive limit limited English proficiency light non-aqueous-phase liquid long-term stewardship Massachusetts Department of Environmental Protection non-aqueous-phase liquid National Academy of Sciences National Oil and Hazardous Substances Pollution Contingency Plan No Further Action National Institute of Standards and Technology National Priorities List National Research Council National Institute for Occupational Safety and Health New York State Department of Health operation and maintenance Office of the Inspector General on-scene coordinator Occupational Safety and Health Administration Office of Solid Waste and Emergency Response Office of Underground Storage Tanks polycyclic aromatic hydrocarbon polychlorinated biphenyl tetrachloroethylene, or equivalently tetrachloroethene preemptive mitigation photoionization detector ix

94 P.E. ppbv PRP QAPP QMP RCRA RfC RFI RI RME ROD RPM SMD SSD TAGA TCE UFP-QAPP UECA USPS UST UU/UE VI VISL VOC Professional Engineer parts per billion by volume potentially responsible party quality assurance project plan quality management plan Resource Conservation and Recovery Act inhalation reference concentration RCRA facility investigation remedial investigation reasonable maximum exposure Record of Decision remedial project manager sub-membrane depressurization sub-slab depressurization trace atmospheric gas analyzer trichloroethylene, or equivalently trichloroethene Uniform Federal Policy for Quality Assurance Project Plans Uniform Environmental Covenants Act U.S. Postal Service underground storage tank unlimited use/unrestricted exposure vapor intrusion vapor intrusion screening level volatile organic compound x

95 EXECUTIVE SUMMARY Definition and Description of Vapor Intrusion Vapor intrusion is the general term given to migration of hazardous vapors from any subsurface vapor source, such as contaminated soil or groundwater, through the soil and into an overlying building or structure. These vapors can enter buildings through cracks in `basements and foundations, as well as through conduits and other openings in the building envelope. Vapors can also enter structures that are not intended for human occupancy (e.g., sewers, drain lines, access vaults, storage sheds, pump houses) through cracks and other openings. All types of buildings, regardless of foundation type (e.g., basement, crawl space, slab-ongrade), have openings that render them potentially vulnerable to vapor intrusion. Buildings subject to vapor intrusion include, but are not limited to, residential buildings (e.g., detached single-family homes, trailer or mobile homes, multi-unit apartments and condominiums), commercial workplaces (e.g., office buildings, retail establishments), educational and recreational buildings (e.g., schools and gyms), and industrial facilities (e.g., manufacturing plants). Vapor intrusion is a potential human exposure pathway -- a way that people may come into contact with hazardous vapors while performing their day-to-day indoor activities. For purposes of this Technical Guide, the vapor intrusion pathway is referred to as complete for a specific building or collection of buildings when the following five conditions are met under current conditions: 1) A subsurface source of vapor-forming chemicals is present (e.g., in the soil or in groundwater) underneath or near the building(s) (see Sections 2.1, 5.3, 6.2.1, and 6.3.1); 2) Vapors form and have a route along which to migrate (be transported) toward the building (see Sections 2.2 and 6.3.2); 3) The building(s) is(are) susceptible to soil gas entry, which means openings exist for the vapors to enter the building and driving forces (e.g., air pressure differences between the building and the subsurface environment) exist to draw the vapors from the subsurface through the openings into the building(s) (see Sections 2.3 and 6.3.3); 4) One or more vapor-forming chemicals comprising the subsurface vapor source(s) is(are) present in the indoor environment (see Sections and 6.4.1); and 5) The building(s) 1 is(are) occupied by one or more individuals when the vapor-forming chemical(s) is(are) present indoors. 1 For purposes of this Technical Guide and its recommendations for evaluating human health risk posed by vaporforming chemicals, building refers to a structure that is intended for occupancy and use by humans. This w ould include, for instance, homes, offices, stores, commercial and industrial buildings, etc., but w ould not normally include sheds, carports, pump houses, or other structures that are not intended for human occupancy. xi

96 A complete vapor intrusion pathway indicates that there is an opportunity for human exposure, which warrants further analysis (see Section 7.4) to determine whether there is a basis for undertaking a response action(s) (see Section 7.7). Depending upon building- and site-specific circumstances, concentrations of chemical vapors indoors arising from a complete vapor intrusion pathway may threaten the health of building occupants (e.g., residents, workers, etc.), which may warrant a response action(s). On the other hand and for purposes of this Technical Guide, if one (or more) of the five foregoing conditions is currently absent and is reasonably expected to be absent in the future (e.g., vapor migration is significantly and persistently impeded by natural geologic, hydrologic, or biochemical (e.g., biodegradation) processes and conditions), the vapor intrusion pathway is referred to as incomplete. EPA recommends that any determination that the vapor intrusion pathway is incomplete be supported by site-specific evidence to demonstrate that the nature and extent of vapor-forming chemical contamination in the subsurface has been well characterized (Section 6.3.1) and the types of vapor sources and the conditions of the vadose zone and surrounding infrastructure do not present opportunities for unattenuated or enhanced transport of vapors (Sections 5.4 and 6.5.2) toward and into any building (see Section 7.3 for further discussion). When the vapor intrusion pathway is determined to be incomplete, then vapor intrusion mitigation is not generally warranted. EPA recommends that site managers also evaluate whether subsurface vapor sources that remain have the potential to pose unacceptable human health risks due to vapor intrusion in the future 2 if site conditions were to change. The vapor intrusion pathway is referred to as potentially complete for a building when: a subsurface source of vapor-forming chemicals is present underneath or near an existing building or a building that is reasonably expected to be constructed in the future; vapors can form from this source(s) and have a route along which to migrate (be transported) toward the building; and three additional conditions are reasonably expected to all be met in the future, which may not all be met currently; i.e., o the building is susceptible to soil gas entry, which means openings exist for the vapors to enter the building and driving forces exist to draw the vapors from the subsurface through the openings into the building; o one or more vapor-forming chemicals comprising the subsurface vapor source(s) is (or will be) present in the indoor environment; and o the building is or will be occupied by one or more individuals when the vaporforming chemical(s) is (or are) present indoors. 2 Both current and reasonably likely future risks need to be considered in order to demonstrate that a site does not present an unacceptable risk to human health and the environment. (EPA 1991a). xii

97 In addition to their toxicity threats, methane and certain other vapor-forming chemicals can also pose explosion hazards depending upon structure-, building-, and site-specific circumstances. Explosion hazards may pose an imminent and substantial danger to human health and public welfare. Technical Guide Development and Recommended Uses To help assess the subsurface vapor intrusion pathway, the Office of Solid Waste and Emergency Response (OSWER) released in November 2002 for comment EPA s Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils ( Draft VI Guidance ). Since the Draft VI Guidance was released, EPA s knowledge of and experience with assessment and mitigation of the vapor intrusion pathway has increased considerably, leading to an improved understanding of and enhanced approaches for evaluating and managing vapor intrusion. In addition, EPA received hundreds of comments from the public since 2002 on the Draft VI Guidance, on a public review draft issued in April 2013, and on emerging practices and science considerations. This Technical Guide presents current technical recommendations of the EPA based on our current understanding of vapor intrusion into indoor air from subsurface vapor sources. One of its main purposes is to promote national consistency in assessing the vapor intrusion pathway. 3 At the same time, it provides a flexible science-based approach to assessment that accommodates the different circumstances (e.g., stage of the cleanup process) in which vapor intrusion is first considered at a site and differences among pertinent EPA programs. This Technical Guide is intended for use at any site (and any building or structure on a site) being evaluated by EPA pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) or the corrective action provisions of the Resource Conservation and Recovery Act (RCRA), EPA s brownfield grantees, or state agencies acting pursuant to CERCLA or an authorized RCRA corrective action program where vapor intrusion may be of potential concern. This document and the accompanying Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (EPA 2015b) 4 supersede and replace the Draft VI Guidance. Although this Technical Guide is intended for use at any site subject to federal statutes, regulations, and rules, it is not intended to alter existing requirements, guidance, or practices among OSWER s programs about development, selection, or documentation of final remediation 5 plans (addressing subsurface vapor sources, for example). 3 If EPA staff w ish to consider using any specific guidance that is not explicitly recommended in this Technical Guide, they should consult w ith Headquarters. 4 For petroleum hydrocarbons that arise from petroleum that has been released from Subtitle I UST systems, EPA has developed a companion to this Technical Guide (Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (EPA 2015b)), w hich provides information and guidance about how EPA recommends vapor intrusion be assessed for petroleum hydrocarbons in these settings. 5 For purposes of this Technical Guide, remediation is intended to apply to interim and final cleanups, w hether conducted pursuant to RCRA corrective action, the CERCLA removal or remedial programs, or using EPA brow nfield grant funds w ith oversight by state and tribal response programs. In addition to permanent remedies for subsurface vapor sources, site remediation may also entail implementation of institutional controls and construction and operation of engineered systems for exposure control. xiii

98 Document Content and Key Recommendations This document is comprised of eleven sections and three appendices, including a list of acronyms, which precedes this summary, and a glossary of terms in Section 10. Section 3 provides an overview of the entire Technical Guide and can be further summarized as follows: Broadly speaking, two general levels of vapor intrusion assessments can be distinguished: 1) A preliminary analysis, which utilizes available and readily ascertainable information to develop an initial understanding of the potential for human health risks to be posed by vapor intrusion, which would typically be performed as part of an initial site assessment (Section 5). 2) A detailed investigation (Section 6), which is generally recommended when the preliminary analysis (e.g., Section 5.3) indicates that subsurface contamination with vapor-forming chemicals may be present underlying or near buildings. A detailed investigation of the vapor intrusion pathway is typically performed as part of the site investigation stage. The approach for assessing vapor intrusion will vary from site to site, because each site will differ in the available data when vapor intrusion is being evaluated. This Technical Guide, therefore, recommends a framework for planning and conducting vapor intrusion investigations, rather than a prescriptive step-by-step approach to be applied at every site. Response actions to address vapor intrusion when it poses unacceptable human health risks (Sections 7.7 and 8) typically entail a combination of: o remediation to reduce or eliminate subsurface vapor sources (Section 8.1); o engineered exposure controls for specific buildings to reduce vapor intrusion or reduce concentrations of vapor-forming chemicals that have already entered the building (Section 8.2); o monitoring to assess and verify the performance and effectiveness of the remediation systems and engineered exposure controls (Section 8.4); and o institutional controls (ICs) to restrict land use and/or to alert parties (e.g., prospective developers, owners, and municipalities) of the presence of subsurface sources of vapor-forming chemicals and to foster operation, maintenance, and monitoring of the remediation systems and engineered exposure controls (Section 8.6). Additional response actions to avoid or reduce human exposure may also warrant consideration in circumstances where early or prompt response action is appropriate to address indoor air exposure conditions or a potential for explosion hazards. xiv

99 Additional key recommendations and policies comprising this document include the following: Planning, Scoping and Conducting Investigations (see Sections 5.4 and 6.2 for further information) Consider site and building access agreements, equipment security, and locations of underground utilities and piping, such as storm and sewer lines within buildings, when planning vapor intrusion investigations (Section 6.2). Develop an initial conceptual site model, use this model to guide planning and scoping of the investigation, and update this model as additional information and insights are generated (Sections 5.4, 7.1, and 7.2). Generally limit chemical analyses to those vapor-forming chemicals known or reasonably expected to be present in the subsurface environment. Consider a worst first approach to prioritize buildings for investigation at sites where numerous buildings are potentially subject to vapor intrusion (Section 6.2.2). To the extent practical, plan and implement investigations within buildings and on individual properties with the goal of limiting return visits, which can cause disruption and inconvenience for building occupants and owners (Section 6.2). Generally assess the vapor intrusion pathway by collecting, weighing, and evaluating multiple lines of evidence (Sections 6.3, 7.1, and 7.2). Utilize 100 feet to define an initial lateral inclusion zone for vapor intrusion assessment (i.e., for identifying buildings that are near a subsurface vapor source and generally warrant assessment) for purposes of a preliminary analysis). Investigate soil vapor migration distance (e.g., define inclusion zone(s) for assessing vapor intrusion in specific buildings) on a site-specific basis. That is, distances larger or smaller than 100 feet (i.e., beyond or within an initial 100-foot inclusion zone) may need to be considered when developing objectives for detailed vapor intrusion investigations and interpreting the resulting data (Section 6.2.1). To support evaluations of sources of indoor air concentrations, identify in individual buildings known or suspected indoor sources of the vapor-forming chemicals also found in the subsurface and characterize ambient air quality in the site vicinity for these same chemicals (Sections and 6.4). Select sampling and analytical methods that are capable of obtaining reliable analytical detections of concentrations less than project-appropriate, risk-based screening levels (e.g., vapor intrusion screening levels, or VISLs). When groundwater is a subsurface source of vapors, collect groundwater samples from wells screened across the top of the water table to characterize the source strength for vapor intrusion (Sections and 6.4.5). Collect indoor air samples to characterize exposure levels in indoor air, account for seasonal variations in climate and the habits of building occupants, and ensure that xv

100 related risk management decisions are based upon a consideration of a reasonable maximum vapor intrusion condition for a given building (Sections and 6.4.1). When sampling indoor air, o o o employ time-integrated sampling methods (e.g., evacuated canisters, sorbent-based sampling devices). Indoor air concentrations can be temporally variable and timeintegrated exposure estimates over appropriate exposure durations (e.g., chronic typically; less-than-chronic in some cases) are generally most useful for exposure and human health risk assessment (Sections and 7.4); remove potential indoor sources 6 of vapor-forming chemicals from the building to strive to ensure that the concentrations measured in the indoor air samples are attributable to the vapor intrusion pathway (Sections and 6.4.1); and measure the pressure difference between the indoors and the subsurface, which provides a complementary line of evidence to support data evaluation and interpretation (Section 6.4.1) and is a more direct means of assessing building under-pressurization than is monitoring weather/climate factors (e.g., air temperature, wind speed). Mathematical modeling of vapor intrusion is most appropriately used in conjunction with other lines of evidence (Section 6.6). Confirm the reliability of modeling results, especially when limited site-specific data are available as inputs (Section 6.6). Collect and evaluate appropriate site-specific information to demonstrate that the property fulfills the conditions and assumptions of the generic conceptual model underlying the vapor intrusion screening levels (Section 6.5.2). Data Evaluation and Decision-making Assess (and seek) concordance among the lines of evidence to more confidently support decision-making (Sections 7.1, 7.2, and 7.3). 7 Multiple lines of evidence are generally recommended for supporting conclusions, such as the following: o The subsurface vapor source(s) at a specific site has the potential to pose an unacceptable vapor intrusion exposure under current or reasonably expected future conditions, due to its vapor strength (Section 6.5) and proximity relative to one or more existing buildings or a building that may be constructed in the future (Section 6.2.1). 6 As mentioned in Section 6.3.5, indoor sources can sometimes be identified and located using portable instruments. 7 Confidence in the assessment and risk management decisions is expected to be higher w hen multiple independent lines of evidence come together to provide mutually supporting evidence for a common understanding of the site conditions/scenarios and the potential for vapor intrusion (EPA 2010b). xvi

101 o o The vapor intrusion pathway is complete for one or more buildings under current or reasonably expected future conditions (Section 7.3). The vapor intrusion pathway is incomplete for one or more buildings near a subsurface source of vapor-forming chemicals (Section 7.3), due to inadequate source strength (i.e., chemicals comprising subsurface contamination and/or their potential vapor concentrations cannot pose an unacceptable human health risk via the vapor intrusion pathway) (Section 6.5); or geologic, hydrologic, and/or biochemical (e.g., biodegradation) processes that provide substantial and persistent attenuation of vapors extending laterally over large distances relative to the footprint of the building(s) and the extent of the vapor source (Section 6.3.2). o o Indoor air concentrations attributable to vapor intrusion pose (or, alternatively, are unlikely to pose) an unacceptable human health risk in one or more existing buildings under current or reasonably expected future conditions, based upon currently available information about a chemical s toxicity (Section 7.4). Indoor air concentrations measured in one or more buildings can (or alternatively, cannot) be reasonably attributed to indoor or ambient air sources (i.e., background see Glossary) (Sections and 7.4.2). Multiple lines of evidence are particularly important for supporting no-further-action decisions regarding the vapor intrusion pathway (e.g., pathway incomplete determinations) to reduce the chance of reaching a false-negative conclusion (i.e., concluding vapor intrusion does not pose unacceptable human health risk, when it actually poses an unacceptable human health risk). Collecting and weighing multiple lines of evidence can also reduce the chance of reaching a false-positive conclusion (i.e., concluding vapor intrusion poses unacceptable human health risk, when it does not). On the other hand, parties may implement engineered exposure controls for vapor intrusion, even though only limited lines of evidence or measurements may be available to characterize the overall vapor intrusion pathway. Consider reasonably expected future conditions, in addition to current conditions, when reaching conclusions about the vapor intrusion pathway (Sections 3.2 and 7.3). For example, EPA recommends that vapor intrusion be evaluated for reasonably expected future land use conditions, including new building construction and new uses and occupants for uninhabited buildings. Identify any conditions that warrant prompt action (Section 7.5) and respond, consistent with applicable statutes and regulations and considering EPA guidance, with actions that eliminate, avoid, reduce or otherwise address the human health risk posed by vapor intrusion (Sections 7.7 and 8.2): o Explosive conditions and threats that warrant prompt action (Section 7.5.1) are reasonably suspected to exist when measured concentrations of vapors in the building, utility conduits, sumps, subsurface drains, or other structure directly xvii

102 connected to the building exceed one-tenth (10%) of the lower explosive limit (LEL). 8 EPA recommends evacuation of buildings with potential explosion and fire hazards, along with notification to the local fire department about the situation. o Conditions posing health concerns that warrant prompt action are reasonably suspected to exist when estimated exposure concentrations of vapors in the building exceed health-protective concentrations for short-term or acute exposure (Section 7.5.2). When making decisions pertaining to the assessment of vapor intrusion at nonresidential buildings, consider the characteristics of the populations potentially exposed to vaporforming chemicals in the indoor air, the relative contributions of vapors from background (including anthropogenic background), and any existing or planned engineering or institutional controls for the building, in addition to the potential for vapor intrusion (Sections 4, 6.3.5, and 7.4.2). When evaluating environmental sampling results to assess the vapor intrusion pathway, first determine that the samples were collected appropriately (Sections 5.5 and 6.4). Before conducting risk-based screening, verify that the site fulfills the conditions and assumptions of the generic conceptual model underlying the VISLs (Section 6.5.2). Compare groundwater concentrations to the VISLs (Section 6.5) for groundwater to estimate the boundaries of the plume, when contaminated groundwater is the subsurface vapor source for vapor intrusion (Section 6.2.1). Generally support the decision to collect indoor air data (Section 6.4.1) by lines of siteor building-specific evidence that demonstrate vapor intrusion has the potential to pose a significant human exposure [e.g., data on strength and proximity of subsurface vapor source(s) (Sections 6.2.1, 6.3.1, and 6.5), or preferential vapor migration in the vadose zone or into buildings (Sections 5.4, 6.3.2, and 6.3.3)]. Consider variability in laboratory analyses when evaluating sampling data. Generally conduct a human health risk assessment to determine whether the potential human health risks posed to building occupants are within or exceed acceptable levels consistent with applicable statutes and considering EPA guidance (Section 7.4). Consider the potential for adverse non-cancer health effects from short-duration exposures (i.e., acute, short-term, or subchronic exposure durations), as well as longer term exposure (i.e., chronic exposure) conditions, and select toxicity values considering OSWER s preferred hierarchy of sources (EPA 2003) (Sections 7.4 and 7.5.2). 8 The Occupational Safety and Health Administration of the U.S. Department of Labor (OSHA) considers concentrations in excess of one-tenth of the LEL to be a hazardous atmosphere in confined spaces [29 CFR (b)]. The National Institute for Occupational Safety and Health (NIOSH) has designated such concentrations as immediately dangerous to life or health (IDLH). xviii

103 Consider collecting multiple rounds of indoor air samples, 9 using time-integrated measurements (Section 6.4.1) to estimate exposure concentrations appropriate for the exposure (occupancy) scenario being evaluated (e.g., residential versus commercial), when the risk assessment for an existing building would support a conclusion that the human health risks are acceptable (Section 7.4). 10 In the risk characterization of the human health risk assessment, discuss background contributions to indoor air exposure and associated human health risks (Section 7.4.2). (For purposes of this Guide, background refers to a vapor-forming chemical(s) or location(s) that is(are) not influenced by the releases from a site see Glossary). Information on background contributions of site-related, vapor-forming chemicals in indoor air is important to risk managers because generally EPA does not clean up to concentrations below natural or anthropogenic background levels 11 (EPA 2002e). If data are available, distinguish the contribution of background to total exposure concentration(s). With such information, EPA can help advise affected individuals about the environmental and human health risks they face. Other parties, including building owners and operators, may help with risk communication. If background vapor sources (see Glossary) are found to be primarily responsible for indoor air concentrations (see Section 6.3.5), then response actions for vapor intrusion would generally not be warranted for current conditions. Engineered Exposure Controls and Building Mitigation When vapor intrusion has been determined to pose unacceptable human health risks, Aim to achieve a permanent remedy by eliminating or substantially reducing the level(s) of vapor-forming chemical(s) in the subsurface source medium (e.g., groundwater, subsurface soil, sewer lines) (Sections 7.7 and 8.1); and o In cases where subsurface vapor sources cannot be remediated quickly, implement engineered exposure controls to reduce or eliminate vapor intrusion in buildings (i.e., mitigate vapor intrusion) or reduce indoor air exposure levels (Sections 7.7 and 8.2). 9 Because w eather conditions and building operations can lead to time-variable contributions from vapor intrusion and ambient air infiltration, indoor air concentrations of vapor-forming chemicals can be expected to vary over time (see, for example, Section 2.6). An individual sample (or single round of sampling) w ould be insufficient to characterize seasonal variability, or variability at any other time scale. 10 EPA recommends basing the decision about w hether to undertake response action for vapor intrusion (i.e., a component of risk management; see Section 7.4) on a consideration of a reasonable maximum exposure (e.g., EPA 1989, 1991a), w hich is a semi-quantitative term, referring to the low er portion of the high end of the exposure distribution (see Glossary). 11 With respect to vapor intrusion mitigation (see Sections 3.5 and 8.2), some options for reducing indoor air exposure levels (e.g., ventilation, indoor air treatment) unavoidably act on background concentrations arising from indoor or outdoor sources, as w ell as vapor concentrations arising from vapor intrusion. Most options for interrupting the vapor intrusion pathw ay (e.g., active depressurization technologies see Section 8.2) unavoidably interrupt the intrusion of naturally occurring radon also. It should also be noted that some EPA regulations (e.g., indoor radon standards under 40 CFR ) are inclusive of background. xix

104 When developing monitoring programs to assess effectiveness of building mitigation, consider the degree of human health risk or hazard being mitigated, the building use, the technology used to mitigate vapor intrusion, and coordination with site remediation efforts. Establish cleanup levels and criteria for terminating engineered exposure controls and other building mitigation methods, institutional controls, and remediation systems for subsurface vapor sources (Sections 7.6 and 8.7). Document Activities and Decisions Document objectives and methods of vapor intrusion investigations, preferably in a vapor intrusion work plan (Section 6.2). Base decisions upon data and information in the administrative record. Base decisions to undertake response actions on lines of site- or building-specific evidence (e.g., characterization of subsurface vapor source(s) strength and proximity to building(s); building conditions) that demonstrate that vapor intrusion has the potential to pose an unacceptable human health risk (Section 7). Document, consistent with statutory requirements and considering prevailing guidance for the respective land restoration program (e.g., CERCLA, RCRA corrective action, brownfields, etc.), any and all decisions pertaining to vapor intrusion, including decisions to undertake (or not to undertake) investigation or mitigation of specific buildings at a contaminated site. Prepare and publish system manuals to document building mitigation and remediation systems (Section 8.5). Prepare and implement operations and maintenance manuals and practices to foster continued effective operation and performance of engineered exposure controls and remediation systems for subsurface vapor sources (Section 8.5). Document monitoring programs that assess the performance and effectiveness of remediation and mitigation systems. Community Outreach and Involvement (Section 9) Develop or refine a community involvement or public participation plan while planning a vapor intrusion investigation and implement this plan throughout the assessment, remediation, and mitigation phases. Conduct building-by-building contact and communication as means of educating the community and obtaining access needed to assess, mitigate, and monitor the vapor intrusion pathway. Personal contact is further recommended to establish a good working relationship with each building owner or occupant and to build trust. xx

105 Generally provide validated results and interpretations (e.g., chemicals of concern, associated risk assessment implications) to property owners and occupants in a timely manner (e.g., within approximately 30 days of receiving these results). Provide adequate opportunities for public participation (including potentially affected landowners and communities) when considering appropriate use of ICs. The science and technology to assess and mitigate vapor intrusion have evolved significantly over the past decade. EPA will continue to monitor these evolving developments and will update these recommendations in the future, if and as appropriate. xxi

106 1.0 INTRODUCTION This technical guide was prepared by the U.S. Environmental Protection Agency (EPA) through the cooperative efforts of a team of EPA Headquarters and Regional staff, known as the Vapor Intrusion Intra-Agency Workgroup (Workgroup). Drafts of this document were subjected to a comprehensive, consultative peer-input process in 2012, as described in EPA s Peer Review Handbook (EPA-SPC 2006), which included comments and other contributions from Workgroup members representing several EPA offices and the EPA s Vapor Intrusion Forum. 12 Public comments submitted from 2002 through 2013 and recommendations of the Office of Inspector General (OIG) were also considered in developing this document. This document comprises EPA s final vapor intrusion technical guide 13 and is referred to herein as this Technical Guide. It describes a recommended framework for assessing vapor intrusion that relies upon collecting and evaluating multiple lines of evidence to support risk management decisions. It also provides technical recommendations about monitoring and terminating building mitigation systems. This Technical Guide relied upon a large body of scientific information found in the peerreviewed literature. Additionally, EPA developed three technical support documents that were externally peer reviewed (EPA 2011a, 2012a, 2012b). This approach is consistent with EPA s peer review handbook and policy (EPA-SPC 2006). Peer-reviewed literature, peer-reviewed technical reports, existing and relevant EPA guidance (e.g., for conducting human health risk assessment; for planning and conducting investigations of environmental contamination), and other pertinent information that support development or implementation of this Technical Guide are cited within. This introductory section: defines the term vapor intrusion ; summarizes EPA s statutory authorities to protect human health from vapor intrusion; summarizes the intended uses of this Technical Guide, including its applicability to petroleum hydrocarbons and other potentially biodegradable chemicals and to nonresidential buildings; identifies key technical resources that facilitate consideration of its recommendations; provides a concise historical accounting of its development; describes how the public was involved in its development; and provides an overview of its organization. 1.1 Definition of Vapor Intrusion Certain chemicals that are released into the subsurface 14 as liquids or solids may form hazardous vapors that migrate or are transported through the vadose zone 15 and eventually 12 The EPA Vapor Intrusion Forum is an intra-agency group engaged in sharing information, technical resources, and perspectives pertaining to vapor intrusion assessment and mitigation. 13 This document is intended to fulfill EPA s commitment to the OIG to issue updated, revised, and finalized vapor intrusion guidance (EPA 2009a, Appendix B; EPA 2010b). 14 For purposes of this Technical Guide, the phrases released into the subsurface and release to the subsurface are intended to encompass any and all mechanisms by w hich chemical contamination arises in the subsurface, including, for example, spills and releases above the ground surface that result in subsurface (e.g., soil and groundw ater) contamination. 1

107 enter buildings as a component of a gas 16 by migrating (being transported) through cracks, seams, interstices, and gaps in basement floors, walls, or foundations ( adventitious openings ), through intentional openings (e.g., perforations due to utility conduits, sump pits), and/or within conduits (e.g., drain and sewer lines). Vapor intrusion is the general term given to migration of hazardous vapors from any subsurface contaminant source, such as contaminated soil or groundwater or contaminated conduit(s), into an overlying building or unoccupied structure via any opening or conduit. Recognition of soil vapor intrusion to buildings and other enclosed spaces occurred in the 1980s with concerns over radon intrusion. 17 Subsequently, there was an increasing awareness that anthropogenic chemicals (e.g., petroleum hydrocarbons and chlorinated solvents) in soil and ground water could also pose threats to indoor air quality via the vapor intrusion pathway (Little et al. 1992; Moseley and Meyer 1992). Vapor intrusion can occur in a broad range of land use settings, including residential, commercial, and industrial, and affect buildings with virtually any foundation type (e.g., basement, crawl space(s), or slab on grade). In the last 20 years, vapor intrusion impacts have been demonstrated in occupied buildings at a number of sites across the country (e.g., Little et al. 1992). As a result, vapor intrusion is widely recognized as a potential pathway of human exposure to volatile hazardous chemicals in indoor spaces. When and where vapor intrusion occurs, concentrations of vapors can increase gradually in amount in buildings or structures as time passes (i.e., accumulate ). Depending upon site- and building-specific circumstances, vapors of potentially toxic chemicals may accumulate to a point where the health of the occupants (e.g., residents, workers, etc.) in those buildings could be threatened. In addition to their toxicity threats, methane and certain other vapor-forming chemicals can pose explosion hazards depending upon structure-, building-, and site-specific circumstances. Explosion hazards may pose an imminent and substantial danger to human health and public welfare. Careful consideration of the vapor intrusion pathway is warranted at all sites where vaporforming chemicals are present in the soil or groundwater aquifer (NRC 2013). Section 2.0 describes the vapor intrusion pathway in greater detail. 15 The vadose zone is the soil zone betw een land surface and the groundw ater table w ithin w hich the moisture content is less than saturation (except in the capillary fringe). It is also referred to as the unsaturated zone. 16 The terms gas and vapor refer the gaseous state, as distinguished from the liquid or solid state, of matter. Whereas vapor refers to a volatile chemical that may comprise only a portion of the total volume, gas refers to the entire volume. For economy of w ords, this Technical Guide refers to vapor concentrations in soil gas as soil gas concentrations. 17 Radon is a colorless, odorless, radioactive gas that is formed from the decay of radium, a radioactive element that occurs naturally in the soil and bedrock in many areas of the United States. Radon can also be emitted from certain uranium- or radium-containing products and w astes. For more information about radon, see: w w.epa.gov/radon/index.html. 2

108 1.2 Statutory Authorities Protection of human health is a critical mandate underlying several federal statutes, including the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), as amended, 18 and the Resource Conservation and Recovery Act (RCRA), as amended. 19 Protection of human health is also a critical objective of the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), which is the federal government's blueprint for responding to oil spills and releases of hazardous substances, pollutants, or contaminants. The sources of authority and requirements for addressing subsurface vapor intrusion are the relevant statutes and regulations. On this basis, the EPA has broad authority and distinct responsibilities 20 to assess and, if warranted, mitigate vapor intrusion in residential and nonresidential 21 settings arising from a chemical release that causes subsurface contamination by volatile hazardous chemicals. 22 These actions may include sampling indoor air to assess exposure levels of building occupants to subsurface vapors and implementing interim mitigation measures to control, reduce, or eliminate exposure indoors to vapors emanating from subsurface vapor sources. Where such subsurface contamination includes vapor-forming chemicals (see Section 3.1) and underlies or is near buildings, EPA recommends that the potential for human health risk from vapor intrusion be evaluated throughout the cleanup life 18 Amendments to CERCLA include the Small Business Liability Relief and Brow nfields Revitalization Act. 19 Application of these statutory authorities to a particular situation generally entails site- and fact-specific analysis. 20 On January 23, 1987, the President of the United States signed Executive Order entitled, Superfund Implementation, w hich delegates to a number of Federal departments and agencies the authority and responsibility to implement certain provisions of CERCLA. The policies and procedures for implementing these provisions (e.g., carrying out response actions) are spelled out in the NCP. The provisions of Executive Order appear at 52 Federal Register The EPA and the Occupational Safety and Health Administration (OSHA) of the Department of Labor each have a distinct statutory responsibility to ensure the safety and health of America's w orkforce through the timely and effective implementation of a number of federal law s and implementing regulations. On November 23, 1990, the Secretary of the Department of Labor and Administration of the EPA signed a Memorandum of Understanding (MOU) w ith the goal of establishing a program for improved environmental and w orkplace health and safety, w hich continues in effect. Implementation of the MOU is intended to improve the combined efforts of the agencies to achieve protection of w orkers, the public, and the environment at facilities subject to EPA and OSHA jurisdiction; to delineate the general areas of responsibility of each agency; and to provide guidelines for coordination of interface activities betw een the tw o agencies w ith the overall goal of identifying and minimizing environmental or w orkplace hazards. An additional MOU w as signed in February 1991 to establish a process and framew ork for notification, consultation and coordination betw een EPA and OSHA to aid both agencies in identifying environmental and w orkplace health and safety problems and to more effectively implement enforcement of their respective national environmental and w orkplace statutes. For additional information, see ww.osha.gov/pls/oshaw eb/owasrch.search_form?p_doc_type=mou&p_toc_level=1&p_keyvalue=agency&p _status=current. EPA s recommended approach for evaluating vapor intrusion exposures is based upon its existing risk assessment guidance, as summarized in Section Section 3.1 of this Technical Guide describes technical criteria for identifying w hich specific chemicals are sufficiently volatile and hazardous to generally w arrant routine evaluation during vapor intrusion assessments, w hen they are present as subsurface contaminants. These sufficiently volatile and hazardous chemicals are referred to as vapor-forming chemicals for purposes of this Technical Guide. 3

109 cycle (i.e., initial site assessment, site investigation, interim and final response actions, 23 and periodic reviews of the selected remedy), as described in Sections 5 and 6 of this Guide. Although this Technical Guide is intended for use at any site subject to federal statutes, regulations, and rules, it is not intended to alter existing requirements, guidance, or practices among OSWER s programs about development, selection, or documentation of final remediation 24 plans (addressing subsurface vapor sources, for example). EPA may need access to private property to conduct investigations, studies and response actions pursuant to CERCLA and RCRA, as amended. The Superfund Amendments and Reauthorization Act of 1986 and RCRA explicitly grant EPA the authority to enter property for these purposes (EPA 1986, 1987, 2010a). EPA generally prefers to obtain access through consent and cooperation. If consent is denied, however, EPA can use the judicial process or an administrative order to gain access. Application of legal doctrines to a particular access situation warrants site- and fact-specific analysis. Provisions under CERCLA, RCRA, federal regulations, and federal guidance also provide authority and support for taking early actions to mitigate actual and potential human health risks, as discussed below. In the context of vapor intrusion, early action may include response measures such as engineered exposure controls to reduce or eliminate vapor intrusion in buildings (i.e., mitigate vapor intrusion) or reduce indoor air exposure levels (see Sections 7.8 and 8.2) and prompt response actions to address more urgent threats to human health or public welfare (see Section 7.5) Taking Action with Limited Data under CERCLA and the NCP CERCLA and the NCP both contain provisions that support and encourage taking early actions to mitigate actual and potential threats to human health associated with vapor intrusion. For example, CERCLA sections 104 and 106 provide the federal government with broad authority to take response action(s) to address a release or threatened release of hazardous substances that may present a human health risk. Similarly, the preamble to the final NCP issued in the Federal Register on March 8, 1990 (55 FR 8704), states, EPA expects to take early action at sites where appropriate, and to remediate sites in phases using operable units as early actions to eliminate, reduce or control the hazards posed by a site or to expedite the completion of total site cleanup. In deciding whether to take early actions, EPA balances a number of considerations, including the desire to definitively characterize site risks and analyze alternative remedial approaches for addressing those threats in great detail with the desire to implement protective measures quickly. EPA intends to perform this balancing with a bias for initiating 23 The w ords response action or response are used generically in this Technical Guide to include remedial and removal actions under CERCLA as amended and similar actions under RCRA as amended. 24 For purposes of this Technical Guide, remediation is intended to apply to interim and final cleanups, w hether conducted pursuant to RCRA corrective action, the CERCLA removal or remedial programs, or using EPA brow nfield grant funds w ith oversight by state and tribal response programs. In addition to permanent remedies for subsurface vapor sources, site remediation may also entail implementation of institutional controls and construction and operation of engineered systems. 4

110 response actions necessary or appropriate to eliminate, reduce, or control hazards posed by a site as early as possible. 25 For sites that are not on the National Priorities List (NPL), EPA may use its removal authority under CERCLA to undertake early action to mitigate vapor intrusion threats. For sites that are on the NPL, EPA's Superfund program may use its remedial or removal authority under CERCLA to undertake early action to ensure the protection of human health during existing or future property uses that could be affected by vapor intrusion. Building mitigation, control of subsurface vapor source(s), and associated ICs could be part of a final remedy selected for the site, or where appropriate, could represent an early action that (1) is evaluated and selected on a faster track and (2) complements the anticipated final remedial action for the site. Because of state cost-share consequences, EPA recommends that state concurrence be sought for any Fund-lead mitigation under CERCLA where there is a reasonable expectation that the state will need to take over responsibility for operations and maintenance (O&M) as part of a long-term, final remedy. EPA s guidance for preparing Superfund decision documents states: An interim action is limited in scope and only addresses areas/media that also will be addressed by a final site/operable unit ROD [Record of Decision].Early actions can be taken throughout the RI/FS [remedial investigation/feasibility study] process to initiate risk reduction activities. Early in this case is simply a description of when the action is taken in the Superfund process. Thus, an early action is one that is taken before the RI/FS for the site or operable unit has been completed. Hence, early actions may be either interim or final (EPA 1999b). The primary goals of an early action are to achieve prompt risk reduction and increase the efficiency of the overall site response (EPA 1992b). Although preparation of an RI/FS Report is not essential for an early action, documentation that supports the rationale for the action and becomes part of Administrative Record is recommended, consistent with the NCP and CERCLA. For interim actions, EPA s guidance for preparing Superfund decision documents states: A summary of site data collected during field investigations should be sufficient to document a problem in need of response. In addition, a short analysis of remedial alternatives considered, those rejected, and the basis for the evaluation (as is done in a focused FS) should be summarized to support the selected action (EPA 1999b). For response actions selected in an Action Memorandum or Record of Decision which are carried out by potentially responsible parties (PRPs), and where the PRP(s) agree to implement preemptive mitigation (PEM) for vapor intrusion, EPA recommends that PRP commitments to proceed with response action (including early action) be obtained through settlements or other enforcement documents (for example, administrative orders). Such response action commitments could include performance of O&M and monitoring. EPA recommends that settlement with PRPs concerning PEM/early action response actions specify that PRPs agree not to challenge the basis of the response based on inadequate characterization. 25 So, for example, EPA cited the NCP in its Compilation of Information Relating to Early/Interim Actions at Superfund Sites and the TCE IRIS Assessment (EPA 2014b). 5

111 1.2.2 Taking Action with Limited Data under RCRA Corrective Action EPA has emphasized the importance of interim actions and site stabilization in the RCRA corrective action program to control or abate ongoing risks to human health and the environment while site characterization is underway or before a final remedy is selected (see the Federal Register of May 1, 1996 [61 FR 19446]). Interim actions encompass a wide range of institutional and physical corrective action activities to achieve stabilization and can be implemented at any time during the corrective action process. EPA recommends that interim actions, including PEM, be employed as early in the corrective action process as possible, consistent with the human health and environmental protection objectives and priorities for the site. EPA recommends that, as further information is collected, program implementers continue to look for opportunities to conduct additional interim response actions. 1.3 Scope and Recommended Uses of this Technical Guide This Technical Guide presents EPA s current recommendations for how to identify and consider key factors when assessing vapor intrusion, making risk management decisions, and implementing mitigation pertaining to this potential human exposure pathway. This Technical Guide and the accompanying Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (EPA 2015b) supersede and replace EPA s Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (EPA 2002c) ( Draft VI Guidance ). One of the main purposes of this Technical Guide is to promote national consistency in assessing the vapor intrusion pathway. 26 At the same time, it provides a flexible science-based approach to assessment that accommodates the different circumstances (e.g., stage of the cleanup process) at a site and differences among pertinent EPA programs. This Technical Guide is intended for use at any site 27 being evaluated by EPA pursuant to CERCLA or RCRA corrective action, EPA s brownfield grantees, or state agencies acting 26 If EPA staff w ish to consider using any specific guidance that is not explicitly recommended in this Technical Guide, they should consult w ith Headquarters. 27 The term site is used generically in this Technical Guide to represent areas of contamination managed in a cleanup project under CERCLA as amended, under RCRA as amended, at a federal facility, or pursuant to an EPA Brow nfields grant. 6

112 pursuant to CERCLA or an authorized RCRA corrective action program 28 where vapor intrusion may be of potential concern. EPA recommends consideration of this Technical Guide when: Making Current Human Exposures Under Control environmental indicator (EI) determinations at RCRA corrective action facilities (EPA 1999a, 2002b) 29 and National Priorities List (NPL) sites under CERCLA (EPA 2008b); Undertaking removal actions, remedial actions, pre-remedial investigations, 30 remedial investigations, and five-year reviews (FYRs) 31 and selecting remedies under CERCLA; and Undertaking RCRA facility investigations and corrective actions and site investigations and cleanups at federal facilities and brownfield sites. This Technical Guide addresses both residential and nonresidential buildings that may be impacted by vapor intrusion from subsurface vapor sources. The broad concepts of this Technical Guide generally may be appropriate when evaluating any of a large number and broad range of vapor-forming chemicals described in Section 3.1 that potentially can provide subsurface sources for vapor intrusion into buildings. These chemicals include, for example, chlorinated hydrocarbons (CHCs), petroleum hydrocarbons, other types of both halogenated and non-halogenated volatile organic compounds (VOCs), 28 EPA believes that states, tribes, and local governments w ill find this Technical Guide useful for their respective programs. EPA recommends that state agencies that have delegated authority to implement CERCLA or RCRA consider this Technical Guide w hen implementing their state-specific guidance for vapor intrusion assessment and mitigation, if any, (e.g., ensure they incorporate features such as: using multiple lines of evidence to support pathw ayincomplete determinations and no-further-action decisions; collecting multiple rounds of indoor air sampling to characterize exposure levels in indoor air in existing buildings and reduce the chance of reaching a false-negative conclusion (i.e., concluding exposure is at an acceptable risk level w hen it is not) or a false-positive conclusion (i.e., concluding vapor intrusion poses unacceptable human health risk, w hen it does not); focusing lab analyses of indoor air, ambient air, and sub-slab soil gas samples on vapor-forming chemicals know n or suspected to be released to the subsurface environment; invoking the recommended criteria described in Section as a condition for using riskbased screening levels for vapor intrusion; assessing human health risk posed by less-than-chronic exposure durations; and considering reasonably expected future conditions, as w ell as current conditions, w hen making risk management decisions and selecting cleanup and building mitigation plans). 29 Also see w w.epa.gov/osw/hazard/correctiveaction/eis/faqs.htm. 30 CERCLA authorizes the EPA to identify and prioritize w hich sites w arrant further investigation to ascertain w hether remedial action is needed. The Hazard Ranking System (HRS) is the statutorily required method for evaluating and identifying sites for placement on the NPL. 31 Section 121 of CERCLA specifies that remedial actions that result in any hazardous substances, pollutants, or contaminants remaining at the site be re-evaluated every five years to ensure that the remedy is and w ill continue to be protective of human health and the environment. OSWER Directive (Assessing Protectiveness at Sites for Vapor Intrusion: Supplemental Guidance to the Comprehensive Five-Year Review Guidance (EPA 2012c)) provides supplemental guidance for considering vapor intrusion w hile evaluating remedy protectiveness in the context of the Superfund five-year review process (even if vapor intrusion w as not addressed as part of the original remedial action). 7

113 elemental mercury, and radon when it arises from uranium- or radium-bearing solid wastes in the subsurface. 32 This Technical Guide addresses risk management (e.g., exposure control or avoidance methods) for indoor air contamination that arises from vapor intrusion from subsurface sources of these vapor-forming chemicals. It is not intended as a guide for assessing or mitigating indoor air exposures that arise solely from other sources (e.g., indoor use and storage of certain consumer products 33 ). The exposure route of general interest for vapor intrusion is inhalation 34 of vapors present in indoor air that have entered via soil gas entry from the subsurface. 35 Other human exposure routes that may warrant consideration during site investigations of subsurface contamination (e.g., ingestion of soil or water, dermal contact with soil or water, inhalation of particulate material, inhalation of vapors while outdoors, and inhalation of vapors while showering or washing with contaminated groundwater while indoors) are not addressed in this Technical Guide. EPA recommends that risk management and response action decisions for the vapor intrusion pathway generally consider reasonably expected future conditions, which may differ from current conditions due to changes in land use, building and infrastructure construction and conditions, and vadose zone hydrology and oxygenation, among other factors. This Technical Guide provides general information regarding how these factors may enhance or impede vapor intrusion. It also provides recommendations for institutional controls and monitoring where a subsurface vapor source(s) is(are) present and has the potential to pose unacceptable human health risks. Although this Technical Guide is intended for use at any site subject to federal statutes, regulations, and rules, it is not intended to alter existing requirements, guidance, or practices among OSWER s programs about circumstances for reviewing past risk management and cleanup decisions. As noted, remedy reviews are required by Section 121 of CERCLA when 32 Radon emanating from natural geological materials may also affect indoor air quality in occupied buildings, but is not a subject of this Technical Guide. According to EPA estimates, inhalation of toxic radon decay products is the leading cause of lung cancer among non-smokers. For more information about radon emanating from natural geological materials, see: w w.epa.gov/radon/index.html. 33 Indoor air in most buildings w ill contain detectable levels of a number of volatile compounds, w hether or not the building overlies a subsurface source of vapor-forming chemicals (EPA 2011a). As discussed further in Section 2.7 of this Technical Guide, these chemicals originate from indoor uses of chemical-containing products (e.g., household or consumer products) and from outdoor (ambient) air. EPA s indoor air quality program provides useful advice for control of indoor air exposures (see w w.epa.gov/iaq/). 34 Among human exposure pathw ays involving contamination of land and w ater, vapor intrusion is distinct. Whereas contact w ith contaminated surface soil, contaminated fish, and contaminated drinking w ater generally can be readily avoided for prolonged periods, breathing cannot. 35 In addition, certain hazardous chemicals (e.g., methane) can pose explosion hazards w hen they gradually increase in amount in structures (e.g., confined spaces) or buildings as time passes to a point w here there is an imminent and substantial danger to human health and public w elfare. 8

114 hazardous substances remain on site. 36 EPA s other land restoration programs (e.g., RCRA corrective action, brownfield redevelopment) will continue to rely upon their existing, respective practices to address the need, if any, for periodic reviews of cleanup decisions, including consideration of the vapor intrusion pathway. Finally, this Technical Guide does not aim or intend to: Offer recommendations for vapor intrusion assessments that private parties choose to conduct as part of real estate transactions; Modify existing guidance regarding landowner liability protection (e.g., all appropriate inquiries, the bona fide prospective purchaser provision); or Offer recommendations for responding to leaks from natural gas transmission lines Petroleum Hydrocarbons The approaches in this Technical Guide are recommended for evaluating the vapor intrusion pathway pursuant to CERCLA or RCRA corrective action for petroleum hydrocarbons that are mixed with other types of volatile hazardous chemicals or are the result of releases from sources other than Subtitle I underground storage tank (UST) systems. 37 For petroleum hydrocarbons that arise from petroleum that has been released from Subtitle I UST systems, EPA has developed a companion to this Technical Guide (Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (EPA 2015b)), which provides information and guidance about assessing vapor intrusion from petroleum hydrocarbons in these settings and may also be useful in informing decisions about vapor intrusion and petroleum hydrocarbons at non-ust sites that are similar in size to a typical Subtitle I UST release. Many petroleum hydrocarbons may naturally biodegrade in the vadose zone through the actions of microorganisms found naturally in soil. When oxygen supply from the atmosphere is sufficient, biodegradation of petroleum hydrocarbons can occur relatively quickly, will generally produce less harmful compounds (i.e., biodegradation products), and can result in substantial attenuation of petroleum hydrocarbon vapors over relatively short distances in the vadose zone. Numerous site-specific factors can influence the biodegradation rate of petroleum hydrocarbons (and other biodegradable vapor-forming chemicals) in the vadose zone. These factors include quantities, distribution, types, and mixtures of vapor-forming chemicals, which can differ substantially among sites where petroleum hydrocarbons are released to the subsurface 36 The NCP states [40 CFR (f)(4)(ii)]: If a remedial action is selected that results in hazardous substances, pollutants, or contaminants remaining at the site above levels that allow for unlimited use and unrestricted exposure, the lead agency shall review such action no less often than every five years after initiation of the selected remedial action. For further information, see, for example, w w.epa.gov/superfund/cleanup/postconstruction/5yr.htm 37 For example, the approaches in this Technical Guide are recommended for evaluating the vapor intrusion pathw ay associated w ith subsurface releases of petroleum, petroleum derivatives, and petroleum hydrocarbons from refineries, bulk storage facilities, oil exploration and production sites, pipelines and transportation, chemical manufacturing facilities, former manufactured gas plants, creosote (w ood-treating) facilities, large-scale fueling and storage operations at federal facilities, and dry cleaners that use petroleum solvents. 9

115 environment. This Technical Guide allows site-specific observations of the effects of biodegradation to be considered in its approach for petroleum hydrocarbons (and any other biodegradable, vapor-forming chemical). Sections and 7.3 expand on EPA s recommended approach to evaluating biodegradation of vapor-forming chemicals in the vadose zone at sites with subsurface contamination Nonresidential Buildings EPA has broad authority and distinct responsibilities to assess and, if warranted, mitigate vapor intrusion in nonresidential settings arising from a chemical release that causes subsurface contamination by volatile hazardous chemicals (see Section 1.2). EPA 38 is authorized to take all appropriate actions to protect human health and the environment from subsurface vapor sources of chemical exposure consistent with applicable federal statutes 39,40 and regulations and considering EPA guidance, 41 taking into account the nonresidential setting. These actions may include sampling indoor air to assess exposure levels of building occupants to subsurface vapor sources and implementing interim mitigation measures to control, reduce, or eliminate exposure indoors to vapors emanating from a subsurface vapor source(s). As used in this Technical Guide, the phrase nonresidential buildings may include, but is not limited to, institutional buildings (e.g., schools, libraries, hospitals, community centers and other enclosed structures for gathering, gyms and other enclosed structures for recreation); commercial buildings (e.g., hotels, office buildings, many (but not all) day care facilities, and retail establishments); and industrial buildings where vapor-forming chemicals may or may not be routinely used or stored. Section 4.0 expands on EPA s recommended approach to evaluating and mitigating vapor intrusion in nonresidential buildings. 1.4 Companion Documents and Technical Resources Technical information pertaining to vapor intrusion has also been prepared to support development of and facilitate implementation of the technical approaches and recommendations in this Technical Guide. Key technical information is described in this section and can be found on OSWER s vapor intrusion website (see Section 11.0 for citations and internet links). 38 On January 23, 1987, the President of the United States signed Executive Order entitled, Superfund Implementation, w hich delegates to a number of Federal departments and agencies the authority and responsibility to implement certain provisions of CERCLA. The policies and procedures for implementing these provisions (e.g., carrying out response actions) are spelled out in the NCP. The provisions of Executive Order appear at 52 Federal Register At federal facilities on the NPL, EPA may not be the lead agency, but does have oversight responsibilities pursuant to CERCLA Section CERCLA and RCRA authorize EPA to protect human health and the environment, as summarized in Section 1.2 of this Technical Guide. The NCP also addresses protection of human health and the environment. 40 See, for example, CERCLA Section 101(22). 41 See, for example, OSWER Directive (Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions) (EPA 1991a) and Rules of Thumb for Superfund Remedy Selection, OSWER Directive , August 1997 (EPA 1997).. 10

116 1.4.1 Vapor Intrusion Screening Level Calculator The Vapor Intrusion Screening Level (VISL) Calculator (2015a) is a technical resource, developed by EPA that: (1) Identifies chemicals considered to be typically vapor-forming and known to pose a potential cancer risk or noncancer hazard through the inhalation pathway (as described further in Section 3.1 herein); (2) Provides generally recommended screening-level concentrations for groundwater, nearsource soil gas (exterior to buildings), sub-slab soil gas, and indoor air based upon default residential or nonresidential exposure scenarios, a target cancer risk level of one per million (10-6 ), and a target hazard quotient of one for potential non-cancer effects; and (3) Facilitates calculation of site-specific screening levels (see Section 6.5) and/or candidate cleanup levels (see Section 7.6) based on user-defined target risk levels, exposure scenarios, and semi-site-specific (Appendix A) or site-specific (Section 7.6) attenuation factors. The VISL Calculator is comprised of an MS Excel workbook. It can be used in evaluating whether the vapor intrusion pathway has the potential to pose a human health risk by helping to: (1) Identify whether volatile hazardous chemicals that can pose a threat through vapor intrusion are present; (2) Determine if those volatile hazardous chemicals are present at potentially explosive levels; (3) Compare subsurface or indoor data against recommended screening levels provided in the VISL Calculator; and (4) Prioritize buildings and sites for investigation and response action. The recommended screening-level concentrations in the spreadsheet are calculated using the recommended approaches in existing EPA guidance for human health risk assessment, as described further in Sections and herein, and are based on current understanding of the vapor intrusion pathway Technical Support Documents Key technical documents supporting development of the technical approaches and recommendations in this Technical Guide include: Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences ( ): A Compilation of Statistics for Assessing Vapor Intrusion (EPA 2011a): This technical report presents (1) a summary of indoor air studies that measured background concentrations of VOCs in the indoor air of thousands of North American residences and (2) an evaluation and compilation of the statistical information reported in these studies. The objective of this compilation is to illustrate the ranges and variability of 11

117 VOC concentrations in indoor air during the study period ( ), resulting from sources other than vapor intrusion. This technical report was externally peer reviewed, consistent with EPA s peer review policy (EPA-SPC 2006) for scientific and technically based work products that are intended to inform Agency decisions. EPA s Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings (EPA 2012a): This technical report presents technical information about sites in the U.S. that have been investigated for vapor intrusion. The primary focus of the report is the evaluation of concentrations of chlorinated VOCs in and underneath residential buildings based upon the EPA's vapor intrusion database as of This report provides the technical basis for the generic and semi-site-specific attenuation factors recommended in this Technical Guide to calculate vapor intrusion screening levels (see Section 6.5 and Appendix A). This technical report was externally peer reviewed, consistent with EPA s peer review policy (EPA-SPC 2006) for scientific and technically based work products that are intended to inform Agency decisions. Conceptual Model Scenarios for the Vapor Intrusion Pathway (EPA 2012b): This technical report provides simplified simulation examples to illustrate graphically how subsurface conditions and building-specific characteristics determine: (1) the distribution of vaporforming chemicals in the subsurface; and (2) the indoor air concentration relative to a source concentration. It was prepared to help environmental practitioners gain insights into the processes and variables involved in the vapor intrusion pathway and to provide a theoretical framework with which to draw inferences about and better understand the complex vapor fate and transport conditions typically encountered at actual, contaminated sites. This technical report was externally peer reviewed, consistent with EPA s peer review policy (EPA-SPC 2006) for scientific and technically based work products that are intended to inform Agency decisions. These technical tools and documents, as well as others, can be found at a website developed to support the development of this Technical Guide and enhance public communication about the topic. This website also allows certain sections of this Technical Guide to be more dynamic and facilitates updates to information. Technical documents intended to facilitate consideration of the recommendations in the Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (EPA 2015b) can be found at Historical Context To help assess the subsurface vapor intrusion pathway, the Office of Solid Waste and Emergency Response (OSWER) released in November 2002 for comment EPA s Draft VI Guidance, which presents EPA s technical information and recommendations for evaluating subsurface vapor intrusion, based on the understanding of vapor intrusion at that time (EPA 2002c). This Technical Guide and the accompanying Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (EPA 2015b) supersede and replace the Draft VI Guidance. 12

118 Since the Draft VI Guidance was released, EPA s knowledge of and experience with assessment and mitigation of the vapor intrusion pathway has increased considerably, leading to an improved understanding of and enhanced approaches for evaluating and managing vapor intrusion. In addition: Other federal agencies with responsibilities and obligations for environmental cleanup or for response to reports of vapor intrusion have developed vapor intrusion guides for their respective programs (e.g., ATSDR 2008; DoD 2009; DoN 2011a; USPS 2009). A number of state agencies involved with environmental quality or public health protection have developed vapor intrusion guides for their programs, which they may continue to implement under their respective statutory authorities (e.g., see ASTSWMO [2009], a compilation). The Interstate Technology & Regulatory Council (ITRC), a state-led coalition of environmental regulatory professionals, prepared three guidelines for assessing the vapor intrusion pathway (ITRC 2007ab, 2014). EPA has considered these guides in developing this Technical Guide. In addition, in December 2009, the OIG made recommendations regarding EPA s Draft VI Guidance, which are documented in the evaluation report Lack of Final Guidance on Vapor Intrusion Impedes Efforts to Address Indoor Air Risks (Report No. 10-P-042; EPA 2009a). Among other things, the OIG recommended that the final guidance incorporate: Updated toxicity values. A recommendation(s) to collect and weigh multiple lines of evidence in evaluating and making decisions about human health risks posed by vapor intrusion. How risks from petroleum hydrocarbon vapors should be addressed. How the guidance applies to Superfund FYRs. When or whether preemptive mitigation is appropriate. Operations, maintenance, and termination of mitigation systems. When institutional controls are appropriate. In its response letter dated March 11, 2010, OSWER generally agreed with OIG s recommendations to finalize guidance on vapor intrusion. In addition, the OIG recommended 13

119 that EPA identify and publicly report the portions of its Draft VI Guidance that remain valid and the portions that would be updated. 42 This Technical Guide and the companion documents identified in Sections 1.3 and 1.4 fulfill EPA s commitment to address the OIG s recommendations. Table 1-1 identifies specific updates prepared by EPA in response to OIG s specific recommendations. Table 1-2 describes additional updates identified and publicly announced by EPA (EPA 2010b). TABLE 1-1 DIRECTORY TO UPDATES IN THIS TECHNICAL GUIDE ADDRESSING RECOMMENDATIONS OF EPA OFFICE OF INSPECTOR GENERAL (EPA 2009A) Topics to Be Addressed Location Within This Technical Guide Companion Documents Update toxicity values VISL Calculator (EPA 2015a) Use of multiple lines of evidence in evaluating and making decisions about risks from vapor intrusion How risks from petroleum hydrocarbon vapors should be addressed How this Technical Guide applies to Superfund Five-year Reviews (FYRs) When or whether preemptive mitigation/early action is appropriate Sections 5, 6, and 7 Sections 1.3.1, and 7.3 Sections 3.3 and 7.8 Operations and maintenance of mitigation systems Section 8.3 Termination of mitigation systems Section 8.7 When ICs and deed restrictions are appropriate. Section 8.6 Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites (EPA 2015b) Assessing Protectiveness at Sites for Vapor Intrusion: Supplemental Guidance to the Comprehensive Five-Year Review Guidance (EPA 2012c) 42 OSWER carried out this recommendation by issuing a memorandum in August 2010, entitled Review of the Draft 2002 Subsurface Vapor Intrusion Guidance (EPA 2010b). The guidance reflected in this memorandum is incorporated in this Technical Guide. 14

120 TABLE 1-2 DIRECTORY TO ADDITIONAL UPDATES IN THIS TECHNICAL GUIDE PUBLICLY IDENTIFIED BY OSWER (EPA 2010B) Topics to Be Updated, Including References to the Draft VI Guidance Location Within This Technical Guide Companion Technical Document or Resource Updated a few chemical-specific physical parameters used for identifying the vapor-forming chemicals of concern. Updated the toxicity-based criteria in Table D-1 in the draft guidance. Section 3.1 Section 3.1 VISL Calculator (EPA 2015a) VISL Calculator (EPA 2015a) Observation-based conservative attenuation factors have been updated w ith a larger database. The generic attenuation factor for external soil gas has been updated, as w ell as the Reliability Assessment, using the new er available data. Observational data since 2002 indicates that the single line of evidence approach w ith site-estimated attenuation factors is generally not appropriate for external soil gas samples. Experiences since 2002 illustrate the value of collecting indoor air samples earlier in the investigations. The indoor air last approach has been updated, w hich w ill allow more flexibility in the sequencing of subsurface and interior/indoor sample collection. The portions addressing background contamination have been updated. EPA also updated w ith more specific methodologies for evaluating and/or decision-making and managing background contamination. The portion of this Technical Guide focusing on testing indoor air has been updated to allow more flexibility in the duration of sampling to take advantage of other sampling durations and methods. The Draft VI Guidance allow s site-specific decisions to be made based on indoor air concentrations in a relatively few representative buildings. This portion of this Technical Guide has been updated to increase the confidence that the approach fully addresses building-by-building variability. Updated and expanded the community involvement information to be more specific to vapor intrusion sites, including guidelines for effective risk communication and available resources, outreach products and tools for outreach. Section and Appendix A Section and Appendix A Sections and Sections 6.3.5, 7.4 and 7.6 Section Sections and 7.8 Section 9 U.S. EPA s Vapor Intrusion Database: Evaluation of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings (EPA 2012a) Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences ( ): A Compilation of Statistics for Assessing Vapor Intrusion (EPA 2011a) 15

121 1.6 Public Involvement in Developing this Vapor Intrusion Technical Guide On November 29, 2002, EPA published a notice in the Federal Register (67 FR 71169) announcing and soliciting comment on its Draft VI Guidance. Since that time, EPA continued to gather information and learn more about vapor intrusion, in part by convening periodic forums where practitioners, regulated parties, and regulators could discuss the emerging science and engineering pertaining to vapor intrusion assessment and mitigation. In addition, on March 17, 2011, EPA published a notice in the Federal Register (76 FR 14660) re-opening the docket and soliciting additional comment on its development efforts for this Technical Guide. The docket was re-opened again in March 2012 to receive comments about specific technical documents that were prepared to support development of this Technical Guide; these technical documents are listed in Section 1.4. Finally, another review draft was released on April 16, 2013 for public comment. In developing and refining this Technical Guide, EPA considered all public comments and input received since EPA also proactively engaged communities beyond the traditional outreach practices, especially environmental justice communities and communities subject to multiple stressors. 43 Aspects of this engagement have included: Conducting public listening sessions in communities impacted by vapor intrusion to solicit input on developing this Technical Guide. Using Internet sites and other communication tools to update stakeholders on the progress of developing this Technical Guide. Table 1-3 identifies specific vapor intrusion topics that have received substantive public comment as a result of EPA s outreach efforts. 1.7 Organization The next nine sections of this Technical Guide are as follows: Section 2.0 Conceptual Model of Vapor Intrusion further describes vapor intrusion and identifies many of the variables that influence vapor migration in the vadose zone and soil gas entry into buildings. Section 3.0 Overview of this Vapor Intrusion Technical Guide provides an overview of this Technical Guide and the general recommended framework for vapor intrusion assessment and response action. Section 4.0 Considerations for Nonresidential Buildings provides information regarding EPA roles, responsibilities, and risk management decision-making in nonresidential settings, including those (e.g., manufacturing facilities) where workers handle volatile hazardous chemicals similar to or different from those contaminating the subsurface. 43 For more information about the Community Engagement Initiative visit: w w.epa.gov/oswer/engagementinitiative/ 16

122 TABLE 1-3 VAPOR INTRUSION TOPICS RECEIVING SUBSTANTIVE PUBLIC COMMENT Topics Applicability to petroleum hydrocarbons Applicability to nonresidential buildings Location Within This Technical Guide Sections 1.3.1, and 7.3 Sections 1.3.2, 4.0 and Companion Document(s) Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites (EPA 2015b) Conditions warranting prompt response action Sections 5.2, 7.5 and Planning investigations and applying data quality objectives Section 6.2 and Appendix B Sampling and monitoring methods for indoor air Section Attenuation factors and risk-based screening Section 6.5 and Appendix A U.S. EPA s Vapor Intrusion Database: Evaluation of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings (EPA 2012a) Semi-site-specific screening and application of mathematical models Sections 6.5 and 6.6 Use of conceptual site models and multiple lines of evidence in evaluating risks posed by vapor intrusion Sections 2, 3.2, 5.4, 6.3 and 7 Risk management benchmarks and decisionmaking Section 7 Use of institutional controls for building mitigation Section 8.6 Monitoring and termination of mitigation systems Sections 8.4 and 8.7 Risk communication Section 7.4 and 9 17

123 Section 5.0 Preliminary Analysis of Vapor Intrusion provides technical information for situations where only limited site-specific data may be available (e.g., initial site assessment). Section 6.0 Detailed Investigation of Vapor Intrusion provides technical information for conducting site-specific vapor intrusion assessments emphasizing multiple lines of evidence, including consideration of background concentrations. Section 7.0 Risk Assessment and Management Framework provides general recommendations about data evaluations and risk-informed decision-making pertaining to vapor intrusion, including consideration of background concentrations. Section 8.0 Building Mitigation and Subsurface Remediation provides technical information for mitigating vapor intrusion and describes how subsurface vapor source remediation and other final cleanup actions are combined with engineered and nonengineered exposure controls to ensure protection of human health. Section 9.0 Planning for Community Involvement provides information and describes available resources for engaging affected communities and communicating risk-related information. Section 10.0 Glossary provides definitions and descriptions of key terms used in this document. This Technical Guide concludes with Section 11.0, Citations and References, and three supporting appendices: Appendix A: Recommended Subsurface-to-Indoor-Air Attenuation Factors. Appendix B: Data Quality Assurance Considerations. Appendix C: Calculating Vapor Source Concentration from Groundwater Sampling Data. 18

124 2.0 CONCEPTUAL MODEL OF VAPOR INTRUSION This section presents a general (i.e., not site-specific) conceptual model of vapor intrusion, borrowing from published depictions (EPA 2008a; EPA 2012b; ITRC 2007a; McAlary et al. 2011; DoD 2009). It identifies and describes the what, where, how and why of vapor intrusion, to provide insights about the many of the lines of evidence pertinent to evaluating vapor intrusion on a site-specific basis, which are discussed further in Sections 5, 6, and 7 of this Technical Guide. 44 It concludes with several general observations that may assist practitioners when planning and conducting detailed vapor intrusion investigations at specific sites, which is the subject of Section 6 of this Technical Guide. Vapor intrusion is a potential human exposure pathway a way that people may come into contact with hazardous vapors while performing day-to-day indoor activities. Figure 2-1 summarizes the vapor intrusion pathway for soil gas entry. For purposes of this Technical Guide, the vapor intrusion pathway is referred to as complete 45 for a specific building or collection of buildings when the following five conditions are met under current conditions: 1. A subsurface source of vapor-forming chemicals is present (e.g., in the soil or in groundwater) underneath or near the building(s); 2. Vapors form and have a route along which to migrate (be transported) toward the building(s); 3. The building(s) is(are) susceptible to soil gas entry, which means openings exist for the vapors to enter the building and driving forces exist to draw the vapors from the subsurface through the openings into the building(s); 4. One or more vapor-forming chemicals comprising the subsurface vapor source(s) is (or are) also present in the indoor environment; and 5. The building(s) is (or are) occupied by one or more individuals when the vapor-forming chemical(s) is (or are) present indoors. 46 If one (or more) of these conditions is currently absent and is reasonably expected to be absent in the future (e.g., vapor migration is significantly and persistently impeded by natural geologic, hydrologic, or biochemical (e.g., biodegradation) processes and conditions), the vapor intrusion pathway is referred to as incomplete. 44 In general, a conceptual site model integrates all lines of site-specific evidence into a three-dimensional conceptualization of site conditions that includes contaminant sources, release mechanisms, vapor migration route(s), and potential receptors. Section 5.4 provides additional information about developing conceptual site models. 45 A complete vapor intrusion pathw ay indicates that there is an opportunity for human exposure in the subject building(s), w hereas an incomplete pathw ay w ould not provide an opportunity for human exposure, 46 The exposure route of general interest for vapor intrusion is inhalation of toxic vapors present in indoor air. Because breathing is not avoidable for prolonged periods, individuals in occupied buildings are presumed to be exposed by the inhalation route to any hazardous vapors present in indoor air. Hence, the presence of a human exposure route is implied in the fifth condition. 19

125 Figure 2-1 Illustration of Key Elements of the Conceptual Model of Soil Vapor Intrusion Note: Q soil represents soil gas entry; Q bldg represents air exchange. 20

126 The first three of these five conditions are further discussed in the next three subsections. Knowledge of potential vapor sources and vapor fate and transport mechanisms is essential for interpreting the data collected during a site-specific investigation of vapor intrusion. Knowledge of the factors that influence the vapor intrusion pathway is also invaluable for identifying, prioritizing, and sequencing data collection activities, which allows a phased and efficient overall investigation plan to be developed. Practitioners are encouraged to refer to quantitative discussions of these subjects, which are provided in Conceptual Model Scenarios for the Vapor Intrusion Pathway (EPA 2012b). The human population of primary interest is comprised of individuals living in, working in, or otherwise occupying a building subject to vapor intrusion. All types of buildings have openings and conduits that render them potentially vulnerable to vapor intrusion. This includes residential buildings (e.g., single-family homes, trailer or mobile homes, multi-unit apartments and condominiums), commercial workplaces (e.g., office buildings, retail establishments), industrial facilities (e.g., manufacturing plants), and educational and recreational buildings (e.g., schools and gyms). Vapor intrusion can occur in buildings with any foundation type (e.g., basement, crawl space, slab-on-grade). As noted previously, methane and certain other vapor-forming chemicals can also pose explosion hazards in buildings and unoccupied structures, 47 depending upon building-, structure-, and site-specific circumstances. The discussion in the next three sections pertains also to methane and other vapor-forming chemicals that can pose explosion hazards, because similar processes and conditions are involved in explosive vapors migrating towards the interior of buildings or non-occupied structures from the subsurface environment; i.e., 1) A subsurface source of vapor-forming chemicals is present (i.e., in the soil or in groundwater) underneath or near the structure(s) or building(s). 2) Vapors form and have a route along which to migrate (be transported) toward the structure(s) or building(s). 3) The structure(s) or building(s) is (or are) susceptible to soil gas entry, which means openings exist for the vapors to enter the structure(s) or building(s) and driving forces exist to draw the vapors from the subsurface through the openings into the structure(s) or building(s). 47 For purposes of evaluating potential explosion hazards, non-occupied structures, in addition to buildings, are relevant structures for intrusion and accumulation of vapors. 21

127 2.1 Subsurface Vapor Sources The originating (i.e., primary) source(s) of subsurface contamination may include, but are not limited to, leaking tanks (above or below ground), discharges to sewer lines 48, septic tanks, and floor drains, landfills and other land disposal management units, fire-training areas, spills, discharge areas, and vapor leaks from pressurized tanks and pipelines. The resulting subsurface contamination may be comprised of non-aqueous-phase liquids (NAPLs) 49 (e.g., solvents; petroleum-related products, such as gasoline) and contaminated soil. These are often referred to as the source zone(s). Groundwater and sewer lines 50 flowing through or underneath 51 the source zone(s) can become contaminated and in turn become a (secondary or derivative) subsurface vapor source of contaminant vapors at locations distant from the source zone. Contaminants in soil, NAPLs, and groundwater can become sources for vapor intrusion if they are likely to volatilize under normal temperature and pressure conditions. Water solubility is also a factor for chemicals in source zones that come into contact with migrating groundwater. Common classes of chemicals of concern for vapor intrusion that exhibit the foregoing characteristics are VOCs, such as tetrachloroethylene (PCE), trichloroethylene (TCE), vinyl chloride, carbon tetrachloride, and benzene, toluene, ethylbenzene and xylenes (collectively, BTEX). Other compounds that are not as volatile as these VOCs (e.g., so-called semi-volatile organic compounds), but that may be cause for concern, include some polycyclic aromatic hydrocarbons (PAHs) (e.g., naphthalene), some polychlorinated biphenyl (PCB) congeners, and elemental mercury, a dense NAPL (DNAPL) Historically, sanitary sew ers and septic tanks have been common disposal points for aqueous and chemical w astes from commercial and industrial operations. Contaminated w ater, non-aqueous phase liquid (NAPL), and VOC vapors can leak from sew er lines through cracks, joints, or breaks. A study of solvent contamination in California arising from dry cleaning operations concluded that discharges to and leakage from sew er lines is an important source of PCE contamination of soil and groundw ater: Where a source investigation has been done in connection w ith PCE contamination, the data strongly indicate that leakage through the sew er lines is the major avenue through w hich PCE is introduced to the subsurface. (Izzo 1992). In the South Weber neighborhood near the Hill Air Force Base in Utah, sew er lines carrying discharged contaminated groundw ater to the municipal treatment system w ere identified as a source of vapor intrusion in homes [Source: EnviroNews - Updating environmental issues and activities at Hill Air Force Base, Utah (March 2011); Currently available on-line at: ww.hillrab.org/new s.aspx] 49 EPA s Contaminated Site Cleanup Information w ebsite ( w w.clu-in.org/) provides information describing NAPLs that are denser than w ater (DNAPLs) or less dense than w ater (LNAPLs), and methods for their detection and remediation in the subsurface environment. 50 In addition to receiving direct discharges, sew ers can be indirect receptacles of subsurface contamination via infiltration of NAPL, soil gas, or contaminated groundw ater through cracks in piping and manholes. For example, Vroblesky et al (2011) found that infiltration of contaminated groundw ater into sew ers and its transport via and exfiltration from sew ers caused complex and unanticipated patterns of groundw ater contamination at a site in South Carolina. 51 Figure 2-1 illustrates a NAPL release/source (near the commercial/industrial building on the left) that fully penetrates the vadose zone. A partially penetrating NAPL release/source may also cause groundw ater contamination, how ever, as infiltrating w ater passes through the source zone and migrates to the groundw ater table. 52 Once volatilized into soil or sew er gas from a subsurface vapor source(s), these less volatile chemicals w ill migrate under the influence of diffusion and advection (see Section 2.2) as do more volatile chemicals, although there may be chemical-specific differences in their susceptibility to biodegradation in the vadose zone. 22

128 Landfill gases, such as methane and hydrogen sulfide, also can be associated with the vapor intrusion pathway for buildings located near current or former landfills or other degrading wastes. These gases are actively produced as a result of anaerobic biodegradation processes. Methane can also be associated with the vapor intrusion pathway for buildings located near degrading petroleum hydrocarbons or fuel-grade ethanol released into the subsurface environment (Ma et al. 2014, 2012; Sihota et al. 2013). Properties with potential contamination by vapor-forming chemicals can be found in many industrial and commercial areas. These properties include current and former manufacturing and chemical processing plants, warehouses, landfills and other land disposal units, coal gasification plants, chemical handling or transfer facilities and areas (e.g., train yards), dry cleaners, and retail fueling outlets (also known as gas stations). Use, storage, or transport of chemicals at these facilities may have resulted in a release of vapor-forming chemicals to the environment creating the potential for future vapor intrusion issues. In addition to industrial and commercial activities, roadside dumping, pesticide spraying, or even disposal of household chemicals via a septic field may also release volatile chemicals that may eventually migrate to the subsurface environment. The primary contamination source need not, however, be on the property of interest to pose a vapor intrusion problem. 53 As illustrated in Figure 2-1, the primary source(s) of vapor intrusion (e.g., contaminated soil, or leaked tanks) may be present on a neighboring property or on a property some distance away. Even greenspace properties that have not previously been occupied or developed may contain contamination by vapor-forming chemicals due to migrating plumes of contaminated groundwater or migrating soil gases. 54 In the case of groundwater as a subsurface vapor source for vapor intrusion, the source strength will be influenced by the vertical distribution of contaminant concentrations in the upper reaches (e.g., top foot) of the water table and by seasonal fluctuations in the groundwater table groundmass flux of vapors. If vapor-forming chemicals are not present in the upper reaches (e.g., within the uppermost foot) of the groundwater table (e.g., due to the presence of an overlying zone of clean water from recharge; i.e., fresh water lens ), 55 vapor transport to the overlying vadose zone will be impeded due to the slower diffusion of volatile chemicals in water 53 Depending on the geology and amount and form of contamination in the source zone(s), contaminated groundw ater plumes can be long and narrow and can flow beneath a property located a mile or more aw ay from the primary source. Soil gas plumes tend to extend in both lateral directions and can be larger in lateral extent relative to groundw ater plumes. 54 See Section for further discussion on w hich buildings and non-occupied structures are considered near for purposes of a preliminary analysis. 55 Infiltrating precipitation is important in recharging aquifers w ith fresh w ater, as w ell as in w etting vadose zone soils. At locations distant from source zones, infiltrated w ater that reaches the upper surface of a plume of contaminated groundw ater (i.e., recharges groundw ater) in an unconfined aquifer w ill tend to dilute concentrations of vapor-forming chemicals and may form a lens of relatively clean w ater at the groundw ater table, w hich overlies the plume. Because diffusion of dissolved-phase volatile chemicals w ill tend to control the mass transfer of vapors into the soil gas at the groundw ater table, the presence of a lens of clean w ater as little as a foot in thickness overlying a plume may be sufficient to impede vapor flux to the vadose zone (McAlary et al. 2011). This condition is less likely to occur w here fluctuations of the groundw ater table are large, relative to local recharge, and w ould not generally be expected in arid climates. 23

129 than in soil gas. For this reason, Figure 2-1 does not show vapors emanating from the leading (i.e., right-most) edge of the plume. If the vapor-forming chemicals are present in the upper reaches of the groundwater table (i.e., volatile chemicals are in the uppermost reaches of an unconfined water table aquifer), fluctuations in the water table will tend to transport the volatile chemicals upward (during periods of rising water table) or expose impacted water above the water table to soil gas (during periods of falling water table). The latter will facilitate the episodic formation of vapors in the vadose zone. Rising water tables also will bring the vapor source closer to the building(s). 2.2 Subsurface Vapor Migration At many sites, the subsurface vapor source (e.g., in soil or groundwater) is not in contact with the bottom of the subject building. Under these circumstances, vapors emanating from the source medium enter the pore space around and between the subsurface soil particles in the soil column above the groundwater table, which is called the unsaturated soil zone or vadose zone. If the subsurface vapor source is in the vadose zone, the vapors have the potential to migrate radially in all directions from the source via diffusion (i.e., upward toward the atmosphere, laterally outward, and downward toward the water table; downward migration may eventually lead to groundwater contamination). If the subsurface vapor source is in the uppermost zone of groundwater, the vapors have the potential to migrate upwards toward the atmosphere via diffusion. Figure 2-1 illustrates these conditions and this process. Regardless of source type, soil gas concentrations emanating from a subsurface vapor source generally attenuate, or decrease, as the volatile chemicals move from the source through the soil and into indoor air. If and when soil vapor monitoring data at a given site are not consistent with this trend, the conceptual site model may be incomplete (e.g., additional, unrecognized sources or a preferential migration route(s) may exist at the site) and/or bias or error may have been imparted by the sampling and analysis techniques. Diffusion, which is caused by the random motion of molecules, affects the distribution of soil vapors when there are spatial differences in chemical concentrations in the soil gas. The net direction of diffusive transport is toward the direction of lower concentrations. Advection occurs in the vadose zone when there is bulk movement of soil gas induced by spatial differences in soil gas pressure. The direction of advective vapor transport is always toward the direction of lower air pressure. Advection is generally expected to occur in the vicinity of buildings, because differences in temperature between the building interior and the subsurface environment or the operation of combustion units or fans within the building can create driving forces for soil gas entry (See Section 2.3). Advection of soil gas may also occur: near the ground surface due to fluctuations in barometric (atmospheric) pressure, which can either release soil gas into the atmosphere (Clements and Wilkening 1974) or 24

130 introduce ambient air into the subsurface environment (the latter process may be important in oxygenating surface soil horizons); 56 wherever methane generation from anaerobic degradation is sufficiently high (e.g., near some landfills, some locations with degrading fuels). Advection may be hindered where extensive surface barriers, such as asphalt, concrete, or frozen soil are present. Vapors also can migrate via advection (and diffusion) along a preferential subsurface pathway, such as a utility corridor or more porous zones of soil or rock, or beneath surface barriers that limit the direction(s) of vapor migration, such as frozen ground or asphalt. 57 Vapor migration in the vadose zone can be impeded by several factors, including high soil moisture, low-permeability (generally fine-grained) soil, and biodegradation: High moisture levels in the vadose zone can significantly reduce the effective rate of diffusive transport, owing to the substantially smaller diffusion coefficient of vaporforming chemicals in water compared to air. Where ground covers, such as asphalt or concrete, are absent, soil cores taken external to building structures can reasonably be expected to show greater soil moisture than underneath buildings (Tillman and Weaver 2007), particularly after episodes of precipitation and infiltration. Fluctuations in the elevation of the groundwater table can also contribute to temporal changes in soil moisture profiles, in addition to changing the thickness of the vadose zone. A low-permeability layer in the vadose zone, particularly one with high moisture content or perched water, may impede or prevent upward migration of vapors from deeper sources in the vadose zone. Figure 2-1 illustrates partial impedance due to a silty or clay layer of limited lateral extent. 58 In some cases, soil or rock can impose sufficient resistance to vapor migration to make the vapor intrusion pathway insignificant, because low-permeability layers are laterally extensive over distances that are large compared to the size of the building(s) or the extent of subsurface contamination with vapor-forming chemicals. 56 Under certain conditions, such as periods during w hich indoor outdoor pressure differences are small, atmospheric pressure fluctuations may contribute to the vapor flux into a building (Robinson and Sextro, 1997). 57 Whether the subsurface vapor source is contaminated soil or groundw ater, soil gas concentrations emanating from a subsurface source generally attenuate, or decrease, as the vapors move from the source through the soil and into indoor air due to diffusion and advection and are subject to any degradation. If and w hen soil vapor monitoring data at a given site are not consistent w ith this trend, the possible existence of a preferential migration route(s) w arrants consideration. Sew er lines also w arrant consideration as potential sources of vapors, as w ell as conduits for preferential (e.g., unattenuated) transport of vapors tow ards buildings. Preferential migration routes are discussed further throughout this Technical Guide, including in Sections 5.4, 6.3.2, and Low -permeability layer(s) overlying contaminated groundw ater (i.e., aquicludes ) can, likew ise, impede the flux of vapors from the contaminated plume to the vadose zone. The aquiclude show n at the base of Figure 2-1 w ould not impede the flux of vapors from the contaminated plume to the vadose zone, how ever, because the aquiclude is below both. The aquiclude w ould impede vapor flux from any additional contaminated plume located below it. 25

131 Some chemicals (e.g., benzene, methane, and other petroleum hydrocarbons; vinyl chloride (Patterson et al. 2013) and some other chlorinated hydrocarbons) may experience reductions in their soil gas concentrations due to biodegradation in the vadose zone under certain conditions. Depending upon the potential for oxygen to migrate into the subsurface and underneath buildings from the ambient air, biodegradation may be anaerobic or aerobic. The rate of biodegradation in situ will be chemical-specific (i.e., chemicals have different degradation rates even within a similar microbial environment), will be site-specific (i.e., the microbial environment will depend upon soil moisture, nutrient and oxygen levels, and the chemical mixture, 59 among other factors (Holden and Fierer 2005)), and may be location-specific (i.e., the microbial environment can change over time and space due to variations in soil moisture, 60 nutrient and oxygen 61 levels). In some cases, biodegradation in the vadose zone can impede vapor migration significantly. Demonstrating the extent, if any, to which these processes act as a barrier to vapor transport at specific sites may entail intensive testing or investigative methods that are very different from the sampling and analysis techniques for indoor air and soil gas (see, for example, Sections and 6.4). Where and when it occurs, biodegradation may result in the formation of byproducts that are potentially hazardous (e.g., methane from ethanol, vinyl chloride from PCE or TCE). The distribution and magnitude of soil gas concentrations immediately beneath a building are expected to reflect the interplay between vapor transport toward the building (via diffusion and advection) in the vadose zone and vapor withdrawal due to soil gas entry into the building (in the case where the building is under-pressurized), which may be spatially and temporally variable (Section 2.3). Likewise, soil vapor may become contaminated as a result of overpressurized buildings forcing contaminated indoor air through openings in the foundation into nearby soil. 2.3 Openings and Driving Forces for Soil Gas Entry into Buildings Hazardous vapors in the vadose zone may eventually enter buildings as a component of a gas by migrating through cracks, seams, interstices, and gaps in basement floors, walls, or foundations ( adventitious openings ) or through intentional openings, such as perforations due to utility conduits and sump pits. Figure 2-2 illustrates some of these types of openings. Buildings can be expected to vary, even within a single community, in the amount of opening 59 For example, aerobic biodegradation of benzene may be impeded by the presence of methane, due to competition for oxygen by methane-oxidizing ( methanotrophic ) bacteria, depending upon site-specific conditions (Ma et al. 2012). 60 Moisture plays a particularly important role for microorganisms in the vadose zone. Microbial grow th and activity can decrease rapidly w ith depth, coincident w ith the soil moisture profile, and increase again in the capillary fringe (Holden and Fierer 2005). 61 Site-specific infrastructure and soil conditions, climate, and other factors w ill determine the extent to w hich oxygen levels underneath a building w ill be different compared to locations outside the building footprint. In addition to buildings, surface covers, such as asphalt or concrete, can impede oxygenation of the vadose zone, relative to the case w here the ground surface is in contact w ith the atmosphere, all other factors being equal. 26

132 Figure 2-2 Illustration of Potential Openings in Various Building Types Note: Blue arrows represent soil gas migration or entry. Source: EPA (2008) 27

133 area available for soil gas entry; for example, buildings with deteriorating basements and foundations or dirt floors are more susceptible to soil gas entry. As mentioned in Section 2.2, advection in the vadose zone can arise in the vicinity of buildings whenever there is a difference between the air pressure within a building and the subsurface environment. The air pressure within a building can be lower than in the subsurface due to: Temperature differences between indoor and subsurface locations (e.g., the winter-time stack effect, when buildings are commonly heated, leading to convection cells driven by heated air that rises to upper levels and leaks through roofs and upper-floor windows). The operation of mechanical devices, such as exhaust fans for ventilation, air conditioners, and clothes dryers, with vents to the outdoors. The operation of fireplaces that vent combustion (exhaust) gases to the outdoors. The operation of furnaces in basements of centrally heated buildings, which can incrementally depressurize the basement (EPA 1993a). Wind load on the building walls. 62 Even small pressure differences may cause advective flow of soil gas into or out of the building through pores, cracks, or openings in the building floor or basement walls 63 or gas present in drain lines, sumps, and sewer lines that do not have adequate vapor traps The w ind effect is caused by differences in building pressure on a building s surfaces. The outdoor air pressure w ill be higher on the w indw ard side of the building, than on the leew ard side, as ambient air flow s around the building. The net effect of this pressure difference w ill vary from building to building, depending upon the location of the primary openings for soil gas entry (and the primary opening for air infiltration through the building envelope see Section 2.4) (EPA 1993a, Section 2.3 therein). 63 As a result of the construction of foundation w alls and floor slabs, a perimeter crack (i.e., space betw een the floor slab and w alls) may be created and serve as an entry location for soil vapors. This perimeter crack is often obscured by w all coverings, and may not be accessible for inspection or direct testing. Vapors have been observed to migrate through w hat appears to be intact concrete floors and w alls, w hich may, in fact, have small unobserved fractures or porous areas from improper curing. In addition, conduits may be present that facilitate soil gas entry into buildings. These conduits may include utility (e.g., sew er, w ater, or electrical) penetrations and floor drains 64 Where sew ers or other conduits contain volatile contaminants, lateral lines connecting buildings to these conduits may facilitate vapor intrusion into indoor air. Although floor drains are designed to allow w ater to drain aw ay from the building, they are usually not designed or constructed to eliminate gas entry. At a test house in Indianapolis, elevated levels of PCE and chloroform w ere found in gas in a laundry drain line, w hich w as suspected of serving as a source of vapors found in indoor air (EPA 2012f). Although building construction codes and toilet designs are intended to prevent sew er gas from entering homes, inadequate maintenance (e.g., plumbing fixture seals) can result in loss of the intended protection. Pennell et al (2013), for example, found sew er gas entry to be a significant source of PCE in indoor air at a home in Massachusetts. In addition, sew er gas w as a suspected source of benzene in indoor air in many buildings near a gasoline spill site in Hazleton, Pennsylvania (w ww.epa.gov/reg3hw md/npl/pa htm), w here sew er vent traps w ere subsequently installed to mitigate intrusion of gasoline vapors into homes. 28

134 To date, most analytical and computational models of vapor intrusion have been predicated on the assumption that residences and other small buildings experience a constant underpressurization (i.e., lower pressure in the building than in the subsurface), which fosters vapor intrusion. Whereas this assumption facilitates analyses and may be reasonable for some purposes (see, for example, Section 2.5), it is highly idealized. To illustrate: fluctuations in subslab-to-building pressure difference (and, hence, soil gas entry rates) over time can be reasonably expected due to: diurnal (daily) and seasonal changes in the temperature of ambient air, whereas indoor temperatures may be more stable, particularly during periods when mechanical heating and cooling systems are in use; changes in ambient air pressure; non-instantaneous response (i.e., lag or delay in response) of subsurface soil gas to changes in ambient air pressure (EPA 1993a, Section 2.3 therein), particularly where low-permeability soil is in direct contact with a building foundation (e.g., basement) below the ground surface; 65 changes in wind direction and speed; and intermittent operation of mechanical ventilation systems and combustion devices that vent exhaust gases to the outside. Theoretically, these processes and variables suggest that soil gas entry rates can be expected: to vary over different time scales (e.g., within an day, and between seasons); to differ geographically due to differences in ambient air temperature, pressure, wind, and building conditions (e.g., leakage area and its distribution over the building envelope); and to be discontinuous over some time periods. 65 On the other hand, w here granular fill is present underneath a building, there is potential for preferential soil gas flow through the fill, especially in locations w here the gas permeability of the surrounding soil is low. Where granular materials have differentially settled, air voids (also highly permeable to soil gas flow ) may form beneath the foundation. Utility penetrations and other conduits may be connected to the granular fill, accentuating the potential pathw ay for soil gas entry into a building. Adding to the complexity, pressure differentials caused by w ind flow s conceivably could create a cross-flow through granular fill underneath the foundation, w hich may episodically dilute vapor concentrations (and oxygenate soil gas) in the building vicinity. 29

135 2.4 Air Exchange and Mixing Air exchange refers to the flows into and out of a building, which are generally in balance, and is composed of three processes: 1) infiltration air leakage through random cracks, interstices, and other unintentional openings in the building envelope; 2) natural ventilation airflows through open windows, doors, and other designed (intentional) openings in the building envelope; and 3) mechanical ventilation air movement controlled and driven by fans. For the vapor intrusion exposure scenario, air exchange by each of these processes will generally tend to mitigate the effects of vapor intrusion (i.e., reduce indoor air concentrations) via dilution, while air inflows will also transport indoors any vapor-forming chemicals in ambient air (see Section 2.7). 66 The air exchange rate is conventionally defined as the ratio of the airflow rate (e.g., cubic meters per second) to the building volume (e.g., cubic meters) and is generally expressed in terms of exchanges per hour (i.e., overall units of hour 1 ). Values for residential air exchange rates are typically on the order of approximately 0.18 to 1.26 air changes per hour (ACH) (EPA 2011b, see Table therein, 10 th and 90 th percentiles). 67,68 Values for non-residential buildings are highly-dependent upon building use and can range widely (on the order of approximately 0.3 to 4.1 ACH) (EPA 2011b, see Table therein, 10 th and 90 th percentiles). 66 The potential diluting effect of air exchange arises w hen ambient air has negligible presence of the volatile chemicals found in site-related contamination in the subsurface environment. In some situations, site-related contamination has the potential to impact ambient air w ith the same vapor-forming chemicals that pose a threat from vapor intrusion. For example, contamination of shallow soil or groundw ater may release site-related vapor-forming chemicals to ambient air. In such situations, air exchange w ould contribute to the presence of site-related contamination in indoor air, rather than only dilute any impacts from vapor intrusion. 67 EPA s Office of Research and Development evaluated eight studies of air exchange rate for residential buildings and selected a 1995 EPA study as the basis for recommending values for risk assessment (EPA 2011b, Table 19-24). The key study analyzed almost 3,000 time-averaged measurements of exchange rate in occupied homes in the United States, w hich w ere generally obtained using a tracer-release method. Median values ranged from 0.35 hour 1 in the mid-w estern region to 0.49 hour 1 in the northeast and southern regions. Tenth percentile values ranged from 0.16 hour 1 in the mid-w estern and southern regions of the U.S. to 0.23 hour 1 in the northeast region. Regional differences in exchange rate reflect differences in w eather (e.g., temperature and w ind speed), prevailing building conditions (e.g., house leakiness ), and the time periods (e.g., season) in w hich measurements w ere made. 68 EPA s Office of Research and Development (EPA 2011b, Section ) also summarized a study that conducted approximately 500 indoor-outdoor air exchange rate (AER) calculations based on residences in three urban locations (metropolitan Elizabeth, NJ; Houston, TX; and Los Angeles, CA). This study highlights how climate and season can influence air exchange rate. In Texas, the measured AERs w ere low er in the summer cooling season (median = 0.37 ACH) than in the w inter heating season (median = 0.63 ACH), likely because w indow s w ere closed w hile air conditioners w ere in use. The measured AERs in California w ere higher in summer (median = 1.13 ACH) than in w inter (median = 0.61 ACH), because summers in Los Angeles County are less humid than NJ or TX and residents are more likely to utilize natural ventilation through open w indow s and screened doors. In New Jersey, air exchange rates in the heating and cooling seasons w ere similar. 30

136 To date, most analytical and computational models of vapor intrusion have been predicated on the assumption that residences and other small buildings are well mixed spaces throughout which concentrations of vapor-forming chemicals are uniform. Whereas this assumption facilitates analyses and may be reasonable for some purposes (see Section 2.5), it is highly idealized. To illustrate: airflow within a building (i.e., inter-zonal airflow) can be impeded by doors, walls, and other partitions that separate rooms and other building areas. Whereas airflows within a building can be facilitated by mechanical means, spatial variation of temperature and humidity suggest that air mixing is not necessarily complete even in buildings that benefit from centralized systems for heating, air condition, and ventilation. Furthermore, many residences do not have such mechanical systems. Therefore, buildings subject to vapor intrusion may exhibit differences in concentration of vapor-forming chemicals among building areas (e.g., rooms) as a result of the differential proximity to openings for soil gas entry (see Section 2.3) and openings for air leakage and ventilation and the magnitude and balance of inter-zonal airflows. For example, rooms with perforations through the foundation (e.g., bathrooms or utility rooms) may have greater concentrations of vapor-forming chemicals in air compared to rooms that do not. Generally, basements can reasonably be expected to exhibit greater concentrations of vapor-forming chemicals than upper occupied levels. Buildings constructed over a crawl space with a dirt floor may benefit from the dilution of soil gas by any ventilation of crawl space air, but would not have the impedance to vapor intrusion that concrete slabs can provide. Trailers enclosed at the bottom by a skirt are expected to have greater potential for vapor intrusion than would non-enclosed trailers. Wind movement between the ground surface and the bottom of the non-enclosed trailer would tend to minimize vapor buildup and associated potential for vapor flux into the building. Similarly, the existence of underground parking for a multi-story building (or other modifications to the foundation that enhance subsurface ventilation) would tend to minimize the potential for vapor intrusion. 2.5 Conceptual Model Scenarios Based upon the foregoing conceptual model, numerous factors can influence the potential indoor air concentration arising from vapor intrusion. Some of these significant factors are illustrated in Figure

137 Vapor Source Vadose Zone Geology Vadose Zone Hydrology Vadose Zone Biochemistry Building Foundation Greater Vapor Intrusion Potential High Source Conc., Highly Volatile Chemicals See Sections 2.1 and Vertically Fractured or Coarse- Grained, Vertically Uniform Media See Sections 2.2 and Low Moisture Content in Vadose Zone, Shallow Water Table, Large Water Table Fluctuations See Sections 2.1, 2.2 and Unfavorable for Complete Degradation or Non- Degradable Chemicals See Sections 2.2 and Cracked Slab, Partial Slabs, Sumps or Drains See Sections 2.3, 6.3.3, and Less Vapor Intrusion Potential Low Source Conc., Less Volatile Chemicals Horizontal and Laterally Extensive Fine- Grained Layers High Moisture Content in Vadose Zone, Deep Water Table, Thick Capillary Fringe Favorable for Complete Degradation and Degradable Chemicals Intact, Extensive, and Thicker Slab Figure 2-3 Some Factors That Affect Vapor Intrusion 32

138 The document Conceptual Model Scenarios for the Vapor Intrusion Pathway (EPA 2012b) provides simplified simulation examples 69 to illustrate graphically how several of the subsurface and building-specific factors work together to determine the distribution of volatile contaminants in the subsurface and the indoor air concentration relative to a source concentration. The conceptual model scenarios document offers insights into the factors influencing the vapor intrusion pathway. It provides a theoretical framework with which to draw inferences about and better understand the complex vapor fate and transport conditions typically encountered at actual, non-idealized contaminated sites. The following general observations can be made from these simplified simulation examples, and may be useful when considering the vapor intrusion pathway at a particular site: The horizontal and vertical distance over which vapors may migrate in the subsurface depends on the source concentration, source depth, soil matrix properties (e.g., porosity and moisture content), and time since the contaminant release to the environment occurred. Months or years of volatilization and vapor migration may be required to fully develop vapor distributions in the vadose zone at sites with deep vapor sources or with impedances to vapor migration arising from hydrologic or geologic conditions. Vapor concentrations, including oxygen, in the vadose zone (i.e., soil gas concentrations) may not be uniform in sub-slab soil gas or in soil gas at similar depths exterior to the building of interest. Therefore, soil gas concentrations at exterior locations (i.e., outside a building s footprint) may be substantially different from the concentration underneath the building (e.g., the sub-slab concentration), depending on site-specific conditions and the location and depth of the exterior soil gas sample. Simulations assuming an idealized, constructed ground cover suggest that shallow soil gas concentrations can be greater under low-permeability ground covers (e.g., asphalt) than under soil open to the atmosphere. The soil gas distribution beneath a building is not the only factor that determines the indoor air concentration. The indoor air concentration is also influenced by building conditions, including the presence of openings (e.g., cracks, utility penetrations) in the foundation, building pressurization, and the air exchange rate. Advective flow into buildings, which is presumed to occur predominantly near cracks and openings in the foundation slab, may affect the distribution of vapor-forming chemicals directly beneath the structure. Heterogeneities in the permeability of geologic materials and backfill, along with wind effects and building and atmospheric pressure temporal variation, may also contribute to the spatial and temporal variability of vapor concentrations in sub-slab soil gas and indoor air. 69 Tw o important simplifications are the assumptions of constant values for the driving force for vapor intrusion (i.e., subslab to indoor air pressure difference) and air exchange rate, w hereas time-variable values are reasonably expected as a result of changing w eather and other conditions (as summarized in Sections 2.3 and 2.4, respectively). 33

139 Subsurface heterogeneities in site geology, such as layering and moisture content, can influence the extent and rate of vapor migration from a contaminant source towards overlying or adjacent buildings. The soil gas distribution of aerobically biodegradable chemicals (e.g., BTEX) can be significantly different than that of other chemicals that are not biodegradable (i.e., are recalcitrant) in similar settings. Specifically, the soil gas concentrations of aerobically biodegradable chemicals exhibit greater attenuation than those of recalcitrant chemicals when the subsurface availability of oxygen is adequate. 2.6 Variability in Exposure Levels Given the foregoing conceptual model of vapor intrusion and summary of modeled scenarios (EPA 2012b), the degree to which vapor intrusion is a pathway of concern can vary widely from site to site and from building to building within a site. Adding to the complexity, theoretical considerations (i.e., soil gas entry rates, air exchange rates, interior compartmentalization and inter-zonal airflows) suggest that indoor air concentrations arising from vapor intrusion can be expected to vary over time and within a building. Field observations and measurements demonstrate that indoor air concentrations can exhibit significant temporal variation within a day and between days and seasons in an individual residential building (EPA 2012a; Holton et al. 2013ab). 2.7 Consideration of Indoor and Outdoor Sources of VOCs Indoor air in many buildings will contain detectable levels of a number of vapor-forming chemicals whether or not the building overlies a subsurface source of vapors (EPA 2011a), because indoor air can be impacted by a variety of indoor and outdoor sources. Indoor sources of volatile contaminants include the use and storage of consumer products (e.g., cleaners, air fresheners, aerosols, mothballs, scented candles, insect repellants, or other household products), combustion processes (e.g., smoking, cooking, and home heating), occupant activities (e.g., craft hobbies, home improvements, automotive repairs), and releases from interior building materials (e.g., carpets, insulation, paint, and wood-finishing products). Outdoor sources of volatile chemicals may arise due to releases from nearby sources such as industrial facilities, vehicles, yard maintenance equipment, fuel storage tanks, and paint or pesticide applications; regional sources such as air emissions from regional industry, vehicle exhaust, agricultural activities, and fires; or global sources, such as distant air emissions. The outdoor air surrounding a building is referred to as ambient air throughout this Technical Guide. The contribution of indoor and outdoor sources of vapors (or both) to indoor air concentrations, which do not arise from site-related contamination, 70 is referred to as background throughout this Technical Guide (see, for example, Sections 2.7, 6.3.5, and and the Glossary). In 70 In some situations, site-related contamination has the potential to impact indoor or ambient air (EPA 1993c) w ith the same vapor-forming chemicals that pose a threat from vapor intrusion. For example, contaminated groundw ater in building sumps or intruding into the building via groundw ater seepage could provide an indoor source of siterelated contamination. Contamination of shallow soil or groundw ater may also release site-related vapor-forming chemicals to ambient air. In such situations, neither of these sources of indoor air contamination w ould be considered background. 34

140 some buildings, background sources by themselves can cause building occupants and visitors to experience significant exposures to vapor-forming chemicals. In contrast to background concentrations in soil arising from naturally occurring minerals, background concentrations in indoor air often are not uniform in time. For example, concentrations of vapor-forming chemicals in ambient air may exhibit temporal variation over several time scales (e.g., daily, seasonal, longer term) and spatial differences across urban, suburban, and rural land use areas, reflecting differences in emission sources and rates and environmental factors that transport, disperse, and remove these pollutants (Jia et al and citations therein). Concentrations of vapor-forming chemicals arising in indoor air in residential buildings due to indoor sources have been observed to depend upon season and other factors. Available studies suggest complex (e.g., patchy) spatial patterns in exposure concentration, which has led some researchers to refer to microplumes in the indoor air environment (McBride et al., 1999 and citations therein). 35

141 3.0 OVERVIEW OF THIS VAPOR INTRUSION TECHNICAL GUIDE This section provides an overview of this Technical Guide and the general recommended framework for vapor intrusion assessment and response action, which is illustrated in Figure 3-1. This section opens with a description of subsurface contaminants that have the greatest potential to pose a health concern via vapor intrusion, based upon their volatility and potential hazards. 3.1 Contaminants of Potential Concern Several physicochemical criteria may be considered for defining and screening for volatility. 71 For purposes of this Technical Guide, a chemical generally is considered to be volatile if: 1) Vapor pressure is greater than 1 millimeter of mercury (mm Hg), or 2) Henry s law constant (ratio of a chemical s vapor pressure in air to its solubility in water) is greater than 10-5 atmosphere-meter cubed per mole (atm m 3 mol -1 ) (EPA 1991b, Section 3.1.1; EPA 2002c, Appendix D). Various other criteria may be considered for identifying when volatile chemicals are present at levels of potential health concern. For purposes of this Technical Guide, a volatile chemical generally is considered to be potentially toxic via vapor intrusion if: 1) the vapor concentration of the pure component exceeds the indoor air target risk level, when the subsurface vapor source is in soil, or 2) the saturated vapor concentration exceeds the target indoor air risk level, when the subsurface vapor source is in groundwater. Each of the chemicals with one or more toxicity values used to derive Regional Screening Levels ( were evaluated for volatility and toxicity, according to the foregoing recommended criteria. These criteria do not include a consideration of whether these chemicals are regulated pursuant to CERCLA, as amended, or RCRA, as amended. The universe of chemicals evaluated and the results of the evaluation are provided in EPA s on-line VISL Calculator (EPA 2015a), which is described further in Sections and of this Technical Guide. Chemicals which satisfy the foregoing screening criteria for volatility and toxicity are designated as vapor-forming chemicals for purposes of this Technical Guide. In addition: 71 In chemistry and physics, volatility refers to the tendency of a substance to form vapors, w hich are molecules in a gaseous state, and escape from a liquid or solid. Volatility is directly related to a substance s vapor pressure and Henry s law constant. EPA (1991b) also cites molecular w eight as a necessary criterion for assessing volatility. Molecular w eight is not retained for this Technical Guide as a volatility criterion, because it is a relatively w eak predictor of volatility. 36

142 cis-1,2-dichloroethylene, a volatile chemical that lacks sufficient toxicity information (to apply the toxicity criteria above), is identified as a vapor-forming chemical due to its potential use as an indicator of vapor intrusion when it is present as a subsurface contaminant; 72 methane is identified as a vapor-forming chemical due to its potential to pose an explosion hazard and to be formed via anaerobic biodegradation processes in the subsurface environment; 73 and radon is identified as a vapor-forming chemical when it arises from uranium- or radiumbearing solid wastes in the subsurface. 74 Chemicals that meet these recommended screening criteria are referred hereafter in this Technical Guide as vapor-forming chemicals. EPA recommends that these chemicals be evaluated during vapor intrusion assessments, when they are present as subsurface contaminants due to a site-related release(s). EPA recommends that chemical analyses be limited to those vapor-forming chemicals known or reasonably expected to be present in the subsurface environment due to a site-related release(s). The list of vapor-forming substances warranting consideration for potential vapor intrusion may be modified in the future Vapor Intrusion Assessment The approach for assessing vapor intrusion will vary from site to site, due to site-specific factors. For example, the information available for evaluating vapor intrusion potential will vary depending upon when vapor intrusion is first considered during a site s investigation-andcleanup life cycle. Many sites can be evaluated for potential vapor intrusion during the normal course of an initial site assessment. Examples include brownfield sites that are intended for redevelopment and buildings where chemical odors have been reported. The data available for evaluating vapor intrusion may be very limited at the outset for these situations. At the other end of the investigation and cleanup life cycle, certain sites with long- term cleanups underway for contaminated groundwater may be evaluated for vapor intrusion during periodic reviews, if any, 72 EPA (2011a) and DoN (2011a) report that cis-1,2-dichloroethylene (cis-1,2-dce) is rarely detected in background indoor air. When they are subsurface contaminants, volatile chemicals, such as cis-1,2-dce, that are rarely or never present in indoor sources can be inferred to arise in indoor air via vapor intrusion w ithout further explanation (DoN 2011a). Brenner (2010), for example, employed this principle to identify buildings susceptible to vapor intrusion and to diagnose the relative contributions of vapor intrusion and infiltration to indoor air concentrations. 73 As noted previously, methane in soil gas may produce tw o other undesirable consequences: (1) it can exacerbate migration and intrusion of other vapors if it is generated at rates sufficient to foster advective flow of soil gas (see Section 2.3); and (2) its biodegradation in the vadose zone can reduce the oxygen available for biodegradation of other hydrocarbons (Ma et al. 2012). 74 Radon emanating from natural geological materials may also affect indoor air quality in occupied buildings, but is not a subject of this Technical Guide. For more information about radon emanating from natural geological materials, see: w w.epa.gov/radon/index.html. 75 For example, inhalation toxicity values for additional volatile chemicals may become available in the future. 37

143 Preliminary Analysis (See Section 5) Assemble, Evaluate, and Review Available Information (Sections , Appendix A) Develop Initial Conceptual Site Model (Section 5.4) Community Involvement (Section 9) throughout Assessment and Response Process Does available information indicate conditions that warrant prompt response action? (Section 5.2) Does available information indicate a potential for vaporforming chemicals to be present in the subsurface? (Sections 3.1 and 5.3) YES Does available information indicate actual or potential future presence of buildings nearby? (Section 5.3) YES Plan and Conduct Detailed Vapor Intrusion Investigation and Evaluate Data (See Figure 6-1) Based on multiple lines of evidence, does subsurface vapor source pose or have the potential to pose a vapor intrusion concern to nearby or overlying buildings? NO NO NO YES No Further Vapor Intrusion Assessment Needed if there are sufficient data of appropropriate quality to support decisions for current and/or future conditions. YES Are institutional controls in place to prevent development or ensure additional VI investigation for new building(s)? NO YES Evaluate response actions, including institutional controls (ICs), to mitigate exposure in current and future buildings. When infrastructure conditions change, EPA recommends a vapor intrusion investigation or pre-emptive mitigation be conducted (Sections 3.3 and 7.8). Implement Response Actions (Section 8), as appropriate (e.g., immediate temporary measures, engineered exposure controls, institutional controls, source removal or treatment, monitoring) No Further Vapor Intrusion Assessment Needed if there are sufficient data of appropriate quality to support decisions for current and/or future conditions. Figure 3-1 Overview of Recommended Framework for Vapor Intrusion Assessment and Response Action 38

144 of remedy performance and groundwater monitoring data. 76 In such situations, detailed information about the nature and extent of subsurface contamination and the relevant hydrogeologic conditions may already exist. In addition, there are different scenarios for vapor intrusion (EPA 2012b), depending on characteristics of the source (e.g., types, chemicals of concern, mass, distribution, and distance from building(s)), subsurface conditions and vapor migration routes (e.g., soil types and layering, existence of preferential migration routes due to geology or infrastructure, and existence of any impediments to vapor migration), building susceptibility (e.g., age, design, construction, condition), lifestyle factors (e.g., keeping windows open or closed), and regional climate. For these reasons, every site (and every building) will not warrant the same approach to or intensity of assessment for vapor intrusion. This Technical Guide, therefore, recommends a framework for planning and conducting vapor intrusion investigations, rather than a prescriptive step-by-step approach to be applied at each and every site. Broadly speaking, two general levels of vapor intrusion assessments can be distinguished: 1) A preliminary analysis utilizes available and readily ascertainable information to develop an initial understanding of the potential for human health risk that are or may be posed by vapor intrusion, which would typically be performed as part of an initial site assessment. The recommended information, approaches, and practices for conducting a preliminary analysis and its potential outcomes are described in Section ) A detailed investigation is generally recommended when the preliminary analysis indicates that subsurface contamination with vapor-forming chemicals may be present underlying or near buildings. A detailed investigation of the vapor intrusion pathway is typically performed as part of the site investigation stage. The recommended approaches and practices for conducting detailed vapor intrusion investigations are described in Section 6.0. Considerable information, primarily empirical, has been generated regarding evaluation of the vapor intrusion pathway since the pathway emerged as a national issue in the late 1990s and especially in the past ten years. Broadly speaking, this information demonstrates that the vapor intrusion pathway can be complex. (The conceptual model of vapor intrusion provided in Section 2.0 identifies many of the factors, variables, and conditions that warrant consideration on a sitespecific basis.) As a result, current practice suggests that the vapor intrusion pathway generally be assessed using multiple lines of evidence. 77 Specific conclusions that EPA recommends be based upon multiple lines of evidence include: 76 These situations can arise, for example, if the groundw ater remedy w as selected in the 1980s (long before vapor intrusion became recognized as a potentially significant exposure pathw ay), or if supplemental groundw ater data indicate that the plume is migrating tow ard new inhabited areas. 77 As discussed further in Section 7.2, confidence in the assessment and risk management decisions is expected to be higher w hen multiple independent lines of appropriate site- or building-specific evidence from, for example, multiple types samples of environmental media (e.g., groundw ater, soil-gas, sub-slab vapor, craw lspace, and indoor air) and/or other data come together to provide mutually supporting evidence for a common understanding of the site conditions/scenarios and the potential for vapor intrusion (EPA 2010b) (i.e., the various lines of evidence are in agreement w ith each other). 39

145 The subsurface vapor source(s) at a specific site has (or, alternatively, does not have) the potential to pose an unacceptable vapor intrusion exposure under current or reasonably expected future conditions, due to its strength (e.g., concentration and mass of vapor-forming chemicals) and proximity relative to one or more existing buildings or a building that may be constructed in the future. The vapor intrusion pathway is complete for one or more buildings under current conditions or is potentially complete under reasonably expected future conditions. The vapor intrusion pathway is incomplete for one or more buildings near a subsurface source of vapor-forming chemicals, due to geologic, hydrologic, and/or biochemical (e.g., biodegradation) processes that provide substantial and persistent attenuation of vapors extending laterally over large distances relative to the footprint of the building(s) and the extent of the vapor source. Indoor air concentrations attributable to vapor intrusion pose (or, alternatively, are unlikely to pose) an unacceptable human health risk in one or more existing buildings under current or reasonably expected future conditions. Indoor air concentrations measured in one or more buildings can (or alternatively, cannot) be reasonably attributed to indoor or ambient air sources (i.e., background). Multiple lines of evidence are particularly important for supporting no-further-action decisions regarding the vapor intrusion pathway (e.g., pathway incomplete determinations) to reduce the chance of reaching a false-negative conclusion (i.e., concluding vapor intrusion does not pose unacceptable human health risk, when it actually poses an unacceptable human health risk). Collecting and weighing multiple lines of evidence can also help avoid reaching a false-positive conclusion (i.e., concluding vapor intrusion poses an unacceptable human health risk, when it does not. In summary, EPA recommends that site assessors generally collect and weigh multiple lines of evidence, including qualitative information, to support decision-making regarding the vapor intrusion pathway. Lines of appropriate evidence to evaluate the vapor intrusion pathway were identified in Section 2 and are discussed further in Sections 5 through 7. As noted in Section 1.3, Figure 3-1, and the preceding discussion of lines of evidence, EPA recommends that site assessors consider reasonably expected future conditions, in addition to current conditions, when reaching conclusions about the vapor intrusion pathway. 78 For this reason, this Technical Guide includes recommendations for evaluating whether subsurface vapor sources that remain have the potential to pose unacceptable human health risks in the future if current conditions were to change. For example: Section recommends that site assessors consider investigating vapor intrusion in non-residential buildings under conditions when the heating, ventilation, and airconditioning system is not operating; and 78 Both current and reasonably likely future risks need to be considered in order to demonstrate that a site does not present an unacceptable risk to human health and the environment. (EPA 1991a). 40

146 Section 7.3 identifies some factors and processes that can make the characteristics of the vadose zone (e.g., soil moisture) transitory. EPA also recommends that vapor intrusion be evaluated for reasonably expected future land use conditions, including new building construction and new uses and occupants for any uninhabited buildings. 3.3 Building Mitigation and Subsurface Remediation The NCP expresses the preference for response actions that eliminate or substantially reduce the level of contamination in the source medium to acceptable levels, thereby achieving a permanent remedy. In the case of vapor intrusion, such a response action would generally entail eliminating or substantially reducing the level of vapor-forming chemicals in the subsurface (e.g., in contaminated groundwater, soil, and/or sewer lines) via treatment or removal (i.e., remediation ). Section 8 discusses source remediation to achieve a permanent remedy and associated institutional controls (ICs) and monitoring for vapor intrusion mitigation, including criteria for their termination. Comprehensive remediation 79 of the subsurface environment often occurs over a prolonged period (e.g., several years) to attain cleanup levels. In the interim, problems of unacceptable vapor intrusion are often addressed by also installing engineered exposure controls to reduce or eliminate vapor intrusion in buildings (i.e., mitigate vapor intrusion) or reduce indoor air exposure levels. Engineered exposure controls can generally be deployed and generally become effective relatively quickly. They can be considered as interim or early response actions, which are also authorized by the NCP (Section 1.2), as necessary and appropriate to promptly reduce threats to human health. Section 8 summarizes technical information about specific exposure controls and provides information about their operation, maintenance and monitoring and associated ICs, including criteria for their termination. Functionally, engineered exposure controls can be categorized into two basic strategies: Those that seek to prevent or reduce vapor entry into a building (e.g., active depressurization technologies). These methods are more commonly implemented when response actions are needed. 80 Those that seek to reduce or eliminate vapors that have entered into a building (e.g., indoor air treatment, ventilation). 79 For purposes of this Technical Guide, "remediation" is intended to apply to interim and final cleanups, w hether conducted pursuant to RCRA corrective action, the CERCLA removal or remedial programs, or using EPA brow nfield grant funds w ith oversight by state and tribal response programs. In addition to permanent remedies for subsurface vapor sources, site remediation may also entail implementation of ICs and construction and operation of engineered systems to reduce risks to human health and the environment posed by environmental pathw ays other than vapor intrusion. Although this Technical Guide is intended for use at any site subject to federal statutes, regulations, and rules, it is not intended to alter existing requirements, guidance, or practices in OSWER s programs about development, selection, or documentation of final remediation plans (addressing subsurface vapor sources, for example) see, for example, Sections 7.6 and Mitigation methods that prevent or reduce vapor entry into a building from subsurface vapor sources w ould generally also be expected to reduce radon entry. 41

147 Neither strategy entails reducing the level of vapor-forming contamination in the subsurface source medium. 81 As reflected in the foregoing conceptual model of vapor intrusion (Section 2.0), entry of the vapors into a building may be prevented or reduced by any of several techniques, which have the following objectives: Remove or reverse the driving forces for vapor intrusion into the building (e.g., install and operate an active depressurization technology to mitigate vapor intrusion from contaminated soil or groundwater; establish over-pressurization within and throughout the footprint of a nonresidential building). Eliminate or minimize identified openings for vapor entry into the building (e.g., caulking, grouting, or otherwise sealing all holes, cracks, sumps and other foundational openings or creating a barrier between the soil and the building that blocks openings for entry of soil gas into the building; install, repair, and/or maintain vapor traps in sewer and drain lines). Engineered exposure controls that entail mechanical systems and forces (e.g., sub-slab depressurization or ventilation systems; building over-pressurization) are often referred to as active. Engineered exposure controls that do not involve mechanical operations (e.g., installing a sub-slab barrier to chemical vapor entry) are often referred to as passive. Many building mitigation systems rely on both active and passive strategies. Engineered exposure controls that seek to reduce or eliminate vapors that have entered into a building can also be effective. In some instances, they can be implemented more readily than engineered exposure controls that reduce or eliminate entry of the vapors into a building. Typically, the simplest approach to limiting the concentration levels in occupied indoor spaces is to increase building ventilation (i.e., increase the rate at which indoor air is replaced with outdoor air), thereby diluting indoor air concentrations (see Section 2.4). 82 Alternatively, vaporforming chemicals are removed from indoor air using an adsorbing material (such as activated carbon) that can be either properly disposed of or recycled. Building mitigation methods that act upon vapor-forming chemicals in indoor air (i.e., rely upon enhanced ventilation or treatment) are generally capable of reducing background levels of chemicals, in addition to reducing indoor levels of vapor-forming chemicals that intrude from subsurface sources. 81 Even w hen operated for prolonged periods, engineered exposure controls are considered interim remedies for purposes of this Technical Guide, because their implementation does not substitute for remediation of the subsurface source(s) of vapor-forming chemicals. Engineered exposure controls may, nevertheless, become part of a final cleanup plan. 82 It can be difficult to establish a ventilation rate that mitigates vapor intrusion and yields an environment conducive to human occupancy (e.g., considering air temperature or moisture). In addition, ventilation may affect the driving forces for vapor intrusion. For example, mechanically exhausting air from the building w ill generally contribute to building under-pressurization (see Section 2.3), w hich may result in increased intrusion of soil gas into the building, w hich may offset the intended dilution effect of ventilation. On the other hand, introducing outdoor air at a rate slightly greater than the exhaust rate can create over-pressurization, w hich opposes the primary driving force for vapor intrusion. 42

148 Selection of an interim response action from these options may depend upon building- and sitespecific factors (EPA 2008). For example, building-specific factors may include: Use (e.g., single-family residential, multi-family residential, commercial, educational, recreational, governmental, religious, industrial) Type of foundation/basement (e.g., basements with concrete slab floors or dirt floors, slab on grade, slab below grade) and other construction features Type of heating/cooling/ventilation systems (e.g., some systems will tend to increase pressure, whereas others will tend to decrease pressure, inside the building). Each of these characteristics can influence the choice of mitigation methodology and, therefore, they are commonly identified during building surveys during a site-specific vapor intrusion investigation. Site-specific considerations may include the degree of risk or hazard being addressed and whether the subsurface vapor source(s) is stable in extent and concentration or is undergoing remediation. Temporary relocation may warrant consideration in instances where explosion hazards are present (see Section 7.5.1), which may pose an imminent and substantial danger to human health and public welfare. Prompt response action may also be warranted where short-term or acute exposures may pose unacceptable human health risk (see Section 7.5.2) that cannot be addressed timely or feasibly by implementing engineered exposure controls. Section 8.2 discusses various prompt response actions for such situations, which may include temporary relocation. There may be situations where a party may wish to implement mitigation or control measures for vapor intrusion, even though only limited lines of evidence or measurements may be available to characterize the overall vapor intrusion pathway. For example, a party may be aware that vapor intrusion has been documented at neighboring structures, where measures are being implemented to mitigate the vapor intrusion pathway. A party may conclude there is a reasonable basis to take action, but each building presents a fact-specific situation that calls for its own individual judgment. Likewise, it may be appropriate and cost-effective to design, install, operate, and monitor engineered exposure controls for individual buildings to mitigate vapor intrusion in newly constructed buildings, or in buildings to be constructed in the future, that are located in areas of vapor-forming subsurface contamination, rather than potentially allow vapor intrusion to occur later and assess vapor intrusion after the fact. The term preemptive mitigation/early action is used in this Technical Guide to describe these situations. 83 The decision for preemptive mitigation/early action arises from precaution and from recognizing that: Installing engineered exposure controls in buildings is typically a cost-effective means of protecting human health and normally can be implemented relatively quickly in many buildings while subsurface contamination is being delineated or remediated. 83 The term preemptive has been used to describe the use of various types of controls that can prevent vapor intrusion from occurring prior to having fully demonstrated that unacceptable vapor intrusion currently exists in specific buildings being considered (EPA 2010a). 43

149 Conventional vapor intrusion investigations can be disruptive for building occupants (residents, workers, etc.) and owners. Comprehensive subsurface characterization and investigation of vapor intrusion can entail prolonged study periods, during which time building occupants and owners and others may have questions and concerns about human health risk that are or may be posed via vapor intrusion. Early action and interim action are allowed by federal environmental protection statutes, regulations, and guidance, including CERCLA, as amended, and RCRA, as amended see Section 1.2 of this Technical Guide, for example. Other aspects of preemptive mitigation/early action are also discussed in Section 7.8, including situations and criteria for decision-makers to consider. As noted in Figure 3-1, EPA recommends that risk managers consider reasonably expected future conditions, in addition to current conditions, when making risk management decisions about the vapor intrusion pathway. For this reason, this Technical Guide includes recommendations for response actions at sites where subsurface vapor sources remain into the future, but do not pose unacceptable human health risk under current conditions (e.g., no building is present nearby). For example, institutional control s are generally recommended to restrict land use and/or alert parties (e.g., prospective developers, owners, and municipalities) of the presence of subsurface sources of vapor-forming chemicals at levels that pose a continuing threat via vapor intrusion (see Sections 7.3, 7.4, and 8.6). When infrastructure conditions change above or near an area of known contamination with vapor-forming chemicals, EPA recommends a vapor intrusion investigation or pre-emptive mitigation be conducted, particularly if a building is constructed for human occupancy (see Section 8.2.3). 3.4 Community Outreach and Involvement EPA is committed to transparency and upfront collaboration with community stakeholders regarding land cleanup, emergency preparedness and response, and management of hazardous chemicals and wastes. OSWER s Community Engagement Initiative (CEI), in particular, is designed to enhance OSWER s and the Regional offices' engagement with local communities and stakeholders (e.g., state and local governments, tribes, academia, private industry, other federal agencies, and nonprofit organizations) to help them participate meaningfully in government decisions regarding OSWER s nationwide programs. Meaningful and sustained community outreach and engagement efforts are critical to the implementation of work plans for site-specific vapor intrusion assessment and mitigation. Because assessing the vapor intrusion pathway may involve sampling in a home or workplace, as well as other temporary inconveniences (e.g., assisting in reducing indoor sources of contaminants), individual, one-on-one communication with each property owner or renter generally warrants consideration. Building-by-building contact and communication are recommended as the most effective means of educating the community and obtaining access needed to assess, mitigate, and monitor the vapor intrusion pathway. Personal contact is further recommended to establish a good working relationship with each building owner or occupant and to build trust. In many instances, local religious and cultural organizations, and other community groups can be sought for assistance in reaching out to affected community members. 44

150 Vapor intrusion education and training are important components of meaningful community outreach and engagement efforts. Informing stakeholders about the vapor intrusion pathway and the cleanup process can help to build trust and can foster community participation in the overall assessment and risk management process. Recognizing the importance of community outreach and engagement efforts, EPA staff are highly encouraged to consult with colleagues experienced in community outreach and utilize available EPA planning resources, including those discussed in Section 9, which provides OSWER s community involvement planning guide for vapor intrusion projects. Like EPA, the ITRC also recommends implementing a community outreach program that provides timely information to concerned community members and property owners. 45

151 4.0 CONSIDERATIONS FOR NONRESIDENTIAL BUILDINGS The approach for investigating and, if necessary, mitigating vapor intrusion can vary from site to site, and from building to building, due to site- and building-specific factors and circumstances, including: the nature (e.g., mixture of vapor-forming chemicals and form), locations, and extent of subsurface contamination; geologic, hydrologic, and biochemical factors in the vadose zone; and the size, structural conditions and uses of buildings and background levels of vapor-forming chemicals in the building. Information on background contributions of site-related, vaporforming chemicals in indoor air is important to risk managers because generally EPA does not clean up to concentrations below natural or anthropogenic background levels (EPA 2003e). These statements hold true for residential and non-residential buildings. Section of this Technical Guide provides specific recommendations about how to evaluate background concentrations. Section 7.4 of this Technical Guide provides clarifications and recommendations about applying the methods in Section to informing risk management decisions and recommendations. The Glossary in this Technical Guide defines various terms and types of vapor sources to foster a common understanding of EPA s approach and recommendations. This section summarizes EPA s general recommendations to consider in making decisions about evaluating and addressing potential vapor intrusion for nonresidential buildings 84 pursuant to CERCLA and RCRA, including decisions that a response action or corrective action is not currently warranted. When evaluating nonresidential buildings at sites that have subsurface contamination with vapor-forming chemicals, EPA generally recommends that building owners or operators (e.g., lessees) be contacted for information about vapor-forming chemicals used or stored or otherwise present in the building, the types of building occupants potentially exposed to subsurface vapor intrusion, as well as any training, equipment, or engineering controls to mitigate inhalation exposures. EPA recommends that information be provided to building owners concerning the potential for vapor intrusion so that this information can be communicated to building employees, tenants, and other occupants. Building occupants include, but are not limited to, facility employees, visitors, customers, suppliers, and building maintenance personnel. Generally, EPA recommends the following factors be considered when making decisions pertaining to vapor intrusion at nonresidential buildings, including as to whether indoor air sampling, soil gas sampling underneath the building, or interim measures to mitigate vapor intrusion to reduce associated indoor air exposures for a nonresidential building may be warranted: 84 As used in this Technical Guide, the phrase nonresidential buildings may include, but is not limited to, institutional buildings (e.g., schools, libraries, hospitals, community centers and other enclosed structures for gathering, gyms and other enclosed structures for recreation), commercial buildings (e.g., hotels, office buildings, many (but not all) day care facilities, and retail establishments); and industrial buildings w here vapor-forming substances may or may not be routinely used or stored. 46

152 1) The types of populations potentially exposed to vapor-forming chemicals in the indoor air of the nonresidential building, including, for example, whether: a) Individuals are or may be present under current or reasonably expected future conditions who would not likely anticipate any chemical exposures (e.g., office workers, visitors, customers, suppliers, and other members of the general public) and may not benefit fully from hazard communication programs and other work practices in place to foster protection of workers who use chemicals, if any. b) Sensitive populations are or may be present under current or reasonably expected future conditions, who may have increased susceptibility or vulnerability. 2) The potential for vapor intrusion versus background vapor sources (See Glossary) to contribute to indoor air concentrations of vapor-forming chemicals found in the subsurface. Questions to consider include, for example: a) Can subsurface vapor intrusion be identified as a potential cause of unacceptable human health risk to building occupants (see Section 5 for further discussion about the preliminary analysis stage and Section 7 for further discussion and definition of acceptable versus unacceptable human health risk)? 85 b) Can subsurface remediation (e.g., excavation of contaminated soil or soil vapor extraction beneath the subject building) that is planned or underway reduce human health risk from vapor intrusion within a time frame that is protective for any potential current or near-term exposures in the building? c) Is there a known source(s) of one or more vapor-forming chemical(s) see Section 3.1 in indoor air in the nonresidential building other than vapor intrusion (e.g., indoor use and storage of chemicals, which would constitute a background vapor source(s) and contribute to indoor air exposure concentrations; see Sections 2.7 and for further discussion and recommendations about background sources and concentrations)? If such a vapor-forming chemical(s) is (or are) present: i. Is(are) it the same as the vapor-forming chemical(s) found in the subsurface? ii. How does the indoor air exposure concentration(s) arising from the indoor vapor source(s) compare to the indoor air concentration(s) estimated or reasonably expected to arise from vapor intrusion? 86 Information on background contributions of site-related, vapor-forming chemicals in indoor air is important to risk managers because generally EPA does not clean up to concentrations below natural or anthropogenic background levels (EPA 2002e). 85 EPA s recommended approaches to human health risk assessment are provided in Sections 7.4 and 7.5 of this Technical Guide. 86 EPA s recommended approaches to distinguishing and considering background are provided in Sections and of this Technical Guide. 47

153 3) Any existing or planned engineering or institutional control(s) in the building or any industrial hygiene/occupational health program that addresses workplace inhalation exposures and its scope. Questions to consider include, for example: a) Do work practices and engineering controls currently in place ensure protection 87 of all building occupants who may be exposed via the vapor intrusion pathway? b) Are enforceable institutional controls (ICs) or other control mechanisms in place to ensure that current land use and workplace practices will be sustained and will remain protective regarding indoor air exposures from vapor intrusion to all building occupants? Have these ICs and control mechanisms been communicated to all appropriate parties and documented to EPA? Can they be readily monitored and, if necessary, be enforced? EPA recommends documenting any decision not to undertake investigation or mitigation for vapor intrusion in a nonresidential building, as well as any decision to pursue such activities. EPA may consider reviewing these decisions, as appropriate and consistent with applicable statutes and regulations and considering EPA guidance, 88 if the land use changes or new information becomes available that suggests circumstances supporting past risk management decisions have changed and prompt the need to revisit those decisions. It is recommended that EPA request from property owners and building tenants/operators timely notification of significant changes in building ownership, uses, access by the general public, or building construction (e.g., renovations), which may affect exposure of occupants and related risk management decisions pertaining to potential vapor intrusion assessment and mitigation, subsurface remediation, or ICs. Regardless of decisions about indoor air sampling, soil gas sampling underneath the building, or interim measures to mitigate vapor intrusion, EPA 89 may proceed, consistent with applicable federal statutes and regulations (see Section 1.2) and considering EPA guidance, with activities such as the following, where appropriate: Subsurface investigation to delineate the areal extent of a subsurface vapor plume. Subsurface remediation to reduce or eliminate subsurface sources of vapors-forming chemicals to protect human health and the environment. 87 EPA s recommended approaches to risk management are provided in Sections 7.4 and 7.5 of this Technical Guide. 88 For the Superfund five-year review process, OSWER Directive (EPA 2012c) provides a recommended framew ork for considering vapor intrusion w hile evaluating remedy protectiveness. 89 On January 23, 1987, the President of the United States signed Executive Order entitled, Superfund Implementation, w hich delegates to a number of Federal departments and agencies the authority and responsibility to implement certain provisions of CERCLA. The policies and procedures for implementing these provisions (e.g., carrying out response actions) are spelled out in the NCP. The provisions of Executive Order appear at 52 Federal Register At federal facilities on the NPL, EPA may not be the lead agency, but does have oversight responsibilities pursuant to CERCLA Section

154 5.0 PRELIMINARY ANALYSIS OF VAPOR INTRUSION When a site is first identified and evaluated for vapor intrusion, 90 the amount, utility, and reliability of available information may be limited. A preliminary analysis utilizes available and readily ascertainable information to develop an initial understanding of the potential for human health risk to be posed by vapor intrusion, which would typically be performed as part of an initial site assessment. This section describes EPA s recommended information, approaches, and practices for conducting preliminary analyses for vapor intrusion using pre-existing and readily ascertainable information to develop an initial understanding of the vapor intrusion potential at a site. This section: Explains the recommended types of information that generally can be obtained when a site is first considered for vapor intrusion (see Sections 5.1, 5.3, 5.4, and 5.5). Identifies some of the site conditions for which prompt action is generally warranted (see Section 5.2). Illustrates some of the site conditions for which further evaluation of the vapor intrusion pathway might be warranted (see Sections 5.3, 5.4, and 5.5). Describes the recommended approaches to evaluating the reliability of pre-existing information, including any sampling data (see Sections 5.1 and 5.5). Depending upon the nature and reliability of the available information, it may be possible to determine whether a vapor intrusion investigation (see Section 6) or a response action (see Sections 7 and 8) is warranted. If the available information is not reliable or adequate for these purposes, however, additional data collection generally is recommended. 5.1 Assemble, Evaluate, and Review Available Information The recommended first step in a preliminary analysis generally entails assembling and reviewing relevant information that is available at the time for the site. At a minimum, EPA recommends that information about potential subsurface sources of vapors and the presence and current use(s) of nearby buildings be developed and evaluated. For some sites, such as sites being evaluated for redevelopment (EPA 2008a), information about contiguous or nearby facilities also may be relevant, because vapors can encroach from nearby facilities due to migration of contaminated groundwater or soil gas, even though vapor-forming chemicals may not have been used at the subject site. The following recommended types of information are often available through documents (e.g., federal, state, tribal and local government records) or through interviews with individuals 90 A site may be identified, for example, based on reports to the National Response Center, citizen complaints or inquiries, state agency referrals, or other information (e.g., site history, land use, site inspections) obtained by EPA. At a brow nfield site subject to an EPA grant, subsurface contamination may be discovered as a result of preacquisition investigation by prospective purchasers, during site redevelopment, or at other project stages. 49

155 knowledgeable about the facility or site and surrounding area (e.g., past and present owners, operators and occupants; area residents or workers): History and descriptions of the types of operations and activities that occurred on or near the site and nearby properties. Information or records about the types of chemicals that may have been used or disposed of at the site and nearby properties or are currently used and disposed at the site. Information about the site and nearby properties, such as the occurrence of odors, reports of dumping liquids, observations of unreported waste disposal practices, or other indications of chemical presence and release. Adverse physiological effects reported by building occupants (e.g., dizziness, nausea, vomiting, confusion). Evidence of subsurface intrusion of groundwater (e.g., wet basements) reported by building owners or occupants. Such information usually can be reviewed and weighed together to assess whether vaporforming chemicals (see Section 3.1) were or are being used, stored, or handled at or near the site and were or may have been released to the subsurface environment. In addition, the following types of information may be available through documents, interviews with individuals knowledgeable about the facility or site, or reconnaissance and site inspection: Locations, ownership, occupancy, and intended and actual use(s) of buildings on or near the site. Current and reasonably anticipated future land use on and near the site. Location of subsurface utility corridors. Evaluation of such information usually can help determine whether humans are present currently or are reasonably expected to be present in the future, and who may become exposed to any intrusion of vapors from the subsurface into a building(s). Zoning, land use planning, and related information may also need to be consulted to identify reasonably anticipated future land use and building types in areas where buildings do not exist or to ascertain whether reasonably anticipated uses of existing buildings are likely to change (EPA 2010c). EPA recommends evaluating the available data to identify any data gaps for purposes of the preliminary analysis. For example, has the history of operations and primary activities been established for the site and all contiguous properties, including currently vacant land? To the extent that there are significant data gaps, EPA recommends that additional data gathering (e.g., interviews, records review) generally be planned and conducted. EPA also recommends evaluating the available data to assess its reliability and internal consistency. For example, if the available information about operations and activities at a specific property comes only from area residents, EPA recommends additional efforts to 50

156 identify, contact, and interview current and past owners to obtain and corroborate this information. Also, if anecdotal information about current activities at a specific property is in conflict with common knowledge about local zoning, EPA recommends that additional data gathering and evaluation be identified (e.g., contact property owner), planned, and conducted to resolve the inconsistency. Section describes additional considerations for evaluating the reliability of sampling data that may be available for some sites at the preliminary analysis stage. 5.2 Identify and Respond to Conditions that Warrant Prompt Action The following conditions may indicate a need for prompt action, including follow-up evaluations to determine whether urgent intervention is warranted to eliminate, avoid, reduce, or otherwise address a human health hazard: Odors reported by occupants, particularly if described as chemical, solvent, or gasoline. The presence of odors does not necessarily correspond to an unacceptable human health risk due to vapor intrusion, and the odors could be the exclusive result of indoor vapor sources; however, it is generally prudent to investigate any reports of odors as the odor threshold for some vapor-forming chemicals exceeds their respective lower explosive limit (LEL) or health-protective concentrations for short-term or acute exposure. Physiological effects reported by occupants (e.g., dizziness, nausea, vomiting, confusion, etc.). These effects may or may not be due to subsurface vapor intrusion (or even indoor vapor sources); however, it is generally prudent to investigate any such reports. Wet basements in areas where groundwater is known to contain vapor-forming chemicals (see Section 3.1) and the associated water table is shallow enough that the basements are prone to groundwater intrusion or flooding. This condition is particularly important where there is evidence of light NAPL (LNAPL) on the water table directly below the building or direct evidence of intrusion of liquid-phase contamination (i.e., liquid chemical or dissolved in water) inside the building. EPA generally recommends testing of indoor air (see Sections and 6.3.4) as soon as practical in buildings where: chemical odors or physiologic effects are reported and there is a credible information to suggest that a release to the subsurface environment may be a contributing factor, or intruding contaminated groundwater is reported and observed. Likewise, EPA generally recommends testing of unoccupied structures for explosive gases as soon as practical where chemical odors are reported and there is a credible information to suggest that a release to the subsurface environment may be a contributing factor. Section 7.4 provides EPA s approach and recommendations for identifying when human health risks are unacceptable. Section describes EPA s recommended approaches to identifying concentration levels indicating a potential need for prompt response action. Section 51

157 8.2.1 identifies potential response actions to reduce or avoid these threats promptly, when the results of testing reveal threats or potential threats warranting prompt response action. EPA recommends health and safety planning for all building- or site-specific actions, as discussed further in Section 6.2, which considers expected work conditions and anticipated hazards. 5.3 Determine Presence of Structures and Vapor-forming Chemicals For purposes of this Technical Guide and as reflected in the conceptual model of vapor intrusion (Section 2), the vapor intrusion pathway is referred to as complete for a specific building or collection of buildings when the following five conditions are met under current conditions: 1) A subsurface source of vapor-forming chemicals is present underneath or near the building(s) (see Sections 2.1, 6.2.1, and 6.3.1); 2) Vapors form and have a route along which to migrate (be transported) toward the building(s) (see Sections 2.2 and 6.3.2); 3) The building(s) is (or are) susceptible to soil gas entry, which means openings exist for the vapors to enter the building(s) and driving forces exist to draw the vapors from the subsurface through the openings into the building(s) (see Sections 2.3 and 6.3.3); 4) One or more vapor-forming chemicals comprising the subsurface vapor source(s) is (or are) present in the indoor environment (see Sections and 6.4.1); and 5) The building(s) is (or are) occupied by one or more individuals when the vapor forming chemical(s) is (or are) present indoors. EPA recommends that site managers also evaluate whether subsurface vapor sources that remain have the potential to pose a complete vapor intrusion pathway in the future if site conditions were to change (e.g., reasonably expected occupancy or construction in the future of a building above or near a subsurface vapor source). A complete vapor intrusion pathway indicates that there is an opportunity for human exposure, which warrants further analysis (see Section 7.4) to determine whether there is a basis for undertaking a response action(s) (see Section 7.7). At the preliminary assessment stage, the available information may not be sufficient to evaluate whether all five conditions are present under current or reasonably expected future conditions. EPA recommends, however, that readily ascertainable information be reviewed for purposes of assessing whether the first and fifth conditions are present; that is: A subsurface source of vapor-forming chemicals is present or is reasonably expected to be present (e.g., in contaminated groundwater, soil, or sewer lines or from a primary 52

158 vapor release). 91 Section 3.1 describes chemicals that have the potential to pose an unacceptable human health risk through the vapor intrusion pathway. In the absence of environmental sampling data, the potential presence of vapor-forming chemicals in the subsurface may be inferred from site information, as identified in Section 5.1 (e.g., site history). At least one building is present or is reasonably expected to be constructed in the future above or near the subsurface vapor source(s), which is or could be occupied by humans. For purposes of this Technical Guide and its recommendations for evaluating human health risk posed by vapor-forming chemicals, building refers to a structure that is intended for occupancy and use by humans. This would include, for instance, homes, offices, stores, commercial and industrial buildings, etc., but would not normally include sheds, carports, pump houses, or other structures that are not intended for human occupancy. However, where the assessment identifies the potential for methane or other potentially explosive vapors to be present in the subsurface, EPA recommends reviewing readily ascertainable information for purposes of assessing whether nonoccupied structures (including, but not limited to, sewers, pits, and subsurface drains) are present, which may also accumulate vapors, in addition to occupied and nonoccupied buildings. Existing buildings (and non-occupied structures) can be identified during inspections of the land areas overlying and near subsurface vapor sources. The potential presence of buildings in the future may be inferred from site information, such as identified in Section 5.1. See Section for further discussion on which buildings and non-occupied structures are considered near for purposes of a preliminary analysis. If the available information is deemed reliable, well documented, and sufficient (see Section 5.1) and indicates that neither of these conditions is met, then further vapor intrusion assessments are not generally warranted. 92 Example: From 1920 to 1931, the ABC Mining Company obtained and shipped iron ore from a local deposit. Ore from the mine was shipped by rail to a different location where it was milled and processed to extract the metal. Although no company records are available for the mine, a review of mining techniques indicates that solvents and other vapor-forming chemicals were not used in the mining process during the 1920s and 1930s. Former mining structures have been removed, and the site is currently vacant. The city has proposed redeveloping the site with bike and hiking trails but no buildings or other structures for storage or site maintenance support. Based on the information and 91 As noted in Section 2.1, the primary contamination source need not be on the property of interest to pose a vapor intrusion problem. The primary source(s) of vapor-forming chemicals (e.g., contaminated soil, leaking tanks) may be present on a neighboring property or on a property some distance aw ay. Even greenspace properties that have not previously been occupied or developed may contain subsurface contamination by vapor-forming chemicals due to migrating plumes of contaminated groundw ater or migrating soil gases. Therefore, EPA recommends that the potential for vapor intrusion be considered at all properties being considered for redevelopment (EPA 2008a) or proximate to industrial and commercial use areas. 92 Consistent w ith federal environmental protection statutes, regulations, and OSWER guidance, a subsurface investigation may still be w arranted for non-volatile substances or for other potential exposure pathw ays such as those identified in Section

159 findings, the need for further assessment of the vapor intrusion pathway due to miningrelated contamination is not indicated. If, on the other hand, there is reliable evidence to indicate that a release of vapor-forming chemicals to the subsurface has occurred (e.g., environmental sampling data indicate detectable levels of a vapor-forming chemical(s) in potential source media) 93 or may have occurred underneath or near a property, then EPA recommends further vapor intrusion assessment in areas where buildings are present or future buildings could be constructed, including development of a conceptual site model (see Section 5.4) and investigation of sitespecific conditions (see Section 6). Example: The XYZ Recycling Center site was used from 1963 to 1984 for the collection and recycling of industrial solvents and other fluids. The site was repeatedly cited by the state and city for improper handling and disposal of solvents, and was closed in Groundwater data indicate the presence of multiple chlorinated hydrocarbons. Buildings overlying the contaminated groundwater are currently used mainly for storage of nonchemical goods, but the site has been proposed for future residential or commercial redevelopment. Based on the foregoing information and findings, further assessment of the potential for vapor intrusion is warranted, possibly including risk-based screening of the groundwater data (see Section 6.5). If a release of vapor-forming chemicals to the subsurface is known or suspected to have occurred at or near the site, but buildings are not present and none are reasonably anticipated in the future (e.g., the contaminated source underlies an open space, recreational area, or wildlife refuge), then further vapor intrusion assessments may not be appropriate under current conditions. It may be appropriate, however, to establish an institutional control (IC) requiring a vapor intrusion investigation or building mitigation 94 in the future, in case land use changes. ICs for building mitigation and subsurface vapor source remediation are discussed further in Sections 3.3 and 8.6 of this Technical Guide. Existing guidance and practice pursuant to CERCLA and RCRA corrective action (CA) recognize and entail various phases of subsurface or site characterization, including a site investigation to determine the full nature and extent of contamination at a site, quantify risks posed to human health and the environment, and gather information to support the selection and implementation of appropriate remedies. On this basis, a subsurface investigation may be warranted at some point to characterize subsurface contamination and assess the need for subsurface remediation to protect the environment and human health for potential exposure pathways other than vapor intrusion (such as those identified in Section 1.3). For example, site investigations to characterize the nature and extent of groundwater contamination and support assessments of risk to human health through the ingestion pathway are typically conducted, consistent with federal statutes and regulations (e.g., CERCLA and RCRA) and considering EPA guidance. 93 Section 6.5 provides information on how such data may be used in a quantitative fashion to screen the site further. 94 If, for example, a developer is considering acquiring and building on land that contains subsurface contamination w ith vapor-forming chemicals, the developer could retrofit existing buildings or build new buildings w ith vapor mitigation systems w ithout first conducting an extensive vapor intrusion investigation (see Sections 3.3 and 7.8). Section identifies additional approaches and considerations for new buildings. 54

160 5.4 Develop Initial Conceptual Site Model EPA recommends that the planning and data review team develop an initial conceptual site model (CSM) for vapor intrusion when the preliminary analysis indicates the presence of subsurface contamination with vapor-forming chemicals underlying or near buildings. The initial CSM (and any subsequent refined CSM) can be used to support evaluations of the adequacy of the available site-specific information, to guide any vapor intrusion investigations (see Sections 6.2 and 6.3), and to support data selection for risk-based screening (see Section 6.5). The CSM can also provide useful information for supporting prompt development of a strategy for early/interim response actions (see Sections 7.8 and 8.2). The remainder of this section discusses recommended information that can be useful for developing a CSM. Note that some of the recommended information may not be readily available when a site is first considered for vapor intrusion. Although the CSM may be updated iteratively (and interim mitigation measures may be undertaken) as the vapor intrusion investigation unfolds, EPA recommends completing the CSM before making final risk management decisions for a given site (see Section 7). As discussed in Section 5.3, the available information may not be sufficient at the preliminary analysis stage to evaluate whether the vapor intrusion pathway is complete under current or future conditions. Therefore, the initial CSM for vapor intrusion is likely to be incomplete. EPA recommends, however, that the initial CSM for vapor intrusion portray the current understanding of site-specific conditions pertaining to the vapor intrusion pathway. Ideally, at a minimum, the initial CSM will address: Nature (i.e., type, chemical composition), location, and spatial extent of the source(s) of vapor-forming chemicals in the subsurface (see Sections 2.1 and 6.3.1, for example). For example, it is useful to know which vapor-forming chemical(s) primarily comprise the subsurface vapor source 95 and whether it is also capable of posing explosion hazards. It is also useful to know whether vapor-forming chemicals are present in groundwater, vadose zone soils, sewer lines, and/or some other source underneath or near buildings. Location, use, occupancy, and basic construction (e.g., foundation type) of existing buildings. The CSM can be updated as additional information is obtained through investigation (Section 6) and building surveys (Section 6.4.1). EPA recommends the CSM also portray the current understanding of the hydrologic and geologic setting in and around the subsurface vapor source(s) and the buildings, which is expected to influence vapor migration and attenuation in the vadose zone (see Sections 2.2 and 6.3.2, for example). When these conditions are not well established from existing information, and the preliminary analysis indicates the presence of subsurface contamination with vapor- 95 EPA also recommends that the CSM identify any site-specific chemicals of concern that may be biodegradable and identify and summarize information and data pertaining to the possible role of biodegradation in situ in limiting vapor migration in the vadose zone (see Section 6.3.2) or generating hazardous, volatile degradation products (e.g., methane from anaerobic biodegradation, vinyl chloride as a byproduct of PCE or TCE biodegradation). 55

161 forming chemicals underlying or near buildings, EPA recommends that a detailed vapor intrusion investigation be scoped and conducted to address these data gaps (see Section 6.3). Furthermore, EPA recommends the CSM identify known or suspected preferential migration routes that could facilitate vapor migration to greater distances and at higher concentrations than otherwise expected. EPA recommends that buildings with significant preferential migration routes be evaluated closely. For the purposes of this Technical Guide, a preferential migration route is a naturally occurring subsurface feature or anthropogenic (human-made) subsurface conduit that is expected to exhibit little resistance to vapor flow in the vadose zone (i.e., exhibits a relatively high gas permeability) or groundwater flow (i.e., exhibits a relatively high hydraulic conductivity), depending upon its location and orientation relative to the water table and ground surface, thereby facilitating the migration of vapor-forming chemicals in the subsurface and/or into buildings. 96 Naturally occurring examples include fractures and macropores, which may facilitate a preferential route for either the vertical or horizontal migration of source materials and/or vapors. Anthropogenic examples include sewer lines and manholes, 97 utility vaults and corridors, elevator shafts, subsurface drains, permeable fill, and underground mine workings that intersect subsurface vapor sources or vapor migration routes. In highly developed residential areas, extensive networks of subsurface utility corridors may be present, which can significantly influence the migration of contaminants. A preferential migration route can be a significant influence on vapor intrusion when it is of sufficient volume and proximity to a building that it may be reasonably anticipated to influence vapor migration towards or vapor intrusion into the building. Significant vertical routes of preferential migration may result in higher than anticipated concentrations in the overlying near-surface soils, whereas significant horizontal routes of preferential migration may result in elevated concentrations in areas on the periphery of subsurface contamination (see Section 6.2.1). CSMs for vapor intrusion assessments often need to consider two distinct exposure situations: 1) At some sites and contaminated locations, there are concerns as to whether vapor intrusion may pose a human health risk to current occupants of an existing building(s). For this situation, EPA recommends that building-specific information be available to support the CSM, which may be obtained through a building survey (see Section 6.4.1, for example). 2) At other sites and contaminated locations, buildings are not present, but are expected to be constructed, and building-specific information may not be available to support the CSM. For this situation, the CSM may need to consider a hypothetical building constructed anywhere over (or near) the subsurface vapor source. 96 For purposes of this Technical Guide, preferential migration routes are distinguished from adventitious and intentional openings in a building that may also facilitate vapor entry from the subsurface (see Section 2.3), but w hich are expected to typically be present in all buildings (e.g., cracks, seams, interstices, and gaps in basement floors and w alls or foundations; perforations due to utility conduits). 97 In addition to receiving direct discharges of aqueous and chemical w astes from commercial and industrial operations, sew ers can be indirect receptacles of subsurface contamination via infiltration of NAPL, soil gas, or contaminated groundw ater through cracks in piping and manholes (see Section 2 of this Technical Guide, for example, for further discussion). 56

162 In general, CSMs identify the potentially exposed populations, potential exposure routes, and potential adverse health effects (i.e., toxicity) arising from these exposures. As such, EPA recommends the CSM also identify and consider sensitive populations, including but not limited to: Elderly, Women of child-bearing age, Infants and children, People suffering from chronic illness, or Disadvantaged populations (i.e., an environmental justice situation). By definition and as noted in Section 2, the exposure route of general interest for vapor intrusion is inhalation of vapors in indoor air and the human population of primary interest is comprised of individuals living or working in or otherwise occupying a building subject to vapor intrusion. However, EPA also recommends that the CSM identify any site-specific chemicals of concern that have potential for explosion hazards (e.g., methane) or for posing other routes of exposure (e.g., dermal exposure to shallow contaminated groundwater seeping into a basement). EPA recommends that the CSM also identify and characterize suspected sources of siterelated, vapor-forming chemicals that are also found in ambient air in the site vicinity. In some situations, site-related contamination has the potential to impact ambient air with the same vapor-forming chemicals that pose a threat from vapor intrusion. For example, contamination of shallow soil or groundwater may release site-related vapor-forming chemicals to ambient air. EPA recommends the CSM identify any such conditions, which have implications for the scope and objectives of the overall site investigation, as well as for data evaluation and the human health risk assessment. To document current site conditions, EPA recommends that a CSM be supported by maps, cross sections, and site diagrams, to the extent practical, and that the narrative description clearly distinguish what aspects are known or determined and what assumptions have been made in its development. EPA generally recommends that developing a CSM be incorporated into the first step in EPA s data quality objective (DQO) process (EPA 2006a). It is rare for a site to have readily available sources of sufficient information to develop a complete CSM when the vapor intrusion potential is first considered. For example, a detailed site-specific investigation may be necessary to characterize the full extent of subsurface vapor sources and geologic conditions underlying nearby buildings (see Sections and 6.3.2) and to demonstrate the absence of preferential routes for vapor migration and intrusion. The CSM normally warrants updating as new information is developed and new questions are framed and answered. A well-defined, detailed CSM may also facilitate the identification of additional data needs and development of appropriate detection limits for laboratory and field analyses, which can support planning of the detailed vapor intrusion investigation (see Section 6.2) and site-specific human health risk assessment, if any (see Section 7.4). Sections 6.3, 6.4, 7.1, and 7.2 provide additional information about data collection and evaluation for purposes of supporting the CSM. 57

163 5.5 Evaluating Pre-Existing and Readily Ascertainable Sampling Data Sites and adjacent facilities that have been the subject of previous environmental investigations or regulatory actions may already have data on contaminant concentrations in site media (i.e., sampling data) when the vapor intrusion pathway is first considered and evaluated. Some of these sites and facilities may be undergoing remediation but warrant a vapor intrusion assessment as a result, for example, of changing toxicity information for vapor-forming chemicals, as part of a periodic review of remediation effectiveness and protectiveness (if any), or for other reasons. If the pre-existing environmental data are deemed reliable and other conditions are met (as described in the remainder of this subsection and in Section 6.5.2), the sampling data may be compared to recommended generic vapor intrusion screening criteria (see Section 6.5) for purposes of developing some preliminary insights about the potential level of exposure and risk posed by vapor intrusion. Such a screening can, for example, help focus a subsequent vapor intrusion investigation (see Section 6) or provide support for considering building mitigation as an early action (see Section 7.8.2), depending upon building- and site-specific circumstances. Note that some of the site-specific information generally recommended for supporting a riskbased screening (see Section 6.5.2) may not be available when a site is first considered for vapor intrusion Evaluate Sampling Data Reliability and Quality To the extent that environmental sampling data are identified for the site or nearby properties, EPA recommends that these data be evaluated to determine whether they are of sufficient quality and reliability to support a comparison to recommended generic vapor intrusion screening criteria (see Section 6.5). Some questions that could be considered when reviewing historical sampling data include: How were the samples collected and analyzed? EPA recommends using pre-existing data when they have been collected and analyzed by methods considered reliable by today s standards. How old are the data? Were analyses conducted for all vapor-forming chemicals known or suspected to be present and reasonably expected degradation products? EPA recommends using pre-existing data when they can be considered representative of current conditions. Were the reporting limits sufficiently low for comparison with vapor intrusion screening criteria? EPA recommends use of pre-existing data with non-detect results only when they can be considered reliable on this basis. Were multiple locations sampled to assess spatial variability of the results? Were multiple sampling events conducted to assess temporal variability of the results? EPA recommends characterizing spatial and temporal variability to increase confidence in 58

164 data evaluation and decision-making and ensure consideration of a reasonable maximum vapor intrusion condition. 98 EPA also recommends that the reliability of any historical sampling data be assessed by considering the principles for collecting subsurface and indoor air samples that are described in Sections and 6.4 of this Technical Guide. In addition, the EPA s Guidance for Data Usability in Risk Assessment, Part A (EPA 1992a) outlines a recommended approach for evaluating whether the data are useable for the human health risk assessment. As such, its recommended approach is also worthwhile and complementary for evaluating the quality and usefulness of historical data collected at a site Evaluate Applicability of the VISLs and Adequacy of the Initial CSM Before performing any comparison of existing sampling data to recommended generic vapor intrusion screening levels (VISLs) (see Section 6.5), it is important to verify that site-specific conditions reflect the conditions and assumptions of the generic model underlying the VISLs, which are summarized in Section To verify that the generic vapor intrusion model applies, there is a need for basic knowledge of the subsurface source of vapors (e.g., location, form, and extent of site-specific vapor-forming chemicals) and subsurface conditions (e.g., soil type in the vadose zone, depth to groundwater for groundwater sources), which are important elements of the CSM (see Section 5.4). When these subsurface data are not available, EPA recommends they be collected (i.e., initiate a vapor intrusion investigation; see Section 6.3.2, for example) before relying upon risk-based screening using pre-existing sampling data Preliminary Risk-based Screening If reliable pre-existing sampling data are available and an adequate CSM has been developed (i.e., sufficient subsurface characterization information exists to adequately characterize the locations, forms, and extent of site-specific vapor-forming chemicals and general subsurface conditions (e.g., hydrologic and geologic setting in and around the source(s) and the buildings)), then a risk-based screening may be useful to obtain some preliminary insights about the potential level of exposure and risk posed by vapor intrusion. Example: A prospective developer of a vacant lot with no history of onsite chemical use is interested in evaluating the potential for vapor intrusion in the future due to potential migration onto the lot of a plume of contaminated groundwater emanating from another property. The extent and nature of this off-property plume have been adequately and recently characterized and geologic conditions near (but not on) the lot have been characterized, as documented in a publicly available report(s). In this circumstance, it may be possible to support a preliminary screening and obtain some useful insights. For example, if the maximum concentration of each chemical of concern in the off-property plume of contaminated groundwater currently and in the future is less than the generic chemical-specific screening level for groundwater, then vapor intrusion may not be a future 98 EPA recommends basing the decision about w hether to undertake response action for vapor intrusion (i.e., a component of risk management; see Section 7.4) on a consideration of a reasonable maximum exposure (e.g., EPA 1989, 1991a), w hich is intended to be a semi-quantitative phrase, referring to the low er portion of the high end of the exposure distribution (see Glossary). 59

165 concern on the vacant lot, provided there are sufficient data to document that conditions on the vacant lot are consistent with the generic model behind the vapor intrusion screening levels, as described in Section Depending upon lot-specific circumstances, additional data collection or evaluation, possibly including on-lot site characterization, may be warranted (i.e., proceed to a detailed vapor intrusion investigation) to verify that the expected conditions hold true (e.g., hydrogeologic conditions on the vacant lot are consistent with the generic model behind the vapor intrusion screening levels). EPA generally also recommends consideration of the vapor intrusion pathway during the development planning or initial post-construction stage (e.g., preemptive mitigation Sections 3.3 and 7.8; mathematical modeling, where parameters are chosen to represent conditions that give a high-impact case Section 6.6; indoor air testing Section to confirm the screening results based upon the groundwater source data) before making final risk management decisions. This example reinforces the following general recommended guidelines: EPA generally recommends that site-specific data be collected and evaluated to verify that the subject property reflects the conditions and assumptions of the generic model underlying the VISLs (see Section 6.5.2). EPA generally recommends that multiple lines of evidence (e.g., hydrogeologic information in addition to sampling data) be collected and weighed together in supporting assessments of the vapor intrusion pathway (see Sections 7.1, 7.2, and 7.3 for further information). Multiple rounds of groundwater (or soil gas) sampling results can be useful in supporting conclusions that a specific vapor source is stable or shrinking and/or is not expected to pose a vapor intrusion concern (see Sections and 6.4.5) under reasonably expected future, as well as current, conditions. Similar recommended guidelines may be appropriate in situations where vapor intrusion potential is being evaluated as part of a periodic review of an existing remedy (prompted, for example, by recent construction of a new building over a contaminated plume that is undergoing remediation) (EPA 2002b, 2012c). 60

166 6.0 DETAILED INVESTIGATION OF VAPOR INTRUSION EPA recommends that the planning and data review team plan and conduct a site investigation for vapor intrusion when the preliminary analysis (Section 5.3) indicates the presence of subsurface contamination with vapor-forming chemicals underlying or near buildings. This section describes EPA s generally recommended approaches and practices for conducting detailed vapor intrusion investigations, which typically entail collecting and weighing multiple lines of evidence to characterize the vapor intrusion pathway. Specifically, this section: Identifies that a wide variety of scenarios may be encountered among sites investigated for potential vapor intrusion, which necessitates site-specific approaches to scoping investigations and sequencing investigation phases and objectives (Section 6.1); Provides EPA s recommendations for planning, scoping, and conducting vapor intrusion investigations (Sections 6.2, 6.3, and 6.4); Presents EPA s recommended screening levels for vapor intrusion and describes EPA s recommended uses of risk-based screening and suggested interpretation of the results (Section 6.5); and Provides recommendations for developing and using mathematical models in vapor intrusion assessments (Section 6.6). Section 7 describes EPA s generally recommended approaches and practices for determining, on the basis of the investigation results, whether the vapor intrusion pathway poses a potential human health risk to building occupants under current and reasonably expected future conditions and whether response actions are warranted for vapor intrusion mitigation at individual facilities, buildings, or sites. 6.1 Common Vapor Intrusion Scenarios Vapor intrusion scenarios can be quite varied, owing to the possible combinations of: Multiple hazardous chemicals that can form vapors. Multiple forms in which these chemicals may be released to or present as contaminants in the subsurface, for example: o o o Residual NAPL and adsorbed-phase chemicals, including LNAPLs that are less dense than water and DNAPLs that are denser than water. Dissolved-phase chemicals in groundwater or soil moisture. Primary vapor releases (e.g., from chemical vapor transmission lines). The variety of geologic and hydrologic characteristics and conditions in the subsurface environment in which this contamination may occur. 61

167 The variety of buildings (in terms of size, age, condition, and use) and current or expected land use settings (e.g., residential, commercial, industrial) that may be subject to vapor intrusion from such subsurface contamination. Circumstances under which subsurface contamination is found or suspected and investigated (e.g., brownfield redevelopment, citizen reports/complaints, reported release) The variety of sources that may contribute to vapor concentrations in ambient air and may serve as indoor vapor sources unrelated to vapor intrusion. A few of the possible scenarios are illustrated in Figure 2-1. Many more can be inferred from the conceptual model of vapor intrusion discussed in Section 2. Some of the common scenarios where vapor intrusion has been documented to occur include: Groundwater contaminant plumes in shallow aquifers underlying residential and nonresidential buildings. Many well-known vapor intrusion sites are in this category, in part because there is generally a greater opportunity to have multiple buildings overlying the vapor source. Specific sites and buildings normally can be prioritized and distinguished based upon their potential for vapor intrusion, which generally would depend upon a number of site-specific factors, such as: o strength, proximity, and extent of the vapor source emanating from shallow groundwater (see Sections 2.1 and 5.4); o the potential for significant attenuation of vapor migration due to geologic, hydrologic, or biochemical conditions in the vadose zone (see Sections 2.2 and 5.4); o the potential for significant attenuation of the contaminant plume due to geologic, hydrologic, or biochemical conditions in the saturated zone; and o type(s), characteristics and structural condition of the overlying building(s) (see Sections 2.3, 2.4, and 5.4). Soil contamination in the vadose zone underlying commercial or industrial buildings. Typically, one or a few buildings may be threatened by potential vapor intrusion. Specific buildings and sites normally can be prioritized and distinguished based upon their potential for vapor intrusion, which generally would depend upon a number of sitespecific factors, such as: o strength, proximity, and extent of the vadose zone source (see Sections 2.1 and 5.4); o the potential for attenuation of vapor migration due to geologic, hydrologic, or biochemical conditions in the vadose zone (see Sections 2.2 and 5.4); and o type(s), characteristics and structural condition of the overlying building(s) (see Sections 2.3, 2.4, and 5.4). 62

168 Sites with residual wastes (e.g., landfills, former manufactured gas plants, former oil production fields) underlying or near buildings. The potential for methane formation may more frequently warrant additional consideration for sites with residual wastes than for contaminated groundwater plumes. EPA s recommended approaches and practices for vapor intrusion investigations aim to be flexible and adaptable to a wide range of reasonably expected scenarios and are not intended to be prescriptive or exhaustive for any specific scenario. 6.2 Planning and Scoping Before information or data are collected, EPA generally recommends conducting systematic and thorough planning during which performance or acceptance criteria are developed for the collection, evaluation, or use of these data (EPA 2006a). 99 EPA recommends the data quality objective (DQO) process as the appropriate systematic planning process for its decision-making and has issued guidance for its application to hazardous waste site investigations pursuant to CERCLA and RCRA (EPA 2000a). 100 When appropriately conducted, planning provides greater assurance that the data collected will fulfill specific project needs and that mitigation and subsurface remediation options will be considered early in the process. 101 A clear and logical plan will often facilitate communication with building owners, occupants, and other stakeholders. Given these considerations, a thorough planning process, guided by a CSM, is usually advisable for detailed vapor intrusion investigations. Figure 6-1 provides a diagram to illustrate such planning and scoping. The initial stages of planning would typically entail gathering readily available existing information and formulating an initial CSM, as described in Section 5.4. The CSM portrays the current understanding of site-specific conditions, including the nature and extent of contamination, contaminant fate and transport routes, potential receptors and contaminant exposure pathways. The term conceptual merely reflects that the model need not be entirely quantitative and mathematical; it does not, however, denote a simplistic or incomplete understanding of site conditions. The CSM normally warrants updating as new information is developed and new investigatory questions are framed and answered. Subsequent to formulating an initial CSM based on readily available information, the scope for an initial phase of vapor intrusion investigation would be developed, preferably along with a logical plan for future directions in response to the reasonably expected outcomes of the initial investigatory phases and in coordination with the objectives and phasing of the broader site 99 In situations w here imminent threats (see Section 5.2) are know n or reasonably expected, the initial planning process may be more truncated and focused, but careful and thoughtful planning is still recommended. 100 Appendix B provides additional information about EPA s quality system and DQO process. 101 Science and Decisions: Advancing Risk Assessment w as prepared by the National Academy of Sciences (NAS) Committee on Improving Risk Analysis Approaches Used by the U.S. EPA (NRC 2009) and is commonly referred to as the Silver Book. Among other recommendations, the NAS Committee encouraged EPA to focus greater attention on design in the formative stages of risk assessment, specifically on planning and scoping and problem formulation, and to view risk assessments as a method for evaluating the relative merits of various options for managing risk, rather than as an end in itself. Consistent w ith these recommendations, plausible mitigation and subsurface remediation options (see Section 8) may w arrant consideration during development of vapor intrusion investigation plans. 63

169 Consider Scenario and Conceptual Site Model - See Sections 5.4 and 6.1 Consider & Prioritize Investigation Objectives - See Section 6.3 Identify "Higher Priority" Buildings - See Section Establish Data Quality Objectives - See Appendix C Community Involvement (Section 9) throughout Assessment and Response Process! Scope and Prepare Investigation Workplan (See Section 6.2) Collect Additional Data NO Collect Samples and Complementary Lines of Evidence (See Sections 6.3, 6.4, and 7.1) - sequence need not follow this order of steps: Characterize Nature and Extent of Vapor Sources (See Sections 6.3.1, 6.4.4, and 6.4.5) Test Indoor Air (Sections 6.3.4, 6.3.5, and 6.4.1) Characterize Vapor Migration in the Vadose Zone (from source to subslab) (See Sections 6.3.2, 6.4.3, and 6.4.4) Evaluate Contribution from Background Sources (See Sections 6.3.5, 6.4.1, and 6.4.2) Update/Refine Conceptual Site Model Identify Data Gaps (Section 5.4) and resolve inconsistencies, if any, between new sitespecific info and existing CSM (Section 7.2) Verify boundaries of inclusion zone (Section 6.2.2) Is site-specific information sufficient to support decision-making? YES! Data Evaluation 1. Compare Sample Concentrations to Health-based Screening Levels (Section 6.5.4) 2. Weigh Site-specific Lines of Evidence and Assess Their Concordance (Sections 7.1 and 7.2) 3. Evaluate Whether the Vapor Intrusion Pathway is Complete or Incomplete (Section 7.3) 4. Conduct and Interpret Health Risk Assessment (Section 7.4) Exclamation point (!) indicates important milestone for communication and engagement efforts with affected building occupants and owners. Figure 6-1 Overview of Planning, Scoping, and Conducting Vapor Intrusion Investigations 64

170 characterization. Initial plans may warrant periodic updates and refinements, particularly when data outcomes are unexpected and prompt the need to reevaluate the CSM. In each case, EPA recommends that the investigation work plan include the identification of and basis for the indoor air screening levels (such as the vapor intrusion screening levels (VISLs)) and/or indoor air action levels (i.e., level of each vapor-forming chemical of potential concern that would trigger a response action if exceeded), which would dictate the DQOs for the sampling and analysis methods. In general, EPA recommends the plan also include a rationale or logic for where and how the data will be collected and over what duration(s), how the data will be interpreted (e.g., weighed with other lines of evidence, compared to risk-based benchmarks), whether confirmatory sampling will be needed if all sample concentrations are less than the action levels, whether response action(s) would be triggered if sample concentrations exceed the target levels, and similar considerations. EPA recommends considering potential health effects and relevant exposure periods (e.g., chronic versus short-term effects and exposure durations and scenarios; see Section 7.4) for site-related, vapor-forming chemicals when developing DQOs and sampling plans for indoor air (see Section 6.4.1, for example). Sections 6.3 through 6.6 below provide additional information for planning and scoping site-specific investigations for vapor intrusion assessment. EPA s fundamental approach to evaluating contaminated sites calls for proceeding in a stepwise fashion with early data collection efforts usually limited to developing a basic understanding of the site, as reflected in the CSM. 102 Subsequent data collection efforts focus on filling gaps in the understanding of the CSM and gathering information necessary to evaluate the relative merits of various options for managing risk. Therefore, EPA generally recommends developing and implementing an overall vapor intrusion investigation plan in multiple stages or phases. Such a phased approach encourages the identification of key data needs early in the process to better ensure that data collection provides information relevant to decision-making (e.g., interim action to mitigate vapor intrusion and selection of a cleanup plan for subsurface contamination). In this way, the overall site characterization effort can be scoped to prioritize data collection and minimize the collection of unnecessary data and maximize data quality. EPA recommends that the objectives and methods of the investigation be documented, preferably in a vapor intrusion work plan. An individual work plan may address a single phase or stage or may address the overall investigation. The vapor intrusion work plan(s) may be 102 Investigations under CERCLA and RCRA corrective action (CA) explicitly recognize phasing. In these cleanup programs, the first investigatory phase is an initial site assessment. The purpose of this activity is to gather information on site conditions (current and historical), releases, potential releases, and exposure pathw ays. Investigators use this information to determine w hether a response action (e.g., removal action or interim cleanup measure) may be needed or to identify areas of concern for further study. Information collected during this phase usually forms the basis for determining w hether the next stage, site investigation, is w arranted. In the RCRA CA program, the initial site assessment is called the RCRA facility assessment. Under CERCLA, this phase is called the preliminary assessment/site inspection. The purpose of the second phase, site investigation, is to determine the nature and extent of contamination at a site, quantify risks posed to human health and the environment, and gather information to support the selection and implementation of appropriate remedies. In the RCRA CA program, this phase is know n as the RCRA facility investigation. Under the CERCLA remedial program, this phase is referred to as the remedial investigation. In addition, the site investigation may itself be conducted in multiple stages (or phases). 65

171 incorporated as part of a comprehensive site investigation work plan or as a stand-alone document, depending upon site-specific circumstances. 103 At a minimum, EPA recommends that the components of the work plan(s) include or reference: Narrative description of the rationale, objective(s), and scope of the investigation. Summary of the CSM, based upon the current understanding of site conditions. Scaled map(s) illustrating known extent of subsurface contamination and readily identifiable landmarks (e.g., streets and buildings). Media to be sampled. Number, type, and location of and rationale for proposed sampling locations. Sampling methods and procedures for each medium. Analytic method(s) to be used to obtain chemical concentrations and a statement about whether a stationary or mobile laboratory will be used. Standard operating procedures of the laboratory and for field instruments. Quality assurance project plan (QAPP). Health and safety plan. 104 EPA recommends that planning for vapor intrusion investigations also consider site and building access agreements, equipment security, and locations of underground utilities. EPA recommends that the planning, data collection, and data review team(s) for vapor intrusion investigations generally include: Individuals with expertise in characterizing subsurface environmental conditions and interpreting and communicating environmental data. On-site (field) personnel with appropriate training and experience in hazard identification, workplace practices to foster health and safety, and recommended sampling protocols. 103 EPA recommends that monitoring programs (see Section 8.4) that assess the performance and effectiveness of remediation and mitigation systems (see Sections 8.1 and 8.2, respectively) also be documented, preferably in w ork plans similar to those recommended herein for characterizing and assessing the vapor intrusion pathw ay. 104 All governmental agencies and private employers are directly responsible for the health and safety of their employees. This general rule applies to many parties involved in the assessment and cleanup of Superfund sites, RCRA corrective action sites, and brow nfield redevelopment sites. Standards established pursuant to the Occupational Safety and Health Act are found in Title 29 of the Code of Federal Regulations (29 CFR), w hich include standards for training, hazard communication, and site-specific health and safety plans. 66

172 Individuals with expertise in human health risk assessment to characterize risks posed by the vapor intrusion pathway. Individuals with expertise in community involvement and outreach. Depending upon the complexity of the CSM (see Section 5.4) and site-specific data evaluations, decision-makers may also find valuable input from individuals with expertise in hydrogeology, inferential statistics, laboratory analysis methods, and building construction, ventilation, and operations and individuals knowledgeable about land use planning, zoning, and land development. EPA recommends that the scope of investigations within buildings and on individual properties be contemplated, planned, and implemented with the goal of limiting, to the extent practical, return visits, which can cause disruption and inconvenience for building occupants and owners. For example, it may be preferable to collect a comprehensive set of data (e.g., indoor air, subslab soil gas, and ambient air samples; pressure readings; see Section 6.4) and confirm information about building occupancy, building usage, heating, cooling, and ventilation (see Section 6.4.1) in a single mobilization, rather than over separate visits, when the investigation objectives include indoor air sampling (see Section 6.3.4) or evaluating contributions of background sources on levels of vapor-forming chemicals in indoor air (see Section 6.3.5) Vapor Intrusion Inclusion Zones Soil gas concentrations generally decrease with increasing distance from a subsurface vapor source, and eventually at some distance the concentrations become negligible. The distance at which soil gas concentrations become negligible is a function of the strength and dimensions of the vapor source, the type of vapor source, the soil types and layering in the vadose zone, the presence of physical barriers (e.g., asphalt covers or ice) at the ground surface, and the presence of preferential migration routes, among other factors (see, for example, EPA 2012b). The extent of the site-specific inclusion zone for vapor intrusion may also expand in the future, depending upon: The age of the chemical release and whether sufficient time has elapsed to allow soil gas to migrate from the source to its maximum potential extent. 105 Whether the subsurface vapor source is expanding (i.e., is migrating) or rising in concentration, including hazardous byproducts of any biodegradation. Because these factors vary among sites, the distance beyond which structures will not be affected by vapor intrusion should be a site-specific determination. Recommended Distance for Initial Evaluation. There are limited published empirical data relating observed indoor air concentrations of subsurface contaminants to distance from a well- 105 EPA (2012b, Section 6.1) presents some information about transient vapor migration after a subsurface vapor source is released. Sites w ith shallow vapor sources (e.g., less than one meter deep) may take only a few hours to a few days for soil gas to migrate to its maximum potential extent. Sites w ith deeper vapor sources (e.g., greater than 10 meters deep) may take months or years for soil gas to migrate to its maximum potential extent. 67

173 defined source boundary. However, a buffer zone of approximately 100 feet (laterally or vertically from the boundary of subsurface vapor concentrations of potential concern) generally has been used in determining which buildings to include in vapor intrusion investigations (i.e., which buildings are near a subsurface vapor source for purposes of a preliminary analysis) when significant surface covers are not present, under the assumption that preferential vapor migration routes are absent. 106 Specifically, a buffer zone of 100 feet (or approximately two houses wide) has been suggested by several states for initial evaluation and is supported, in general, by: theoretical analyses that assume the absence of a preferential vapor migration route(s) and that diffusion is the predominant mechanism of vapor migration in the vadose zone (Lowell and Eklund 2004); and reports that vapor intrusion impacts generally have not been observed at distances greater than one or two houses beyond the estimated extent of the groundwater plume, at sites where contaminated groundwater is the subsurface vapor source (Folkes et al. 2009). However, we would note that vapor source types for which use of a 100-foot buffer would typically be inappropriate include: Landfills where methane is generated in sufficient quantities to induce advective transport in the vadose zone. 107 Commercial or industrial settings where a vapor-forming chemical(s) has been released within an enclosed space at a density that may result in significant advective transport of the vapor(s) downward through cracks or openings in floors and into the vadose zone. Leaking vapors from pressurized gas transmission lines. In each of these cases, the diffusive transport of vapors may be overridden by advective transport and the vapors may be transported in the vadose zone several hundred feet from the source of contamination. 108 Moreover, we would also note that anecdotal evidence indicates that in some settings buildings greater than 100 feet from a plume boundary are affected by vapor intrusion, even when 106 Preferential migration routes are defined and discussed in Section 5.4. When present, they may facilitate subsurface vapor migration over distances greater than 100 feet. 107 EPA has also published Guidance for Evaluating Landfill Gas Emissions from Closed or Abandoned Facilities (EPA 2005), w hich provides procedures and a set of tools for evaluating landfill gas emissions to ambient air and soil gas migration due to pressure gradients. 108 For example, Little et al (1992) describe a landfill in southern California, w here methane w as detected in enclosed spaces in nearby homes at concentrations approaching 1% by volume and chlorinated hydrocarbons had migrated into a house 180 meters from the landfill. 68

174 diffusion is the presumed mechanism of vapor migration. 109 Furthermore, the presence of conduits (e.g., sewer and drain lines that intercept and carry subsurface contamination (Vroblesky et al. 2011), as well as permeable bedding for sewer lines or other utilities) or preferential hydrogeologic pathways that facilitate unattenuated vapor migration in the vadose zone, and other factors (e.g., presence of extensive surface covers, uncertainties in delineating the boundaries) may extend the recommended inclusion distance for a vapor intrusion investigation. For these reasons, EPA recommends investigating soil vapor migration distance on a site-specific basis. That is, larger or smaller distances may need to be considered when developing objectives for detailed vapor intrusion investigations and interpreting the resulting data. Data from sub-slab and exterior soil gas sampling (see, for example, Sections 6.4.3, and 6.4.4, respectively) 110 and indoor air testing (see, for example, Sections and 6.4.1) can be collected and evaluated to delineate or confirm areas at specific sites within which buildings are potentially subject to vapor intrusion. Criteria for Establishing Boundaries of the Plumes that Contain Vapor-forming Chemicals. This Technical Guide is intended to be applied to existing groundwater plumes as they are currently defined (e.g., Maximum Contaminant Levels, state standards, or risk-based concentrations). However, it is important to recognize that some non-potable aquifers may have plumes that have been defined by threshold concentrations significantly higher than drinking-water concentrations. In these cases, contamination that is not technically considered part of the plume may still have the potential to pose unacceptable human health risk via the vapor intrusion pathway. Consequently, the plume definition may need to be expanded for purposes of defining an inclusion zone for a vapor intrusion investigation. When groundwater is the subsurface vapor source, EPA generally recommends comparing groundwater concentrations to the VISLs to estimate the boundaries of the plume, when contaminated groundwater is a subsurface vapor source, for purposes of establishing the boundaries of the vapor intrusion inclusion zone. Criteria for Establishing Boundaries of NAPL Plumes that Contain Vapor-forming Chemicals. EPA generally recommends comparing soil gas concentrations to the respective VISLs to estimate the boundaries of the vapor plume, when residual or free-phase NAPL is a subsurface vapor source, for purposes of establishing the boundaries of the vapor intrusion inclusion zone Prioritizing Investigations with Multiple Buildings At sites where numerous buildings are potentially subject to vapor intrusion (e.g., developed areas with an extensive plume of contaminated groundwater), it may not be feasible or practical at the outset to sample indoor air in each building or soil gas underneath or near each building. In such circumstances, EPA generally recommends a worst first approach to prioritize 109 Among other possibilities, vapor intrusion impacts observed to occur at distances greater than 100 feet in the absence of a preferential migration route(s) may reflect imprecision in the interpolated edge of a plume, based upon sampling data from sparse monitoring w ells, and/or use of screening levels for drinking w ater, rather than for vapor intrusion (i.e., VISLs), to delineate a plume s extent. 110 For assessing the extent of soil gas migration from the subsurface vapor source, EPA generally recommends measuring soil gas concentrations, either sub-slab soil gas (preferably) or exterior soil gas, w ith a sufficient density to characterize and understand spatial variability (Section 6.3.2). 69

175 buildings for investigation. Factors that, if known, may warrant consideration in prioritizing buildings for investigation include: Source strength and proximity. Buildings overlying and near a source of vapors in the vadose zone would generally be expected to have a greater potential for vapor intrusion than buildings that do not overlie this same vapor source. Where the subsurface vapor source is groundwater, buildings located over higher concentrations or shallower water levels would generally be expected to have a greater potential for vapor intrusion than buildings located over lower concentrations and deeper groundwater plumes. Building types and conditions. Buildings that are continuously occupied may pose a more immediate concern than buildings that are not currently occupied, if all other factors (e.g., source strength and proximity) are equivalent. Nonresidential buildings with bay-style doors that are routinely open may be better ventilated than other types of nonresidential buildings, providing greater potential for dilution of vapor-forming chemicals that enter the building via vapor intrusion. Vapor migration ease. Buildings overlying vadose zones comprised of coarse geological materials (e.g., gravel, boulders) generally would be expected to have a greater potential for vapor intrusion than buildings overlying vadose zones comprised of fine-grained materials (e.g., silts, clays), provided significant preferential migration routes (e.g., geologic fractures, utility corridors) are not present in the fine-grained layers. Interviews and building surveys during development of the investigation work plan (or during the preliminary analysis see Section 5) also can provide useful information for prioritizing buildings, when phased testing is chosen or indicated. Sections 6.3 and 6.4 provide additional examples of survey information that can support planning, in addition to supporting data interpretation. In situations where higher-priority buildings and locations are investigated initially, investigation of locations of other buildings may still be warranted, for example, to ensure that the CSM is complete and accurate and that variability in the subsurface conditions and building conditions is understood. There usually is substantial spatial variability in the concentrations of subsurface vapors, caused by heterogeneities in the subsurface materials and other factors, that can result in variability among buildings in vapor flux and indoor air concentrations arising from vapor intrusion. Additionally, building construction, building age and maintenance, and occupants activities that affect soil gas entry and air exchange rate will vary from building to building, further adding to the variability in indoor air concentrations between buildings. Therefore, it may be difficult to identify a priori either a representative or reasonable worst case 111 building or group of buildings, when it is determined that sampling all buildings is not practical. 111 For purposes of this Technical Guide, reasonable w orst case is intended to be a semi-quantitative phrase, referring to the upper portion of the high end of the exposure distribution, but less than the absolute maximum exposure (see Glossary). Because EPA generally recommends a w orst first approach to prioritize buildings for investigation of the vapor intrusion pathw ay, reasonable w orst case buildings w ould w arrant a higher priority than representative or typical buildings. 70

176 When sampling all buildings is not practical, but other lines of evidence suggest that vapor intrusion may be occurring, the site management team may wish to consider installing engineered exposure controls for vapor intrusion mitigation in buildings without baseline indoor air data (i.e., building mitigation as an early action see Sections 3.3 and 7.8) Planning for Community Involvement Community involvement is an important component of any vapor intrusion investigation. EPA recommends that a community involvement or public participation plan (see Section 9.1) be developed or refined while planning a vapor intrusion investigation. Proper and sustained community outreach and engagement efforts are critical to effectively implementing work plans for vapor intrusion investigations, particularly when they involve sampling in a home or workplace or on private property. Resuming and conducting community involvement at legacy sites (i.e., sites that have a past history of agency involvement; see Section 9.6) can be particularly complex. The site planning team is encouraged to consult with appropriate EPA colleagues experienced in community outreach and involvement efforts and utilize available EPA planning resources, including those discussed in Section Characterize the Vapor Intrusion Pathway As discussed in Section 2, the vapor intrusion pathway entails emanation of volatile chemicals from a subsurface source(s) in a vapor form that migrates in the vadose zone, gradually increases in amount underneath buildings as time passes, and enters buildings through openings and conduits. As a result, detailed vapor intrusion investigations designed to develop or enhance the CSM for a specific site will typically address one or more of the following objectives, often in phases: 112 Characterize the nature and extent of subsurface sources of vapors. Characterize the subsurface migration paths between vapor sources and buildings (potential receptors ). Assess building(s) for their susceptibility to soil gas entry. Evaluate the presence and concentration of a site-related subsurface contaminant(s) in indoor air. Identify and evaluate contributions of indoor and ambient air sources to concentrations of hazardous vapors in indoor air. 112 The order of presentation is not intended to convey a suggested sequencing of objectives; rather, it follow s the presentation of the conceptual model of vapor intrusion in Section 2. 71

177 These objectives are described in the following subsections for purposes of identifying the primary lines of evidence typically developed and evaluated for each objective and describing how the objectives fit together in developing and enhancing the CSM for a specific site an characterizing vapor intrusion potential. This information is provided to assist the site planning team in selecting and sequencing objectives for vapor intrusion investigations Characterize Nature and Extent of Subsurface Vapor Sources Where the preliminary analysis indicates that subsurface contamination with vapor-forming chemicals may be underlying or near buildings, EPA recommends that the nature and extent of such contamination be well characterized. Source characterization data are critical to developing a sound CSM and supporting confident, final decisions about the vapor intrusion pathway. Investigations to characterize the nature and delineate the extent of potential sources of vapors may rely upon the results of groundwater sampling, soil sampling, or soil gas sampling, as dictated by the site-specific source(s) and subsurface conditions. 72

178 Groundwater Sources: Where contaminated groundwater is a vapor source located near buildings, EPA recommends that groundwater observation wells (i.e., monitoring wells) be installed at strategic locations and used to assess groundwater flow and contaminant concentrations; i.e., verify the nature and extent of groundwater contamination through groundwater sampling and analysis. 113 Groundwater samples obtained from the uppermost portion of the aquifer 114 that underlies the study area of interest (i.e., where buildings are located) are recommended for characterizing representative vapor source concentrations for vapor intrusion assessment. For this purpose, wells (or multi-level samplers) that are screened across the water table interface are preferred and EPA recommends samples be collected as close as possible to the top of the water table using approved sampling methods designed to minimize loss of volatiles while sampling (EPA 2002a, EPA-ERT 2001a). 115 Ideally, the plume can be shown as stable or shrinking (i.e., is not migrating or rising in concentration, including hazardous byproducts of any biodegradation), through multiple rounds of sampling, so that vapor source concentrations can be confidently evaluated under reasonably expected future, as well as current, conditions. Otherwise, the inclusion zone for vapor intrusion (see Section 6.2.1) may expand over time and/or current sample concentrations in or beneath a given building may under-estimate the reasonable maximum vapor intrusion condition in the future. For purposes of assessing vapor intrusion for specific buildings, groundwater samples from wells nearer to buildings are generally recommended over those from more distant wells. Interpolation of the results obtained from two or more wells in the uppermost portion of the aquifer may be warranted for these purposes when the spatial pattern suggests significant lateral gradients in contaminant concentrations within the area of interest. However, for purposes of determining whether contaminated groundwater poses acceptable human health risk from vapor intrusion on an area-wide basis, it may be more appropriate to utilize sampling results for the most greatly impacted well within the area of interest. In addition, EPA generally recommends that a soil gas sample be collected immediately above the groundwater table (and above the capillary fringe) (i.e., near-source soil gas sample) 116 to help characterize the subsurface vapor source. The results of such near 113 Although a soil gas survey can also be employed as a screening tool to assist w ith the delineation of a plume of contaminated groundw ater, EPA recommends that plume delineation ultimately be supported by the collection and analysis of confirmatory groundw ater samples at appropriate locations. 114 EPA recommends that, to the extent practical, groundw ater samples be collected over a narrow interval (e.g., a few feet or less) just below the w ater table w hen the data are to be used for assessing the potential for vapor intrusion. Of course, the broader objectives of a site characterization w ill generally necessitate installation and sampling of additional w ells, from other depth intervals, to accurately characterize the full nature and extent of groundw ater contamination. Such w ells and the broader topic of site characterization are not discussed in this Technical Guide, w hich is focused instead on recommended guidelines that are pertinent specifically to vapor intrusion. 115 If available groundw ater data do not meet these criteria, the site data review team may consider w hether they are nevertheless representative of potential vapor source concentrations emanating from groundw ater. 116 In this context and for purposes of this Technical Guide, near means w ithin a practically short distance. Siteand location-specific circumstances and project-specific objectives typically w ill influence the quantitative definition of near for purposes of collecting near-source soil gas samples. 73

179 source soil gas samples can be compared to calculations of the vapor concentration expected when the soil gas is in equilibrium with the concentrations measured in shallow groundwater (see Appendix C). A favorable comparison (i.e., the two concentrations are equivalent for each vapor-forming chemical in groundwater) would help to support the results of the groundwater characterization. On the other hand, a fresh water lens (or other site-specific conditions; see, for example, Section 6.3.2) could account for measured soil gas concentration(s) being significantly lower than the calculated equilibrium concentration(s). Because fluctuations in water table elevation can lead to elevated vapor concentrations in the vadose zone, EPA also recommends that near source soil gas sampling (and possibly a soil gas survey) be considered in different seasons that coincide with groundwater fluctuations. Vadose Zone Sources: Where contaminated soil or non-aqueous-phase liquid (NAPL) in the vadose zone is a subsurface vapor source, soil sampling using coring techniques for sample retrieval or using sensors, such as a membrane interface probe, can be used to characterize the chemical composition and general location of contamination; that is, bulk soil concentration data can be used in a qualitative sense for this purpose. For example, high soil concentrations generally would indicate impacted soil. Unfortunately, the converse is not always true. Nondetect results for soil samples cannot be interpreted to indicate the absence of a subsurface vapor source, because of the potential for vapor loss due to volatilization during soil sampling, preservation, and chemical analysis. Alternatively or in addition, a soil gas survey can be used to locate the primary source zone and delineate the areal and vertical extent of the vapor-affected area. Generally, EPA recommends that the soil gas survey include a soil gas sample collected immediately above each contaminant source in the vadose zone (i.e., near-source soil gas samples) to help characterize the vapor source. Although a soil gas survey can generally be used to characterize many other subsurface vapor sources (e.g., sewer and drain lines; landfills and other land-based disposal units; impoundments and other land-based storage and/or treatment units, pressurized tanks and pipelines), additional approaches tailored to the specific source type may also warrant consideration. These sampling options are generally coupled with an understanding of the site-specific subsurface conditions that control the location and extent of contamination (e.g., geologic properties, including stratigraphy and level of heterogeneity; hydrogeologic conditions; sewers, drains, and other conduits that lie underneath or intersect areas of groundwater and soil contamination). Such understanding is generally developed by interpreting the data obtained through borehole logging (i.e., visually inspecting soil cores and determining soil texture) or geophysical tools. EPA generally recommends sample locations be of sufficient density to adequately account for spatial variability and heterogeneity in subsurface conditions. EPA generally recommends consulting with individuals who have expertise in characterizing subsurface environmental conditions (e.g., a geologist) when determining appropriate sampling locations and spacing. 74

180 When combined with the data demonstrating that the property reflects the conditions and assumptions of the generic model invoked in the VISLs (see Section 6.5.2), groundwater and near-source soil gas samples can be compared to medium-specific screening levels to develop an initial quantitative perspective about the potential level of exposure and human health risk posed by vapor intrusion. Section 6.5 provides additional information about riskbased screening of vapor source concentrations Characterize Vapor Migration in the Vadose Zone As described in Section 2, geologic, hydrologic, biochemical factors in the vadose zone, as well as elapsed time since the environmental release, can influence vapor migration and attenuation in soil gas concentrations between subsurface vapor sources and nearby building(s). 117 As noted in Section 5.4, EPA recommends the CSM portray the current understanding of these vadose zone conditions in and around the subsurface vapor source(s) and nearby building(s). Furthermore, EPA recommends the CSM identify known or suspected preferential migration routes that could facilitate vapor migration to greater distances and at higher concentrations than otherwise expected. When these conditions are not well established from existing information, EPA recommends that a detailed investigation be scoped to address these data gaps. When combined with other data, as discussed further in Section 7.3, information about subsurface vapor migration can support determinations that the vapor intrusion pathway is complete under current conditions or may be complete under future conditions. In some cases, vadose zone conditions may impose sufficient resistance to vapor migration to make the vapor intrusion pathway insignificant. In these circumstances, information about subsurface vapor migration, combined with other lines of evidence, can support determinations that the vapor intrusion pathway is incomplete under current conditions, as discussed further in Section 7.3. Investigations seeking to characterize vapor migration in the vadose zone generally entail, at a minimum, a soil gas survey. Because soil gas concentrations can exhibit considerable spatial variability, due to a variety of factors, 118 EPA generally recommends that soil gas surveys collect soil gas samples at multiple locations and depth intervals between the vapor source and building(s) (potential receptors ). As a result, the soil gas survey may include samples collected immediately outside the building ( exterior soil gas ) at various depths or several depth intervals, 117 The horizontal and vertical distance over w hich vapors may migrate in the subsurface depends on the source concentration, source depth, soil matrix properties (e.g., porosity and moisture content), and time since the release occurred. For example, months or years of volatilization and vapor migration may be required to fully develop vapor distributions in the vadose zone at sites w ith deep vapor sources or w ith impedances to vapor migration arising from hydrologic or geologic conditions (Section 2.5; EPA 2012b). Under such circumstances, soil gas surveys conducted soon after an environmental release may not yield data indicating the maximum extent of vapor migration. 118 Modeling of idealized scenarios provides additional demonstrations about spatial variability of soil gas concentrations. For example, vertical profiles of soil gas concentration(s) can be very different underneath buildings compared to locations exterior to the building and soil gas concentrations may not be uniform laterally, particularly in the vicinity of the building, even w hen the vapor source is a laterally extensive plume of contaminated groundw ater (EPA 2012b). These simulation results indicate w hy EPA recommends that soil gas generally be sampled in multiple sampling locations, w hen assessing subsurface vapor migration routes. 75

181 as well as immediately beneath it (e.g., sub-slab soil gas sampling). 119 If any shallow soil gas samples are collected, EPA recommends they be collected as close as possible to the building and at depths below the respective building foundation and no less than five feet below ground surface, depending on site-specific conditions. Where crawl spaces are present, crawl space air sampling may also be conducted. Generally, EPA recommends that the soil gas survey include a near-source soil gas sample collected immediately above each source of contamination to help characterize the subsurface vapor source (see Section 6.3.1). The results of such near source soil gas samples can be compared to calculations of the vapor concentration expected when the soil gas is in equilibrium with the concentrations measured in shallow groundwater (see Appendix C), when the subsurface vapor source is in the groundwater. Geologic, hydrologic, or biologic impedances to vapor migration may be indicated if the measured near source soil gas concentrations are significantly lower than the calculated equilibrium concentrations. To characterize subsurface migration in the vadose zone, soil gas survey data are generally coupled with an understanding of the site-specific subsurface conditions that influence vapor migration and attenuation (e.g., geologic properties, including stratigraphy and level of heterogeneity; hydrologic conditions, including groundwater elevation and soil moisture; 120 and biological properties, including availability of oxygen to support aerobic biodegradation). 121 Such geologic understanding is generally developed by interpreting the data obtained through borehole logging and geophysical tools. Soil permeability to air flow can be measured in the field (McHugh et al. 2013) and would be used to corroborate inferences based upon borehole logging data. Hydrologic conditions can be characterized by analyzing soil samples for porosity and moisture content and by hydrologic modeling. For potentially biodegradable contaminants, an intensive soil gas survey to establish current vertical profiles for contaminant vapors and oxygen (and, in some cases, biodegradation products, such as carbon dioxide or methane) 122 may be able to demonstrate that biodegradation is responsible for attenuating vapor migration 119 EPA recommends that spacing of soil gas sampling locations generally consider the extent and location of the subsurface vapor source, distance betw een the building and the source, and other site-specific factors. 120 Tillman and Weaver (2007) conducted hydrologic modeling and collected field data, w hich show ed that moisture content determined from soil cores taken external to a building may over-estimate soil moisture underneath the building. They inferred that vapor intrusion assessments based upon moisture content in soil from open areas betw een buildings may under-estimate vapor intrusion potential. 121 As noted in Section 2, vapor migration in the vadose zone can be impeded by several factors, including soil moisture, low -permeability (generally fine-grained) soils, and biodegradation. Significant characterization of the vadose zone may be needed to demonstrate that such geologic, hydrologic, and biologic features are laterally extensive over distances that are large compared to the footprint of the building and the extent of the subsurface vapor source at a specific site. 122 Interpretation of profiles for carbon dioxide and methane can be challenging, due to the presence of natural sources unrelated to contaminant biodegradation (Holden and Fierer 2005). 76

182 123, 124 to a greater extent than can be attributed to advection and diffusion in the vadose zone. For both purposes, samples collected directly underneath the building will tend to be more representative of conditions influencing vapor intrusion potential than samples collected outside the building footprint, all else being equal. When conducted contemporaneously for multiple buildings, a soil gas survey and characterization of the vadose zone can help identify distances from subsurface vapor sources beyond which threats from vapor intrusion are not reasonably expected, as mentioned in Section At sites with a limited number of potentially affected buildings, it may be feasible to characterize the subsurface vapor migration near and surrounding all of them. However, at sites where a large number of buildings may be affected, this approach is not likely to be feasible; in these cases, EPA generally recommends that the site manager seek the advice of an individual familiar with the site-specific subsurface conditions (typically a geologist) to help guide selection of appropriate sampling locations and assess whether representative or reasonable worst case locations can be identified, as appropriate to the objectives of the investigation. Because there usually is substantial spatial variability in the concentrations of subsurface vapors, caused partially by heterogeneities in the subsurface materials, it may be difficult to identify a priori locations that are either representative or are reasonable worst case subsurface conditions. Subsurface investigations of vapor intrusion also generally warrant an evaluation of utility corridors, which can facilitate unattenuated vapor transport over longer-than-anticipated distances and/or vapor migration towards and into buildings that are serviced by the utility. EPA also recommends subsurface investigations of vapor intrusion consider whether sewers and other man-made conduits have the potential to transport NAPLs, contaminated groundwater, and/or vapors (through soil) towards and/or directly into buildings. Public and facility records may be useful sources of information about utility and sewer locations, which may provide maps, as built diagrams, or construction specifications. Depending upon the CSM, sampling of vapors within the utility corridor (or within a sewer, if present) may be warranted to characterize vapor migration in the subsurface (or characterize a secondary source of vapors see Sections and Section 2.1). Reasonably expected future risks posed by the subsurface vapor source(s) warrant consideration, in addition to risks posed under current conditions, in order to demonstrate that a site does not present an unacceptable risk to human health and the environment (EPA 1991a). For example, when evaluating subsurface vapor migration and attenuation in locations where buildings do not exist, it is important to recognize that the conditions in the vadose zone and soil 123 At sites w here aerobic biodegradation is limiting the upw ard migration of petroleum hydrocarbon vapors, for example, the vertical concentration profile w ill typically show higher concentrations of petroleum hydrocarbons and low er (or non-detect) concentrations of oxygen in deeper soil gas samples. At these same sites, the vertical concentration profile w ill typically show low er (or non-detect) concentrations of petroleum hydrocarbons and higher concentrations of oxygen in shallow er soil gas samples. Because w eather events can affect rates of oxygen replenishment in the vadose zone (Lundegard et al. 2008), multiple rounds of such sampling are recommended to demonstrate that biodegradation consistently poses a significant impedance to upw ard vapor migration. This recommendation is particularly apt w here the subsurface vapor source is strong (e.g., unw eathered NAPL in the vadose zone) relative to time-variable processes supplying oxygen to the vadose zone. 124 In this context, mathematical modeling (see Section 6.6) can be employed to characterize vapor migration attributable to advection and diffusion in the vadose zone. 77

183 gas concentrations may be changed as a result of constructing a new building and/or supporting infrastructure. The moisture content may decrease and the moisture profile change in the vadose zone as a result of reduced infiltration of rainwater below a building footprint (Tilman and Weaver 2007). The permeability to vapor flow in the vadose zone may be altered in the foundation vicinity due to construction. Finally, the future presence of extensive surface covers and/or utility corridors may also modify the vertical and horizontal profile of soil gas concentrations in the subsurface (EPA 2012b). As a result, EPA recommends that appropriate lines of evidence in addition to a soil gas survey (e.g., mathematical modeling, where parameters are chosen to represent conditions that give a high-impact case Section 6.6) be developed and considered to support any determination that a future building will not be subject to vapor intrusion or will not pose unacceptable human health risk for occupants. Owing to the potentially unpredictable plans for building construction and site redevelopment, as well as potentially unpredictable changes in the transitory soil characteristics (e.g., soil moisture) and soil gas concentrations, institutional controls may be warranted (e.g., to inform the need for a confirmatory evaluation of the vapor intrusion pathway) when new buildings are constructed in areas where the subsurface vapor source(s) has(have) significant potential to pose a vapor intrusion threat Assess Building Susceptibility to Soil Gas Entry When elevated concentrations of vapor-forming chemicals accumulate in the soil gas immediately underneath the foundation, surrounding the basement, or within the crawl space of a vulnerable building, then soil gas entry (i.e., vapor intrusion) can lead to unacceptable levels of subsurface contaminants in indoor air, depending upon building- and site-specific circumstances. As discussed in Section 2.3, soil gas can enter a building when openings are present and driving forces exist to draw the vapors from the subsurface through the openings into the indoor environment. Single-family detached homes can generally be presumed to have openings for soil gas entry; as such, they will generally be susceptible to soil gas entry unless a mitigation system (e.g., radon mitigation system) is present and operating as intended. Some buildings are more susceptible to soil gas entry than others. For example, buildings with significant openings, such as: buildings with deteriorating basements or dirt floors, which generally provide poor barriers to vapor (soil gas) entry; and buildings with sumps (or other openings to the subsurface) that can facilitate transport of vapors via soil gas entry. EPA recommends that appropriate lines of evidence be employed to assess susceptibility to soil gas entry, when this objective is selected as part of a site-specific investigation plan for vapor intrusion assessment. Vulnerability to soil gas entry can be assessed for a specific building by using any of several methods, including: 78

184 Concurrently monitoring indoor air samples for presence of radon and finding radon in indoor air at levels greater than in ambient air. 125 Concurrently monitoring indoor air and ambient air (see Section 6.3.5) and finding cis- 1,2-dichloroethylene, vinyl chloride, 1,1-dichloroethylene, or 1,1-dichloroethane in indoor air at levels greater than in ambient air, when and where they are present in the subsurface vapor source(s), but are not used indoors. 126 Employing a photoionization detector (PID) or other real-time in-field device, capable of detecting parts per billion by volume (ppbv) levels, to directly survey suspected locations of soil gas entry (e.g., utility penetrations, sumps) and finding elevated readings of vapors. Conducting a visual inspection for cracks and holes in concrete foundation slabs, basement walls, or any floor drain(s). (Openings for soil gas entry will not necessarily be visible or accessible for inspection, so the absence of visible openings, by itself, is insufficient to demonstrate that a building is not susceptible to soil gas entry.) Monitoring pressure differences between the building and subsurface environment to characterize the driving force for soil gas entry and the effects of the heating, ventilation, and air-conditioning (HVAC) systems. Injecting tracers into the subsurface at selected concentrations and subsequently finding it in indoor air samples. Certain complementary information obtained for the building, as identified in Section 6.4.1, can also support such assessments. Relevant information includes the operating characteristics of HVAC systems. In many commercial buildings, the HVAC system brings outdoor air into the building, potentially creating building over-pressurization relative to the outdoor environment. When the building is 125 Because vapor intrusion and radon intrusion entail similar mechanisms for subsurface vapor migration and gas entry into buildings and structures (Section 2.3), naturally occurring radon may serve as a tracer to help identify those buildings that are more susceptible to soil gas entry than others. Buildings w ith radon concentrations greater than levels in ambient air are likely susceptible to soil gas intrusion and w ould likely be susceptible to intrusion of any chemical vapors in the subsurface. On the other hand, the radon concentration in a building is not generally expected to be a good quantitative indicator of indoor air exposure concentrations of vapor-forming chemicals arising from subsurface contamination. Hence, radon measurement is not generally recommended as a proxy for directly measuring vapor-forming chemicals in indoor air. Among other factors, the distribution of radon-emanating rock and soil and the spatial and temporal variability of their source strength are generally expected to be very different (e.g., tending to be broader and more uniform) than the distribution and source strength variability for subsurface sources of chemical vapors. 126 EPA (2011a) reports that vinyl chloride, 1,1-dichoroethylene, cis-1,2-dichloroethylene, and 1,1-dichloroethane are rarely detected in background indoor air. DoN (2011a) also reports that vinyl chloride and cis-1,2-dichloroethylene are rarely detected in background indoor air. When they are subsurface contaminants, volatile chemicals that are rarely or never present in indoor sources can be inferred to arise in indoor air via vapor intrusion w ithout further explanation (DoN 2011a). Brenner (2010), for example, employed this principle (and cis-1,2-dichloroethylene) to identify buildings susceptible to vapor intrusion and to diagnose the relative contributions of vapor intrusion and infiltration to indoor air concentrations. 79

185 over-pressurized sufficiently to eliminate the driving force for soil gas entry over at least a portion of the building foundation, vapor intrusion potential is diminished. 127 Reasonably expected future risks posed by subsurface contamination warrant consideration, in addition to risks posed under current conditions, in order to demonstrate that a site does not present an unacceptable risk to human health and the environment (EPA 1991a). For example, current building use and HVAC systems might not be sustained perpetually. Therefore, when the subsurface vapor source(s) underneath or near a building with an over-pressurizing HVAC system has(have) significant potential to pose a vapor intrusion threat, it may be useful to assess susceptibility to soil gas entry and diagnose vapor intrusion (also see Sections and 6.4.1) in such buildings under conditions when the HVAC system is not operating. (In addition, indoor air testing could be conducted during periods when the HVAC system operates with diminished flows, such as weekends or evenings.) The results of such testing can be used to support determinations about whether the vapor intrusion pathway is potentially complete and is reasonably expected to pose unacceptable human health risk (see Section 7.4) in the future, 128 in which case a response action(s) may be warranted (see Section 7.7). For example, if the results indicate susceptibility to soil gas entry when the HVAC system is not in operation and vapor intrusion under these conditions has the potential to pose a health concern, then the building may warrant future monitoring (e.g., continuous monitoring of the pressure gradient across the foundation or indoor air testing) and/or engineered exposure controls, which may be enforceable through an institutional control (IC) (see Section 8.6). Likewise, well-designed and operated radon mitigation systems generally should diminish vapor intrusion via soil gas entry under current conditions. Therefore, buildings with pre-existing radon mitigation systems, which overlie or are near subsurface vapor sources, could be tested under conditions where the radon mitigation system is temporarily not operated to support decisions about monitoring and ICs as part of a vapor intrusion remedy Evaluate Presence and Concentration of Subsurface Contaminants in Indoor Air Indoor air sampling (see Section 6.4.1) using time-integrated sampling methods or grab samples can confirm the presence, if any, of a site-related vapor-forming chemical (i.e., one comprising the subsurface vapor source(s)) in the indoor environment. When combined with data characterizing subsurface vapor migration and demonstrating the building is (or is not) susceptible to soil gas entry, indoor air sampling data can support determinations that the vapor intrusion pathway is (or is not) complete for a given building, as discussed further in Section 7.3. When conducted contemporaneously in multiple buildings, indoor air sampling can, in concert with soil gas survey data and data delineating subsurface vapor sources, help identify the boundaries of the land area(s) within which buildings are known or suspected to have indoor air concentrations of subsurface contaminants arising from vapor intrusion (also see Section 6.2.1). 127 Over-pressurization may not be uniform throughout a building, particularly in large buildings. Over-pressurization in portions of a building w ill not necessarily mitigate all openings for soil gas entry. 128 Both current and reasonably likely future risks need to be considered in order to demonstrate that a site does not present an unacceptable risk to human health and the environment. (EPA 1991a). 129 EPA recommends that state and local law s be researched before any such testing is conducted. Some areas have local ordinances governing operation and maintenance of radon mitigation systems. 80

186 Indoor air sampling is most commonly conducted using time-integrated sampling methods, when characterizing exposure concentrations for building occupants (see Section 6.4.1), which may include contributions from indoor or ambient air sources of these chemicals (see Section 2.7). For example, time-integrated concentrations of hazardous vapors in samples of indoor air can be compared to appropriate, risk-based screening criteria (see Section 6.5) to obtain some preliminary insights about the potential level of exposure and risk posed by vapor intrusion or can be used to support a human health risk assessment (Section 7.4) about vapor-forming chemicals found in the subsurface environment. 130 When sampling indoor air (or sub-slab soil gas) to characterize exposure concentrations arising from vapor intrusion, EPA recommends removing potential indoor sources of vapor-forming chemicals (see Section 2.7 and 6.4.1) from the building to strive to ensure that the concentrations measured in the indoor air samples are attributable to the vapor intrusion pathway. However, even after removing indoor sources, their effects may linger depending on source strength, relative humidity in the building, the extent to which the contaminants have been absorbed by carpets and other fabrics or sinks, and air exchange rate. In addition, field experience suggests that it may not be possible to remove all indoor sources. It may be particularly impractical to do so in industrial settings where vapor-forming materials are used or stored Identify and Evaluate Contributions from Indoor and Ambient Air Sources As noted in Section 2.7 herein, indoor air is likely to contain detectable levels of a number of vapor-forming chemicals regardless of whether the building overlies a subsurface vapor source, because indoor air can be impacted by a variety of indoor and outdoor vapor sources unrelated to site contamination. The contribution of indoor and outdoor vapor sources (or both) to indoor air concentrations is referred to as background throughout this Technical Guide, when they do not arise from site-related contamination (see Glossary). Information on background contributions of site-related, vapor-forming chemicals in indoor air is important to risk managers because generally EPA does not clean up to concentrations below natural or anthropogenic background levels (EPA 2002e). To determine if a subsurface vapor source(s) is (or are) responsible for indoor air contamination, EPA recommends that such background sources of site-specific analytes be identified and distinguished from vapor-forming chemicals arising from vapor intrusion. A comprehensive investigation of all background substances found in the environment is usually not recommended. For example, sub-slab soil gas and ambient air samples typically would not be analyzed for radon for purposes of characterizing background exposures per se, whereas EPA would recommend analyzing for radon if its precursor was part of a regulated release to the subsurface environment (EPA 2002e). 131 Generally, EPA recommends the site planning and 130 In certain cases, depending in part on the results (e.g., concentrations exceed risk-based screening levels), indoor air sampling data may be a sufficient basis for supporting decisions to undertake pre-emptive mitigation/early action (see Sections 3.3 and 7.8) in lieu of additional rounds of sampling and analysis or an evaluation of the contribution of background sources to indoor air concentrations. 131 Sub-slab soil gas and indoor air samples might also be analyzed for radon, w here its precursor w as not part of a release to the subsurface environment, for purposes of diagnosing vulnerability to soil gas entry (see, for example, Section 6.3.3), depending upon the objectives of the vapor intrusion investigation. 81

187 data evaluation team limit chemical analyses to those vapor-forming chemicals known (based upon subsurface contaminant characterization) or reasonably expected (based upon site history) to be present as a result of a release to the subsurface environment. To support evaluations of sources of indoor air concentrations, EPA recommends conducting a building survey (see Section 6.4.1) that identifies in individual buildings known or suspected indoor sources of the vapor-forming chemicals also found in the subsurface (see Section 2.7) and characterizing ambient air quality (see Section 6.4.2) in the site vicinity for these same chemicals. Key supporting information includes: (1) the locations and types of known or potential indoor vapor sources; (2) information about outdoor vapor sources related to the site (e.g., locations of chemical storage, use, and/or release to the environment); (3) information about outdoor vapor sources un-related to the site, such as nearby commercial or industrial facilities and mobile sources (e.g., cars, trucks, and other equipment); and (4) data on the local ambient air quality. Interviews of building occupants and inspections of buildings can be helpful initial sources of information about indoor uses and storage of vapor-forming consumer and commercial products. 132 In addition, vapor-detecting field instruments and in-field gas chromatographs 133 can be used to locate indoor vapor sources. Grab (essentially short-duration) samples of indoor air, as described in Section 6.4.1, can be useful for identifying specific vapor-forming chemicals emanating from indoor vapor sources of consumer or commercial products. When the objective is to quantitatively distinguish contributions to indoor air concentrations from vapor intrusion versus contributions from indoor and ambient air sources, as described below, EPA recommends obtaining indoor air concentrations using time-integrated sampling methods (see Section 6.4.1) instead of grab samples. If the subsurface vapor source(s) is (or are) comprised of multiple vapor-forming chemicals and the subsurface source medium (e.g., soil, groundwater) and location are identical for these chemicals, then contemporaneous samples of sub-slab soil gas (see Section 6.4.3) and indoor air (see Section 6.4.1) can be compared, potentially supporting one of the following conclusions: Results indicating vapor intrusion as solely responsible for vapor concentrations in indoor air. The predominant vapor-forming chemicals in the sub-slab soil gas and their relative proportions in indoor air and sub-slab vapor samples would be expected to be similar, whereas their concentrations in sub-slab soil gas would be expected to be substantially higher than in indoor air, 134 if vapor intrusion is solely responsible for indoor air 132 Information about the chemical composition of commonly encountered products is provided by the U.S. Navy (DoN 2011a, Appendix A) in its guidance for background analysis for the vapor intrusion pathw ay. 133 Gorder and Dettenmaier (2011) reported on the use of a field-portable gas chromatograph and mass spectrometer to identify specific sources of vapor-forming chemicals and estimate their mass emission rate(s). EPA s Environmental Response Team has employed the Trace Atmospheric Gas Analyzer (TAGA) mobile laboratory for similar purposes. 134 Based upon the generic sub-slab attenuation factor identified in Section herein, sub-slab soil gas concentrations can be expected to typically exceed indoor air concentrations by 33 times or more in residences that are impacted by vapor intrusion (i.e., 33 is the inverse of an attenuation factor of 0.03), w hen background sources are negligible and the building is under-pressurized relative to the subsurface during indoor air sampling. 82

188 concentrations. 135 If recalcitrant (i.e., not subject to biodegradation in the vadose zone), the predominant vapor-forming chemicals and their relative proportions in the subsurface vapor source would likewise tend to be similar to those in indoor air if vapor intrusion is solely responsible for indoor air concentrations. 136 Results indicating indoor vapor sources as primarily responsible for indoor air concentrations. If a vapor-forming chemical is present with an elevated concentration in indoor air, but is not present or is negligibly present in sub-slab soil gas samples (or representative samples of the subsurface vapor source), then the presence of this contaminant in indoor air may not arise from the vapor intrusion pathway, but rather from indoor sources or other background sources (e.g., ambient air). In these circumstances, EPA recommends considering additional attempts to identify and temporarily eliminate indoor sources, where practical, and re-sample indoor air and sub-slab soil gas after doing so. Likewise, outdoor (ambient) air samples can be collected (see Section 6.4.2) contemporaneously with indoor air (see Section 6.4.1) and sub-slab soil gas (see Section 6.4.3) samples, as recommended in Section 6.4. Results indicating outdoor vapor sources as primarily responsible for indoor air concentrations. If a vapor-forming chemical(s) is(are) detected in outdoor air and indoor air at similar concentrations, but is(are) not present in sub-slab soil gas samples (or representative samples of the subsurface vapor source) or is present in the subsurface samples at concentration(s) similar to indoor air), 137 then the presence of this contaminant(s) in indoor air may not arise from the vapor intrusion pathway, but rather from outdoor sources (i.e., ambient air). Concentrations of vapor-forming chemicals in indoor air, sub-slab soil gas, and ambient air can be compared, as described above, using an individual time-integrated sample for each medium. Recognizing that weather conditions and building operations can lead to variable contributions from vapor intrusion and ambient air infiltration over time, EPA recommends, however, that such 135 Conversely, if there is an interior source of a vapor-forming chemical in indoor air samples, the relative proportion of this chemical in indoor air w ill be greater than its respective proportion in the sub-slab soil gas, even w here vapor intrusion is occurring, assuming that the other vapor-forming chemicals in the sub-slab soil gas do not have background sources. 136 Conversely, if there is an interior source of a vapor-forming chemical in indoor air samples, the relative proportion of this chemical in indoor air w ill be greater than its respective proportion in the subsurface vapor source or in nearsource soil gas samples (see Section 6.3.1), even w here vapor intrusion is occurring, assuming that the other vaporforming chemicals in the sub-surface do not have background sources. 137 Sample concentrations of vapor-forming chemicals in indoor air and sub-slab soil gas can be compared to conservative, risk-based screening levels to provide a complementary line of evidence. Generally, vapor-forming chemicals w ith concentrations that consistently fall below screening levels (see Section 6.5) through multiple sampling events (see Section 6.4) w arrant no further action or study, so long as the exposure assumptions match those taken into account by the calculations and the site fulfills the conditions and assumptions of the generic conceptual model underlying the screening levels (see Section 6.5.2). 83

189 comparisons be made for multiple sets of paired samples, collected in different seasons, 138 to support any conclusion that vapor intrusion is not a significant contributor to indoor air concentrations, which can instead be attributed to indoor and outdoor sources unrelated to the subject site. Even with a few sets of such samples, rigorous statistical tests may not be feasible. Nevertheless, comparing contemporaneously measured concentrations and proportions of vapor-forming chemicals in indoor air, subsurface media, and ambient air can be effective for this investigation objective, particularly when one (or more) of the analytes is known to be present only in the subsurface or in ambient air. The following hypothetical example illustrates how site-specific sampling data might inform conclusions about the relative contributions of indoor versus subsurface vapor sources in a building overlying contaminated groundwater: Example: Time-integrated samples of indoor air, outdoor air, and subslab soil gas were collected contemporaneously for a building that overlies shallow groundwater that is contaminated with a suite of vapor-forming chemicals (designated as VFCA, VFCB, VFCC, and VFCD). The sampling results are summarized as follows: Vapor-forming Chemical in Groundwater Time-weighted Sample Concentrations (µg/m 3 ) Subslab Soil Gas Indoor Air Outdoor Air Ratio of Subslab Concentration to Indoor Air Concentration VFCA VFCB 33, ,300 VFCC 5, VFCD 15, ,000 Based upon the conceptual site model, the presence of these vapor-forming chemicals in outdoor (ambient) air is believed to be due to anthropogenic sources that are not associated with the environmental release responsible for the subsurface contamination. The building is presumed to be susceptible to vapor intrusion, as indicated by pressure monitoring data that indicate building under-pressurization, relative to the subsurface environment, during the sampling event (as discussed further in Section 6.4.1). Based upon these findings, the presence of VFCB, VFCC, and VFCD in indoor air appears to be solely or primarily attributable to vapor intrusion. The relative proportions 138 A goal of collecting multiple samples is to observe and characterize a reasonable maximum vapor intrusion condition for the respective building. Because w eather conditions and building operations can lead to time-variable contributions from vapor intrusion (e.g., driving forces for vapor intrusion; see Section 2.3) and ambient air infiltration (see Sections 2.4), indoor air concentrations of vapor-forming chemicals can be expected to vary over time. An individual sample, collected at a randomly chosen time, may under-estimate or over-estimate average and reasonable maximum exposure conditions (see Section 6.4.1) to different degrees, depending upon the season of sample collection and other factors. 84

190 of these subsurface contaminants in indoor air and sub-slab vapor samples are similar, as indicated by a similar ratio of subslab to indoor air concentration, considering analytical uncertainty. In addition, their indoor air concentrations exceed those found in the paired sample of ambient air. By contrast, the presence of VFCA in indoor air may be entirely attributable to infiltration of ambient air, as the sample concentrations in indoor air and outdoor are similar, considering analytical uncertainty. Recommended next steps in the investigation might include a human health risk assessment (see Section 7.4) and a review of the conceptual site model (see Section 5.4) to evaluate whether the different conclusion for VFCA can be reasonably explained (e.g., by vapor attenuation in the vadose zone that is expected to be substantially greater than for VFCB, VFCC, and VFCD). EPA has compiled and published an evaluation of studies pertaining to indoor air concentrations of volatile organic compounds in North American residences in (EPA 2011a), which can be employed to identify whether measured indoor air concentrations in residences exceed the historical range of background concentrations. Specifically, if measured indoor air concentrations are found to greatly exceed the historical range of background levels, there is a greater likelihood that the indoor air concentrations are the result of vapor intrusion. This conclusion is supported by the expectation that current levels of vapor-forming chemicals in ambient air and in indoor air due to indoor and ambient air sources are likely to be lower than those observed historically, 139 due to regulations and business practices fostering less use of toxic chemicals in consumer products and industrial processes and reduced emissions from mobile and stationary sources. As a result of this expectation, EPA does not recommend the use of generic values of historical background concentrations, even those cited in peerreviewed publications or available from databases maintained by regulatory agencies, to characterize current levels in any building, for purposes of supporting conclusions that indoor air concentrations are due to background sources. Rather, EPA recommends that site-specific data (e.g., sub-slab, indoor air and ambient air sampling data) be obtained (as described in Sections 6.4.1, 6.4.2, and 6.4.3), and evaluated, as described above, when the investigation objectives include determining whether indoor air concentrations arise from indoor or ambient air sources. The following additional approaches for identifying and characterizing background sources may warrant consideration in special situations: McHugh et al. (2012) have demonstrated the principle that building over-pressurization can be employed temporarily to minimize vapor intrusion and facilitate measuring indoor 139 McCarthy et al. (2007), for example, analyzed ambient air data for 25 toxic substances collected in the United States from 1990 through 2005 and found that concentrations of many halogenated volatile organic compounds w ere declining at most sites and evaluation periods (i.e., , , and ). They found that concentrations of petroleum hydrocarbons, such as benzene, associated w ith mobile sources w ere all consistently decreasing over the three evaluation periods at most sites. 85

191 air concentrations under conditions where only indoor sources may be contributing. 140 At this time, however, there are no standard practices for using over-pressurization to assess background contributions, which is a research and development need (SERDP- ESTCP 2014). Forensic and multi-variate statistical methods have been described and illustrated by the U.S. Navy (DoN 2011a) in its guidance for background analysis for the vapor intrusion pathway Select, Prioritize, and Sequence Investigation Objectives Site-specific investigations of potential vapor intrusion frequently begin with pursuing one or more of the objectives presented in Sections through Criteria potentially warranting consideration by the site planning team when making decisions about prioritizing and sequencing investigation objectives include, but are not limited to: site scenario (see Section 6.1); building occupants who may be particularly sensitive to the potentially toxic effects of vapors; buildings that are more susceptible to soil gas entry (e.g., buildings with deteriorating basements or dirt floors; whether there are any significant data gaps in the CSM (see Section 5.4); and relationships with and perspectives of the owners and occupants of potentially impacted buildings. Characterizing subsurface vapor sources (Section 6.3.1), characterizing subsurface vapor migration (Section 6.3.2), and evaluating the presence of subsurface contaminants in indoor air (Section 6.3.4) are frequently candidates for an initial objective and each can be pursued separately. For example, characterizing subsurface vapor sources (Section 6.3.1) may be a useful initial choice when responding to an initial report about a release of hazardous, vaporforming chemicals to the subsurface from a commercial or industrial operation or when buildings do not exist currently, but are expected in the future. Characterizing subsurface vapor sources may also be a useful initial choice when building owners or occupants are reluctant to grant access for indoor air testing. In this situation, the site planning team may need to pursue subsurface investigations more intensely to characterize vapor intrusion potential before being granted building access. On the other hand, testing indoor air is recommended as an initial objective when responding to reports of odors in buildings or clusters of inhalation-related symptoms and there is credible information to suggest that a subsurface environmental release may be a contributing factor (see Section 5.2). In a different scenario, characterizing subsurface vapor migration (Section 6.3.2) may be a useful starting point when addressing sources that are comprised of potentially biodegradable chemicals or that are suspected to occur below an extensive geologic layer that might impede upward diffusive migration. For large buildings with HVAC systems that may over-pressurize the interior relative to the subsurface environment, EPA generally recommends: a building assessment early in the investigation, which obtains and weighs the complementary information 140 Indoor air concentrations measured after sufficient periods of over-pressurization may be indicative of background levels, w hereas indoor air concentrations detected before and after a sufficient period of rebound from temporary over-pressurization may be indicative of joint contributions from background sources and any vapor intrusion from the subsurface. 86

192 identified in Section 6.4.1, to support investigation planning; and an evaluation of susceptibility to soil gas entry under conditions when the HVAC system is not operating (see Section 6.3.3). Each of the investigation objectives described in Sections through may, in some cases, be conducted iteratively with increasing complexity as the investigation proceeds and the CSM is refined. For example, field instruments can be useful for locating potential background sources (e.g., household or commercial cleaning products) (see Section 6.3.5) and grab (essentially short-duration) samples of indoor air, as described in Section 6.4.1, can be useful for characterizing the chemical composition of identified indoor sources of vapors during an initial building reconnaissance while potential background sources are surveyed. These activities might be followed by indoor air and sub-slab soil gas sampling, using time-integrated sampling methods as described in Section and 6.4.2, to distinguish subsurface contributions from indoor sources. More advanced methods of distinguishing the various potential contributions to indoor air might be utilized, if warranted, in intermediate phases of the investigation under such an iterative approach. 6.4 General Principles and Recommendations for Sampling Sampling of indoor air, outdoor air, soil gas, and groundwater and analysis for vapor-forming chemicals can play an important role in vapor intrusion investigations for one or more of the objectives identified in Section 6.3. This subsection summarizes for indoor air, outdoor air, subslab soil gas, exterior soil gas, and groundwater the following: Principal methods for collecting samples. Potential uses of the resulting sampling data. Recommended practices for sample collection. Unique or frequently encountered logistical issues. We would note that soil and NAPL sampling has been and may be used to characterize the nature (e.g., chemical composition) and general location of subsurface vapor sources (see Section 6.3.1). Information about soil sampling can be found in Standard Operating Procedures, Soil Sampling (EPA-ERT 2001b). However, bulk soil (as opposed to soil gas) sampling and analysis is not currently recommended for estimating the potential for vapor intrusion to pose unacceptable human health risk in indoor air, because of the potential for vapor loss due to volatilization during soil sampling, preservation, and chemical analysis. In addition, there are uncertainties associated with soil partitioning calculations. To ensure that the sampling data will meet the site-specific data quality needs, EPA recommends that the sampling and analytical methods selected by the site planning team be capable of obtaining reliable analytical detections of concentrations less than projectappropriate, risk-based screening levels (e.g., VISLs). Towards that end, EPA recommends that, as part of establishing site-specific data quality objectives (DQOs), the planning and data collection team(s) consult with a laboratory skilled in the analysis of air and soil gas samples and choose sampling and analytical methods capable of routinely attaining the desired detection sensitivity for each medium. 87

193 EPA also recommends that the site planning team identify and utilize appropriate sampling locations and durations and address spatial and temporal variability to fulfill the specific objectives of the investigation, which may include obtaining data to characterize the potential human exposure in a building(s). EPA recommends the CSM, the objective(s) of the investigation, and other site-specific information be considered in determining the number and types of samples used at a specific site. The sampling duration depends on the type of medium being sampled (for example, soil gas, sub-slab soil gas, and indoor or outdoor air) and analytical methods (for example, Method TO- 15). Some of the key recommended considerations are provided in the following subsections. Several rounds of sampling are recommended to develop an understanding of temporal variability 141 to ensure that final risk management decisions are based upon a consideration of a reasonable maximum vapor intrusion condition Indoor Air Sampling Indoor air sampling results are used to assess the presence of and level of human health risk posed by vapor-forming chemicals in indoor air (see Sections and 7.4), and to diagnose whether vapor intrusion is occurring (see Sections 6.3.3, 6.3.5, and 7.3). These two uses of indoor air sampling in vapor intrusion investigations are discussed further below with recommended methods for each. As discussed further in Sections 8.4 and 8.7, indoor air sampling may also be useful for supporting performance evaluations of vapor intrusion mitigation systems and verifying the health protectiveness of subsurface remediation systems. EPA recommends that the decision to collect indoor air data be supported by lines of site- or building-specific evidence (e.g., characterization of subsurface vapor source(s) strength and proximity to building(s), vadose zone conditions, and building conditions) that demonstrate that vapor intrusion has the potential to pose a significant human exposure. Confidence in the assessment is expected to be higher when multiple lines of site- or building-specific evidence, in addition to indoor air data, come together to provide mutually supporting evidence for a common understanding of the site conditions/scenarios and the potential for vapor intrusion (i.e., the various lines of evidence are in agreement with each other). A potential shortcoming of indoor air testing is that indoor sources and outdoor sources unrelated to subsurface contamination and to releases from the subject site background (see Glossary) may contribute to the presence of volatile chemicals in occupied buildings (see Section 2.7), particularly if these sources cannot be removed from the building prior to and throughout the duration of sampling indoors. This shortcoming of indoor air testing is 141 Seasonally variable conditions (e.g., moisture levels, depth to groundw ater) can lead to seasonally variable concentrations and distributions of vapors n the vadose zone. Likew ise, w eather conditions and building operations can lead to time-variable contributions from vapor intrusion (e.g., driving forces for vapor intrusion; see Section 2.3) and ambient air infiltration (see Sections 2.4). Collectively, these processes cause indoor air concentrations of vaporforming chemicals to vary over time (see Section 2.6). An individual sample (or single round of sampling) w ould be insufficient to characterize seasonal variability, or variability at any other time scale. 142 EPA recommends basing the decision about w hether to undertake response action for vapor intrusion (i.e., a component of risk management; see Section 7.4) on a consideration of a reasonable maximum exposure (e.g., EPA 1989, 1991a), w hich is intended to be a semi-quantitative phrase, referring to the low er portion of the high end of the exposure distribution (see Glossary). 88

194 unavoidable when the subsurface environment contains the very same volatile chemicals that contemporaneously arise in indoor air due to background sources, which is common for some chemicals and relatively rare for others (EPA 2011a). In this circumstance, additional lines of evidence, possibly including special procedures and analyses, may warrant evaluation to distinguish background contributions from those originating from vapor intrusion (see Section 6.3.5). After discussing recommended sampling methods and practices for the primary uses of indoor air sampling data, this sub-section concludes by discussing: Recommended measures to reduce the impact of indoor sources of vapor-forming chemicals. Recommended approach to establishing analyte lists for indoor air samples. Complementary, building-specific data (i.e., additional lines of evidence) that can be collected contemporaneously while indoors. Characterize Human Exposure Levels. Indoor air sampling and analysis provide a direct approach to obtaining concentrations of vapor-forming chemicals in indoor air to which building occupants can be exposed. For this purpose, EPA generally recommends time-integrated sampling methods, since indoor air concentrations can be temporally variable 143 and timeintegrated exposure estimates over appropriate exposure durations (e.g., chronic typically; lessthan-chronic in some cases) are generally most useful for assessing human exposure and human health risk (see Section 7.4). Because of variability, a single indoor air sample, collected at a randomly chosen time, is insufficient information to estimate an average exposure. On the other hand, it is impractical to collect indoor air samples continuously over a chronic exposure period (i.e., up to 30 years for a reasonable maximum exposure duration in a residence (EPA 2014a)), which would also entail deferring risk management decisions for a prolonged period while human exposures from vapor intrusion could occur unabated. Hence, current and past practice has generally relied upon collecting multiple indoor air samples for purposes of estimating long-term average (i.e., chronic) exposures and assessing human health risk (see Section 7.4). All else being equal, a longer collection period for each individual sample would be expected to yield a more reliable basis for estimating long-term, time-average exposure than would a one-day sample collection period. When investigating short-term exposure conditions that might warrant prompt response action to protect human health (see, for example, Sections 5.2 and 7.5.2), time-integrated indoor air samples can provide useful estimates of exposure for the location and time period of sample collection. (A short-term exposure is defined as a repeated exposure for more than 24 hours, 143 Because w eather conditions and building operations can lead to time-variable contributions from vapor intrusion (e.g., driving forces for vapor intrusion; see Section 2.3) and ambient air infiltration (see Sections 2.4), indoor air concentrations of vapor-forming chemicals can be expected to vary over time (see Section 2.6). Field observations indicate that indoor air concentrations arising from vapor intrusion can be temporally variable w ithin a day and betw een days and seasons in an individual residential building (EPA 2012f; Holton et al., 2013ab). 89

195 up to 30 days see Glossary.) All else being equal, a longer collection period for an individual sample would be expected to yield a more reliable basis for estimating time-average short-term exposure than a one-day sample. As noted above, EPA also recommends considering potential health effects and relevant exposure periods for site-related, vapor-forming chemicals when developing DQOs and sampling plans for indoor air. Variability in laboratory analyses can be considered when evaluating these data in support of risk management decisions. 144 Time-integrated samples provide a direct measurement of the average chemical concentration over a fixed period of time (e.g., ranging from 8 hours to several weeks, depending upon the sampling method, its capabilities, and its deployment). Time-integrated samples can be collected using either evacuated canisters, which collect gas in a container, or sorbent samplers, which collect vapor-forming chemicals on a sorbent material. Evacuated canisters Evacuated canisters are spherical- or cylindrical-shaped stainless steel or silica-lined containers that are prepared to be under negative pressure relative to the environment and certified by the laboratory to be clean and leak-free. 145 As described in EPA Method TO-14A (EPA 1999c), evacuated canisters can be used as passive (sub-atmospheric pressure sampling) or active (pressurized sampling) samplers. In both cases, the canister is initially evacuated to a standard vacuum in preparation for sampling. For sub-atmospheric sampling, when the canister is opened for sample collection, the differential pressure causes air to flow into the canister without use of a pump. In this case, sampling must end before the vacuum is fully dissipated, else the sample collection period will be unknown. For pressurized sampling, a pump is used to pass air into the canister until a specified pressure (up to two atmospheres) is reached. In both cases, a flow-control device is used to maintain a constant flow into the canister over the desired sample period. To ensure that the canisters are filling at the proper rate, EPA recommends checking the flow rate periodically during sample collection. EPA Methods TO-14A and TO-15 provide further information on measuring and controlling flow rates into canister-type samplers. 144 For a recently published study, EPA s ORD determined The acceptance criterion to demonstrate equivalency is +30% based on w hat is defined as acceptable reproducibility in vapor intrusion field studies (EPA 2012f). 145 Canisters are cleaned and re-used because they are too expensive to dispose routinely. The certification process entails cleaning the interior of the container using a combination of dilution, heat, and high vacuum. Canisters are then analyzed for a large suite of vapor-forming chemicals to establish that they are free of detectable chemicals at a suitably low (sensitive) detection level. The cleanliness of canisters can be certified individually (i.e., direct testing of each canister, or 100% certification), w hich is generally desirable in instances w here the data are to be used for exposure/risk assessment purposes. Alternatively, canisters can be certified by batch (or lot), in w hich a subset of the canisters are tested directly (e.g., 10%) and results are extrapolated to the remainder of the batch. Batch-certified canisters may be sufficient w hen concentrations of target analytes are expected to be high, relative to potential levels of residual contamination in the canister after cleaning. EPA recommends that flow controllers also be cleaned betw een uses to avoid artificial contamination. 90

196 Typically, for vapor intrusion investigations, indoor air samples are collected using six-liter canisters using sub-atmospheric pressure sampling over a 24-hour period in residences or over an 8-hour period (or workday equivalent) in commercial and industrial settings, when using these devices. Larger canisters (i.e., 15-liter) allow higher flow rates and may be preferable for longer sampling events or to collect a larger volume of sample. 146 A capillary flow controller has been developed and demonstrated for use in industrial hygiene applications (Rossner et al. 2002; Rossner and Wick 2005), which may hold promise for extending sampling time periods for indoor air with standard-sized canisters. Details for selecting and utilizing sampling canisters are provided in EPA Methods TO-14A (EPA 1999c) and TO-15 (EPA 1999d). EPA s Environmental Response Team has developed a standard operating procedure for sampling air with evacuated canisters (EPA- ERT 1995). An advantage of using evacuated canisters for sample collection is the capability of analyzing multiple sub-samples from the same canister (because these canisters obtain a whole air sample). They are also reasonably easy to deploy and retrieve. However, sample recovery and representativeness can be affected by ambient conditions; for example, low humidity conditions in the sample may lead to losses of certain volatile compounds on the canister walls (EPA 1999c). Fourteen days is the most commonly cited hold time for air samples in canisters. Some analytes, however, may be stable in canisters for up to 30 days. Sorbent Samplers Sorbent sampling devices are hollow containers that hold one or more adsorbent media that can bind vapor-forming chemicals. They have been developed and tested over several decades for industrial hygiene monitoring and have more recently been employed for other purposes, including vapor intrusion investigations. Sorbent samplers can be used in an active or passive mode. In the active mode, a pump is used to draw air at a known rate through the device. The flow rate and sampling volume are determined based on the type of sorbent used, the target constituent(s), and the amount of sorbent contained in the device. Care must be taken to ensure that the volume of air drawn through the tube does not exceed the breakthrough volume 147 (i.e., the volume of air which may be passed through the sorbent tube before a detectable level of the analyte concentration elutes from the non-sampling end), else the time-weighted average concentration will be biased low by an unknown amount. In the passive mode, no pump is used, and vapor-forming chemicals enter the device due to diffusion. Consequently, passive (diffusion) samplers may be placed in locations of interest without consideration of power availability. 146 Alternatively, tw o (or more) large canisters can be connected together to allow collection of time-integrated samples over longer durations, w hich is generally desirable for characterizing long-term average exposure levels. 147 For this reason, sample volumes in the one- to four-liter range are generally recommended for this method (EPA 1999e). 91

197 Although passive (diffusion) samplers have been less commonly used to quantify indoor air concentrations, their use may grow as a result of recent demonstrations that they can yield results comparable to those obtained using evacuated canisters (EPA-Region ; EPA 2012f; Odencrantz et al. 2009; Odencrantz et al. 2008), 148 and a recognition that they may be less intrusive for some building owners and occupants and more convenient for field staff (EPA-Region ). Passive samplers are also capable of being deployed for longer durations than evacuated canisters, thereby providing a more economic means of obtaining average indoor air concentrations over longer periods of exposure. Time-integrated samples of indoor air over longer periods than one day are also indicated by field observations demonstrating that indoor air concentrations arising from vapor intrusion can be temporally variable within a day and between days and seasons (EPA 2012f; Holton et al., 2013a). The basic configuration of a passive sampler is a solid, typically granular, sorbent contained in a metal, glass of plastic container with openings of known dimensions. Several different containers and a wide range of adsorptive media are commercially available, which function similarly. After sample collection, adsorbed mass is measured in a laboratory for each analyte; the two most common analytical methods involve thermal desorption or solvent extraction combined with gas chromatography/mass spectrometry. The air concentration for each analyte is calculated from the adsorbed mass, the duration of sampling, and the uptake rate. The uptake rate is dependent upon the geometry of the sampling device and the diffusion coefficient of the analyte. The uptake rate is the most critical variable for accurately measuring air concentrations with passive samplers, since the sampling duration and adsorbed mass can generally be measured very accurately. Fortunately, most commercially available passive samplers have published uptake rates for several compounds, which collectively address many of the vapor-forming chemicals described in Section Once the target analyte(s) and uptake rate(s) are known, the sample duration needed to attain data quality objectives (i.e., reporting limit equal to or lower than the risk-based screening level or risk-based action level) can be calculated for each analyte. Uptake rates of deployed samplers can be affected by ambient conditions (e.g., temperature, because chemical-specific diffusion rates are temperature-dependent; and humidity, which influences the uptake of water vapor, which may interfere with retention and stability of the analyte and/or with laboratory analysis). EPA, therefore, recommends that ambient conditions be recorded during deployment of passive samplers. One potential advantage of passive samplers is that they can be left unattended for relatively longer durations, thereby conveniently providing estimates of longer-term time- 148 For example, EPA s National Exposure Research Laboratory found that Radiello charcoal passive samplers performed w ell for sampling periods up to 28 days for TCE (EPA 2012f). In that study, one-w eek (7-day) Radiello passive samplers w ere utilized as a primary measurement tool and the resulting data w ere used as a basis of comparison to longer-duration samples (e.g., tw o-w eek, four-week (monthly), and 13-w eek (quarterly) samples). 149 Standard methods for determining uptake rates have been published by a few organizations. Ideally, the selected passive sampling device w ill have vendor-supplied uptake rates supported by controlled chamber tests or a considerable body of field-calibrated uptake rates for most, if not all, of the target compounds. 92

198 weighted average concentrations. However, similar to active sorbent sampling, the duration of passive sampling must be such that the adsorptive capacity of the media is not approached or exceeded, else the time-weighted average concentration will be biased low by an unknown amount. One potential disadvantage of sorbent sampling, compared to canister sampling, is that only one analysis is possible from an individual device, because it does not collect a whole air sample. Thus, if an error occurs in laboratory handling or there is an instrument malfunction, the sample is lost. Such errors generally are not common. Therefore, this potential disadvantage will not generally offset the benefits of sorbent sampling, the foremost of which is the ability to obtain time-integrated samples over longer periods (i.e., up to a few months for some compounds) than with evacuated canisters. For a typical-size residential building or a commercial building less than 1,500 square feet, EPA recommends that the site teams generally collect one time-integrated sample in the area directly above the foundation floor (basement or crawl space) and one from the first floor living or occupied area, at least for the initial sampling round. 150 In general, EPA recommends samples be collected at the breathing zone level for the most sensitive exposed population. 151 EPA recommends the site planning and data evaluation team discuss the number of sample locations per building for atypical situations, which include: (1) very large homes or buildings; 152 (2) multi-use buildings, particularly ones with segmented areas that are occupied by different populations (e.g., day care with young children versus office with adult workers) or have different occupancy patterns over time. Additional samples may also be warranted, depending on internal building partitions, HVAC layout, contaminant distribution in the subsurface, and occurrence of observable locations of potential soil gas entry (e.g., basement sumps or drains, relatively large holes or spaces in the foundation floor, entry points for utilities). Closed rooms located below ground may have appreciably higher contaminant concentrations originating from vapor intrusion. Closed rooms may warrant sampling to characterize the reasonably maximum exposure levels, if occupied, or to diagnose vapor intrusion (e.g., see below), even if not occupied. 150 Placement of indoor air sampling devices may entail compromises. Whereas the ideal location may be a central location that is unobstructed and representative of the actual used area of a room, placement at breathing zone height in a heavily used area w ell aw ay from any w all is likely to interfere w ith normal occupant activities. 151 The most sensitive exposed population may be identifiable by combining information about the types of human occupants in a given building and the types of potential toxic effects for vapor-forming chemicals found in the subsurface environment. For example, the most sensitive exposed population could be children, pregnant w omen, or elderly adults, depending upon building- and chemical-specific characteristics. 152 Larger commercial and residential buildings (e.g., multi-family residences) may w arrant additional discussion w ith the site planning team and perhaps a statistician to select the appropriate number and placement of indoor air samples to meet DQOs. 93

199 Indoor air concentrations vary over time, due to time-dependent changes in soil gas entry rates, exchange rates, intra-building mixing, among other factors (see Section 2). 153 Therefore, multiple rounds (and often several rounds) of indoor air sampling is generally recommended in order to reduce the chance of reaching a false-negative conclusion (i.e., concluding exposure is at an acceptable risk level when it is not) or reaching a false-positive conclusion (i.e., concluding exposure is at an unacceptable risk level when it is not). 154 Also, multiple sampling events generally are considered necessary to account for seasonal variations in climate and the habits of building occupants and ensure that related risk management decisions are based upon a consideration of a reasonable maximum vapor intrusion condition. 155 In many geographic areas in the continental United States, indoor air sampling during the heating season may yield higher indoor air concentrations than at other periods, because stack effects are generally more significant and, therefore, higher rates of soil gas entry are reasonably expected. Another scenario that may yield higher indoor air concentrations is when a building is sealed and the ventilation system is not operating. When sampling indoor air (or sub-slab soil gas), EPA generally recommends removing potential indoor sources of vapor-forming chemicals (see Section 2.7) from the building to strive to ensure that the concentrations measured in the indoor air samples are attributable to the vapor intrusion pathway. 156 After removal of indoor sources, their effects may linger longer depending on source strength, relative humidity inside the building, the extent to which the contaminants have been absorbed by carpets and other fabrics or sinks, and air exchange rate of the building. In residential settings, EPA generally recommends that potential indoor sources be removed from the structure and stored in a secure location at least 24 to 72 hours prior to the start of sampling, based on an approximate air exchange rate of 0.25 to 1.0 per hour in 153 Because w eather conditions and building operations can lead to time-variable contributions from vapor intrusion (e.g., driving forces for vapor intrusion; see Section 2.3) and ambient air infiltration (see Sections 2.4), indoor air concentrations of vapor-forming chemicals can be expected to vary over time. Holton et al. (2013ab) obtained and reported a set of long-term, high-frequency, indoor air data for an unoccupied house (except for periodic visits by researchers) in Utah overlying a plume of chlorinated hydrocarbons. TCE concentrations in indoor air varied by approximately tw o to three orders of magnitude, exceeding variations in measured air exchange rate. 154 An individual sample, collected at a randomly chosen time, may under-estimate average and reasonable maximum exposure conditions. From their high-frequency, measured data, Holton et al. formulated a synthetic data set (simulating one-day-average concentrations), w hich they used to estimate that a single, randomly draw n, one-day sample had a forty percent chance of being less than the true mean (Holton et al. 2013b; see Table 1 therein). When the true mean w as assumed to exceed the risk-based action level ( target concentration in their parlance) by tw o or five times, they estimated that a single, randomly draw n, one-day sample had a tw enty percent or six percent chance, respectively, of not detecting the exceedance. These data support EPA s recommendation to collect multiple rounds of indoor air sampling to reduce the chance of reaching a false-negative conclusion. Collecting multiple rounds of indoor air sampling can also reduce the chance of reaching a false-positive conclusion (i.e., concluding that vapor intrusion poses unacceptable human health risk w hen it does not), because an individual sample, collected at a randomly chosen time, may over-estimate the average exposure condition. 155 Given EPA s over-arching duty to protect human health and recognizing the disruption to building ow ners and occupants caused by indoor air sampling, risk managers may choose to pursue pre-emptive mitigation (i.e., early action) at some buildings (see Sections 3.3 and 7.8) rather than, for example, conduct multiple rounds of sampling over a few years to establish an estimate of long-term average exposure concentration and characterize temporal variability. 156 Vapor-detecting field instruments and in-field gas chromatographs can be used to locate indoor sources of vapors. For example, Gorder and Dettenmaier (2011) reported on the use of a field-portable gas chromatograph and mass spectrometer to identify specific sources of vapor-forming chemicals. EPA s Environmental Response Team has employed the Trace Atmospheric Gas Analyzer (TAGA) mobile laboratory for similar purposes. 94

200 residential buildings. In residences with attached garages, keeping the door(s) between the garage and the living space closed prior to and during indoor air sampling may also be warranted, in situations where the site-specific chemicals of potential concern include petroleum hydrocarbons or are components of products stored in the garage. Diagnose Vapor Intrusion and Background Sources. When access is granted for indoor air sampling, EPA generally recommends concurrently collecting samples of sub-slab soil gas (see Section 6.4.3) and outdoor (ambient) air (see Section 6.4.4) over similar durations using the same methods. Comparing these results to each other and to results for subsurface vapor sources can foster insights and support findings about the relative contribution of vapor intrusion and background sources to indoor air concentrations (as described in Section 6.3.5). In this case, time-integrated sampling methods are recommended for indoor air, because concentrations of vapor-forming chemicals can vary significantly over time (see Section 2.6). Grab (essentially short-duration) samples can, however, be useful for: confirming the presence of a subsurface contaminant in indoor air 157 (see Section 6.3.4) or in gas in a drain line or sewer lateral that enters a building, identifying specific vapor-forming chemicals emanating from indoor sources of consumer or commercial products 158 (see Section 6.3.5), and identifying specific vapor-forming chemicals emanating from suspected openings for soil gas entry into buildings (see Section 6.3.3). Grab samples can provide a convenient and less intrusive means of confirming the presence, if any, of a site-related subsurface contaminant(s) in the indoor environment. However, an individual grab sample is not reliable for purposes of demonstrating that vapor intrusion is not occurring in a specific building; among other considerations, vapor intrusion and indoor air concentrations can exhibit significant temporal variability (EPA 2012f, Holton et al., 2013ab). Consequently, EPA recommends collecting multiple time-integrated samples to support any such building-specific determination. Indoor air samples can also be concurrently collected for radon testing, which may be useful in evaluating building susceptibility to soil gas entry (see Section 6.3.3). Evaluate and Develop Analyte Lists. EPA recommends the site planning and data evaluation team generally limit chemical analyses to those vapor-forming chemicals known (based upon subsurface contaminant characterization) or reasonably expected (based upon site history) to be present in the subsurface environment. For example, if the site history and reliable subsurface sampling data do not identify benzene as a subsurface contaminant, it would be appropriate for site managers to exclude benzene as a target analyte for indoor air samples. Benzene could originate indoors as a result of a car, lawnmower, or snow blower in a garage. In 157 For this purpose, EPA generally recommends collecting one sample directly above the foundation floor (e.g., basement or craw l space) and one from the first floor living or occupied area. 158 For characterizing indoor sources or openings for soil gas entry, one round of grab sampling of indoor air may be sufficient. 95

201 this hypothetical case, benzene would not typically be amenable to reduction by vapor mitigation systems or subsurface remediation efforts. In fact, requesting an extensive list of analytes that are not related to subsurface contamination may unnecessarily complicate risk communication if indoor air testing reveals volatile chemicals unrelated to vapor intrusion. Collect Complementary Data While Indoors. A variety of useful information can be gathered during a building survey conducted in advance of or during indoor air sampling. EPA recommends that the following complementary data be gathered by observation, interviews, or reports (e.g., mechanical test-and-balance reports) when buildings are to be sampled to analyze indoor air: Building Occupancy o Characteristics and locations of building occupants (e.g., residents, including children or other sensitive populations; expectations for presence of general public in commercial or industrial settings; presence of multiple exposure units due to different uses or activities and occupants within a building other than a single-family residence). o Hours of building occupancy under current conditions (and reasonably expected future conditions, as appropriate), particularly for a nonresidential setting. Because this information is pertinent to the human health risk assessment and data evaluation, EPA recommends considering hours of building occupancy when establishing the sampling duration for characterizing indoor air exposure levels. Susceptibility to Soil Gas Entry Under Current Conditions o EPA recommends that the pressure difference between the indoors and the subsurface be measured whenever indoor air samples are collected. Ideally, differential pressure data would be collected continuously starting several days before sampling and throughout the sample collection period. 159 The magnitude and direction of the pressure difference during sampling can support insights about whether a driving force for vapor intrusion is present during indoor air sampling; if not, then the resulting sampling data are unlikely to characterize a reasonable maximum vapor intrusion exposure condition. Differences in driving forces (direction or magnitude) among indoor air sampling events may help to explain any significant differences in observed indoor air concentrations over time. 160 Measuring pressure difference between the indoors and the subsurface 159 These data can be collected using portable pressure monitors installed in a dedicated sub-slab probe at one or more locations. Pressure transducers w ere employed for this purpose during high-frequency sampling as part of a research study in Indianapolis (EPA 2012f, see Section therein); readings w ere recorded every 15 minutes. Technical information about pressure-measuring instruments (e.g., description, operation, and calibration) can be found in Section 4 of Technical Guidance Document: Compliance Assurance Monitoring (EPA 1998). 160 Pre-mitigation measurements of the pressure difference betw een indoors and the subsurface may also be useful for supporting design of active depressurization technologies to reduce vapor intrusion (EPA 1993a, see Section 3 therein). 96

202 is a more direct means of assessing building under-pressurization than is monitoring weather/climate factors (e.g., air temperature, wind speed). Pressure difference monitoring in large buildings can help identify any areas with significant under-pressurization. o Presence and operation of a mitigation system, which would generally be expected to mitigate intrusion of vapor-forming chemicals even if designed for radon. o Physical conditions that indicate potential openings to soil gas entry (e.g., potential conduits, such as cracks or floor drains; presence of structures such as utility pits, sumps, and elevators; basements or crawl spaces; modifications to the original foundation). Building Heating, Ventilation, and Cooling o Building ventilation, including zones of mechanical influence and stagnation. As noted in Section 2.4, greater ventilation is intended to result in smaller vapor concentrations in indoor air. Any non-ventilated or passively ventilated rooms (such as mechanical rooms) may be subject to greater accumulation of vapors. For commercial and industrial buildings, each distinct zone of influence may warrant sampling, when indoor air testing is selected as part of a site-specific investigation plan for vapor intrusion assessment. o Operating characteristics of HVAC systems. In many commercial buildings, the HVAC system brings outdoor air into the building, potentially creating building over-pressurization relative to the outdoor environment. EPA recommends noting any areas with significant over-pressurization, relative to the outdoors. Indoor and Outdoor Sources of Vapor-Forming Chemicals o Chemicals and consumer products used or stored within the building that can act as potential sources of toxic vapors. Vapor-forming chemicals are used in many commercial and most industrial buildings. 161 As noted in Section 2.7, consumer products that can emit vapors may be common in residential buildings. In some circumstances, a photoionization detector (PID) can be used to directly screen the building for locations with vapor-forming chemicals and materials; however, the PID may not be sensitive enough for very low concentration sources. More sensitive options include use of the HAPSITE gas chromatograph/mass spectrometer (Gorder and Dettenmaier 2011) or the TAGA Mobile Laboratory (EPA-ERT 2012). o HVAC systems that bring outdoor air into the building potentially bring contaminated outdoor air into the building, depending on the location of the vent and exhaust with regard to other spaces. For example, HVAC intakes adjacent to 161 Depending upon it history of uses and operations, buildings undergoing renovation, redevelopment or reuse may have lingering presence of vapor-forming chemicals due to a past release(s) also. 97

203 or near a dry-cleaning facility may introduce vapors of the dry-cleaning solvent into the building. In some cases, contaminated groundwater seeps into or actively collects in the building (for example, in sumps), possibly serving as a direct source of vapors. It may be appropriate to collect water samples concurrently with indoor air (and any sub-slab) samples in these circumstances. Presence and operation of any indoor air treatment system (e.g., in-line carbon adsorption) that can reduce indoor exposure levels of vapor-forming chemicals. In general, EPA recommends that the foregoing complementary information be collected during investigation planning and scoping to help determine where to sample and prioritize or sequence buildings for testing. Then, the information can be confirmed during indoor sampling. Field experience in residential settings suggests that it may not be possible to remove all indoor sources of vapor-forming chemicals. It may be particularly impractical to do so in industrial settings where vapor-forming materials are used or stored. It may also be impractical when deploying passive samplers, owing to their longer deployment period. Therefore, EPA recommends asking building occupants to document indoor sources (and relevant building operations) during indoor air sampling, using an activity log or questionnaire Outdoor Air Sampling Outdoor air concentration data can be useful in identifying potential contributions to indoor air concentrations from ambient air sources (see Section 6.3.5). Therefore, EPA generally recommends collecting ambient air samples using similar sampling and analysis methods, whenever indoor air samples are collected. Normally, EPA recommends one or two outdoor air sample locations to characterize the conditions surrounding a single or a few buildings. 162 Additional outdoor air samples may be warranted if the investigation is assessing multiple buildings over a wide area. EPA also recommends that sample locations be designed to characterize representative conditions in the absence of site-related subsurface contamination (e.g., avoid collecting ambient air samples near locations of known or suspected chemical release(s), including any atmospheric releases from remediation equipment). It also is suggested that observable potential outdoor sources of pollutants (e.g., air emissions from nearby commercial or industrial facilities) be recorded during all building surveys. Because concentrations of vapor-forming chemicals in ambient air can vary with time, EPA recommends that ambient air samples generally be collected over the same sampling period as indoor air, which will facilitate data evaluations when contaminant concentrations are compared between media. For residential buildings, EPA generally recommends beginning ambient air sampling at least one hour, but preferably two hours, before indoor air monitoring begins and continuing to sample until at least 30 minutes before indoor monitoring is complete. EPA recommends this practice because most residential buildings have an hourly air exchange rate in the range of 0.25 to 1.0, causing air that enters the building before indoor air sampling to 162 For buildings w here outdoor air is mechanically brought into the building, an outdoor sample may be co-located near the HVAC intake. 98

204 remain in the building for a long time (for example, see Section D.10, ITRC 2007a). Recommended lag times may warrant adjusting for nonresidential buildings. Evaluate and Develop Analyte Lists. To characterize potential concentrations entering a building via ambient air, EPA generally recommends that chemical analyses for ambient air samples be limited to those vapor-forming chemicals known (based upon subsurface testing) or suspected (based upon site history) to be present in the subsurface environment. Requesting an extensive list of analytes that are not related to subsurface contamination, as discussed previously, may unnecessarily complicate risk communication. Consider Collecting Complementary Data. Monitoring air exchange during ambient air sampling events can provide useful complementary data. Ideally, these data would be collected continuously starting before sampling and throughout the sample collection period. Information about air exchange can support insights about the amount of ambient air infiltration during sampling Sub-slab Soil Gas Sampling Sub-slab sampling is intended to draw soil gas from the air space immediately below the floor slab of a building. Depending upon building construction and condition, this air space may be an air gap that forms beneath a concrete foundation due to differential settlement over time or a pore space within a granular layer that may have been placed below the concrete slab. Access to this air space is generally provided by drilling or coring through the concrete and inserting a probe, which is sealed into the floor. EPA s Environmental Response Team has developed a standard operating procedure for constructing and installing sub-slab soil gas sampling probes (EPA-ERT 2007). Sub-slab soil gas samples can provide useful data for characterizing the levels of hazardous, vapor-forming chemicals that can enter a building via soil gas intrusion. When combined with other soil gas data, sub-slab soil gas data can be used to assess whether the subsurface vapor migration route is complete (i.e., subsurface vapor migration is capable of transporting hazardous vapors from the source to building; see Section 6.3.2). When combined with an appropriate attenuation factor (e.g., a conservative generic value see Section 6.5.3), sub-slab soil gas data can be used to estimate a potential upper-bound indoor air concentration 163 that may arise from vapor intrusion. In this way, sub-slab data can be used to assess the potential for the vapor intrusion pathway to pose a health concern For purposes of this Technical Guide, the term upper bound indoor air concentration is intended to be a semiquantitative phrase, referring to the high end of the exposure distribution. EPA recommends basing the decision about w hether to undertake response action for vapor intrusion (i.e., a component of risk management) on a consideration of a reasonable maximum exposure (e.g., EPA 1989, 1991a), w hich is intended to be a semiquantitative phrase, referring to the low er portion of the high end of the exposure distribution (see Glossary). Alternatively, a w orst case or reasonable w orst case (see Glossary) indoor air concentration w ould refer to the upper portion of the exposure distribution. Section 6.6, w hich discusses mathematical modeling of vapor intrusion, notes that consideration of a w orst case exposure condition may be particularly useful w here the predicted w orst case indoor air concentrations can be show n to pose acceptable human health risk. 164 The sub-slab soil gas concentration provides only half of the information for estimating vapor flux into a building. The other information needed is the soil gas flow rate (Qsoil), w hich is embodied in the attenuation factor. The soil gas flow rate can also be explicitly calculated using a model. 99

205 Field experience indicates there may be substantial spatial variability in sub-slab soil gas concentrations even over an average-sized footprint of a residential building. EPA, therefore, recommends site planning and data review teams consider collecting multiple samples per building when sub-slab soil gas sampling is conducted. 165 Three sub-slab samples have been collected in a number of EPA investigations of a typical size residential building or commercial building less than 1,500 square feet in area. EPA recommends the site planning and data evaluation team discuss the number of sample locations per building for atypical situations, which include: (1) very large or small homes or buildings; 166 (2) buildings with more than one foundation floor type; 167 (3) subsurface structures or conditions that might facilitate or mitigate vapor intrusion; and 4) multi-use buildings with distinct segmented areas that differ significantly by occupying population or exposure frequency. In addition, EPA recommends multi-point subslab samples be considered to support data interpretation and resolve uncertainties that may arise when: There are fewer surrounding buildings that are being sampled (that could have helped the understanding of typical sub-slab values and variability). 168 The indoor and sub-slab concentrations for a specific building(s) are out of line with expectations based on data from neighboring homes and other information. EPA generally recommends that sub-slab sampling include centrally located sub-slab samples in buildings identified for testing when the subsurface vapor source is laterally extensive relative to the building footprint (e.g., a broad plume of contaminated groundwater). 169 In addition, EPA recommends that site teams consider internal building partitions, HVAC layout, contaminant distribution, utility conduits, and openings for preferential soil gas entry in selecting any additional locations for collecting sub-slab samples. Several rounds of sampling are generally recommended to develop an understanding of temporal variability of sub-slab soil gas concentrations, particularly when these data are used with the recommended attenuation factor (see Section 6.5.3) to estimate a potential upperbound indoor air concentration that may arise from vapor intrusion. 165 An individual sample, collected at a randomly chosen time, may under-estimate or over-estimate average subslab conditions. Collecting multiple subslab soil gas samples can, therefore, reduce the chance of reaching a falsenegative conclusion (i.e., concluding subsurface vapor source strength is limited, w hen vapor intrusion actually poses an unacceptable human health risk) or a false-positive conclusion (i.e., concluding subsurface vapor source strength is unacceptably elevated, w hen vapor intrusion actually poses an acceptable human health risk). 166 For larger structures, a statistician may assist in identifying the number and placement of sampling ports to meet the desired DQOs. 167 In basements w ith a partial slab, but one large enough to allow vapors to accumulate (for example, if the slab covers more than 50 percent of the building footprint), EPA generally recommends that one sub-slab port be installed on the slab portion and an indoor air sample be collected directly over the dirt portion. 168 In these cases, EPA recommends multiple ports be installed in a specific percentage (e.g., more than 10 percent) of the buildings sampled to provide a check for variability in the study area. 169 Based on w ork conducted in New York as of the spring of 2010, it appears that the sub-slab concentrations beneath the central area of a home are usually (75 percent of the time) higher than (or as high as) the concentrations closer to the perimeter of the home. This field observation is supported by modeling results for idealized scenarios, w hich show greater sub-slab soil gas concentrations near foundation centers in under-pressurized residential buildings w hen the vapor source is laterally extensive relative to the building footprint (EPA 2012b). 100

206 If a site team decides to proceed with sub-slab sampling, EPA recommends that leak-testing be performed to ensure the hole is properly sealed, for example through the use of a helium tracer gas shroud. Because installing soil gas probes can disturb subsurface conditions, EPA recommends that the site team allow some time after the sampling probe has been installed for the subsurface to return to equilibrium conditions. An EPA study of the time needed for the subsurface conditions to come back to equilibrium (equilibration rate) after they have been disturbed by installation of the soil gas probes found that an equilibration time of two hours generally was sufficient because most sub-slab material consists of sand or a sand-gravel mixture even for buildings built directly on clay (Section 5.0, EPA 2006b). There also may be special considerations for sub-slab soil gas samples because of either a unique construction (for example, pretension concrete slab) or environmental situation. Key EPA recommendations include, but are not limited to: Identify the location of cables in post-tensioned concrete (e.g., using ground-penetrating radar) before sub-slab sampling, as drilling through a cable poses a significant health and safety concern and may damage the slab. Avoid locating sub-slab samples in areas where groundwater might intersect the slab. Identify and avoid the location(s) of underground utilities and structures (for example, electric, gas, water, or sewer lines) to prevent damage to these lines; however, sample collection in close proximity to these lines may be warranted as building penetrations for these lines may pose openings for soil gas entry. Consider whether to augment sub-slab samples with samples through the basement walls, as the primary entry points for vapors in basements might be through the sidewalls rather than from below the floor slab. Evaluate and Develop Analyte Lists. To characterize potential concentrations entering a building via soil gas, EPA generally recommends that chemical analyses for sub-slab soil gas samples be limited to those vapor-forming chemicals known (based upon subsurface testing) or suspected (based upon site history) to be present in the subsurface environment. Requesting an extensive list of analytes that are not related to subsurface contamination, as discussed previously, may unnecessarily complicate risk communication. Collect Complementary Data While Indoors. When sub-slab soil gas samples are collected, EPA recommends that the following complementary information be gathered by observation or interviews: Physical conditions and characteristics that are pertinent to assessing the building s susceptibility to soil gas entry, if any (e.g., potential conduits, such as cracks or floor drains; presence of structures, such as utility pits and elevators; basements or crawl spaces). Such information may help interpret spatial differences in sub-slab or indoor air concentrations within a building. Areas with potentially significant over- or under-pressurization relative to the outdoors. Such information may assist in interpreting spatial differences in sub-slab or indoor air concentrations within a building. 101

207 Where outdoor air is mechanically brought into the building by the HVAC system and building(s) interiors are over-pressurized, it may be helpful to also collect ambient air samples to support interpretations of the sub-slab sampling results. If the predominant vapor-forming substances and their respective concentrations in sub-slab soil gas and outdoor air samples are similar, then ambient air may be influencing sub-slab soil gas conditions. EPA recommends that the pressure difference between the indoors and the subsurface be measured whenever sub-slab soil gas samples are collected. Ideally, differential pressure data would be collected continuously starting several days before sampling and throughout the sample collection period. 170 EPA recommends measuring pressure at locations away from where sub-slab sampling probes are installed to avoid any pressure artifacts caused during purging and sampling. The magnitude and direction of the pressure difference during sampling can support insights about whether a driving force for vapor intrusion is present during sampling. When any sub-slab soil gas sample is collected, EPA recommends that relevant meteorological data that can influence soil gas concentration patterns at the time of sampling, such as wind speed, snow or ice cover, significant recent precipitation, and changes in barometric pressure, be recorded, using direct observation (e.g., for snow or ice cover) or readily available data sources (e.g., regional weather stations). These data may be helpful qualitatively in data interpretation; for example, in reconciling soil gas data collected on multiple occasions. A potential shortcoming of sub-slab soil gas testing is that gaining access may be difficult (or, in some cases, infeasible). This difficulty can often be overcome by implementing a program of community outreach and engagement that fosters trust and good relationships (see Section 9.0). When access is granted for indoor sampling, EPA recommends collecting sub-slab and indoor air samples contemporaneously using similar sampling and analysis methods and sampling durations to allow for data comparison. The sub-slab sampling ports can be installed after the indoor air sample is deployed and collected (8-24 hours later) to avoid biasing the indoor air concentrations with potentially higher sub-slab gas infiltration rates during port installation. Alternatively, the sub-slab ports may be installed prior to indoor air sampling and sampled concurrently with the indoor air samples, provided sufficient time is allowed for the indoor air concentrations to return to normal after installation of the sub-slab port These data can be collected using portable pressure monitors installed in a dedicated sub-slab probe at one or more locations. Pressure transducers w ere employed for this purpose during high-frequency sampling as part of a research study in Indianapolis (EPA 2012f, see Section therein); readings w ere recorded every 15 minutes. Technical information about pressure-measuring instruments (e.g., description, operation, and calibration) can be found in Section 4 of Technical Guidance Document: Compliance Assurance Monitoring (EPA 1998). 171 EPA generally recommends delaying indoor air testing for at least 24 to 72 hours based on an approximate air exchange rate of 0.25 to 1.0 per hour. Note that the effects of any spike in indoor air concentration may linger depending on source strength, relative humidity inside the building, and the extent to w hich the contaminants have been absorbed by carpets and other fabrics or sinks. 102

208 6.4.4 Soil Gas Sampling Data obtained from a soil gas survey can be used to identify, locate, and characterize subsurface vapor sources (see Section 6.3.1) and characterize subsurface vapor migration routes, including any impedances from geologic, hydrologic, or biochemical conditions (see Section 6.3.2). Soil gas survey data can also be useful in supporting the design of soil vapor extraction systems and other subsurface remediation systems and the performance assessment of these systems (see Section 8.1). For each of these purposes, EPA recommends that soil gas survey data be supported by site-specific geologic information (i.e., site geology and subsurface lithology). Soil gas sampling generally consists of installing a probe into the ground, drawing gas out of the probe, and collecting the gas for transport to a location for analysis. Inert materials (e.g., stainless steel, copper, brass, polyvinyl chloride, high-density polyethylene) are recommended for constructing soil gas probes. To ensure that data collected are representative of conditions in situ (e.g., are not adversely impacted by artificial infiltration of ambient air), a reliable seal of the annulus between the probe and the probe housing and leak testing for the seal are generally recommended. In addition, purging of the probe before collecting the soil gas sample is recommended, analogous to purging of monitoring wells before collecting groundwater samples. EPA s Environmental Response Team has developed a standard operating procedure for soil gas sampling, including constructing and installing sampling probes (EPA-ERT 2001c). Typically, grab (rather than time-integrated) samples are collected when sampling soil gas. EPA recommends that the site team allow some time after the sampler has been installed for the subsurface to return to equilibrium conditions because installing temporary or permanent soil gas probes can disturb subsurface conditions. The equilibration time may depend on the degree of soil disturbance during installation, which is influenced by the type of drilling techniques used to install the soil gas probes (e.g., with more time needed for auger drilling compared with hand drilling). For example, the California Environmental Protection Agency recommends an equilibration time of two hours for temporary driven probes and 48 hours for probes installed using augered borings (CalEPA 2012). EPA recommends documenting wind direction, precipitation information, temperature, and other site-specific information that can influence soil gas concentration patterns at the time of sampling, using readily available data sources. These data may be helpful qualitatively in data interpretation; for example, in reconciling soil gas data collected on multiple occasions or assessing concordance of sampling data from various media, when not collected contemporaneously. EPA recommends that soil gas samples be taken as close to the areas of interest as possible and preferably from directly beneath the building structure. As vapors are likely to migrate upward through the coarsest or driest material in the vadose zone, EPA recommends that soil gas samples be collected from these materials. Using vertical boring or drilling techniques, it is generally practical to collect soil gas samples only in locations exterior or adjacent to a building s footprint ( exterior soil gas samples). Modeling results for idealized scenarios show that, in homogeneous soil, soil gas concentrations tend to be greater beneath the building than at the same depth in adjacent open areas when the vapor source is underneath the building, even if the source is laterally extensive relative to the building footprint (e.g., broad plume of contaminated groundwater) (EPA 2012b). Given these 103

209 predictions and supporting field evidence (EPA 2012a, see Figure 6; Luo et al. 2009; Patterson and Davis 2009, see Figure 1), individual exterior soil gas samples cannot generally be expected to accurately estimate sub-slab or indoor air concentrations. This potential limitation may be particularly valid for shallow soil gas samples collected exterior or adjacent to a building footprint. On the other hand, when the subsurface vapor source is not underneath the building, exterior soil gas samples collected from depths below a building s foundation and along the side of the building closest to the source may be useful for characterizing a reasonable worst case condition underneath the building in the absence of routes for preferential vapor migration or soil gas entry. Deeper soil gas samples collected in the vadose zone immediately above the source of vapor contamination (i.e., near-source soil gas samples; see Section 6.3.1) can reasonably be expected to be less susceptible to the diluting effects of ambient air, compared to shallow soil gas samples. On this basis, deeper soil gas samples collected in the vadose zone immediately above the source of vapor contamination will tend to be more suitable than will be shallow soil gas samples for assessing vapor concentrations that may be in contact with the building s subslab. 172 Several rounds of sampling are generally recommended to develop an understanding of temporal variability of near-source soil gas concentrations, particularly when these data are used with the recommended attenuation factor (e.g., a conservative generic value see Section 6.5.3) to estimate a potential upper-bound indoor air concentration that may arise from vapor intrusion Groundwater Sampling Groundwater sampling and analysis also feature prominently in many vapor intrusion investigations, for example, to help characterize plumes that can serve as vapor sources. Groundwater sampling methods are not discussed here because practitioners typically are relatively experienced and trained to collect samples that meet site-specific data quality needs (see, for example, EPA-ERT 2001a). However, Section provides a few recommended guidelines for groundwater sampling that are pertinent for characterizing representative vapor source concentrations for vapor intrusion assessment. One key consideration in sampling groundwater for vapor intrusion investigations is focusing on characterizing water table 172 Luo et al. (2009) also point to the shortcomings of relying on exterior sampling data, citing significant differences in vapor concentrations and soil gas composition betw een interior and exterior sampling locations at a maintenance w arehouse located at a former refinery. They also observed that the spatial variability in the soil-gas distribution w as smaller for soil-gas samples draw n from the source zone, suggesting greater confidence in the assessment of source zone or near source vapor concentrations. 173 For purposes of this Technical Guide, the term upper bound indoor air concentration is intended to be a semiquantitative phrase, referring to the high end of the exposure distribution. EPA recommends basing decisions about w hether to undertake response action for vapor intrusion (i.e., a component of risk management) on a consideration of a reasonable maximum exposure (e.g., EPA 1989, 1991a), w hich is intended to be a semi-quantitative phrase, referring to the low er portion of the high end of the exposure distribution (see Glossary). Alternatively, a w orst case or reasonable w orst case (see Glossary) indoor air concentration w ould refer to the upper portion of the exposure distribution. Section 6.6, w hich discusses mathematical modeling of vapor intrusion, notes that consideration of a w orst case exposure condition may be particularly useful w here the predicted w orst case indoor air concentrations can be show n to pose acceptable human health risk. 104

210 concentrations. EPA recommends that groundwater samples be taken from wells screened (preferably over short intervals) across the top of the water table. 174 Groundwater data can be compared to the groundwater VISLs (see Section 6.5). 175 When combined with an appropriate attenuation factor (see Section 6.5.3), groundwater data can be used to estimate a potential upper-bound indoor air concentration that may arise from vapor intrusion. 176 In these ways, groundwater data can be used to assess the potential for vapor intrusion from groundwater sources to pose a health concern Planning for Building and Property Access Vapor intrusion investigations generally entail gaining legal access to buildings and properties to conduct sampling. To address this practical and logistical concern during the planning stage, EPA recommends that an access agreement be executed between the property owner, any occupants, and the investigating entity. Section 9.3 provides additional information for addressing building and property access for sampling. Obtaining and scheduling access to a property and building can be difficult, whether the structure is a commercial or institutional building or a private residence. This potential difficulty can often be overcome by implementing a program of community outreach and engagement that fosters trust and good relationships. EPA recommends conducting public outreach and communication for this purpose considering the site-specific community involvement plan (See Section 9.1). 6.5 Overview of Risk-Based Screening Risk screening for vapor intrusion generally is performed using site-specific data collected via appropriate methods, as described in Section 6.4. In some cases, pre-existing data identified during a preliminary analysis can be deemed reliable and adequate for use in risk-based screening (see Section 5.5) Objectives of Screening The primary objective of risk-based screening is to identify sites or buildings unlikely to pose a health concern through the vapor intrusion pathway. Generally, at properties where subsurface concentrations of vapor-forming chemicals (e.g., groundwater or near source soil gas concentrations) fall below screening levels (i.e., VISLs), no further action or study is warranted, so long as the exposure assumptions match those taken into account by the calculations and the site fulfills the conditions and assumptions of the generic conceptual model underlying the 174 EPA recommends that, to the extent practical, groundw ater samples be collected over a narrow interval (e.g., a few feet or less) just below the w ater table w hen the data are to be used for assessing the potential for vapor intrusion. 175 If available groundw ater data do not meet the criteria set forth in Section 6.4.5, the site data review team may judge w hether they are nevertheless representative of potential vapor source concentrations emanating from groundw ater. 176 EPA recommends basing decisions about w hether to undertake response action for vapor intrusion (i.e., a component of risk management) on a consideration of a reasonable maximum exposure (e.g., EPA 1989, 1991a). 105

211 screening levels. In a similar fashion, the results of risk-based screening can help the data review team identify areas, buildings, and/or chemicals that can be eliminated from further assessment. Subsurface concentrations of vapor-forming chemicals that exceed the VISL for the respective medium (e.g., groundwater, soil gas, subslab soil gas) would not automatically trigger mitigation or subsurface remediation (i.e., they are not offered as response action levels or cleanup levels). Exceeding a subsurface screening level generally suggests, however, that further evaluation of the vapor intrusion pathway is appropriate. In this way, risk-based screening, along with other lines of evidence, can help focus a subsequent site-specific investigation, the results of which would provide support for considering building mitigation and other risk management options (see Section 8.0). For example, the results of vapor source strength screening can help identify and prioritize buildings for indoor testing. Finally, risk-based screening can also support: a preliminary evaluation of human health risk using individual building data (e.g., indoor air concentrations), which would consider the magnitude of the concentration exceedance of the indoor air screening level and site-specific risk management benchmarks (see Section 7.4.1); and identification of buildings and structures that may warrant prompt action due to potential explosion threats (see Section 7.5.1) Scope and Basis for Health-based, Vapor Intrusion Screening Levels EPA developed VISLs for human health protection that are generally recommended, mediumspecific, risk-based screening-level concentrations intended for use in identifying areas or buildings that may warrant further investigation of the vapor intrusion pathway. These VISLs are calculated and documented in the VISL Calculator and are based on: Current toxicity values selected considering OSWER s hierarchy of sources for toxicity values (EPA 2003). Physical-chemical parameters for vapor-forming chemicals. EPA-recommended approaches for human health risk assessment (e.g., EPA 2009c, 2014a). The VISLs for human health protection include indoor air screening levels for long-term (i.e., chronic) exposures, which consider the potential for cancer and noncancer effects of vaporforming chemicals. 177 The VISLs for human health protection also include subsurface screening levels for comparison to sub-slab soil gas, near-source soil gas, and groundwater sampling 177 The VISL Calculator does not include information about radon. Information about characterizing the human health risk posed by radon can be found on-line at: 106

212 results. These screening levels are derived from the indoor air screening levels for chronic exposures using medium-specific, generic attenuation factors described further in Section and Appendix A. The user s guide for the VISL Calculator provides additional information about derivation of the indoor air and subsurface screening levels (EPA 2015a). The medium-specific VISLs for human health protection are intended to be compared to: Building-specific data, such as results from sub-slab soil gas samples, crawl space samples, or indoor air samples; or Site- or building-specific data that characterize subsurface vapor sources (e.g., groundwater samples, near-source soil gas concentrations) to determine if there is a potential for the vapor intrusion pathway to pose a health concern to building occupants. The medium-specific VISLs for health protection are developed considering a generic conceptual model for vapor intrusion consisting of: A source of vapors underneath the building(s) either in the vadose zone or in the uppermost, continuous zone of groundwater. Vapor migration via diffusion upwards through unsaturated soils from these sources toward the ground surface and overlying buildings. Buildings with poured concrete foundations (e.g., basement or slab-on-grade foundations) that are susceptible to soil gas entry. A critical assumption for this generic model is that site-specific subsurface characteristics will tend to reduce or attenuate soil gas concentrations as vapors migrate upward from the source and into overlying structures. Specific factors that may result in relatively unattenuated or enhanced transport of vapors into a building include the following: Significant openings to the subsurface that facilitate soil gas entry into the building (e.g., sumps, unlined crawl spaces, earthen floors) other than typical utility penetrations. 178 Very shallow groundwater sources (e.g., depths to water less than five feet below foundation level) (see, for example, EPA (2012a), Section 5.2). Significant routes for preferential, subsurface vapor migration whether naturallyoccurring (e.g., fractured bedrock) or anthropogenic (see Sections 5.4 and 6.3.2). 178 For purposes of this Technical Guide, the term significant openings is intended to refer to forms and amounts of openings, other than adventitious and intentional openings in a building that are expected to typically be present in all buildings (e.g., cracks, seams, interstices, and gaps in basement floors and w alls or foundations; perforations due to utility conduits). Such an atypical opening w ould be significant w hen it is of sufficient volume and proximity to a building that it may be reasonably anticipated to influence vapor migration tow ards or soil gas entry into the building. 107

213 These specific factors are likely to render inappropriate the use of the recommended attenuation factors and the sub-slab, groundwater, and soil gas VISLs for purposes of identifying sites or buildings unlikely to pose a health concern through the vapor intrusion pathway. On the other hand, further evaluation of the vapor intrusion pathway is still appropriate when the sub-slab, groundwater, and soil gas VISLs are exceeded for samples from a building or site where these specific factors are present. Vapor source types that typically make the use of the recommended attenuation factors and health-based VISLs for groundwater and soil gas inappropriate include: Those originating in landfills where methane is generated in sufficient quantities to induce advective transport in the vadose zone. Those originating in commercial or industrial settings where vapor-forming chemicals can be released within an enclosed space and the density of the chemicals vapor may result in significant advective transport of the vapors downward through cracks and openings in floors and into the vadose zone. Leaking vapors from pressurized gas transmission lines. In each case, the diffusive transport of vapors may be overridden by advective transport, and the vapors may be transported in the vadose zone several hundred feet from the source of contamination with little attenuation in concentration. In general, EPA recommends considering whether the assumptions underlying the generic conceptual model are attained at a given site. If they are not attained, then EPA recommends that the medium-specific VISLs not be relied upon as a line of evidence for identifying sites or buildings unlikely to pose a health concern through the vapor intrusion pathway. Where the assumptions regarding the subsurface attenuation factors do not or may not apply, EPA generally recommends collecting indoor air samples. As noted in Section 6.5.1, these VISLs are not automatically response action levels, although EPA recommends that similar calculation algorithms be employed to derive cleanup levels (see Section 7.6). Comparison of sample concentrations to the VISLs is only one factor recommended for use in determining the need for a response action at a site. As discussed further in Section 6.5.4, an individual subsurface sampling result that exceeds the respective, chronic screening level does not establish that vapor intrusion will pose an unacceptable human health risk to building occupants. Conversely, these generic, single-chemical VISLs do not account for the cumulative effect of all vapor-forming chemicals that may be present. Thus, if multiple chemicals that have a common, non-cancer toxic effect are present, a significant health threat may exist at a specific building or site even if none of the individual substances exceeds its VISL (see discussion of non-cancer hazard index in Section 7.4.1) Recommended Attenuation Factors for Health-based Screening Vapor attenuation refers to the reduction in volatile chemical concentrations that occurs during vapor migration in the subsurface, coupled with the dilution that can occur when the vapors enter a building and mix with indoor air (Johnson and Ettinger 1991). The aggregate effect of these physical and chemical attenuation mechanisms can be quantified through the use of a vapor intrusion attenuation factor, which is defined as the ratio of the indoor air concentration 108

214 arising from vapor intrusion to the soil gas concentration at the source or a depth of interest in the vapor migration route (EPA 2012a). 179 EPA compiled a database of empirical attenuation factors for chlorinated VOCs and residential buildings through review of data from 913 buildings at 41 sites with indoor air concentrations paired with sub-slab soil gas, groundwater, exterior soil gas, or crawl space concentrations (EPA 2012a). After removing data that do not meet quality criteria and data likely to be influenced by background sources, the distributions of the remaining attenuation factors were analyzed graphically and statistically. 180 Based upon these analyses, the attenuation factors in Table 6-1 are recommended by EPA to derive the VISLs for health protection. With the exception of the near-source exterior soil gas attenuation factor, the recommended values for residential buildings are the estimated 95 th percentile values, rounded to one significant figure. 181 The rationale for these recommendations and related analyses are provided in Appendix A. These recommended values are proposed to apply to all vapor-forming chemicals for use in estimating potential upper-bound concentrations in indoor air that may arise from vapor intrusion. 182 The recommended groundwater and near-source soil gas attenuation factors do not, however, include the effects of biodegradation. 183 On the other hand, because biodegradation is not expected to occur indoors (i.e., in indoor air in the absence of an air treatment system), the sub-slab soil gas and crawl space attenuation factors are expected to apply equally to vapor-forming chemicals that biodegrade in the vadose zone and those that do not. As with the medium-specific VISLs, EPA recommends considering whether there are site- or building-specific factors that may result in unattenuated or enhanced transport of vapors toward and into a building, such as the presence of preferential migration route(s) as described in Sections 5.4 and The presence of such factors is likely to render inappropriate the use of any of these generic attenuation factors. 179 As defined here, the vapor attenuation factor is an inverse measurement of the overall dilution that occurs as vapors migrate from a subsurface vapor source into a building; i.e., low er attenuation factor values indicate low er vapor intrusion impacts and greater dilution; higher values indicate greater vapor intrusion impacts and less dilution (EPA 2012a, b). Johnson and Ettinger (1991) utilized the symbol α for the vapor intrusion attenuation factor. For example, the subslab soil gas attenuation factor is intended to account for concentration dilution arising during migration through openings in the foundation and from mixing of subsurface contaminants inside the building. The groundw ater attenuation factor is intended to account for concentration dilution arising during vapor migration from the groundw ater table through the vadose zone, in addition to concentration dilution arising during migration through openings in the foundation and from mixing of subsurface contaminants inside the building. 180 A summary of the resulting distributions is provided in Appendix A of this document. 181 The recommended near-source exterior soil gas attenuation factor corresponds to approximately the estimated 75 th percentile value. 182 EPA recommends basing decisions about w hether to undertake response action for vapor intrusion (i.e., a component of risk management) on a consideration of a reasonable maximum exposure (e.g., EPA 1989, 1991a). 183 Appropriate data can be collected and evaluated, as described in Section 6.3.2, to characterize and document the occurrence of biodegradation in the vadose zone and its effects in attenuating vapor concentrations of biodegradable vapor-forming chemicals. 109

215 TABLE 6-1 RECOMMENDED VAPOR ATTENUATION FACTORS FOR RISK-BASED SCREENING OF THE VAPOR INTRUSION PATHWAY 184 Sampling Medium Groundwater, generic value, except for shallow water tables (less than five feet below foundation) or presence of preferential vapor migration routes in vadose zone soils Medium-specific Attenuation Factor for Residential Buildings 1E-03 (0.001) Groundwater, specific value for fine-grained vadose zone soils, when laterally extensive layers are present 185 5E-04 (0.0005) Sub-slab soil gas, generic value 3E-02 (0.03) Near-source exterior soil gas, generic value except for sources in the vadose zone (less than five feet below foundation) or presence of routes for preferential vapor migration in vadose zone soils 3E-02 (0.03) Crawl space air, generic value 1E-00 (1.0) The VISL Calculator ( also facilitates calculation of groundwater screening levels based on the recommended attenuation factor for fine-grained soil. EPA recommends that any use and application of this semi-site-specific groundwater attenuation factor be supported by site-specific geologic information (i.e., site geology and subsurface lithology). Significant characterization of the vadose zone may be needed to demonstrate that fine-grained layers are laterally extensive over distances that are large compared to the size of the building(s) or the extent of vapor contamination at a specific site, which is the recommended support for using the semi-site-specific attenuation factor for 184 Use of these attenuation factors for estimating indoor air concentrations is contingent upon site conditions fitting the generic model of vapor intrusion described in Section and subsurface conditions being characterized considering the recommendations in Sections 6.3 and The Draft VI Guidance allow ed for the modification of VISLs for groundw ater by incorporating a low er attenuation factor, based upon some site-specific inputs, w hich estimates a greater reduction in vapor concentrations in the vadose zone than the generic value (EPA 2002c, 2010b). In the Draft VI Guidance, graphs w ere provided from w hich such semi-site-specific attenuation factors could be selected and justified based upon site-specific soil type and depth to the w ater table. Based upon analysis of EPA s expanded database, a single groundw ater attenuation factor is provided in this Technical Guide for fine-grained soils. 110

216 fine-grained soil. 186 For purposes of applying the groundwater attenuation factors, EPA recommends the depth to groundwater be estimated relative to the bottom of the building foundation and be based upon the seasonal high groundwater table Comparing Sample Concentrations to Health-based Screening Levels When evaluating environmental sampling results to assess the vapor intrusion pathway, it is important to first determine that the samples were collected appropriately. Section 6.4 provides information about recommended sampling locations and procedures for vapor intrusion investigations. In addition, EPA recommends collecting and evaluating appropriate site-specific information to demonstrate that the property fulfills the conditions and assumptions of the generic conceptual model underlying the VISLs, as described in Section After verifying that the CSM justifies the use of the VISLs, the individual sample concentrations may be compared to the appropriate medium-specific screening levels. In order to select the appropriate target media concentrations for comparison, it generally is important to identify whether a source of vapors for a building or a developed area occurs in the unsaturated zone, which is an important aspect of the CSM. This allows the site data to be segregated into two categories: Data representing areas where contaminated groundwater is the only source of contaminant vapors. In this first case, groundwater VISLs are generally appropriate to use to evaluate groundwater concentrations (also see sampling recommendations in Sections and 6.4.5). Under these circumstances, EPA recommends that the plume be shown to be stable or shrinking (i.e., is not migrating or rising in concentration, including hazardous byproducts of any biodegradation) to establish that the potential for vapor intrusion to pose a human health risk from vapor intrusion will not increase in the future. Nearsource soil gas data (i.e., soil gas samples collected immediately above the water table) could also be compared to the soil gas VISLs to obtain a corroborating line of evidence (see recommendations in Section 6.3.1). When the anticipated outcome of the screening is a finding that groundwater poses acceptable human health risk from vapor intrusion on an area-wide basis, it may be appropriate to compare sampling results for the most greatly impacted well within the area of interest and show that these results are less than the groundwater VISLs. Data representing areas where the underlying vadose zone soil contains a source of vapors (e.g., residual NAPL). In this second case, EPA recommends that only soil gas VISLs be used and compared to results from near-source soil gas samples collected near the vapor source zone 186 The general soil type assigned to paired vapor intrusion data in the EPA s database generally represents the coarsest soil described in the vadose zone near the sample location unless sufficient stratigraphic information w as available to indicate finer sediments are laterally continuous (EPA 2012a). EPA recommends that similar criteria be applied to justifying the use of the semi-site-specific attenuation factor for groundw ater (or selection of soil-related parameters for modeling); see Section 6.6. For these purposes, soil classified as clay, silty clay, silty clay loam, or silt consistent w ith the U.S. Soil Conservation Service classification system can be considered to be fine-grained. 111

217 (also see sampling recommendations in Sections and 6.4.4). In this situation, the groundwater VISLs (and vapor attenuation factors for groundwater) are not recommended for estimating potential upper-bound indoor air concentrations, because they have been derived assuming no other vapor sources exist between the water table and the building foundation. In both cases, because of the complexity of the vapor intrusion pathway, EPA recommends that professional judgment be used when applying the VISLs. Generally, if all subsurface sample concentrations for a given building or area are less than the respective medium-specific screening level, then vapor intrusion is less likely to pose an unacceptable human health risk to building occupants. On the other hand, when individual sample concentrations exceed the respective screening level, additional assessments may be warranted. So, for example, if a groundwater or near-source soil gas concentration exceeds the respective screening level, it is recommended that sub-slab soil gas testing and indoor air testing be conducted. However, we would note that any individual subsurface sampling result that exceeds the respective, chronic screening level does not establish that vapor intrusion will pose an unacceptable human health risk to building occupants. For one, the subsurface screening levels are expected to be conservative (i.e., are likely to over-estimate the contribution to indoor air levels arising from vapor intrusion) for many buildings due to the use of a high-end attenuation factor (see Section 6.5.3). In many cases, indoor air concentrations arising from vapor intrusion would be expected to be lower than those estimated using the recommended generic attenuation factors. For carcinogens, the screening levels are set using a one-per-million lifetime cancer risk (i.e., 10-6 ), whereas EPA recommends consideration of a cancer risk range when making risk management decisions (see Section 7.4.1). Finally, sampling results can be expected to be variable spatially and temporally and these screening levels assume a long period of exposure at the stated concentration. Owing to the temporal variability in building-specific data and the potential temporal and spatial variability in soil gas vapor concentrations, EPA generally recommends multiple samples be collected (see Section 6.4) and compared to the respective medium-specific screening level. In addition, the results of risk-based screening are generally most useful when they can be evaluated for indoor air and subsurface vapor sources concurrently and in the context of the CSM. EPA, therefore, generally recommends that multiple lines of evidence be developed and their results weighed together when evaluating and making risk-informed decisions pertaining to vapor intrusion. EPA generally recommends that concordance among the multiple lines of evidence be obtained, particularly when considering a determination that the vapor intrusion pathway is incomplete or does not pose an unacceptable human health risk. Sections 7.1, 7.2, and 7.3 provide additional information and recommendations about developing and using multiple lines of evidence and risk management decision-making Planning for Communication of Sampling Results EPA recommends the community involvement or public participation plan (See Section 9.1) describe and address community questions, concerns, and preferences for participation regarding sampling results. Generally, EPA recommends that the site planning team provide validated results to property owners and occupants. These results can be transmitted to relevant parties in a letter, along with a description of what future actions, if any, may be 112

218 warranted. In addition, the site planning team may choose to hold a community meeting to discuss the sampling results in general terms and EPA s plans, if any, for response actions. Section 9.4 provides additional information for communicating sampling results. 6.6 General Principles and Recommendations for Mathematical Modeling When suitably constructed, documented, and verified, mathematical models can provide an acceptable line of evidence supporting risk management decisions pertaining to vapor intrusion. In certain situations (e.g., for future construction on vacant properties), it is particularly useful to employ mathematical modeling to predict reasonable maximum indoor air concentrations, because indoor air testing is not possible. Mathematical modeling is most appropriately used in conjunction with other lines of evidence. For example, in the brownfield development case (i.e., yet-to-be-constructed building), EPA generally recommends these additional lines of evidence include, at a minimum, data that characterize potential subsurface vapor sources and associated geologic and hydrologic conditions in the vadose zone (see Sections and 6.3.2). Generally, mathematical models transform empirical values of input parameters into predictions of chemical concentrations in environmental media. The model input parameters are equally as important to the results as the mathematical components of the model (i.e., governing equations and solution algorithms). As a consequence, the results critically depend on the choices for the inputs. Historically, to assure confidence in predictions of mathematical models, they have been compared to measured, site-specific values. When measured and predicted values do not reasonably match, model input parameters are adjusted through calibration. For example, calibration is commonly used in groundwater flow modeling, in which model-predicted groundwater levels are matched to measured groundwater levels for a baseline condition to gain insight into hydrogeologic properties. The calibrated input parameters must reasonably represent the underlying phenomena and the characteristics of the model must reasonably match the field situation. Calibration of mathematical models is known to be non-unique, so that different sets of parameters can be used to fit the same observed data. This means that calibration does not produce a theoretically correct set of parameters. Because various values of input parameters could be used in the calibrated model, there will always be uncertainty as to the actual values. Three approaches exist for applying mathematical models in these circumstances: 1) Calibrating the mathematical model to the measured indoor air concentration (and, possibly, the sub-slab soil gas concentration) considered to be representative of vapor intrusion (i.e., background vapor sources have been identified and removed prior to sampling and data evaluation indicates that the concentration is reasonably attributable to vapor intrusion). Calibration entails adjusting the input parameters within plausible and realistic ranges so that the predicted indoor air concentrations (or sub-slab soil gas concentrations) are similar to the measured vapor concentrations. The adjusted input parameters can then be compared to site-specific conditions and data to verify that the CSM and calibrated model are coherent and sound. 113

219 2) Conducting an uncertainty analysis (perhaps using an automated uncertainty analysis (see as only one example)) to understand where, within the probability distribution of results, model results with pre-selected default parameters lie. This approach may be particularly useful where indoor air concentrations have not been measured or non-site-specific inputs have been used. 3) Using a bounding case analysis, where parameters are chosen to represent conditions that give a high-impact (e.g., reasonable worst ) case see Glossary or worst (maximum plausible) 187 case. This approach may be particularly useful where the predicted indoor air concentrations for the bounding case can be shown to pose acceptable human health risk. 188 The range of predicted indoor air concentrations can be established if the analysis also includes a low-impact ( best ) case. Unless site-specific parameter values are obtained for input parameters and the mathematical model is calibrated to field data, use of default input parameter values will generate model results that lie at an unknown point within an uncertainty band of the model outcomes. Because the combined effect of parameter uncertainty is large, a one- or two-order of magnitude error might be made unknowingly. To reduce these errors, sub-slab vapor sampling could be used to characterize the vapor concentration(s) beneath a building. Model results (i.e., predicted subslab soil gas concentrations) that match measured values would have increased confidence. Alternately, using bounding estimates of parameter values could provide a conservative model result that would be expected to represent the reasonable worst case of potential exposure. Three examples follow where differing applications of mathematical models would be useful in vapor intrusion assessment: Verify General Magnitude. Modeling using site-specific inputs can be useful for verifying the general magnitude of measured indoor air sample concentrations, which may allow risk managers to reach supportable conclusions not to conduct additional indoor air testing. In this situation, the model could be calibrated to indoor air measurements and the plausibility of the calibrated input parameters evaluated. If the calibrated model input parameters are plausible, then they can be considered an additional line of evidence supporting risk management decisions. Explore Range of Outcomes through Uncertainty Analysis. In certain situations, indoor air testing is not possible (e.g., for future construction on vacant properties) or feasible. 187 For purposes of this Technical Guide, the phrase w orst case indoor air concentration is intended to be a semiquantitative phrase, referring to the high end of the exposure distribution. No-further-action decisions can normally be supported more confidently w hen the w orst case indoor air concentration can be show n to pose acceptable health risks. Under these conditions, the reasonable maximum exposure (see Glossary) typically w ould also pose acceptable health risks. 188 "Bounding estimates" purposely overestimate the exposure or dose in an actual population for the purpose of developing a statement that the risk is "not greater than... (EPA 1992c). 114

220 Here the range of possible outcomes could be explored with the model through an uncertainty analysis. For example, model input parameters, including building and vadose zone soil properties, could be varied within plausible ranges to determine the parameters to which the model is most sensitive to guide field investigations. Uncertainty analyses can also be used to ascertain whether the subsurface vapor source concentrations are such that indoor air samples would not be expected to contain detectable levels of vapor-forming chemicals arising from vapor intrusion. Generate Bounding Estimates. If the range of parameter values is known with confidence for the site, then parameters can be chosen to represent the bounding case of maximum plausible vapor intrusion (i.e., worst case). In each of these examples, model parameters might vary in space and time because of subsurface heterogeneity, transient hydrologic conditions, or variation in building operation. Thus, there is a need for characterizing spatial and temporal variability. Mathematical models provide opportunities to predict conditions that cannot be observed directly, but the reliability of the results need to be confirmed, especially when limited sitespecific data are available and the model is not calibrated to observed indoor air concentrations. Use of a generic, conservative attenuation factor (see Section 6.5.3) to predict potential, upperbound indoor air concentrations (based upon soil gas concentrations see Sections and 6.4.4) implicitly represents use of a mathematical model, even when the attenuation factor is selected from an empirical data set. Whether the mathematical model is implicit (e.g., generic, conservative attenuation factor) or explicit (e.g., mathematical model that generates a bounding estimate), both analytic approaches make the assumption that site-specific attenuation is likely to be greater and the indoor air concentration(s) is (are) likely to be lower than predicted value(s). The use of extreme and non-representative assumptions or parameter values is the most common weakness of mathematical modeling for environmental assessments. Mathematical modeling typically yields more reliable results when used with high-quality, site-specific data inputs (that is, representative groundwater or soil gas concentrations, depth to groundwater, soil type and moisture content underneath the building, and the building conditions (e.g., air exchange rate, building mixing height), for example); in these cases, the site-specific data inputs and CSM provide additional lines of evidence supporting the use of mathematical modeling as a line of evidence. Whenever mathematical modeling is used to make predictions pertaining to vapor intrusion, EPA recommends that the site planning and data team: Identify the underlying mathematical model and include appropriate references to document that it has been peer-reviewed. Verify that the selected model fits the CSM and is appropriate for the chosen purpose. Document all inputs and outputs in a readily recognizable and understandable format. Identify the critical parameters and conduct a sensitivity analysis for the most critical parameters. 115

221 Determine and document the appropriate modeling approach (e.g., calibration, uncertainty analysis, bounding case analysis). Perform new individual measurements (i.e., field sampling) to confirm one or more results of the modeling. A critical assumption underlying almost all mathematical models of vapor intrusion is that sitespecific subsurface characteristics will tend to reduce or attenuate soil gas concentrations as vapors migrate upward from the source and into overlying structures. Mathematical modeling of vapor intrusion is, therefore, not generally recommended for sites and buildings where unattenuated or enhanced transport of vapors toward and into a building is reasonably expected. Sections 5.4, 6.3.2, and identify several factors that may result in unattenuated or enhanced transport of vapors toward and into a building. 116

222 7.0 RISK ASSESSMENT AND MANAGEMENT FRAMEWORK This section provides general recommendations about risk-informed decision-making pertaining to vapor intrusion. The risk management information described herein presumes that a sound CSM has been developed (see Sections 5.4 and 6.3), which is supported by multiple lines of evidence, and that subsurface vapor sources have been characterized (see Section 6.3.1) sufficiently to support the risk management decisions for the site. EPA also notes that temporal and spatial variability of sampling data can span at least an order of magnitude and often more. Site-specific decisions potentially supported by the information described in this section include: Whether to install engineered exposure controls to prevent or reduce the impacts of vapor intrusion in specific buildings. Whether to remediate subsurface vapor sources for the site to reduce risks posed by vapor intrusion. Whether the vapor intrusion pathway is incomplete and there is no potential for unacceptable human exposure under current or future conditions. Whether to collect additional information as part of the detailed vapor intrusion investigation or monitor indoor air as part of an overall vapor intrusion remedy. As conditions warrant and resources allow, EPA generally recommends that officials responsible for overseeing cleanups pursuant to RCRA and CERCLA ensure that past decisions pertaining to vapor intrusion continue to be supported by current conditions (EPA 2002b). Finally, EPA encourages systematic approaches to decision-making, which can foster scientific rigor, consistency, and transparency. 7.1 Collect Site-specific Lines of Evidence Current practice suggests that the vapor intrusion pathway generally be assessed using multiple lines of evidence. As discussed in Sections 5.1, 5.4, 5.5.2, 6.3, 6.4, and 6.5, appropriate lines of evidence to support development of the CSM and evaluate the vapor intrusion pathway may include, but are not limited to: Subsurface Vapor Sources Site history and source of the contaminants to demonstrate that vapor-forming chemicals have been or may have been released to the underlying and surrounding subsurface environment and identify the type of vapor source (e.g., vapor-forming chemicals dissolved in groundwater or present in a NAPL). Groundwater data (generally recommended from more than one sampling event), as appropriate, to confirm the presence of a water-table aquifer, if present, as a source of vapors and establish its chemical and hydrogeologic characteristics. 117

223 Soil gas data, bulk soil sampling data, 189 and/or NAPL sampling data to confirm the presence of contamination in the vadose zone, if present, as a source of vapors and establish its chemical and physical characteristics. Sub-slab (or crawl space) soil gas data to assess concentrations potentially available for entry with any intruding soil gas (generally recommended from multiple sampling events and in multiple locations to reduce the chance of reaching a false-negative conclusion (i.e., concluding subsurface vapor source strength is limited when vapor intrusion actually poses an unacceptable human health risk) or a false-positive conclusion. Comparison of groundwater and/or soil gas concentrations to VISLs to evaluate source strength and potential for a health concern if the vapor intrusion pathway is complete. Vapor Migration and Attenuation in the Vadose Zone Soil gas survey data, including some level of vertical and spatial profiling, as appropriate, to confirm soil gas migration and attenuation along anticipated routes in the vadose zone between sources and buildings. Data on site geology and hydrology (e.g., soil moisture and porosity) to support the interpretation of soil gas profiles, the characterization of gas permeability, and the identification of anticipated soil gas migration routes in the vadose zone or the identification and characterization of impeded migration. Vertical profiles of chemical vapors, electron acceptors for microbial transformations (e.g., oxygen), and degradation products (e.g., methane, vinyl chloride) to characterize attenuation due to biochemical (e.g., biodegradation) processes. Utility corridor assessment to identify preferential migration routes, if any, that facilitate subsurface vapor migration between sources and towards and into buildings Building Foundation Assessment, Including Susceptibility to Soil Gas Entry Building construction and current conditions, including utility conduits or other preferential routes or openings for soil gas entry, heating and cooling systems in use, and any segmentation of ventilation and air handling. Instrumental (e.g., PID) readings to locate and identify potential openings for soil gas entry into buildings. 189 As noted in Section 6.4, bulk soil sampling and analysis can be used to characterize the chemical composition and general location of contamination; for example, high soil concentrations generally w ould indicate impacted soil. On the other hand, non-detect results for soil samples cannot be interpreted to indicate the absence of a subsurface vapor source, because of the potential for vapor loss due to volatilization during soil sampling, preservation, and chemical analysis. Therefore, bulk soil (as opposed to soil gas) sampling and analysis is not currently recommended for estimating the potential for vapor intrusion to pose unacceptable human health risk in indoor air. 118

224 Grab samples of soil gas or indoor air near openings to characterize the composition of presumptive soil gas entering buildings. Pressure data to assess the driving force for soil gas entry into building(s) via advection. Tracer-release data to verify openings in building foundations for soil gas entry or assess fresh air exchange within buildings. Interior Assessment Indoor air sampling data (Section 6.4.1) to assess the presence of subsurface contaminants in indoor air (Section 6.3.4), estimate potential exposure levels to building occupants to support site-specific human exposure and human health risk assessments (see Section 7.4), and otherwise diagnose vapor intrusion and characterize background concentrations (Section 6.3.5). 190 Indoor and Outdoor Sources of Vapor-forming Chemicals Found in the Subsurface Building-specific indoor sources of volatile chemicals (Section 2.7). Concurrent outdoor air data to assess potential contributions of ambient air to indoor air concentrations (Sections and 6.4.2). Comparative evaluations of indoor air and sub-slab soil gas data (e.g., Section 6.3.5), including calculation and comparison of building-specific, empirical attenuation factors (EPA 2012a, Section 3.0) (e.g., to assess their consistency among subsurface contaminants to assist in identifying indoor vapors arising from vapor intrusion). Additional Supporting Lines Results of statistical analyses (e.g., data trends, contaminant ratios) to support data interpretation. Results of mathematical modeling that rely upon site-specific inputs (Section 6.6). The relative utility of these and other individual lines of evidence will depend on site-specific factors, as described and documented in the CSM (Section 5.4), and the objectives of the investigation (Section 6.3). For example: When the primary subsurface vapor source is residual NAPL in the vadose zone, bulk soil data would typically be collected to characterize the chemical composition and general location of contamination; for example, high soil concentrations generally would 190 In certain cases, depending in part on the results (e.g., concentrations exceed risk-based screening levels), indoor air sampling data may be a sufficient basis for supporting decisions and recommendations to undertake pre-emptive mitigation (see Sections 3.3 and 7.8) in lieu of additional rounds of sampling and analysis or an evaluation of the contribution of background sources to indoor air concentrations. 119

225 indicate impacted soil in the vadose zone, as discussed in Sections and In this situation, near source soil gas data, rather than groundwater data, would be recommended for assessing the potential for vapor intrusion to pose an unacceptable human health risk to occupants of any building overlying the NAPL zone. On the other hand, when the subsurface vapor source underneath a building is shallow groundwater, groundwater sampling data from the uppermost hydrogeologic unit would be an appropriate line of evidence for purposes of assessing the potential for vapor intrusion to pose an unacceptable human health risk, unlike the previous example. In both of the preceding cases, information about the soil conditions (e.g., soil type and moisture) underlying the buildings would be useful for characterizing the subsurface vapor migration route between the subsurface vapor source and the building. Sub-slab soil gas samples and indoor air samples (if background sources are removed or accounted for), in concert with other lines of evidence, can provide a strong line of evidence regarding whether the vapor intrusion pathway is complete. For an industrial building, indoor air testing while the HVAC system is not operating (see Section 6.3.3) could be useful for diagnosing vapor intrusion. On the other hand, singlefamily detached homes can generally be presumed susceptible to soil gas entry when heating or cooling systems are operating. 7.2 Weigh and Assess Concordance Among the Lines of Evidence To the risk manager, the ideal outcome from collecting multiple lines of appropriate evidence is a concordant set of site-specific information that unambiguously supports decisions that can be made confidently. However, based upon observations at many buildings and sites, the vapor intrusion site where all available information is in agreement and is unambiguous may be the exception rather than the rule. Some lines of evidence may not be definitive (e.g., indoor air and subsurface concentrations can be greatly variable temporally and spatially). At worse, some individual lines of evidence may be inconsistent with other lines of evidence. In general, when lines of evidence are not concordant and the weight of evidence does not support a confident decision, EPA recommends re-evaluating the CSM, which may warrant adjusting the CSM to better represent the weight of the available evidence. For example, a building overlying contaminated shallow groundwater may have high concentrations of vapor-forming chemicals in the sub-slab soil gas samples, but lower concentrations in soil gas samples collected exterior to the building at intermediate depths. In this example, the exterior soil gas data suggest there may not be a connected vapor migration path between the groundwater source and the building that exhibits continuous attenuation along the path. Nevertheless, the data review team may conclude that vapor migration is capable of transporting hazardous vapors from the source to building(s) if the groundwater and sub-slab soil gas samples share common contaminants that are known or suspected to have been released at the site (for example, samples of both groundwater and 191 Because of the large uncertainties associated w ith measuring concentrations of volatile contaminants introduced during soil sampling, preservation, and chemical analysis, bulk soil (as opposed to soil gas) sampling and analysis is not currently recommended for estimating the potential for vapor intrusion to pose unacceptable human health risk in indoor air. In addition, there are uncertainties associated w ith soil partitioning calculations. 120

226 the sub-slab soil gas contain TCE). In this circumstance, the data review team may wish to consider whether the occurrence of a higher TCE concentration in the sub-slab soil gas than in the exterior soil gas sample(s) can be explained by: (1) a previously unknown or unrecognized utility corridor or other preferential migration route that provides relatively unattenuated vapor transport between the groundwater and the building; (2) a previously unknown or unrecognized source of TCE in the vadose zone; or (3) the possibility that the exterior soil gas samples were not well located for purposes of characterizing subsurface vapor migration. This example also underscores the importance of developing an adequate CSM (e.g., identify all sources and preferential routes of subsurface vapor migration) and illustrates why EPA generally recommends that the vapor intrusion pathway not be deemed incomplete based upon any single line of evidence (EPA 2010b), such as exterior soil gas in this example. When lines of evidence are not concordant and the weight of evidence does not support a confident decision, it may also be appropriate to collect additional lines of evidence, possibly including additional samples, depending upon the CSM. For example: Appropriate site-specific testing (see Section 6.3.5) can be conducted to assess the contribution of background sources of vapor-forming chemicals, including comparisons among chemicals of their relative concentrations in indoor air, outdoor air, and soil gas. Background sources of vapor-forming chemicals may help to explain situations where the indoor air concentration is higher than can be accounted for by the subsurface vapor source or the sub-slab soil gas data. Diagnostic testing of indoor air (see Section 6.4.1), building condition assessments or utility surveys, or supplemental hydrogeologic characterization (see Section 6.3.2) can be used to investigate the suspected presence of preferential migration routes, such as those described in Sections 5.4 and Such investigations may help to explain situations where the sub-slab or indoor air concentration appears to reflect unattenuated vapor transport from the subsurface vapor source. Building susceptibility to vapor intrusion can be tested (see Section 6.3.3), which may help to explain situations where the indoor air concentration is significantly lower than expected based upon the sub-slab soil gas data. Vapor migration in the vadose zone can be further characterized to identify impedances to vapor migration (see Section 6.3.2), appropriate semi-site specific attenuation factors can be considered (see Section 6.5.3), and appropriate modeling can be conducted (see Section 6.6) to investigate site-specific vapor attenuation. Such data and analyses may help to explain situations where the sub-slab soil gas concentration is significantly lower than expected based upon groundwater source or near-source soil gas concentrations and the respective medium-specific attenuation factor (Section and Appendix A). In some of these situations, the vapor intrusion pathway may be impeded, or perhaps even incomplete, due to geologic, hydrologic, or microbial characteristics in the vadose zone (see Sections and 7.3). Recognizing the temporal and spatial variability of indoor air and subsurface concentrations and the potentially episodic nature of vapor intrusion at some sites (Section 2), EPA generally recommends collecting multiple rounds of sampling in the respective media from multiple locations (see Section 6.4) to reduce the chance of reaching a false-negative or false-positive 121

227 conclusion. Considerable judgment may be necessary when evaluating multiple data sets from individual sampling events to support decision-making. In summary, EPA recommends the appropriate use and evaluation ( weighing ) of multiple lines of evidence for determining whether the vapor intrusion pathway is complete or not, whether any elevated levels of contaminants in indoor air are likely caused by subsurface vapor intrusion versus an indoor source or an ambient (outdoor) air source, whether concentrations of subsurface contaminants in indoor air may pose a health concern, and whether interim response measures to mitigate vapor intrusion are warranted. 7.3 Evaluate Whether the Vapor Intrusion Pathway is Complete or Incomplete For purposes of this Technical Guide, and as reflected in the conceptual model of vapor intrusion (see Section 2), the vapor intrusion pathway is referred to as complete for a specific building or collection of buildings when the following five conditions are met under current conditions: 1) A subsurface source of vapor-forming chemicals is present underneath or near the building(s) (see Sections 2.1, 5.3, 6.2.1, and 6.3.1); 2) Vapors form and have a route along which to migrate (be transported) toward the building(s) (see Sections 2.2 and 6.3.2); 3) The buildings are susceptible to soil gas entry, which means openings exist for the vapors to enter the building and driving forces exist to draw the vapors from the subsurface through the openings into the building(s) (see Sections 2.3 and 6.3.3); 4) One or more vapor-forming chemicals comprising the subsurface vapor source(s) is (or are) present in the indoor environment (see Sections and 6.4.1); and 5) The building is occupied by one or more individuals when the vapor-forming chemical(s) is (or are) present indoors. Considerable scientific and professional judgment will likely be needed when weighing lines of evidence to determine whether the vapor intrusion pathway is complete or incomplete. Each of the first four conditions generally entails obtaining and weighing multiple lines of evidence, whereas the fifth condition generally can be confidently determined by direct observation. EPA recommends considering and evaluating together the various lines of evidence in determining completeness of the vapor intrusion pathway under current conditions. As noted previously (e.g., Section 3.2), EPA recommends that risk management decisions also consider whether the vapor intrusion pathway is potentially complete under reasonably expected future conditions. The vapor intrusion pathway is referred to as potentially complete for a building when: a subsurface source of vapor-forming chemicals is present underneath or near an existing building or a building that is reasonably expected to be constructed in the future; vapors can form from this source(s) and have a route along which to migrate (be transported) toward the building; and 122

228 three additional conditions are reasonably expected to all be met in the future, which may not all be met currently; i.e., o the building is susceptible to soil gas entry, which means openings exist for the vapors to enter the building and driving forces exist to draw the vapors from the subsurface through the openings into the building; o one or more vapor-forming chemicals comprising the subsurface vapor source(s) is (or will be) present in the indoor environment (see Sections and 6.4.1); and o the building is or will be occupied by one or more individuals when the vaporforming chemical(s) is (or are) present indoors. This determination also generally entails obtaining and weighing multiple lines of evidence. A complete pathway indicates that there is an opportunity for human exposure, which warrants further analysis to determine whether there is a basis for undertaking a response action(s). Specifically, a complete exposure pathway does not necessarily mean that an unacceptable human health risk exists due to vapor intrusion. Rather, specific exposure conditions, such as the magnitude, frequency, and duration of exposures, and the contribution from background concentrations warrant examination; hence, EPA recommends additional analyses be conducted to assess and characterize human health risk to building occupants where the vapor intrusion pathway is determined to be complete (see, for example, Sections 7.4 and 6.3.5). On the other hand, human exposure, and hence human health risk, from the vapor intrusion pathway would not exist if the pathway is incomplete. The conceptual model described in Section 2 identifies the characteristics of the vadose zone that could render the vapor intrusion pathway incomplete under current and future conditions. These individual characteristics include, but are not limited to: Soil layers that significantly and persistently impede vapor transport due to geologic or hydrologic conditions (e.g., fine-grained soil, soil with high moisture content) and are laterally extensive over distances that are large compared to the size of the building(s) or the extent of subsurface contamination with vapor-forming chemicals; and A biologically active vadose zone that can significantly and persistently attenuate soil gas concentrations due to biodegradation, in which all appropriate conditions (e.g., nutrients, moisture, and electron acceptors, such as dissolved oxygen in the case of aerobic biodegradation) are readily available over a laterally extensive area. EPA recommends demonstrating these characteristics, when present, by collecting, evaluating, and documenting multiple lines of evidence, as identified in Section In addition, EPA recommends that any determination that the vapor intrusion pathway is incomplete be supported by site-specific evidence to demonstrate that: The nature and extent of vapor-forming chemical contamination in the subsurface has been well characterized, as discussed in Sections and 6.4. Ideally, where groundwater is the source of vapors, the plume has been shown to be stable or 123

229 shrinking to establish that the potential for vapor intrusion to pose a health concern will not increase in the future. The types of vapor sources and the conditions of the vadose zone and surrounding infrastructure do not present opportunities for unattenuated or enhanced transport of vapors toward and into any building (e.g., via a preferential migration route(s)), as discussed in Sections 5.4, 6.2.1, 6.3.2, and When the vapor intrusion pathway is determined to be incomplete, then vapor intrusion mitigation is not generally warranted under current conditions. EPA recommends that site managers also evaluate whether subsurface vapor sources that remain have the potential to pose a complete vapor intrusion pathway and unacceptable human health risk due to vapor intrusion in the future if site conditions were to change. For example, potentially unpredictable changes in the transitory soil characteristics (e.g., soil moisture) and soil gas concentrations may occur as a result of constructing a new building or supporting infrastructure. Either type of change could result in the potential for unacceptable human health risk due to vapor intrusion in the future. Response actions may, therefore, be warranted to protect human health wherever and as long as subsurface vapor sources remain that have the potential to pose unacceptable human health risk in the future due to vapor intrusion. These response actions (see Section 7.7) may include institutional controls (see Section 8.6) (e.g., to record and alert parties about the presence of subsurface vapor sources and/or to inform the need for a confirmatory vapor intrusion investigation in case infrastructure or geologic conditions are modified in the future). In addition, subsurface remediation may be warranted to protect human health or the environment via other exposure pathways (e.g., groundwater discharge to surface water bodies), consistent with applicable statutes and considering EPA guidance. 7.4 Conduct and Interpret Human Health Risk Assessment EPA generally recommends that a human health risk assessment be conducted to determine whether the potential human health risk posed to building occupants by a complete or potentially complete vapor intrusion pathway are within or exceed acceptable levels, consistent with applicable statutes 192 and considering EPA guidance (EPA 1991a, 2009c). The primary purpose of this risk assessment is to provide risk managers with an understanding of the actual and potential risks to human health posed by vapor intrusion under current and reasonably expected future conditions. This information may be useful in determining whether a current or potential future threat to human health exists, as described in Sections 7.4.1, 7.4.2, and 7.5.2, 193 which warrants response action(s), as described in Sections 7.7 and In the RCRA corrective action program, any human health risk assessment w ould typically be conducted during the RCRA facility investigation, if a release to the environment is identified. Under the CERCLA remedial program, a human health risk assessment w ould typically be conducted during the remedial investigation and is generally referred to as a baseline (i.e., pre-cleanup) risk assessment. 193 In appropriate circumstances (e.g., w here time is of the essence to ensure protection of human health; see, for example, Section 7.5.2), a formal human health risk assessment need not be completed and documented before taking a response action, but a preliminary evaluation of human health risk using individual building data or aggregated community data is generally recommended (also see Section 7.8). 124

230 The human health risk posed to building occupants by intrusion of a given vapor-forming chemical will depend upon its toxicity, its concentration in indoor air, the amount of time the occupants spend in the building, and other variables (e.g., human life stage (e.g., child) can matter for some chemicals (e.g., those with a mutagenic mode of action for carcinogenicity)). EPA recommends that its risk assessment guidance (e.g., EPA 2009c, EPA 2003) be used to identify, develop, and combine information about these variables and characterize human health risk due to vapor intrusion from subsurface contaminant sources. For the vapor intrusion pathway, the inhalation route is the primary means of human exposure. Therefore, the human health risk assessment uses estimates of indoor air exposure concentrations, exposure duration and frequency for building occupants, and the potential toxicity of the vapor-forming chemicals found in the subsurface (e.g., inhalation unit risk and noncancer reference concentration) to characterize risks of cancer and noncancer effects (EPA 2009c). Generally, exposure concentrations in existing buildings can be estimated using direct measurements of indoor air (see Sections and 6.4.1). EPA recommends that timeintegrated measurements from multiple sampling events be used to estimate exposure concentrations appropriate for the exposure (occupancy) scenario being evaluated (e.g., residential versus commercial), when the risk assessment for an existing building would support a conclusion that the human health risk is acceptable (see Section 7.4.1). 194,195 Generally, modeling would be used to conservatively estimate exposure concentrations under future conditions in buildings yet to be constructed in areas with subsurface contamination by vaporforming chemicals (see Section 6.6). EPA recommends the noncancer assessment consider the potential for adverse health effects from short-duration inhalation exposures (i.e., acute, shortterm, or subchronic exposure durations), 196 as well as longer term inhalation exposure (i.e., chronic exposure) conditions. EPA recommends that inhalation toxicity values be selected 194 An individual sample, collected at a randomly chosen time, may under-estimate (or over-estimate) average and reasonable maximum exposure conditions. From their high-frequency, measured data, Holton et al. formulated a synthetic data set (simulating one-day-average concentrations), w hich they used to estimate that a single, randomly draw n, one-day sample had a forty percent chance of being less than the true mean (Holton et al. 2013b; see Table 1 therein). When the true mean w as assumed to exceed the risk-based action level ( target concentration in their parlance) by tw o or five times, they estimated that a single, randomly draw n, one-day sample had a tw enty percent or six percent chance, respectively, of not detecting the exceedance. These data support EPA s recommendation to collect multiple rounds of indoor air sampling data to reduce the chance of reaching a false-negative conclusion (i.e., concluding exposure is at an acceptable risk level w hen it is not). Collecting multiple rounds of indoor air sampling can also reduce the chance of reaching a false-positive conclusion (i.e., concluding that vapor intrusion poses unacceptable human health risk w hen it does not), because an individual sample, collected at a randomly chosen time, may over-estimate the average and reasonable maximum exposure conditions. 195 Given EPA s assigned mission to protect human health from environmental contamination and recognizing the disruption to building ow ners and occupants caused by indoor air sampling, risk managers may choose to pursue pre-emptive mitigation (i.e., early action) at some buildings (see Sections 3.3 and 7.8) rather than, for example, conduct multiple rounds of sampling over a few years to establish an estimate of long-term average exposure concentration and characterize temporal variability. 196 The inhalation reference concentration (Rf C) (expressed in units of mass concentration in air) is defined as an estimate (w ith uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be w ithout an appreciable risk of deleterious effects during a lifetime. Reference values may be derived for acute ( 24 hours), short-term (>24 hours, up to 30 days), subchronic (>30 days, up to approximately 10% of the life span), and chronic (greater than 10% of the life span) exposure durations, all of w hich are derived based on an assumption of continuous exposure throughout the duration specified. See ww.epa.gov/ncea/iris/help_ques.htm#w hatiris 125

231 considering OSWER s hierarchy of sources (EPA 2003) and that relevant existing guidance (e.g., EPA 2009c) be followed in situations where a desired toxicity value is not available. When a single vapor-forming chemical is present in the subsurface and intrudes as a vapor into occupied building spaces, the noncancer human health risk can be characterized by calculating the noncancer hazard quotient (HQ) (EPA 2009c,Chapter 8). When multiple vapor-forming chemicals are present in the subsurface and intrude as vapors into occupied building spaces, the HQ estimates for each chemical are aggregated (as a simple sum, which is the Hazard Index (HI)), based upon the assumption that each chemical acts independently (i.e., there are no synergistic or antagonistic toxicity interactions among the chemicals). If the HI exceeds one, there may be concern for potential adverse non-cancer effects and risk assessors should consider segregating the chemicals by target organ or toxic effect to derive separate hazard index (HI) values for each (EPA 2009c, Chapter 8). EPA recommends that noncancer HQ and HI values be estimated for each type of exposure period identified in the conceptual site model or indicated by measurements of indoor air levels of vapor-forming chemicals (e.g., chronic, subchronic, short-term, acute), evaluating inhalation reference concentrations that match the characterization of the exposure scenario (EPA 2009c, Chapter 4). 197 The carcinogenic risks can be characterized by calculating the excess cancer risk over a lifetime (LCR) and, if multiple vapor-forming chemicals are present, aggregating the LCR estimates for each carcinogen (as a simple sum), based upon the assumption that each chemical acts independently (EPA 2009c, Chapter 8). A well-crafted risk characterization section (EPA 1992c, 1995ab, 2000b, 2009c) puts risk calculations into context for risk managers, so that they may effectively weigh and interpret risk assessment results and recognize key uncertainties (e.g., in the exposure and dose-response assessments and risk estimation). 198 Additional recommendations for promoting and increasing the utility and transparency of human health risk assessments can be found in Framework for Human Health Risk Assessment to Inform Decision Making (EPA-RAF, 2014). 197 For example, w hen evaluating situations in w hich vapor concentrations in indoor air exceed the chronic reference concentration (see Section 7.4.1), and there are shorter periods of significantly higher vapor intrusion exposure, EPA recommends that noncancer risks for the shorter periods also be characterized using toxicity values appropriate for the respective period(s). On the other hand, if vapor concentrations in indoor air are consistently less than benchmarks for acceptable chronic exposure, then exposures for less-than-chronic scenarios are unlikely to pose unacceptable human health risk. 198 For example, EPA recommends that the risk characterization for existing buildings describe the uncertainty in the exposure assessment arising from: (i) inherent variability of indoor air exposures over time and space; (ii) the match betw een the sampling data [e.g., sampling frequency (i.e., number of samples and time intervals betw een samples); and time period over w hich each sample w as collected] and the exposure period represented by the selected toxicity value (e.g., chronic); and (iii) the ability to distinguish and apportion the contribution to indoor air concentrations arising from vapor intrusion versus background sources. EPA recommends that the risk characterization for future buildings describe the principal uncertainties in the exposure assessment, w hich may be associated w ith the type(s) of building use, building construction and operations (e.g., HVAC system), frequency and duration of occupancy, vapor concentrations in indoor air, or other factors. 126

232 EPA recommends that any human health risk assessment be documented; a summary in a decision document is also generally warranted. 199 EPA also recommends that human health risk information for individual buildings be communicated to building occupant(s) and owners. Section 9.4 provides additional information for communicating sampling results Risk Management Benchmarks EPA recommends that OSWER programs make the risk management determination to take response action consistent with their statutes and regulations and considering existing program guidance. 200 The carcinogenic risk and non-cancer HI values used in this determination generally are the cumulative risks that include all exposure pathways that a given population may consistently face. 201 In making such risk management determinations, EPA generally recommends reporting the HQ and HI to one significant figure. EPA generally uses a cancer risk range of 10-6 to 10-4 as a target range within which to manage human health risk as part of site cleanup. For judging whether indoor air exposures may pose acceptable health risk based upon potential non-cancer effects, EPA generally recommends that the target HQ or HI not exceed 1. Once a decision has been made to undertake a response action, EPA has expressed a preference for cleanups that are at the more protective end of the cancer risk range. Thus, EPA recommends using an individual lifetime cancer risk of 10-6 as a point of departure for establishing cleanup levels based upon potential cancer effects (see Section 7.6). 202 The EPA risk manager may determine that a response action achieving reductions in human health risk 199 Devices that have been found to improve comprehension and retention of textual materials include a table of contents, clear section headings, and a summary (Morgan et al. 1992). It is most helpful to provide a summary that translates the risk assessment into relatively simple language that non-expert risk managers, stakeholders, and w ider audiences can understand (Lundgren and McMakin, 2013). Hazards and risks posed by vapor intrusion are more likely to be misunderstood or misinterpreted if they are not explained in simple terms. 200 See, for example: The Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions, OSWER Directive , April 22, 1991 (EPA 1991a); Rules of Thumb for Superfund Remedy Selection, OSWER Directive , August 1997 (EPA 1997); and Advanced Notice of Proposed Rulemaking: Corrective Action for Solid Waste Management Units at Hazardous Waste Management Facilities (61 Federal Register 19432, May 1, 1996). So, for example, EPA cited OSWER Directive (EPA 1991a) in its Compilation of Information Relating to Early/Interim Actions at Superfund Sites and the TCE IRIS Assessment (EPA 2014b). 201 In some site-specific situations, a population might be exposed to a substance or combination of substances through several exposure pathw ays (i.e., not only the vapor intrusion pathw ay). For example, individuals might be exposed to substance(s) from a contaminated site by consuming contaminated drinking w ater from a groundw ater supply, as w ell as from vapor intrusion. Once reasonably expected exposure pathw ays have been identified, EPA recommends examining w hether it is likely that the same individuals w ould consistently face the reasonable maximum exposure for each pathw ay or a combination of some of these pathw ays. Under such circumstances, the total exposure to each chemical w ould equal the sum of the exposures by all consistently faced pathw ays (EPA 1989, Section 8.3) and EPA recommends that the risk assessor clearly identify those exposure pathw ay combinations for w hich a total risk estimate or hazard index is being developed. When characterizing human health risk arising from multiple pathw ays and posed by a vapor-forming chemical(s) w ith potential adverse noncancer effects, EPA recommends that the toxicity values for each pathw ay match the characterization of the exposure scenario (EPA 2009c, Chapter 4). 202 See: National Oil and Hazardous Substances Pollution Contingency Plan (55 Federal Register 8717); and Advanced Notice of Proposed Rulemaking: Corrective Action for Solid Waste Management Units at Hazardous Waste Management Facilities (61 Federal Register 19432, May 1, 1996). 127

233 within the 10-6 to 10-4 cancer risk range is acceptable, however, depending on site-specific conditions or remedial factors. For establishing cleanup levels based upon potential non-cancer effects, EPA generally recommends that the target HI not exceed 1 (see Section 7.6) Accounting for Background Contributions As noted previously, EPA recommends including in the human health risk assessment vaporforming chemicals that are related to releases to the subsurface environment. Some of these vapor-forming chemicals may be present in indoor air due to background sources (see Section 2.7). If data are available, EPA recommends that the contribution of background to total exposure concentration(s) be distinguished in the human health risk assessment (EPA 2002e). If background vapor sources (see Glossary) are found to be primarily responsible for indoor air concentrations (see Section 6.3.5), then response actions for vapor intrusion would generally not be warranted for current conditions. In any event, EPA recommends that the risk characterization include a discussion of background contributions to indoor air exposure and associated human health risk. With such information, EPA can help advise affected individuals about the environmental and public health risks they face that are within their control (e.g., indoor sources of vapor-forming chemicals in residences). 203 Other parties, including building owners and operators, may help with risk communication. If background contributions are unknown and such data are sought to support risk management decisions, EPA recommends that additional data be collected (see, for example, Section 6.3.5). Information on background contributions of site-related, vapor-forming chemicals in indoor air is also important to risk managers because generally EPA does not clean up to concentrations below natural or anthropogenic background levels (EPA 2002e) Occupational Exposure Limits Permissible exposure limits (PELs) are enforceable occupational exposure standards developed by the Occupational Safety and Health Administration (OSHA) in the U.S. Department of Labor. Most of OSHA s PELs were adopted in 1971 from then-existing secondary guidance levels, such as Threshold Limit Values (TLVs) developed by the American Conference of Governmental Industrial Hygienists (ACGIH) to protect workers from adverse effects of occupational exposure to airborne chemicals. They were intended to protect workers against catastrophic effects (such as cardiovascular, liver, kidney, and lung damage), as well as more subtle effects (such as narcosis, central liver system damage, and sensory irritation). PELs (and TLVs), however, are not intended to protect sensitive workers, may not incorporate the most recent toxicological data, and may differ from EPA derivations of toxicity values with respect to weight-of-evidence considerations and use of uncertainty factors. For these and other 203 In cases w here background contamination (e.g., due to indoor use of a consumer product or household chemical in a residence) may pose a human health risk, but its remediation is beyond the authority of the applicable statute, risk communication to the public may be most effective w hen coordinated w ith public health agencies (EPA 2002e). 128

234 reasons, 204 EPA does not recommend using OSHA s PELs (or TLVs) for purposes of assessing human health risk posed to workers (EPA 1991c, Appendix C) by the vapor intrusion pathway or supporting final no-further-action determinations for vapor intrusion arising in nonresidential buildings. Rather, EPA s recommendations for assessing human health risk posed by vapor intrusion are set forth herein in Sections and Concentration Levels Indicating Potential Need for Prompt Response Action In some circumstances, human health risk arises from vapor intrusion, which warrants prompt response action. This Section provides some recommendations for identifying such circumstances Potential Explosion Hazards EPA recommends using the chemical-specific LELs 205 to identify potential explosion hazards (e.g., for methane and other petroleum hydrocarbons). Whenever building-specific data (such as results from sub-slab soil gas samples and crawl space samples for any building type, indoor air samples from sheds or pump houses, or gas samples from confined or semi-confined spaces (e.g., sewers)) exceed one-tenth (10%) of the LEL for any chemical, a hazard is indicated that generally warrants prompt action. 206,207 EPA recommends to building owners and occupants the evacuation of buildings with potential explosion and fire hazards, along with immediate notification to the local fire department about the threat. Construction and operation of engineered systems that can reduce or eliminate intrusion of explosive vapors into existing buildings or unoccupied structures may also warrant consideration to reduce the potential for future explosion hazards Considering Short-term and Acute Exposures EPA may identify health-protective concentration levels for vapor-forming chemicals based upon potential noncancer health effects that can be posed by air exposures over short-term or acute exposure durations, considering EPA guidance for human health risk assessment (e.g., EPA 204 OSHA s w ebsite (May 2015) currently states: OSHA recognizes that many of its permissible exposure limits (PELs) are outdated and inadequate for ensuring protection of w orker health. Most of OSHA s PELs w ere issued shortly after adoption of the Occupational Safety and Health (OSH) Act in 1970, and have not been updated since that time. Since 1970, OSHA promulgated new PELs for 16 agents, and standards w ithout PELs for 13 carcinogens. Industrial experience, new developments in technology, and scientific data clearly indicate that in many instances these adopted limits are [also] not sufficiently protective of w orker health. This has been demonstrated by the reduction in allow able exposure limits recommended by many technical, professional, industrial, and government organizations, both inside and outside the United States. [On-line source: ww.osha.gov/dsg/annotated-pels/] On October 10, 2014, OSHA issued a Chemical Management Request for Information (79 FR 61384), in w hich it acknow ledges many of its PELs are not sufficiently protective and seeks comment on strategies to address this problem; available on-line at: ww.osha.gov/fedreg_osha_pdf/fed pdf 205 The Vapor Intrusion Screening Level Calculator (EPA 2015a) provides LELs for vapor-forming chemicals to facilitate identification of potential explosion hazards. 206 NIOSH has designated such concentrations as immediately dangerous to life or health (IDLH). 207 Although the building-specific data may vary temporally, any short-term exceedance of one-tenth of the LEL indicates vapor concentrations that, given an ignition source and available oxygen, may be capable of causing an explosion. 129

235 2009c) and using sources of toxicity information considering OSWER s hierarchy (EPA 2003). For example, subchronic reference concentrations, developed by the EPA Office of Research and Development/National Center for Environmental Assessment/ Superfund Health Risk Technical Support Center (STSC), are currently available for some vapor-forming chemicals as Provisional Peer Reviewed Toxicity Values (PPRTVs), which are designated as a Tier 2 source of toxicity values by OSWER (EPA 2003). Acute and intermediate Minimal Risk Levels (MRLs) 208 adopted by the Agency for Toxic Substances and Disease Registry (ATSDR) are currently available for some vapor-forming chemicals and are designated as a Tier 3 source of toxicity values by OSWER (EPA 2003). PPRTVs and ATSDR MRLs are peer reviewed and are publicly available (see, and Historically, toxicity values for short-term or acute exposure durations have not been derived or published in EPA s IRIS, which otherwise is EPA s preferred source of toxicity values (EPA 2003). EPA, under its authority, will work to develop expanded science policy direction to address short-term exposures and develop and identify appropriate toxicity values for additional chemicals for consideration for vapor intrusion assessment and related OSWER regulatory frameworks. EPA recommends that relevant existing guidance (e.g., EPA 2009c) be followed in situations where a desired toxicity value is not available, using sources of toxicity information considering OSWER s hierarchy (EPA 2003). Although the indoor air concentrations may vary temporally, an appropriate exposure concentration estimate (e.g., time-integrated or time-averaged indoor air concentration measurement in an occupied space see Section 6.4.1) that exceeds the health-protective concentration levels for acute or short-term exposure (i.e., generally considered to be a hazard quotient (HQ) greater than one for an acute or short-term exposure period) 209 indicates vapor concentrations that are generally considered to pose an unacceptable human health risk. 210 As noted in Section 7.4 of this Technical Guide, a well-crafted risk characterization section (EPA 1992c, 1995ab, 2000b, 2009c) puts risk calculations into context for risk managers, so that they may effectively weigh and interpret risk assessment results and recognize key uncertainties (e.g., in the exposure and dose-response assessments and risk estimation). Uncertainties include the derivation of an RfC, which is defined as an estimate (with uncertainty spanning perhaps an order of magnitude) (See Sections 3.3 and 7.7 identify other EPA-recommended considerations for risk managers. When indoor air concentrations in an occupied space exceed health-protective concentration levels for short-term or acute inhalation exposures arising from a complete vapor intrusion 208 Minimal Risk Levels (MRLs) published by ATSDR are estimates of the daily human exposure to a hazardous substance that is likely to be w ithout appreciable risk of adverse non-cancer health effects over a specified duration of exposure. The ATSDR MRLs are peer review ed and are publicly available ( w w.atsdr.cdc.gov/mrls.html). 209 See Glossary for definitions of acute and short-term exposure durations. 210 See, for example: The Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions, OSWER Directive , April 22, 1991 (EPA 1991a); and Rules of Thumb for Superfund Remedy Selection, OSWER Directive , August 1997 (EPA 1997). In addition, the NCP states For systemic toxicants, acceptable exposure levels shall represent concentration levels to w hich the human population, including sensitive subgroups, may be exposed w ithout adverse effect during a lifetime or part of a lifetime, incorporating an adequate margin of safety [40 CFR (e)(2)(i)(1)]. 130

236 pathway, ventilation, indoor air treatment, temporary relocation, and other response actions may be implemented to reduce or avoid these threats promptly (see Section 8.2.1). Construction and operation of engineered systems that can reduce or eliminate vapor intrusion into existing buildings (see Section 8.2) may also warrant consideration after urgent threats to human health have been addressed. 7.6 Risk-based Cleanup Levels When response action is determined to be warranted to reduce or eliminate indoor air exposures from vapor intrusion (see Sections 7.4 and 7.5), EPA recommends that cleanup levels be established and documented consistent with statutes and regulations and considering guidance for the respective OSWER program. 211 These cleanup levels would be used to evaluate when building mitigation measures, subsurface remediation, and associated monitoring can be terminated and to assess cleanup progress in the meantime (see Section 8.7). Candidate risk-based cleanup levels can be calculated using information from the risk assessment (Section 7.4). Results of the human health risk assessment indicate, for example, which site-related vapor-forming chemicals warrant building mitigation and subsurface remediation. The exposure factors and toxicity values used in the human health risk assessment can be used to calculate chemical-specific cleanup levels, considering EPA risk assessment methods (e.g., EPA 2009c, EPA 2003). Candidate cleanup levels are usually developed for potential cancer and non-cancer effects. The lower (or lowest if there are multiple potential non-cancer effects) of the candidate values, based upon cancer risk and non-cancer HQ/HI targets, is generally recommended for selection as the cleanup level (EPA 1991c, Section 3.4 therein). 212 The VISL Calculator ( can be used to support these calculations, including input of alternative attenuation factor(s) based upon site- or buildingspecific information. Calculating candidate cleanup levels based upon potential cancer effects entails selecting a target cancer risk. As noted above (Section 7.4.1), once a decision has been made to undertake a response action, EPA has expressed a preference for cleanups achieving the lower end of the cancer risk range (i.e., 10-6 ) (EPA 1991a). Response actions achieving reductions in human health risk anywhere within the cancer risk range may be deemed acceptable by the EPA risk manager, however. To protect human health from potential noncancer effects, EPA generally recommends using a target value of one for the non-cancer HQ (if there is a single vapor-forming chemical of health concern for vapor intrusion) or for the non-cancer HI (if there are multiple vapor-forming chemicals of health concern for vapor intrusion acting by a common effect). 211 See, for example: RCRA Corrective Action Plan (Final), OSWER Directive A (EPA 1994); and A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents, OSWER Directive P (EPA 1999b). 212 An exception arises w hen background sources pose elevated exposures, because generally EPA does not clean up to concentrations below natural or anthropogenic background levels (EPA 2002e). 131

237 Cleanup levels for indoor air can be readily calculated, as described above, without additional assumptions or modeling about vapor intrusion processes. On the other hand, cleanup levels for groundwater and/or soil gas in the vadose zone will entail developing a medium-specific vapor attenuation factor, which EPA recommends be conservatively estimated based upon sitespecific information. The cleanup level for soil gas can be calculated by dividing the chemicalspecific indoor air cleanup level by the site-specific soil gas vapor attenuation factor. The cleanup level for groundwater can be calculated by dividing the chemical-specific indoor air cleanup level by the site-specific vapor attenuation factor for groundwater vapors and assuming equilibrium between the aqueous and vapor phases at the groundwater table. EPA recommends that site-specific attenuation factors intended to be protective of chronic exposure conditions: be conservatively estimated when based upon mathematical models; and be based upon multiple measurements of indoor air concentration in different seasons, which have negligible influences from background sources, when based upon site-specific measurements. EPA recommends that cleanup levels be documented with at most two significant figures, even though some of the input values may carry additional significant figures (EPA 1991b, see page 19). 7.7 Options for Response Action When response action is determined to be warranted to reduce or eliminate indoor air exposures from vapor intrusion (see Sections 7.4 and 7.5), EPA recommends that OSWER programs select, recommend, and document response action(s) consistent with statutes and regulations and considering their existing program guidance. 213 The selection of a health-protective interim response action(s) for existing buildings will generally depend on site-specific considerations, which can include: nature of subsurface vapor source (e.g., groundwater, vadose zone soils, sewer lines), magnitude of the exposure above cleanup levels; the severity of the potential adverse health effects or health hazard; building features and conditions (e.g., construction; heating, ventilation, and air conditioning equipment); climate and season (which influence the feasibility of ventilation, for example); the quality of ambient air in the vicinity; and the feasibility of implementing a given option quickly. 214 In general, EPA recommends that response actions limit the amount of time individuals are exposed to concentrations that correspond to unacceptable human health risk, as described in Sections 7.4 and See, for example: RCRA Corrective Action Plan (Final), OSWER Directive A (EPA 1994); and A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents, OSWER Directive P (EPA 1999b). 214 Most response actions cannot be implemented immediately upon determining that a response is w arranted. For example, engineered exposure controls ordinarily entail from tw o to four w eeks of lead time (at a minimum) for planning, design, any permit acquisition, material acquisition and construction. In many circumstances, ventilation measures to reduce exposure can be implemented more quickly, but local climate or air quality may render this option less attractive during some seasons. 132

238 TABLE 7-1 MATRIX OF OPTIONS TO RESPOND TO HUMAN HEALTH RISK POSED BY THE VAPOR INTRUSION PATHWAY Option for Response Action Applicability of Response Action for Common Sources of Sub-surface Vapors Groundwater Vadose Zone Soil Sewer & Drain Lines Remediation of Source* Removal of contaminated soil via excavation Treatment of contaminated soil in situ Treatment of contaminated groundw ater in situ Removal of contaminated groundw ater (e.g., pump-and-treat) Decontaminating and/or rehabilitating sew er and drain lines # # Interim Measures to Reduce or Eliminate Vapor Intrusion* Subslab de-pressurization and ventilation systems Sealing major openings for soil gas entry, w here know n and identified + Building over-pressurization Installing, repairing, or maintaining vapor traps Interim Measures to Reduce or Avoid Exposure to Vapors Notification to local fire department about potential explosion hazards + Notification and risk communication to building occupants and ow ners, including institutional controls (e.g., deed notices) Increasing building ventilation* Treating indoor air* Temporary relocation + Monitoring Indoor Air to Characterize Human Exposure KEY: designates potentially appropriate response action for indicated vapor source FOOTNOTES: * includes: associated institutional controls to maintain operations and provide public notification of residual contamination; and associated monitoring to assess effectiveness and protectiveness of the response action # remediation of soil may also be w arranted for purposes of protecting groundw ater from further contamination, even if contaminated soil in the vadose zone is not a source for vapor intrusion directly (e.g., due to the absence of an existing building near the contaminated soil) + response option primarily applies to existing buildings 133

239 Table 7-1 presents an overview of key candidate response options for the vapor intrusion pathway, which are discussed further in Section 8. Response actions that may be recommended for and implemented in existing buildings include: Interim measures that can be implemented relatively quickly (see Section 8.2.1), if prompt action is warranted to reduce or eliminate exposures to vapor-forming chemicals (see Sections 5.2 and 7.5.2) or to mitigate explosion hazards (see Section 7.5.1); Engineered exposure controls (see Section 8.2.2) with associated monitoring and institutional controls (see Section 8.6), as an interim (but potentially long-term) measure to reduce or eliminate vapor intrusion into buildings; and Remediation of the subsurface vapor source (see Section 8.1) with associated monitoring and institutional controls (see Section 8.6). Response actions that may be warranted in buildings that may be constructed in the future include: Remediation of the subsurface vapor source (see Section 8.1) with associated monitoring and institutional controls (see Section 8.6); and Institutional controls (see Section 8.6) to inform the need for building mitigation (see Section 8.2.2) and/or a confirmatory vapor intrusion investigation before the building is occupied, in case the building is to be or may be constructed before subsurface vapor sources are remediated to cleanup levels. Indoor air monitoring has frequently been selected as a response action in circumstances where subsurface vapor sources are present and the vapor intrusion pathway has not been shown to be incomplete. Indoor air monitoring may be deemed warranted, for example: To better characterize spatial or temporal variability; To address uncertainty in the characterization of the vapor intrusion pathway when subsurface vapor sources have the potential to pose a health concern in overlying or nearby buildings (e.g., incomplete pathway characterization, concern about the potential for changes in building conditions, discordant lines of evidence); or For other site-specific or situation-specific reasons. EPA generally prefers to obtain building access and undertake response actions through consent and cooperation from building owners, tenants, and other stakeholders (see Section 1.2). 7.8 Pre-emptive Mitigation/Early Action It may be appropriate to implement mitigation of the vapor intrusion pathway as an early action, even though all pertinent lines of evidence have not yet been completely developed to characterize the vapor intrusion pathway for the subject building(s), when sufficient site-specific data indicate that vapor intrusion: (1) is occurring or may occur due to subsurface contamination that is being addressed by federal statutes, regulations, or guidance for environmental protection; and (2) is posing or may pose a health concern to occupants of an existing 134

240 building(s). Likewise, it may be appropriate and cost-effective to design, install, operate, and monitor mitigation systems (including passive barrier systems) in newly constructed buildings (or buildings planned for future construction) that are located in areas of vapor-forming subsurface contamination, rather than allow vapor intrusion (if any) to occur and address vapor intrusion after the fact. As described in Section 3.3, preemptive mitigation/early action is the term used to describe both situations. Preemptive mitigation (PEM) is recognized as an early action that is intended to ensure protectiveness of human health. In this context and as described further in Section 8.2, mitigation refers to methods that seek to: Prevent or reduce vapor entry into a building. Reduce or eliminate vapors that have entered a building. Note that the selection and implementation of PEM, when it occurs, is not necessarily intended to pre-judge final decisions about remediation of subsurface vapor sources; however, EPA generally recommends that decision-making about PEM include a consideration of the O&M and monitoring obligations. In addition, EPA recommends that the selection of PEM be based upon data and information in the administrative record and be documented in the administrative record, consistent with statutes and regulations and considering EPA guidance for the respective land restoration program (e.g., CERCLA, RCRA corrective action, brownfields, etc.), in order to provide an adequate basis for actions undertaken Rationale In ensuring protectiveness of human health, PEM generally may be an appropriate approach to consider for buildings with potential vapor intrusion for a number of reasons, including: Building mitigation typically is an effective means of protecting human health and is cost effective for many buildings. The potential exposure scenario (e.g., inhalation of potentially toxic vapors) cannot generally be readily avoided by building occupants. Involuntary and unavoidable exposures and hazards are generally sources of anxiety and concern for affected building occupants and the general public, particularly when they occur in homes and in the workplace. Comprehensive subsurface characterization and investigations of vapor intrusion (to conclusively characterize unacceptable, but variable, levels of vapor-forming chemicals in soil, groundwater, and indoor air, as described in Section 6) can entail prolonged study periods, during which building occupants may be exposed and owners and environmental stewardship groups may remain anxious and concerned about potential indoor air exposures to subsurface vapors in the absence of mitigation. Conventional vapor intrusion investigations in and of themselves can be disruptive, particularly when indoor access is sought to acquire interior samples and assess interior building conditions. 135

241 Mitigation can typically be implemented relatively quickly, while subsurface contamination is being more fully delineated or remediated. EPA s experience with residential communities suggests that many affected residents seek and prefer that mitigation systems be installed when vapor intrusion is suspected. Mitigation can be a cost-effective approach to help ensure protectiveness of human health during ongoing vapor intrusion investigations to acquire multiple lines of evidence and characterize spatial and temporal variability in subsurface and indoor air concentrations, as well as while subsurface remediation is being planned and conducted to reduce or eliminate subsurface vapor sources. In summary, PEM, based on limited but credible subsurface and building data, can be an appropriate approach to begin to implement response actions quickly and ensure protectiveness of current building occupants. In such circumstances, resources can be used appropriately to focus first on mitigation of buildings and subsurface remediation, rather than site and building characterization efforts, which may be prolonged. Although PEM may be an effective tool to reduce the human exposure and human health risk, building mitigation is not generally intended to address the subsurface vapor source; as such, EPA recommends that it typically be used in conjunction with remediation of the subsurface source of vapor-forming chemicals (e.g., source removal or treatment), as discussed in Section General Decision Framework To consider PEM, EPA recommends that reliable data supporting a preliminary analysis, as described in Section 5.0, and risk-based screening, as described in Section 6.5, be obtained and documented in the administrative record. In appropriate circumstances (e.g., where time is of the essence to ensure protection of human health; see, for example, Section 7.5.2), a formal human health risk assessment need not be conducted and documented before selecting PEM, but a preliminary evaluation of human health risk using individual building data or aggregated community data is generally recommended. If there are insufficient data to perform a preliminary risk analysis, but subsurface vapor sources are known to be present near buildings (see Section 5.3), EPA recommends that an appropriate vapor intrusion investigation (see Section 6) be conducted to obtain sufficient data. EPA generally recommends that the decision to undertake building mitigation be supported by appropriate lines of site- or building-specific evidence (e.g., characterization of subsurface vapor source(s) strength and proximity to building(s); building conditions) that demonstrate that vapor intrusion has the potential to pose an unacceptable human health risk. Sections 5, 6, and 7 herein provide information about the types of evidence obtained and relied upon in assessing vapor intrusion potential and the types of analyses that can support determinations of whether the vapor intrusion pathway is complete for a specific building or collection of buildings and poses or has the potential to pose a health concern to building occupants. This information is equally pertinent for supporting final remediation and mitigation decisions and for supporting PEM consistent with applicable statutes and regulations. The premise of PEM, however, is to protect human health first without necessarily waiting to collect all lines of pertinent evidence or multiple rounds of sampling data. 136

242 Certain types of subsurface conditions may have greater potential to facilitate vapor intrusion when subsurface sources of vapors are present. These conditions include, but are not limited to: Shallow aquifers (for example, five feet or less from the building foundation to the seasonal high water table). High-permeability (e.g., gravelly) vadose zone soils that are fairly dry, which are favorable to upward migration of gases. Preferential migration routes, such as fractured sediments or bedrock, buried streambeds, subsurface drains, and utility conduits, as they can facilitate vertical or lateral migration of vapor with limited attenuation of chemical concentrations. Under these conditions, it may be easier to determine that PEM may be warranted if a structure is located near a subsurface vapor source that has the potential to pose an unacceptable human health risk. Other factors to consider include the following: Susceptibility to soil gas entry. Some buildings have greater potential for vapor intrusion (i.e., are more susceptible to soil gas entry; see Section 2.3) than others. For example, buildings with deteriorating basements or dirt floors generally provide poor barriers to vapor (soil gas) entry. Buildings with sumps or other openings to the subsurface that can facilitate soil gas entry are also more susceptible to vapor intrusion. Actions undertaken or planned to address the subsurface source of vapors. For example, if the source of vapors (e.g., contaminated soil in the vadose zone) is being removed (e.g., excavation of contaminated soil or soil vapor extraction underneath the building) or is to be removed within a time frame that is protective for any potential current or near-term exposures in the overlying or nearby building, then PEM may not be warranted Some General Scenarios Where Pre-emptive Mitigation May be Warranted Three general scenarios where PEM may be warranted are summarized below. The first two scenarios address situations where building(s) currently exist, while the third scenario addresses a situation where building(s) may be constructed in the future. Site with High Potential to Facilitate Vapor Intrusion. In this scenario, indoor air concentration data have not been collected, but other lines of evidence support a conclusion that the vapor intrusion pathway is likely complete and may pose an unacceptable human health risk. Figure 7-1 shows a hypothetical residential area located near a shopping center that contains an active dry-cleaning facility. In this hypothetical example, a sufficient number of appropriately screened monitoring wells have been installed throughout the neighborhood to characterize a historical groundwater plume emanating from the dry cleaner that has migrated under eight homes and continues to migrate. Groundwater is encountered at approximately five feet below ground surface, and site geology consists of dry gravel and sands. Near-source soil gas samples have also been collected from several locations throughout the neighborhood and found to corroborate a high-strength vapor source near the buildings. All homes have crawl spaces with dirt floors. In this hypothetical example, PEM may be warranted for the eight buildings located above, near, or downgradient of the groundwater plume, based on the groundwater concentration and soil gas data available (i.e., PCE concentrations significantly exceeding 137

243 screening levels in this example), 215 and the likelihood that the proximity of the groundwater table, characteristics of the vadose zone, and building conditions will collectively facilitate vapor migration and intrusion. Note that if a groundwater restoration system is constructed and operated and plume migration is thereby controlled, additional buildings downgradient of the plume may not warrant PEM in the future. In the meantime, an IC may be appropriate for the undeveloped parcel hydraulically down-gradient of the current leading edge of the plume. Site with Indoor Air Data for Some Buildings but Not for All Buildings. Depending on individual owners and occupants in the affected community, it may be difficult to obtain adequate data for all buildings within a specified area. Challenges include gaining timely access into each building and other practical considerations. In such circumstances, it may be appropriate to characterize a limited number of buildings under a reasonable maximum vapor intrusion condition, 216 by collecting and weighing multiple lines of evidence, and then extrapolating those findings to similar buildings nearby. The following hypothetical scenario describes one such situation, which is represented in Figure 7-2. In this hypothetical example, a sufficient number of appropriately screened monitoring wells have been installed throughout the neighborhood to characterize a historical groundwater plume. Near-source soil gas samples have also been collected from several locations throughout the neighborhood and found to corroborate the measured groundwater concentrations. Indoor air has been sampled and analyzed for a few homes and found to exhibit concentrations that pose an unacceptable human health risk. In this scenario, the assumption can be made that buildings with similar construction and built about the same time may have similar susceptibility to soil gas entry. As a result, it may be determined to use a PEM approach to offer mitigation systems to all buildings within a specified area of subsurface contamination. 215 Several site-specific factors render inappropriate the use of the recommended attenuation factors and groundw ater and soil gas VISLs for purposes of identifying sites or buildings unlikely to pose a health concern through the vapor intrusion pathw ay, as discussed in Section Nevertheless, response actions for vapor intrusion can be supported w hen the groundw ater and soil gas VISLs are exceeded for samples from a building or site w here these specific factors are present. 216 EPA recommends basing decisions about w hether to undertake response action for vapor intrusion (i.e., a component of risk management) on a consideration of a reasonable maximum exposure (e.g., EPA 1989, 1991a), w hich is intended to be a semi-quantitative phrase, referring to the low er portion of the high end of the exposure distribution (see Glossary). 138

244 Figure 7-1 Sample Depiction of Subsurface Vapor Source and Data to Support Pre-emptive Mitigation/Early Action for Multiple Buildings, Each with Limited Data 139

245 Figure 7-2 Sample Depiction of Subsurface Vapor Source and Data to Support Pre-emptive Mitigation/Early Action for Multiple Buildings, Some with Only Limited or No Data 140

246 Future Construction and Development. If current data (e.g., near-source soil gas) indicate that there is potential for unacceptable human health risk arising from vapor intrusion in an area where a building(s) is expected to be constructed in the future, EPA recommends that the remediation decision document record the known facts and data analyses and clearly state that vapor intrusion mitigation or site re-evaluation may be needed when the property is developed or occupied. EPA generally recommends appropriate ICs to ensure enforcement of such remediation decisions. 217 Prior site use (see Section 5) can be particularly relevant where residential development is planned or occurring on property formerly used for commercial or industrial purposes. In these situations, it is not uncommon for residual NAPLs or shallow plumes to remain. Under this circumstance, PEM may be warranted for new construction as a precautionary measure without direct evidence of a vapor intrusion pathway. Incorporating mitigation systems into newly constructed buildings is generally easier to implement and incurs lower cost when compared with retrofitting existing structures. On the other hand, if response actions to treat or remove the subsurface vapor source(s) are being conducted or will be conducted before a building is constructed and occupied, then building mitigation for the vapor intrusion pathway may not be warranted in the future Additional Considerations EPA recommends that the following factors also be considered in evaluating PEM and determining whether to implement it. Weighing Relative Costs of Characterization versus Engineered Exposure Controls. EPA recommends that cost not be the primary criterion for deciding whether or how to mitigate vapor intrusion because protection of human health could be compromised. On the other hand, cost effectiveness is addressed by CERCLA and the NCP and can be an important consideration when evaluating response alternatives. Cost can be a factor in deciding when and whether to pursue PEM, in relation to continuing to investigate and assess actual or potential vapor intrusion, and in ensuring effective human health protection through installing and operating a vapor intrusion mitigation system. At PRP-lead sites, for example, PEM may be viewed favorably where the costs associated with a complete site characterization or continued monitoring are estimated to easily exceed the cost of installing a mitigation system (and associated system monitoring). The number of buildings that would need to be characterized, or the order of priority, may be a factor in considering whether to implement PEM. Institutional Controls. For existing vapor intrusion mitigation systems, ICs may be warranted to ensure that the system is operated, maintained, and monitored. Maintenance and monitoring of the mitigation system, which are discussed in Sections 8.3 and 8.4 of this document, are generally appropriate to ensure that the system is performing as intended. In addition, ICs may facilitate access to property to conduct routine maintenance and monitoring activities, although 217 At undeveloped sites, or at sites w here land use may change in the future, ICs may be important to ensure that the vapor intrusion pathw ay is effectively addressed in the future. ICs at undeveloped sites could include mechanisms to inform the need for PEM in new buildings. Selecting and implementing PEM for new buildings avoids some of the difficulties associated w ith attempting to predict the potential for vapor intrusion prior to building construction. 141

247 separate access agreements also warrant consideration. Additional information regarding ICs is provided in Section 8.6 of this document. Community Input and Preferences. Community acceptance of early action may vary widely, depending on the human health risk to building occupants and past experiences at the site, including interaction with site stakeholders and regulators and perceptions of the site. Some owners and occupants may view PEM as a precautionary measure and be willing to have mitigation systems installed; some may even request them before characterization is completed. On the other hand, some home owners may not agree to have a mitigation system installed unless the pathway is demonstrated to be complete. Others may be reluctant to install mitigation systems because of the operation costs or the inconvenience associated with the installation and subsequent monitoring. Although some owners may view mitigation systems as an advantage when they sell a property, others may be concerned with the possible negative effect on property values. Issues and concerns about equity and fairness can also arise when some homes within a neighborhood receive mitigation systems and others do not. In some situations, it may be easier to persuade property owners to install vapor intrusion mitigation systems if the entire street, block, or neighborhood is found to warrant early action. Public meetings and one-on-one meetings provide opportunities to discuss PEM with affected property owners and building occupants and obtain information and input. Section 9.0 of this document provides additional information about community involvement and engagement. Refined Conceptual Site Model Decisions to undertake pre-emptive mitigation may warrant re-evaluation as additional monitoring and/or site and/or building characterization data become available and are evaluated in the context of the conceptual site model. If and when such data shift the weight of evidence towards a conclusion that the vapor intrusion pathway is incomplete or otherwise does not pose unacceptable health risk, then EPA recommends re-considering whether continued operation, maintenance, and monitoring of the interim response action (Section 8.2) is warranted. 142

248 8.0 BUILDING MITIGATION AND SUBSURFACE REMEDIATION This section summarizes information and recommendations on potential response options to mitigate and manage vapor intrusion. It is organized as follows: Section 8.1 summarizes the role of subsurface remediation in mitigating vapor intrusion. Section 8.2 provides an overview of engineered exposure controls (i.e., building mitigation technologies) for existing and new buildings. Sections 8.3 and 8.4 summarize information about operating and monitoring building mitigation systems, respectively. Section 8.5 summarizes information about documenting building mitigation systems. Section 8.6 describes and provides information about institutional controls (ICs). Section 8.7 provides information about exit strategies (e.g., termination of: subsurface remediation for vapor source control; building mitigation system operation; and associated ICs). Sections 5.2, 7, and 9 discuss potential bases for deciding to implement response options for vapor intrusion. Sections 3.3 and 7.7 introduced some of the response options and policies discussed in the remainder of this Section regarding components and development of cleanup plans. 8.1 Subsurface Remediation for Vapor Source Control The preferred long-term response to the intrusion of vapors into buildings is to eliminate or substantially reduce the level of contamination in the subsurface vapor source (e.g., groundwater, subsurface soil, sewer lines) by vapor-forming chemicals to acceptable-risk levels, thereby achieving a permanent remedy. Remediation of the groundwater plume or a source of vapor-forming chemicals in the vadose zone will eventually eliminate potential exposure pathways and can include the following actions, among others: Removal of contaminated soil via excavation; Removal of contaminated groundwater with pump-and-treat approaches; Decontaminating and/or rehabilitating sewer lines that harbor vapor-forming chemicals; and Treatment of contaminated soil and groundwater in situ, using technologies such as soil vapor extraction, multiphase extraction, and bioremediation, or natural attenuation. Because there is a substantial body of EPA and other guidance on selection, design, construction, and operation of technologies for remediation of subsurface vapor sources (e.g., EPA 1993b, 2006c; NRC 2004), these topics are not discussed further here. 143

249 When monitoring to assess the performance and effectiveness of remediation technologies for subsurface vapors, EPA recommends employing the methods, approaches, and recommendations described in Sections 5.4, 6.2, 6.4 and 7.0 of this Technical Guide. ICs may be necessary to help ensure the continued integrity of the cleanup. In some cases, therefore, ICs such as zoning or deed restrictions, may accompany implementation of vapor source remediation methods. Section 8.6 provides information about ICs and their application to the vapor intrusion pathway. 8.2 Building Mitigation for Vapor Intrusion In cases where subsurface vapor sources cannot be remediated quickly, it may be appropriate to also undertake (interim) measures in individual occupied buildings (i.e., building mitigation for vapor intrusion) to reduce threats to human health more quickly. EPA recommends that building mitigation for vapor intrusion be regarded as an interim action that can provide effective human health protection, which may become part of a final cleanup plan. Mitigation of vapor intrusion in specific buildings generally is not a substitute for remediation of subsurface vapor sources. Thus, EPA recommends that building mitigation generally be conducted in conjunction with vapor source remediation where at all possible. The purpose of this section is to provide an overview of vapor intrusion mitigation for new and existing buildings where response action is determined to be warranted. Section summarizes response options that generally can be implemented relatively quickly to reduce indoor air concentrations. Section identifies and summarizes the most commonly implemented engineered control methods for reducing vapor intrusion into existing buildings. Section identifies and describes some approaches and considerations for addressing vapor intrusion for new buildings. Additional detailed information about technologies for reducing vapor intrusion into buildings and their selection, design, operation, and monitoring is provided in other EPA documents (EPA 1993a, 2008c). Building owners and occupants may find EPA s Consumer s Guide to Radon Reduction (EPA 2013b) a useful source of additional information, in light of similarities in technologies for reducing vapor intrusion and radon intrusion. ICs may be necessary to help ensure the continued integrity of building mitigation systems. In many cases, therefore, ICs may accompany implementation of engineered exposure controls, for example to ensure that an active system remains operational and passive membranes are not disturbed (EPA 2008c). Additional information about ICs is provided in Section Prompt Response Options for Existing Buildings For buildings with potential explosion and fire hazards, EPA recommends evacuation, along with notification of the local fire department about the threat. If, on the other hand, prompt action is warranted to reduce or eliminate vapor intrusion exposures in an existing building (e.g., measured indoor air concentrations pose an unacceptable human health risk for an acute or short-term exposure scenario (see Section 7.5.2)), it may be appropriate to implement response options such as the following: Sealing major openings for soil gas entry, where known and identified; Over-pressurizing nonresidential buildings by adjusting the HVAC system; 144

250 Installing, repairing, or maintaining vapor traps for sewer or drain lines that are sources of vapor intrusion; Increasing building ventilation, for example using fans or natural ventilation; Treating indoor air (e.g., adsorption using activated carbon); and Temporary relocation The fore-going response actions may take several days to a few weeks to plan (e.g., arrange, design) and implement, which generally is quicker than other interim response actions (e.g., active depressurization technologies). The first three options seek to reduce or eliminate vapor entry into the building. The last three options seek to reduce, eliminate, or avoid vapors that have entered the building by vapor intrusion. Specifically: Vapor intrusion into the building via soil gas entry from vadose zones soils can be reduced by sealing foundational openings using products such as synthetic rubbers, acrylics, oil-based sealants, asphalt/bituminous products, swelling cement, silicon, epoxy or elastomeric polymers. EPA recommends screening the selected sealant(s) (e.g., checking the composition, relying upon manufacturer s data) to ensure they do not contain or emit vapor-forming chemicals that might pose a human health risk to building occupants. This interim mitigation approach is among the easiest and least expensive to implement; however, its effectiveness relies upon being able to identify and access openings for soil gas entry. EPA recommends appropriate monitoring of indoor air concentrations be conducted to ensure that sealing attains and sustains sufficient reduction in vapor intrusion. In some cases, however, sealing openings may not be capable of reducing indoor air concentrations to acceptable levels and/or some openings may not be visible and accessible. EPA recommends that this response option generally be supplemented by installing, operating, and maintaining an engineered exposure control (e.g., an active depressurization technology) that reduces or eliminates vapor entry into the building until remediation of subsurface vapor sources is complete and terminated. For commercial and industrial buildings where HVAC units blow air into the building and are well maintained, it may be advantageous to increase pressurization in the building to prevent or reduce vapor intrusion. In some cases (e.g., buildings with few doors and other openings), relatively small increases in building pressure may be sufficient, which may be accomplished by increasing the air flow rate and using specialized equipment to monitor and balance air flow rates. EPA recommends appropriate monitoring of pressure and other indicators (e.g., indoor air monitoring) be conducted to ensure that adequate pressurization is sustained throughout areas of the building that could be subject to vapor intrusion. In some climates and for some buildings, this response option may be impractical or prohibitively expensive. Vapor intrusion into the building via gas entry from sewer and drain lines can be reduced or eliminated by installing, repairing, and maintaining vapor traps. Increasing building ventilation (i.e., increasing the rate at which indoor air is replaced with outdoor air) can reduce the buildup of indoor air contaminants within a structure. Natural ventilation may be accomplished by opening windows, doors, and vents. Forced 145

251 or mechanical ventilation may be accomplished by using a fan to blow air into or out of the building. Increased ventilation is easiest and least costly to implement in locations where the air is not conditioned (heated or cooled). If indoor air is conditioned, increased ventilation can be a costly option because the conditioned air is ventilated to the outdoors. This drawback can be partly overcome by use of heat exchangers, but they are also costly. Another concern is that exhausting air from the building will generally contribute to under-pressurization of the building, relative to the subsurface, thereby potentially resulting in an increased rate of soil gas entry (i.e., vapor intrusion) unless ambient air entry into the building is increased equivalently. EPA recommends appropriate monitoring of indoor air concentrations be conducted to ensure that ventilation attains and sustains sufficient reduction in exposures to vapor-forming chemicals. In some cases, ventilation may not be capable of reducing indoor air concentrations to acceptable levels. In addition, building occupants may find it uncomfortable to increase the air exchange rate by more than a factor of three or four. EPA generally recommends that this response option be supplanted, when feasible, by installing, operating, and maintaining an engineered exposure control that reduces or eliminates vapor entry into the building until remediation of subsurface vapor sources is complete and terminated. Commercially available indoor air cleaners, which include both in-duct models and portable air cleaners, is another response option. These devices operate on various principles, including zeolite and carbon sorption and photocatalytic oxidation. Methods that rely on adsorption generate a waste that must be disposed of appropriately or regenerated and warrant periodic replacement of the adsorption medium. EPA recommends appropriate monitoring of indoor air concentrations be conducted to ensure that adequate treatment is sustained throughout the building. EPA generally recommends that this response option be supplanted, when feasible, by installing, operating, and maintaining an engineered exposure control that reduces or eliminates vapor entry into the building until remediation of subsurface vapor sources is complete and terminated. Temporary relocation may be implemented for buildings where conditions warranting prompt response action (see Section 7.5) and cannot be adequately addressed by other means. 218 None of these options entails reducing the level of vapor-forming contamination in the subsurface medium (see Section 8.1). EPA generally recommends that these response options be supplanted, when feasible, by installing, operating, and maintaining an engineered exposure 218 For response actions carried out under Sections 104(a) and 106(a) of CERCLA, OSWER Directive (Superfund Response Actions: Temporary Relocations Implementation Guidance (EPA 2002d)) states: Temporary relocation should not be selected if health and safety risks or circumstances that pose an unreasonable inconvenience can be adequately addressed by other means w ithout significantly increasing the overall cost or duration of the response action. Similarly, OSWER Directive P (Interim Policy on the Use of Permanent Relocations as Part of Superfund Remedial Actions (EPA 1999f)) states: EPA s preference is to address the risks posed by the contamination by using w ell-designed methods of cleanup w hich allow people to remain safely in their homes and business. OSWER Directive provides recommended procedures and other policies for temporarily relocating residents w hen this response action is selected and implemented under Sections 104(a) and 106(a) of CERCLA. 146

252 control that reduces or eliminates vapor entry into the building (see Section 8.2.2), until remediation of subsurface vapor sources is complete and terminated Active Depressurization Technologies for Existing Buildings This section provides a brief overview of engineered systems that can be used to reduce or eliminate soil vapor intrusion in existing buildings, along with a summary of steps and considerations for selecting an appropriate technology for a given building. The focus is on active depressurization technologies most commonly employed for reducing soil vapor intrusion into buildings. This focus does not mean, however, that active depressurization technologies are always preferred over other mitigation methods or that they will be the best option for every site. More detailed information on vapor intrusion mitigation systems for existing buildings, including sub-membrane ventilation systems and passive technologies, 219 can be found in several EPA publications (e.g., EPA 2008c). Active depressurization technologies (ADT) have been used successfully to mitigate the intrusion of radon into buildings and have also been successfully installed and operated in residential, commercial, and school buildings to control vapor intrusion from subsurface vaporforming chemicals. ADT systems are widely considered the most practical vapor intrusion mitigation strategy for most existing buildings, including those with basement slabs or slab-ongrade foundations. ADT systems are generally recommended for consideration for vapor intrusion mitigation because of their demonstrated capability to achieve significant concentration reductions in a wide variety of buildings 220 and their moderate cost. Sub-slab depressurization (SSD) systems, a common type of ADT system, function by creating a pressure difference across the building slab to prevent soil gas entry into the building (i.e., overcoming the building s natural under-pressurization, which is the driving force for vapor intrusion; see Section 2.3). Creating this pressure difference is accomplished by extracting soil gas from beneath the slab and venting it to the atmosphere. 221 For the system to be effective by this mechanism, 222 this soil depressurization must be established and maintained at least near the primary openings for soil gas entry (EPA 1993a). Construction of SSD systems entails opening one or more holes in the existing slab, removing soil from beneath the slab to create a suction pit (6 18 inch radius), placing vertical suction pipes into the holes, and sealing the 219 As noted in Section 3.3, engineered exposure controls that do not involve mechanical operations (e.g., creating a barrier betw een the soil and the building that blocks openings from soil gas entry into the building) are referred to as passive. 220 Folkes and Kurz (2002) describe a case study of a vapor intrusion mitigation program in Denver, Colorado. Subslab depressurization systems and/or sub-membrane depressurization systems w ere installed in 337 residential homes to control indoor air concentrations of 1,1-dichloroethylene (DCE) resulting from migration of vapors from groundw ater w ith elevated 1,1-DCE concentrations. Over three years of monitoring data for 301 homes have show n that these systems are capable of achieving the very substantial reductions in concentrations in indoor air. Approximately one quarter of the systems w arranted minor adjustment or upgrading after initial installation in order to achieve the state standards established for indoor air exposure. 221 Depending, in part, upon location and prevailing statutes and regulations, governmental permits or authorizations may be required for venting systems that exhaust to the atmosphere. 222 A second mechanism by w hich ADT systems can function is diluting the vapor concentrations beneath the slab and foundation (EPA 1993a, 2008c). Engineered controls designed and operated to use this mechanism predominately are often referred to as sub-slab ventilation systems. 147

253 openings around the pipes. These pipes are then connected together to a fan, which draws soil gas from the sub-slab area through the piping and vents it to the outdoors. 223 Sealing known and accessible openings in the slab and foundation can reduce the flow rate of conditioned indoor air that can be pulled into the sub-slab region by the suction wells and the sub-slab depressurization (EPA 2008). SSD systems were first developed for radon reduction (EPA 1993a) and operate under similar design principles as radon mitigation methods. Figure 8-1 illustrates such an SSD system. When sumps and associated drain tile systems are present, they may also be depressurized to prevent soil gas entry into the building (again, overcoming the building s natural underpressurization). This variation on active depressurization is often referred to as drain-tile depressurization (DTD). Depressurization of drain tiles located near a foundation wall can help control soil gas entry at the joint between the foundation wall and slab. Figure 8-2 illustrates such a DTD system. If the building has hollow block walls, the usual sub-slab suction point may not adequately mitigate the wall cavities, which may be particularly important if the outside surfaces are in contact with the soil. In these situations, the void network within the wall may be depressurized by drawing air from inside the wall and venting it to the outside. This method, called block-wall depressurization (BWD) is often used in combination with SSD. Because uniform depressurization of block walls can be difficult, BWD is generally recommended only when subslab or DTD prove inadequate to control vapor intrusion. Figure 8-3 illustrates such a BWD system. In buildings with a crawl space foundation or a basement with a dirt floor, a flexible membrane may be installed over the floor to facilitate depressurization of the soil gas beneath the membrane, which prevents vapors from intruding into the crawl space or basement air. To maximize the effectiveness of a sub-membrane depressurization (SMD) system, EPA recommends the membrane cover the entire floor area and be sealed at all seams and penetrations. Figure 8-4 illustrates such an SMD system. Extensive guidance is available for the design, sizing, installation, and testing of ADT systems for radon control in existing and new homes and large institutional (e.g., school) and commercial buildings. EPA recommends that ADT systems be designed and installed by qualified persons, typically environmental professionals and licensed radon contractors. EPA guidance for design of ADT systems can be found in several publications (e.g., EPA 1993a, 2008c). EPA recommends documenting each constructed ADT system via a system manual, as described further in Section 8.5. The Vapor Intrusion Mitigation Quick Guide provided in Table 8-1 summarizes a list of steps for selecting and implementing a vapor intrusion mitigation system in existing buildings. 223 A central issue that determines the design and effectiveness of ADT systems is the ease w ith w hich suction at one location can extend to other subsurface areas underneath the building. Where a good and uniform layer of aggregate (e.g., gravel or crushed rock) w as placed underneath a slab foundation during construction, for example, such hydraulic control and communication can generally be expected to be good (EPA 1993a). Where the layer of aggregate under a slab is interrupted or uneven to a significant degree, additional suction pipes w ill generally be needed and their location w ill be increasingly important. 148

254 TABLE 8-1 VAPOR INTRUSION MITIGATION QUICK GUIDE FOR EXISTING BUILDINGS Step 1: Consider Prompt Response Actions It may be appropriate to implement certain interim measures before engineered controls are constructed and operated, as w arranted and feasible. For example, building ventilation can be increased, cracks and other openings in the floor or foundation (that otherw ise allow soil gas entry) can be sealed, or indoor air treatment can be conducted (refer to Section 8.2.1). Step 2: Select a Building Mitigation System The initial step in selecting the appropriate vapor intrusion mitigation technology is to conduct a visual inspection of an existing building. The selection of a vapor intrusion mitigation system primarily depends on building characteristics and contaminant concentrations. In the majority of cases, a type of active depressurization technology (ADT) can be an efficient, reliable, and cost-effective vapor intrusion mitigation technique. In some cases, how ever, other approaches may be preferable. Factors that may prompt consideration of vapor intrusion mitigation approaches other than ADT include foundation conditions that prevent development and extension of a suction field below the building. If there are no factors that w ould rule out an ADT technology, appropriate systems that can be considered include: Sub-slab depressurization (SSD) systems, particularly in houses having slabs (basements and slabs on grade) w here drain tiles are not present. Drain-tile depressurization (sump/dtd or remote discharge/dtd) w hen drain tiles are present. Sub-membrane depressurization (SMD) in buildings w ith a craw l space foundation or a basement w ith a dirt floor, Block-w all depressurization (BWD), usually used only as a supplement to SSD, DTD, or SMD to better mitigate vapors found to be migrating through the w all. Step 3: Design Building Mitigation System EPA recommends the final detailed design of the selected vapor intrusion mitigation technology specify the number and location of suction points, location and size of piping, suction fan, piping netw ork and exhaust system, and sealing options to be used in conjunction w ith the ADT technology. Pre-mitigation diagnostic testing can provide information about the suction field underneath a building and pressure differences that w ill need to be overcome (EPA 1993a) if the ADT system is to be effective. Diagnostic testing during installation can also help verify the adequacy of the design. Step 4: Install Building Mitigation System EPA recommends that the vapor intrusion mitigation system be installed consistent w ith design specifications by equipment manufacturers, local permit conditions and regulations, and relevant industry standards. Step 5: Confirm the Installed System is Operating Properly EPA recommends a visual inspection of the installed system as a routine quality assurance step to confirm that all construction details have been completed. Post-construction monitoring is recommended (refer to Section 8.4) to demonstrate the ADT system is operating appropriately and effectively. Where a vapor intrusion mitigation system is not performing adequately, post-construction diagnostic tests can be helpful in trouble-shooting (EPA 1993a). Step 6: Ensure Proper Operation and Maintenance of Vapor Intrusion Mitigation System (refer to Sections 8.3 and 8.4) EPA recommends proper system maintenance and periodic inspections and monitoring to ensure the system is operating as designed and is effective at reducing indoor air concentrations to (or below ) target levels. EPA recommends that site managers provide the building ow ner/occupant w ith information to help ensure proper operation and maintenance of the system. EPA recommends that periodic inspections include periodic measurements to confirm that the building mitigation system is continuing to perform adequately. 149

255 The U.S. Navy has issued a concise fact sheet that contains useful technical information (DoN 2011b) Approaches and Considerations for New Buildings The ADT systems described above are generally available for new buildings also. However, a wider array of approaches and technical options is typically available to mitigate or avoid vapor intrusion for new buildings, compared to existing buildings. These options potentially include the choice of building location and opportunities to modify the building design and construction, which are not available for existing buildings. For example: At some sites, contaminated areas most likely to produce unacceptable vapor intrusion exposures can be avoided and designated for another purpose, such as recreational space or undeveloped landscape. Mitigation needs can also be considered in the selection of heating and cooling systems, which are normally selected based only on economics, aesthetics, preference, and custom. A system design that avoids creating under-pressurization inside the structure and maintains over-pressurization inside the structure may be effective in mitigating vapor intrusion. Passive barriers, such as a low-permeability membrane, can be more readily installed between the soil and the building during new building construction. Passive barriers are intended to reduce vapor intrusion by limiting openings for soil gas entry. However, passive barriers as stand-alone technologies may not adequately reduce vapor intrusion owing to difficulties in their installation and the potential for perforations of the barrier during or after installation. They are commonly combined with ADT systems or with submembrane ventilation systems to help improve their efficiency. Venting layers can be more readily installed between the soil and the building during new building construction. 224 New buildings may be designed to include a highly ventilated, low-occupancy area at ground level, such as an open parking garage. Steps 2-6 of the Vapor Intrusion Mitigation Quick Guide provided in Table 8-1 are also pertinent to newly constructed buildings. EPA guidance for selecting, designing, and installing vapor intrusion mitigation systems for new buildings can be found in several publications (e.g., EPA 2008c). The U.S. Navy has issued a concise fact sheet that contains useful technical information (DoN 2011c). 224 Constructed sub-slab ventilation systems typically consist of: a venting layer (e.g., filled w ith porous media such as sand or pea gravel; or suitably fabricated w ith continuous voids) below a floor slab to allow soil gas to move laterally to a collection piping system for discharge to the atmosphere; and a sub-slab liner that is installed on top of the venting layer to reduce entry points for vapor intrusion. These and other sub-slab ventilation systems function by draw ing outside air into and through the sub-slab area, w hich dilutes and reduces concentrations of vapor-forming chemicals, and provides a route for soil gas to vent to the atmosphere or migrate outside the building footprint, rather than into a building. 150

256 8.2.4 Owner/Occupant Preferences and Building Access Building owners and occupants can initially be notified in various ways that their home or building warrants construction and operation of a building mitigation system. Section 9.5 provides information regarding such notifications and other messages pertaining to building mitigation. Whereas EPA managers and mitigation system designers may be primarily concerned with the performance, cost-effectiveness, and reliability of any mitigation system, the building owners and occupants may have additional perspectives and opinions that warrant consideration during technology selection, design, construction, and operation. For example, owners and tenants will often have strong opinions about where fans and piping are located, what level of fan noise is acceptable, and what quality of construction craftsmanship is satisfactory. When there are multiple mitigation options (for example, at a large commercial building), EPA recommends these options be presented fairly to the building owner and tenants, explaining the advantages and disadvantages associated with each and describing the rationale for the preferred alternative. In some cases, obtaining and scheduling access to a building can be difficult, whether the structure is a commercial or institutional building or a private residence. Commercial building tenants may not want construction activities disrupting business operations. Some homeowners/tenants may resist granting access to their home. Other homeowners/tenants may prefer to schedule tests before or after their work-day. To address these practical and logistical concerns, EPA recommends that an access agreement(s) be executed between the property owner, any tenants, and the mitigating entity to ensure appropriate access as needed to operate, maintain, and monitor the engineered exposure controls in each impacted building. 8.3 Operation and Maintenance of Vapor Intrusion Mitigation Systems For purposes of this Technical Guide, operation and maintenance (O&M) is used generically to refer to periodic inspections, component maintenance or replacements, repairs, and related activities that are generally necessary to ensure continued operation and effectiveness of engineered exposure controls to mitigate vapor intrusion. EPA generally recommends that such O&M activities be conducted routinely, be documented in an O&M plan (as described further in Section 8.5), and consider recommendations of equipment manufacturers, if any, and sitespecific factors. Additional information about ensuring continued effectiveness of systems is available in EPA (2009b). Design specifications for vapor migration systems may include (1) a maintenance frequency that varies over the operating period of the mitigation system and/or (2) a provision to evaluate and modify the frequency based on data or information obtained during monitoring and maintenance. For example, it may be acceptable to reduce inspection or maintenance frequency once efficient system operation has been demonstrated for at least an initial year, with triggers for additional, unscheduled inspections following alarms (from warning devices) and floods, earthquakes, and building modifications, if any. Typical O&M activities for either passive or active systems may include, but are not limited to: Routine inspection of all visible components of the vapor intrusion mitigation system, including fans, piping, seals, membranes and collection points, to ensure there are no 151

257 signs of degradation or blockage. EPA recommends that the as-built drawing for the vapor intrusion mitigation system be examined to verify the system configuration has not been modified. Visual inspection of the building to evaluate whether any significant changes were made (such as remodeled basement, new furnace) that would affect the design of the vapor intrusion mitigation system or the general environment in which it is operated. A crawl space SMD membrane, for example, may warrant repair or replacement if its integrity is compromised. Visual inspection of the area of concern (including basement floor and wall seals, sumps, floor drains and utility penetrations) to ensure there are no significant changes in conditions that would warrant modification of the system design. Routine monitoring of vent risers for flow rates and pressures generated by the fan to confirm the system is working and moisture is draining correctly. Routine maintenance, calibration and testing of functioning components of the venting system consistent with the manufacturers specifications. o Pressure readings for both active and passive depressurization systems as well as positive pressurization systems (e.g., periodic verification of measurable pressure differences across the slab). o Confirmation that the extraction fan is operating. o SSD system fans generally can function well for prolonged periods without maintenance; however, EPA recommends fans be replaced periodically throughout the operating life of the system (e.g., every 4 to 10 years) to avoid breakdowns and associated problems. Inspection of external electrical components to identify undesirable conditions, such as excessive noise, vibration, moisture, or corrosion, and to verify that the fan cut-off switch is operable. o Inspection of the fan(s) is important throughout the operating period but may be particularly important near the end of its expected lifespan. Noisy fans typically indicate problems with ball bearings and warrant replacement on that basis. o Confirmation of adequate operation of the warning device or indicator. Confirmation that building owner/occupants are knowledgeable about how to maintain system operation. Confirmation that a copy of the O&M manual is present in the building and has been updated as necessary. EPA also recommends that the site team determine if there has been any change in ownership/occupant. If such a change has occurred, EPA recommends the site manager work with the new owner/occupant to ensure continued integrity and operation of the vapor intrusion mitigation system. 152

258 8.4 Monitoring of Vapor Intrusion Mitigation Systems Regardless of the type of system selected for mitigating vapor intrusion in a given building, EPA recommends monitoring to demonstrate that performance standards are achieved at the time of installation and that those performance standards continue to be met throughout the operating period of the mitigation system. EPA recommends that any monitoring program developed for a building mitigation system be based upon site-specific considerations, including the degree of risk or hazard being mitigated, the building use, the technology used to mitigate vapor intrusion, whether the subsurface vapor source(s) is stable in extent and concentration, and coordination with site remediation efforts. For example: An older building with highly volatile chemicals at high concentrations may need a more intense level of monitoring than a new building with lower concentrations of less volatile chemicals. Passive systems are generally less predictable and less efficient at preventing vapor intrusion than active systems and, therefore, typically warrant more intensive monitoring, all else being equal. When contaminated groundwater plumes are migrating to new areas (i.e., expanding) or concentrations in shallow groundwater are increasing, increased frequency and intensity of mitigation monitoring may be warranted. During start-up, some remediation methods have the potential to alter soil gas conditions in ways and to a degree that may be difficult to predict. Increased frequency and intensity of mitigation monitoring may be warranted when such remediation methods are implemented near buildings undergoing mitigation. Mitigation monitoring will generally entail two phases: (i) an initial post-construction phase, which is generally more intensive; and (ii) a subsequent phase, which may be comprised of fewer diagnostic tests to be conducted periodically. As with radon mitigation systems (EPA 1993a, Section ), results of indoor air sampling during initial post-construction monitoring may be used to demonstrate that the occupant s exposure to vapor-forming subsurface contaminants has been reduced as anticipated. In addition, pressure field measurements in the subslab region can be used to demonstrate that the system has attained hydraulic control and communication (e.g., depressurization in the case of an ADT system) over the footprint of the building (or portion of a large building, as appropriate, considering the extent of subsurface contamination). Adjustments to the mitigation system and/or additional diagnostic testing (EPA 1993a, 1993c) may be warranted if the results of such testing do not clearly demonstrate that the system is achieving its intended performance and effectiveness. Once an adequate demonstration of effectiveness has been made for the vapor intrusion mitigation system, periodic monitoring is recommended to verify that this performance is sustained; for this purpose, monitoring may be comprised of fewer types of tests than during the immediate postconstruction (i.e., start-up) phase at the discretion of EPA when the subsurface vapor source(s) is stable. Examples of various monitoring scenarios for these two phases are provided in Table 4 of CalEPA (2011), Table 6-2 of NJDEP (2012), and Table 3-1 of MADEP (2011). Additional information about ensuring continued effectiveness is available in the Operational and Functional Determination and the Transfer of Fund-lead Vapor Intrusion Mitigation Systems to the State (EPA 2009b). 153

259 When monitoring to assess the performance and effectiveness of building mitigation technologies, EPA recommends employing the methods, approaches described in Sections 5.4, 6.2, 6.4 and 7.0 of this Technical Guide. EPA also recommends that monitoring programs that assess the performance and effectiveness of remediation and mitigation systems be documented, preferably in work plans similar to those recommended herein for characterizing and assessing the vapor intrusion pathway (see Section 6.2). Such vapor intrusion monitoring plans may be incorporated as part of a comprehensive remedial design and operations manual or as a stand-alone document, depending upon site-specific circumstances. In addition, EPA recommends that data and other results obtained through such monitoring programs be documented (e.g., in the administrative record), as they become available. The remainder of this section identifies and further discusses some elements commonly incorporated in monitoring programs for active depressurization technologies. Pressure Measurements Sub-slab probes can be used to monitor differential pressures for a direct indication of the hydraulic performance of ADT systems (i.e., the pressure difference across the slab prevents soil gas entry); see Section 2.3. For basements, the walls that are underground become part of the critical building envelope that must prevent soil gas entry. For subsurface depressurization systems, EPA recommends that the pressure gauge be monitored quarterly to verify the system is operating efficiently. A reduced monitoring frequency may be appropriate after one year of successful operation of the remedial system. Tracer Testing Openings within the building or leaks in the mitigation system can affect system performance. Tracers can be used either for leak detection through barriers, building materials or system components (piping, for example) or to measure the air exchange rate in the building. Smoke testing is a qualitative form of tracer testing used to detect leaks (e.g., at seams and seals of membranes in SMD systems or at potential leakage points (openings) through floors above sealed crawl space systems or through conduits that facilitate preferential vapor migration), or to test airflow patterns. A limitation of smoke testing in existing structures is that non-noxious smokes can be expensive, and cheaper high-volume smoke sources can leave undesirable residues. The efficacy of smoke testing in some applications has been questioned on the grounds that many leaks are too small for visual detection using this method (Maupins and Hitchins 1998, Rydock 2001), and that leaks large enough to detect using smoke could be detected other ways. More quantitative methods have been recommended, such as tracer testing with instrumentation for quantitative results. Air Sampling Once an adequate demonstration of vapor intrusion mitigation system effectiveness has been made, indoor air quality generally will be acceptable as long as an adequate pressure difference is maintained throughout the footprint of the building. Periodic or intermittent sampling of indoor air, nevertheless, warrants consideration, since indoor air data can provide direct confirmation that the system is reducing exposure levels of vapor-forming chemicals and because depressurization technologies can be expected to alter the distribution of vapors in the vadose zone and available for soil gas entry, if any. 154

260 Weather-Related Considerations EPA recommends that weather conditions be noted during monitoring activities (EPA 1993a). Weather conditions, such as temperature and precipitation, can affect the performance of a vapor intrusion mitigation system. For example, cold temperatures may increase the building depressurization created by the thermal stack effect and thus increase the driving force for soil gas entry, depending upon the height of the house and the temperature difference between indoors and outdoors (see Section 2.3). As a result, the ADT system may need to overcome more building depressurization than originally considered when designed. Precipitation may also increase moisture in the fill under the slab, which may affect the performance of the system, and is a factor to consider in developing a monitoring program. Alarms Alarms generally are used as part of a monitoring program to ensure that malfunctions of vapor intrusion mitigation systems are timely and readily detected and addressed. According to ASTM (2003), All active radon mitigation systems shall include a mechanism to monitor system performance (air flow or pressure) and provide a visual or audible indication of system degradation and failure (i.e., an alarm ). ASTM goes on to say, The mechanism shall be simple to read or interpret and be located where it is easily seen or heard. The monitoring device shall be capable of having its calibration quickly verified on site. Such devices may indicate operational parameters (such as on/off or pressure indicators) or hazardous gas buildup (such as percent LEL indicators). EPA concurs with the cited advice from ASTM and recommends it be considered when monitoring and maintaining mitigation systems for vaporforming chemicals and sites addressed by this Technical Guide. In particular, EPA recommends that system failure alarms be installed on active depressurization systems, and appropriate responses to alarms be communicated by the building owner/occupants. EPA also recommends that alarms be placed in readily visible, frequently trafficked locations within the respective building and their proper operation be confirmed on installation and monitored periodically. Placards EPA also recommends that permanent placards be placed on the system to describe the system s purpose and operational requirements (e.g., power source) and instructions on what to do if the system does not operate as designed (for example, a phone number to call for corrective action). EPA recommends the placard provide information about how to read and interpret the monitoring instruments or warning devices provided. EPA also recommends that these placards be placed as close to the monitoring/alarm part of the system as possible, as well as close to the fan or other active parts of the system. 155

261 8.5 Documentation of Engineered Exposure Controls for Vapor Intrusion Mitigation EPA recommends that documentation be provided to building owners and occupants and appropriate regulatory agencies 225 describing the vapor intrusion mitigation system (i.e., a system manual ) and its associated O&M (i.e., an O&M plan ). The system manual provides a detailed record about the mitigation system, including as-built drawings, permits (if any), copies of agreements, and construction/layout plans, whereas the O&M manual describes the O&M activities to be conducted routinely and identifies which party is responsible for these O&M activities. Additional information about ensuring continued effectiveness is available in Operational and Functional Determination and the Transfer of Fund-lead Vapor Intrusion Mitigation Systems to the State (EPA 2009b). O&M Plan O&M plans generally are prepared on a site-specific basis, and they often are particularly useful at sites where: Monitoring is needed to verify remedial effectiveness. The remedial system warrants periodic adjustments and maintenance. Human health risk would result if the system fails or if site conditions change. Conditions that would trigger specific contingent response may occur sporadically or episodically. Some site remedial systems may also warrant the use of a regulatory agency-approved contingency plan or similar corrective response document approved by the regulatory agency to identify conditions that may trigger the need for additional maintenance, collection of additional data, modifications of monitoring frequency, or other responses to ensure the remedy remains effective. Communication with building owners and occupants about vapor intrusion and the O&M of a vapor intrusion mitigation system is critically important. For example, building owners may be concerned about some aspect of system operation and decide to turn it off. It is important to communicate that turning off the system may result in harmful indoor air concentrations inside the building. System Manual The specific contents of the system manual will depend on the type of system. EPA recommends, however, that the system manual generally include at least the following information or items: Cover/transmittal letter; 225 For example, EPA recommends the potentially responsible party (PRP) provide a system manual and O&M plan to EPA at PRP-lead Superfund sites. 156

262 Description and diagram of final as-built system layout with components labeled; Building permits for a vapor intrusion mitigation system; Pre- and post-mitigation air and gas sampling data; Pre- and post-mitigation diagnostic test data; Copies of contracts and warranties; Proper operating procedures of the system; Contact information of the contractor or installer; Copy of signed access agreement; Copy of vapor mitigation system O&M agreement; Copy of pre-mitigation sample result letter (see Section 9.4); Copy of post-construction sample result letter; Contact information in case of future questions; and Inspection and maintenance guidelines. User s Guide Documentation typically is also provided to the property owner and occupant in the form of a user s guide suitable to keep lay persons informed about the system and to provide a summary reference in case questions or issues arise pertaining to the system. A user s guide is a brief summary of why a vapor intrusion mitigation system was installed at a property and how the system works, and may include the following: (1) a brief description of the system and its proper range of operation; (2) contact information for the party responsible for responding to malfunctions and ensuring the system performs properly; and (3) information about routine maintenance to be conducted by the owner/occupant, if any. EPA recommends that a user s guide be placed near the system for quick access and easy reference (e.g., into a clear protective sleeve and attached to the main extraction pipe of the ADT system). An easy-toread user s guide may be especially helpful at rental properties because the guide informs each new tenant about what the system is and why it was installed. 8.6 Use of Institutional Controls ICs may be used to restrict certain land uses, buildings, or activities that could otherwise pose an unacceptable human exposure via the vapor intrusion pathway. Response actions for vapor intrusion may include ICs to restrict land use for protection of human health regardless of whether a vapor intrusion mitigation system provides interim measures to control (i.e., reduce, limit) human exposures. ICs can be used as either an interim 157

263 response until site cleanup goals are reached or as part of a long-term response where vaporforming waste remains in place. General EPA guidance on ICs is provided in Institutional Controls: A Guide to Planning, Implementing, Maintaining, and Enforcing Institutional Controls at Contaminated Sites ( PIME IC Guidance ) (EPA 2012d). As discussed in the PIME IC Guidance, ICs are non-engineered instruments, such as administrative or legal controls, that help to minimize the potential for human exposure to contamination and protect the integrity of a response action. ICs typically operate by imposing land or resource use restrictions at a given site or by conveying notice to stakeholders regarding subsurface contamination or the possible need to refrain from certain actions that may result in human exposure to hazardous chemicals. For example, ICs may be used to restrict the development and use of properties for certain land uses (e.g., prohibiting residential housing, hospitals, schools, and day care facilities). In some situations, ICs can be used to restrict access to a property, facilitate response activities conducted by a responsible party or EPA, such as the installation or maintenance of vapor intrusion mitigation systems, or help ensure the integrity of vapor mitigation systems. ICs may also be used to help inform the need for vapor intrusion mitigation for future construction where vapor-forming waste remains in place and may pose unacceptable human health risk due to vapor intrusion. As described further in Section 2.2 of the PIME IC Guidance, ICs can be described in four general categories: Proprietary controls. Governmental controls. Enforcement and permit tools with IC components. Informational devices. The first three categories (i.e., proprietary controls, governmental controls, and enforcement and permit tools with IC components) typically memorialize and prescribe substantive use restrictions concerning the land or resource use, while informational devices generally operate to provide notice of contamination and any remedial activities to parties. Depending on the nature of the site and the particular jurisdiction in which it is located, certain instruments may not be available or feasible for a particular site. Certain ICs may help facilitate how interim response actions and subsurface remediation are carried out, such as provisions addressing access, O&M of vapor intrusion mitigation systems, and design specifications for buildings (see Example #3 box below) Evaluating ICs in the Overall Context of Response Selection As a site moves through a program s response selection process (for example, a Superfund remedial investigation/feasibility study [RI/FS] or RCRA facility investigation/corrective measures study [RFI/CMS]), EPA recommends that site managers develop information about reasonably anticipated future land uses and infer reasonably expected exposure pathways related to land use. This information may be incorporated in the conceptual site model and often can be used to evaluate whether ICs will be needed to ensure protectiveness of current and 158

264 reasonably anticipated future land uses over time. EPA s land use guidance (EPA 1995a, 2010c) recommends that the site manager discuss reasonably anticipated future land uses of the site with local land use planning authorities, local officials, property owners, and the public, as appropriate, as early as possible during the scoping phase of the RI/FS, RFI/CMS, or equivalent phase under other cleanup programs. EPA recommends that the Region s decisions to implement ICs be documented in proposed cleanup plans and in final cleanup decision documents. For example, for CERCLA cleanups, the proposed restriction, and need for ICs would normally be identified in the Proposed Plan for notice and opportunity to comment by potentially affected landowners and the public. Such use restrictions or notices typically are then selected and memorialized in the Record of Decision (ROD). In some cases, unanticipated changes in land use may occur after the response action is implemented, which may impact the protectiveness of a completed response action and raise questions concerning the effectiveness of the ICs. As a result, vapor intrusion may be identified as a potential human exposure pathway in a subsequent periodic review. In this case, EPA recommends that site managers evaluate options for modifying the original response decision, including the need for new or additional ICs consistent with existing and reasonably anticipated future land uses and other response selection considerations Common Considerations and Scenarios Involving ICs The evaluation of whether an IC is needed at a contaminated site, including one where the vapor intrusion pathway poses a current or potential threat to human health, is a site-specific determination. When evaluating whether an IC will be needed, EPA recommends that EPA Regional staff consider whether the site meets unlimited use and unrestricted exposure (UU/UE), among other factors. UU/UE is generally the level of cleanup at which all exposure pathways present an acceptable level of human health risk for all land uses, including reasonably anticipated future land use scenarios that are considered during response selection. Common scenarios where ICs may be a useful instrument for fostering protectiveness at a site involving vapor intrusion threats include, but are not limited to, the following: 1. Existing buildings overlie soil or groundwater contamination, or a migrating groundwater plume that is moving toward existing buildings potentially poses a future vapor intrusion threat; 2. Future construction is planned or is reasonably anticipated on a site that overlies subsurface contamination with vapor-forming chemicals; 3. Changes to building construction/design (such as remodeling or ventilation changes) or building use (such as commercial building converted for residential use) potentially affect exposure to the vapor intrusion pathway; 4. Vapor intrusion mitigation systems are needed in buildings, or existing ventilation systems are being utilized for vapor intrusion mitigation, and continued access is sought to facilitate their O&M; 159

265 5. Response actions to reduce source contamination will not immediately meet response objectives; and 6. Response actions to reduce or eliminate source contamination will not be taken (for example, where it is technically impracticable to treat groundwater that is the source of vapor intrusion). Informational ICs may also serve to provide notice to parties, including prospective purchasers, about what land or building uses are compatible with human health risk that may be posed by vapor intrusion at the site. For example, modifications to a building s ventilation or air conditioning system may affect building under-pressurization in a way that fosters a greater potential vapor intrusion threat. Various ICs can be tailored to address construction and design specifications of both existing and future buildings a local ordinance, for example, may require parties to submit a building design to its building department that incorporates mitigation measures as determined appropriate by a Professional Engineer (P.E.) (see IC Example #1). In addition to restricting land, building, or resource use, some types of ICs may provide an effective means for addressing O&M at vapor intrusion sites consistent with decision documents and enforcement documents. This could happen, for instance, when an IC specifies that mitigation systems be installed and maintained in future construction or if the use of an existing building changes (e.g., industrial building use changes to mixed commercial or residential uses). Provisions regarding access to and periodic maintenance and testing of the mitigation systems, and other site-specific obligations may be incorporated into the IC (see IC Example #2). 160

266 IC EXAMPLE 1: City of Mandan, North Dakota Ordinance No (City of Mandan 2006) In 2006, the City of Mandan, North Dakota, enacted an ordinance that created an Environmental Institutional Control Zoning District to define an area of downtown Mandan impacted by petroleum contaminated soil and groundwater and to establish ICs for the protection of human health and the environment. Among other provisions, the ordinance requires any person proposing redevelopment, demolition, excavation, grading, or construction activities at properties within the District to submit to the city administrator or their appointee a contingency plan, approved by the North Dakota Department of Health, to evaluate and manage any petroleum contaminated soils or groundwater and any potential petroleum vapor impacts. The contingency plan must be prepared by a P.E. with experience in the environmental field, and the plan must consider and protect against, among other things, the vapor intrusion pathway. In addition, the ordinance also provides for restrictions on construction of new structures within the District. In pertinent part, the ordinance provides: Any person proposing to construct a new structure within the District shall submit a design for that structure that incorporates engineered controls to mitigate the effects of the potential presence of petroleum in the subsurface to the city administrator or their appointee. The design must be prepared by a P.E. and the design must be approved by the North Dakota Department of Health and must meet additional applicable codes and standards relative to the presence of petroleum. The design shall protect the public health and the environment by considering, at a minimum a) historic water/product intrusion; b) historic petroleum vapor/odor issues; c) potential future water/product intrusion; and d) potential future petroleum vapor/intrusion. The design shall incorporate vapor barriers, venting system, groundwater suppression/collection, and specialized HVAC as determined appropriate by a P.E. 161

267 IC EXAMPLE 2: State IC Legislation Some states have enacted statutes that directly authorize proprietary controls for the purpose of preventing use in conflict with environmental contamination or remedies. These state statutes divide into ones modeled after the Uniform Environmental Covenants Act (UECA) 226 and other non-ueca statutes. 227 These UECA and non-ueca state statutes tend to provide advantages over traditional common law proprietary controls by reducing certain legal and management complications associated with their use. The Model UECA, for instance, contemplates that the grantee or holder of the environmental covenant may be given specific rights or obligations with respect to future implementation of the environmental covenant. 228 This ability to oblige parties to undertake affirmative actions at a site, such as long-term maintenance of a cap or O&M of a vapor intrusion mitigation system, through a UECA environmental covenant, is different from traditional common law proprietary controls. Proprietary controls that bind current and subsequent landowners (that is, the proprietary control runs with the land ) to use restrictions at properties, as well as oblige them to undertake affirmative obligations, may have utility at vapor intrusion sites. For instance, at a contaminated site in Bucks County, Pennsylvania, an environmental covenant executed pursuant to the Pennsylvania Uniform Environmental Covenants Act contained provisions to address vapor intrusion threats. In addition to provisions for access, annual inspections, compliance reporting, and other specifications related to cleanup activities, parties to the environmental covenant agreed to construct slab-on-grade buildings without basements and install vapor barriers as an engineered control to mitigate the potential for vapor intrusion as part of the eventual development of the property. Further, the environmental covenant provided that engineering plans for the vapor barriers first be submitted to and approved by EPA prior to construction. For examples of environmental covenants executed pursuant to the Pennsylvania Uniform Environmental Covenants Act, Act No. 68 of 2007, 27 Pa. C.S : _environmental_covenants_act/ UECA w as developed by the National Conference of Commissioners on Uniform State Law s. See: w ww.uniformlaw s.org. 227 See, for example, Colo. Rev. Stat (2011); Cal. Civ. Code 1471 (2011). 228 Grantee is a traditional property law term describing a person to w hom property is conveyed. States that have passed legislation based on UECA have created different legal concepts specific to those jurisdictions. For example, UECA jurisdictions typically define holder and environmental covenant to reflect, respectively, the grantee and the servitude that imposes the land or resource use restrictions. The model UECA provides that [h]older means the grantee of an environmental covenant See definition 6 in Section 2.0 of the model UECA. 162

268 8.6.3 Selecting the Right Instrument(s) When evaluating potential IC instruments, EPA recommends that site managers and site attorneys balance the relative advantages and limitations of IC instruments under consideration for example, consider legal implementation issues, jurisdictional questions, permanence and enforceability concerns and select those that best achieve the response objectives. (IC Example #3 describes how these factors were considered at the Middlefield-Ellis- Whisman Study Area.) EPA guidance on ICs provides detailed considerations regarding the selection of ICs and the relative strengths of the different categories of IC instruments. 229 Ultimately, the selection of ICs is a site-specific evaluation based on the characteristics of the site (for example, the nature and extent of the vapor intrusion threat) and the particular jurisdiction in which it is located. There are times when multiple IC instruments can be layered to best ensure protectiveness of the response action while meeting the response objectives outlined in the decision documents. 230 Because many ICs are created pursuant to state and other non-federal laws, the authority to implement and otherwise oversee these ICs resides with government entities other than EPA. Units of local governments, for instance, typically have jurisdiction to implement, maintain, enforce, and terminate certain governmental controls, such as zoning ordinances and building permit conditions. Therefore, it is important to evaluate the capacity (financial, technical, etc.) and willingness of the entity ultimately responsible for taking over IC responsibilities prior to IC selection. 231 Site managers and site attorneys are encouraged to coordinate early with IC stakeholders so that adequate assurances may be acquired and then subsequently maintained as necessary over time. Given the potential role of non-epa entities, it may be appropriate for EPA to facilitate or recommend a process by which IC stakeholders provide similar assurances or otherwise reach a common understanding 232 regarding their respective IC responsibilities to ensure that selected ICs are effectively implemented, maintained, and enforced. At a vapor intrusion site, for example, a zoning ordinance may be effective in preventing or ensuring responsible future development of properties overlying a contaminated groundwater plume that presents a vapor intrusion pathway threat. Such zoning ordinances generally are designed and enacted by the local government. Once enacted, the ordinance must be followed and enforced for it to serve as an effective IC over its lifespan. One inherent limitation of governmental controls, however, is that their implementation, modification, and termination generally follow a legislative process 229 See Site Manager s IC Guide and Section 3.2 of the PIME IC Guide for a framew ork to consider w hen deciding among available ICs. 230 See Section 3.2 of the PIME IC Guide for more discussion on layering ICs. 231 See Section 3.8 of the PIME IC Guide on IC stakeholder capacity considerations. 232 Parties may be able to provide assurances or otherw ise reach a common understanding regarding their respective IC roles and responsibilities through various mechanisms that may be available under state law (for example, a Memorandum of Understanding, Memorandum of Agreement, Administrative Order on Consent, contract, City Resolution, or enforceable agreement, etc.). For additional discussion about obtaining or memorializing IC assurances, see Sections 3.3, 3.8, and 4.3 of the PIME IC Guide. 163

269 IC EXAMPLE 3: Efforts to Address VI at the Middlefield-Ellis-Whisman Study Area The Middlefield-Ellis-Whisman (MEW) Study Area is composed of four separate CERCLA sites Raytheon Corp., Intel Corp. (Mountain View Plant), Fairchild Semiconductor Corp. (Mountain View Plant), and portions of the former Naval Air Station Moffett Field Superfund site and many distinct parcels with land uses including residential, commercial, and light industrial. In 2009, EPA finalized a Supplemental FS for the MEW Study Area that presented an evaluation of a variety of remedial alternatives that could be used to mitigate potential vapor intrusion into current and future buildings overlying the shallow plume of contaminated groundwater. The FS provided an analysis of ICs using the NCP evaluation criteria: overall protection of human health and the environment; long-term protectiveness and permanence; compliance with applicable or relevant and appropriate requirements; reduction of toxicity, mobility, or volume through treatment; short-term effectiveness; implementability; and cost. The other two NCP evaluation criteria, state acceptance and community acceptance, were evaluated in the ROD Amendment for the vapor intrusion pathway remedy at the MEW Study Area. In 2009, EPA published the Proposed Plan for the MEW Study Area that identified EPA s preferred alternatives for the vapor intrusion remedy. The Proposed Plan identified the adoption of a municipal ordinance as EPA s preferred IC, but the City of Mountain View and concerned property owners raised concerns that this was not necessary. Instead, EPA worked with the City of Mountain View, California, to have the City formalize its permitting procedures that apply to future construction. These permitting procedures oblige those proposing new building construction within the MEW Study Area to obtain EPA approval of construction plans to ensure that, where necessary, the appropriate vapor intrusion control system is integrated into building construction. In a 2010 ROD Amendment, EPA presented its selected remedy for the vapor intrusion pathway for the MEW Study Area. The ROD Amendment identified a combination of ICs for use at the site. In place of a municipal ordinance as called for in the Proposed Plan, the ROD Amendment selected reliance upon the internally modified permitting procedures by the City of Mountain View s Building, Planning, and Permitting Departments. The City will also implement remedy requirements for projects subject to the California Environmental Quality Act through that law s procedures. With regard to existing commercial buildings where an active remedy is necessary, EPA selected the use of recorded agreements that will help provide notice to current and future owners and occupants, notice to EPA and the MEW Companies when there is a change in building ownership or configuration, and the necessary access to install, maintain and operate the vapor intrusion remedy. These agreements will be binding on and enforceable against future property owners. Additionally, EPA selected the use of a tracking service to provide notice when changes are made to properties within the MEW Study Area. Additional controls that will be implemented by the City of Mountain View include creation of a mapping database to help ensure that parties interested in properties within the MEW Study Area are informed of the appropriate construction specifications when making inquiries with the City. For more information on the MEW Study Area, see the Final Supplemental Feasibility Study for the Vapor Intrusion Pathway (June 2009), Proposed Plan for the Vapor Intrusion Pathway (July 2009), and Record of Decision Amendment for the Vapor Intrusion Pathway (August 2010), available at: 164

270 outside the authority of EPA that may raise questions regarding the reliability and continued sustainability of the IC. Obtaining early and continued assurances from a local government specifying its commitment to the governmental control is recommended to help address this limitation prior to its selection as part of a final cleanup plan. Certain IC instruments may not be available for use at a site, depending on federal, state, local, tribal, or other applicable laws. Therefore, after determining the universe of ICs available for use at a particular site, the practical and legal limitations can be evaluated. For example, large sites with widespread contamination pose unique IC challenges. These challenges could arise, for instance, where a contaminated groundwater plume underlies many distinct parcels with multiple property owners/occupants and vapor intrusion is the exposure pathway of concern. Negotiating and implementing proprietary controls with many property owners, some of whom may not be PRPs, may present legal, administrative, and other challenges Long-term Stewardship Long-term stewardship (LTS) activities are intended to help ensure that cleanups remain protective of human health and the environment over time and that reuse activities remain compatible with residual site contamination and associated human health risk potentially posed by the vapor intrusion pathway. LTS procedures vary widely, but they generally are intended to help assure compliance with the response actions at the site, including IC compliance, by providing relevant information in a timely manner to stakeholders who may use the property (e.g., owners, excavators, developers, prospective purchasers or tenants) or to parties who otherwise have IC responsibilities (i.e., an entity with enforcement authority). LTS procedures, for example, may entail provisions to monitor and then inform those responsible for the response actions of potential changes in land use, ownership, tenancy, or building construction at a site. Also, LTS procedures may facilitate monitoring IC(s) so that they remain effective and reliable over time. EPA guidance on ICs generally speaks to LTS procedures in terms of IC maintenance 234 and enforcement activities. 235 Periodic Reviews A key part of IC maintenance is a periodic process over the IC life cycle to critically review and evaluate the IC instrument(s). Site managers and other stakeholders can evaluate the status of IC implementation, maintenance and enforcement activities at a site and address any potential IC deficiencies during the periodic review. The CERCLA FYR process, 236 for example, allows site managers to evaluate overall protectiveness of the remedy, including ICs See Section 4.4 of the PIME IC Guide for strategies for implementing proprietary controls. 234 The term maintenance generically refers to those activities, such as monitoring and reporting, that ensure ICs are implemented properly and functioning as intended. 235 See Sections 8 and 9 of the PIME IC Guide discussing IC maintenance and enforcement activities. 236 See CERCLA section 121(c). 237 For general FYR guidance, see Comprehensive Five-Year Review Guidance (EPA 2001) at w ww.epa.gov/superfund/cleanup/postconstruction/5yr.htm. For a more detailed discussion on IC considerations during the CERCLA FYR process, see Recommended Evaluation of Institutional Controls: Supplement to the Comprehensive Five-Year Review Guidance, (EPA 2011c). 165

271 A list of possible IC-specific issues arising from any periodic review of a vapor intrusion site may include: ICs that are specified by the decision documents but are not yet in place; ICs that are in place but are not attaining compliance with the use restrictions specified by the decision documents (e.g., land use not compatible with IC-specified use restrictions); ICs are not identified in the decision documents but are necessary for the remedy to be protective of human health because of the vapor intrusion pathway; and Response selection assumptions change (e.g., toxicity values, potential exposure pathways, or land uses change) and warrant the need for new or different response actions, including additional IC(s). IC Planning Documents Responsibilities to monitor and report on IC compliance, among other obligations, may be documented in an Institutional Controls Implementation and Assurance Plan (ICIAP) 238 or other IC-related planning documents. 239 An ICIAP can serve to: (1) document the activities necessary to implement and ensure the long-term effectiveness and permanence of ICs (that is, the IC life cycle); and (2) identify the person(s) or organization(s) who, under state or local law, are responsible for conducting those activities. Some ICs generally fall within the jurisdiction of a particular category of stakeholders. Therefore, in addition to developing a comprehensive planning document, such as an ICIAP, it may be useful for parties who share IC responsibilities (e.g., a PRP and local government regarding the use of governmental controls, such as an ordinance or permitting system) to reach a common understanding and acknowledge various IC roles and responsibilities in a formalized manner. Where possible, EPA recommends that these types of arrangements among IC stakeholders be documented to describe commonly understood roles and responsibilities for proper and effective monitoring, reporting, and other IC maintenance and enforcement activities Community Involvement and ICs EPA recommends that site managers and site attorneys provide adequate opportunities for public participation (including potentially affected landowners and communities) when considering appropriate use of ICs (EPA 2012e). Those opportunities may include providing appropriate notice and soliciting comments about cleanup plans. Community acceptance of the need for ICs to provide protection from residual contamination and public understanding of the legal and administrative steps for maintaining ICs often are important to the long-term effectiveness of ICs. 238 For further guidance on developing ICIAPs, EPA developed Institutional Controls: A Guide to Preparing Institutional Control Implementation and Assurance Plans at Contaminated Sites (EPA 2012e). 239 For example, other types of documents may address IC-related activities and responsibilities at a site, such as a ROD, O&M plan, and land use control and implementation plan for federal facility sites. 166

272 8.7 Termination/Exit Strategy This sub-section focuses on the termination/exit strategy for vapor mitigation response actions. Termination for vapor mitigation activities implemented under CERCLA, RCRA, Brownfields, and federal facilities cleanups can occur when the objectives of these cleanup activities have been met. For purposes of this sub-section, termination refers to the cessation of all activities related to building mitigation, control of subsurface vapor source(s), ICs, and monitoring. When mitigating vapor intrusion through subsurface source remediation, building mitigation, and ICs, it is important to develop termination criteria, including the rationale for their selection, early in the remedy planning (e.g., alternatives development) process. (Termination criteria generally refer to numeric cleanup levels for each site-specific contaminant and narrative cleanup objectives that are to be attained by the response actions.) EPA recommends that these termination criteria be recorded in decision documents, in any other planning reports, and in monitoring reports. EPA generally recommends also developing and documenting an exit strategy, which clarifies how it will be determined that the termination criteria have been attained (e.g., monitoring data and associated statistics that will be used to demonstrate attainment). This document could be developed in conjunction with the O&M plan and monitoring program so that all stakeholders are provided with a clear and comprehensive set of termination criteria for the remediation and mitigation systems and ICs. If site conditions (e.g., building usage, vapor flux) change during the cleanup activities, it may become necessary to modify the termination criteria and/or strategy. When reviewing vapor intrusion activities, considerations for evaluating termination activities may include: Termination of subsurface remediation activities; Termination of engineered exposure controls (building mitigation); Termination of the associated ICs; and Termination of monitoring Termination of Subsurface Remediation Activities Where feasible, the preferred response to address vapor intrusion is to eliminate or substantially reduce the level of volatile chemical contamination in the source media (e.g., groundwater and subsurface soil) to levels that eliminate the need to mitigate or monitor vapor intrusion, as noted in Section 8.1 of this Technical Guide. If subsurface remediation activities are being conducted at the site, termination of these activities will be contingent on demonstrating that the chemicalspecific cleanup levels for the subsurface media have been attained. EPA recommends that the termination criteria and exit strategy for these remediation activities be documented to foster collection and evaluation of appropriate data to support eventual termination of these subsurface activities. EPA recommends that site-specific monitoring data be evaluated to determine if the termination criteria have been met. Typically, monitoring will continue until the source(s) are remediated to cleanup levels that eliminate the need to mitigate vapor intrusion at the point of exposure. As appropriate, the exit strategy may provide criteria for phased remediation, resulting in a 167

273 termination evaluation as source cleanup levels are achieved in parts of the contaminated area. If the subsurface vapor source(s) is not remediated, it is generally anticipated that remediation (and monitoring and any building mitigation) will continue. Monitoring, in part, could be based on data similar to those that were used in a multiple-lines-ofevidence approach for characterizing the pathway and human health risk or for supporting the decision to undertake preemptive mitigation/early action (e.g., soil gas sampling, sub-slab sampling, or vapor sampling within potentially affected structures). EPA recommends identifying and documenting target concentration(s) that would allow for remediation termination, along with recommended monitoring/sampling frequencies. If evaluation of the site-specific data indicates an increase in subsurface vapor concentrations during the monitoring period, it may be appropriate to evaluate whether the subsurface remediation plan and the CSM are adequate and appropriate. Typically, once it is preliminarily determined that the subsurface remediation system(s) may be terminated, EPA recommends a period of attainment monitoring. During the attainment period, EPA recommends that the remediation system (e.g., reagent delivery equipment, soil vapor extraction wells) not be operated for a sufficient period to allow subsurface vapors reach equilibrium and indicate post-remediation conditions. The type and frequency of data collected during attainment monitoring entails a site-specific determination. Additionally, EPA recommends that criteria be described and documented, as part of exit strategy development, to determine when ending the attainment monitoring period is appropriate. To develop an exit termination strategy, site-specific fate and transport data may be used to identify an appropriate time period to allow the vapor concentrations to equilibrate. In addition, the termination of the attainment monitoring period may involve an evaluation of the contaminant attenuation in the vadose zone Termination of Building Mitigation For purposes of this Technical Guide, termination of building mitigation refers to ending the use of an engineered exposure control(s) that reduces or eliminates human exposure via the vapor intrusion pathway. Typically, vapor mitigation is implemented when it is determined that (1) unacceptable human health risk to inhabitants is identified, or (2) the system(s) was(were) installed as part of an early action strategy (see Sections 3.3 and 7.8 for a discussion of building mitigation as an early action). As described in Section 8.2, vapor intrusion can be mitigated in specific buildings using either an active or passive vapor mitigation system (or a combination thereof). Active Building Mitigation Generally, building mitigation systems are implemented in conjunction with the investigation and remediation of subsurface vapor source(s). Typically, building mitigation systems will be operated until the source(s) are remediated to attain the cleanup levels (e.g., for the subsurface vapor source(s)) that eliminate the need to mitigate vapor intrusion at the point of exposure. If subsurface vapor source(s) are not remediated, it is generally anticipated that mitigation activities will continue indefinitely. As appropriate, the termination strategy may provide criteria for phased evaluation of system cessation as source cleanup levels are achieved in parts of the contaminated area. 168

274 Generally, once the subsurface vapor source(s) is remediated to levels that meet the remedial objectives and protect human health from the vapor intrusion pathway, EPA recommends that the site-specific monitoring data be evaluated to determine if the termination criteria for the building mitigation system have been met. These monitoring data, in part, could be based on data similar to those that were used for characterizing human health risk or for supporting the decision to undertake preemptive mitigation/early action during the vapor intrusion investigation (e.g., sub-slab soil gas sampling and/or indoor air sampling). EPA recommends identifying and documenting target concentration(s) that would allow for system termination, along with recommended monitoring/sampling frequencies. In addition, certain site-specific performance assessment data (e.g., standpipe vapor sampling) may also warrant consideration to make this determination. Typically, once it is determined that the building mitigation system may be terminated, EPA recommends a period of attainment monitoring. During the attainment period, EPA recommends that the mitigation system (e.g., subslab suction wells or ventilation fans) be offline for a sufficient period to allow vapors beneath the structure reach equilibrium and indicate postremediation conditions. The type and frequency of data collected during attainment monitoring entails a site-specific determination. Additionally, EPA recommends that criteria be established in the exit strategy to determine when ending the attainment monitoring period is appropriate. To develop an exit termination strategy, site-specific fate and transport data may be used to identify an appropriate time period to allow the vapor concentrations to equilibrate. In addition, the termination of the attainment monitoring period may involve an evaluation of the contaminant attenuation in the vadose zone. If the attainment criteria evaluation indicates that cleanup levels and objectives are not being met, it may be necessary to continue or resume subsurface remediation and mitigation activities. Once it is determined that the cleanup levels and objectives have been met, the active components of the system may be removed from the building; on the other hand, the building owner may elect to continue to operate the mitigation system under their own discretion and for their own purposes (e.g., radon reduction and moisture control). Once the cleanup levels and objectives have been met, all O&M and monitoring of active mitigation systems specified by EPA can cease. Passive Building Mitigation The termination of passive vapor mitigation systems will typically be similar to the criteria established for the termination of active mitigation systems. In summary: Like active mitigation systems, passive mitigation systems are typically implemented in conjunction with the investigation and remediation of subsurface vapor source(s). Generally, once the subsurface vapor source(s) is remediated to levels that meet the cleanup levels and objectives that will protect human health from the vapor intrusion pathway, EPA recommends that the site-specific monitoring data be evaluated to determine if the termination criteria have been met. If the site-specific criteria evaluation indicates that cleanup levels and objectives are not being met, it may be appropriate to evaluate the current system s effectiveness or the possible application of an active mitigation system. Once it is determined that contaminant cleanup levels and objectives have been met, all O&M and monitoring specified by EPA can cease. EPA 169

275 generally does not have a need to seek removal of barriers or seals that comprise a passive mitigation system as part of termination activities Termination of ICs Termination of ICs, as used in this Technical Guide, refers to discontinuing any and all ICs specified by EPA because restrictions on land or resource use and/or notices and other informational devices are no longer necessary to help ensure protectiveness of human health (i.e., human health risk from exposures to vapor intrusion, if any, are expected to be acceptable in the absence of all IC(s)). Generally, ICs are implemented in conjunction with the investigation and remediation of source(s). It is anticipated that ICs selected and implemented will be needed until (1) subsurface vapor source(s) are adequately remediated, or (2) restrictions on land, resource, or building use are no longer necessary based on current and reasonably anticipated future exposure scenarios. Therefore, when developing a termination strategy for ICs that have been selected as part of a response action, the strategy is typically based on data collected from the affected media. EPA recommends that the exit strategy consider and identify cleanup levels for the subsurface vapor source(s). As long as the subsurface vapor source exceeds such cleanup levels, it is generally anticipated that the associated ICs will continue. As appropriate, the termination/exit strategy may provide criteria for a phased IC termination evaluation as source cleanup levels are achieved in parts of the contaminated area. If the site-specific criteria evaluation indicates that terminating the ICs is appropriate, EPA may conclude that site conditions no longer warrant ICs being used as part of the response action for the vapor intrusion pathway. At this point, EPA could notify the appropriate entity(s), such as local or state government, tribe, affected landowner, or responsible parties, in writing that EPA s response objectives have been met and that the IC need not be maintained. As such, EPA s oversight of the IC(s) can cease Termination of Monitoring For purposes of this Technical Guide, monitoring includes activities conducted to verify that the vapor intrusion pathway does not pose a health concern to building inhabitants while remediation and mitigation activities are underway and in the event that the remediation and mitigation activities are terminated. Termination of monitoring, for purposes of this Technical Guide, refers to ending any monitoring that was needed to verify that no further response action, including IC-related activity, is necessary to protect human health from indoor air exposures posed by vapor intrusion. When developing termination criteria for monitoring, the decision is generally based on data collected from all the affected media. As noted above, monitoring is generally implemented in conjunction with the remediation of subsurface vapor sources(s). EPA recommends that the exit strategy consider cleanup levels for all contaminated media. Typically, monitoring will continue until the source(s) are remediated to cleanup levels that eliminate the need to mitigate vapor intrusion at the point of exposure (i.e., allow building mitigation systems to be terminated). If the subsurface vapor source is not remediated, it is generally anticipated that any associated monitoring will continue. As appropriate, the exit strategy may provide criteria for phased monitoring, resulting in a termination evaluation as source cleanup levels are achieved in parts of the contaminated area. 170

276 Figure 8-1 Illustration of Sub-slab Depressurization (SSD) System Note: Shows one example of how a sub-slab depressurization system might be constructed. In this case, the example suction pipe has been inserted vertically downward through the slab from inside the house. Two options are indicated for location of the exhaust fan: one exterior to the building; and the other within an attic. In both of these cases, the exhaust gas stream is to be vented outside and above the building. Source: EPA (1993a; Figure 1) 171

277 Figure 8-2 Illustration of Drain-tile Depressurization (DTD) System Note: Shows one example of how a drain-tile depressurization system might be constructed. In this case, tiles are shown draining to a sump in the basement, to which an air-tight cover is sealed. The example suction pipe has been inserted vertically downward through the slab at a location remote from the sump. Two options are indicated for location of the exhaust fan: one exterior to the building; and the other within an attic. In both of these cases, the exhaust gas stream is to be vented outside and above the building. Source: EPA (1993a; Figure 3) 172

278 Figure 8-3 Illustration of Block-wall Depressurization (BWD) System Note: Shows one example of how a block-wall depressurization system might be constructed. In this case, individual suction pipes are inserted into the void space in the basement wall, which are connected to one or more fans. Source: EPA (1993a; Figure 5) 173

279 Figure 8-4 Illustration of Sub-membrane Depressurization (SMD) System Note: Shows one example of how a sub-membrane depressurization system might be constructed. In this case, the example suction pipe penetrates the membrane overlying a dirt floor. Source: EPA (1993a; Figure 6) 174

280 9.0 PLANNING FOR COMMUNITY INVOLVEMENT Communicating information about environmental risk is one of the most important responsibilities of site managers and community decision-makers. Simply stated, risk communication, whether written, verbal, or visual statements concerning risk, is the process of informing people about potential and perceived hazards to their person, property, or community. EPA recommends that human health risk be described in context, recognizing there are personal, cultural and societal dimensions of risk. EPA also recommends providing advice about risk-reduction behavior and encouraging a dialogue between the sender and receiver of the message. The best risk communication occurs in contexts in which the participants are informed about risks they are concerned about, the process is fair, and the participants are free and able to solve whatever communication difficulties arise. Risk Communication in Action: The Risk Communication Workgroup (EPA 2007) is one of several resources available that explain the elements of successful risk communication and describe communication tools and techniques. Thus, community involvement is a key component of any site investigation or other EPA response action. Members of the public affected by environmental contamination can be made aware of what EPA is doing in their community and have a say in the decision-making process. Stakeholder and community involvement is particularly important for sites with vapor intrusion issues, in part because the exposure to toxic vapors may pose a significant human health risk that is unknown to inhabitants (in the absence of mitigation systems), as they potentially arise in homes, workplaces, schools, and places of commerce and gathering. Because of the potentially intrusive nature of assessment and mitigation for vapor intrusion, stakeholder involvement is important throughout the process. EPA generally recommends that stakeholder and community involvement be conducted from the earliest stage of the site assessment and risk assessment process, with on-going education, two-way communication, and discussion throughout the entire process to create community trust and acceptance. For example, EPA recommends initiating community involvement activities as soon as possible after determining that vapor intrusion may exist at a particular site. Informing the community about vapor intrusion concerns and plans to conduct an assessment, including sampling, can be resource intensive. Thus, EPA recommends evaluating each project, in coordination with appropriate state and tribal officials, to assess the level of stakeholder interest and need for community involvement during various stages of the decision-making process. Public Participation and Risk Communication A meaningful community involvement process is founded upon knowledge of effective public participation and risk communication practices. Public participation refers to the full range of activities that EPA uses to engage communities in the Agency's decision-making process. In 2003, EPA updated its Public Involvement Policy. 240 Its foundation includes seven basic steps to support effective public participation: 240 EPA Public Involvement Policy (2003): w w.epa.gov/publicinvolvement/policy2003/index.htm. 175

281 1) Plan and budget. 2) Identify those to involve. 3) Consider providing assistance. 4) Provide information. 5) Conduct involvement. 6) Review and use input and provide feedback to the public. 7) Evaluate involvement. To help implement the steps, EPA developed a series of brochures 241 on effective public participation that outline how to budget for, plan, conduct, and evaluate public participation. EPA Program-Specific Community Involvement Guidance and Recommendations CERCLA and other EPA regulations 242 identify specific community involvement activities that are appropriate at certain points throughout the cleanup process. Specifically, in 2005, OSWER published the Community Involvement Handbook 243 (EPA 540-K ). The handbook presents legal and policy motivations for Superfund community involvement and includes additional suggestions for involving the community in the Superfund process. In addition, EPA s Proposed Guidelines for Brownfields Grants encourages applicants to describe their plans for involving community-based organizations in site cleanup and reuse decisions. 244 The Grant Funding Guidelines for State and Tribal Response Programs for brownfields funding also encourage programs to establish, at a minimum, mechanisms and resources to provide meaningful opportunities for public participation. 245 In addition, in 1995, EPA promulgated the RCRA Expanded Public Participation rule (60 FR , December 11, 1995) 246 which created additional opportunities for public involvement in the permitting process and increased access to permitting information EPA Public Involvement Brochures: ww.epa.gov/publicinvolvement/brochures/index.htm CFR EPA Superfund Community Involvement Handbook: w w.epa.gov/superfund/community/cag/pdfs/ci_handbook.pdf 244 EPA Brow nfields Grants w ebsite: w w.epa.gov/brow nfields/cleanup_grants.htm 245 EPA Brow nfields State and Tribal Response Program Grants w ebsite: w w.epa.gov/brownfields/state_tribal/fund_guide.htm 246 Section 7004(b) of the Resource Conservation and Recovery Act provides EPA broad authority to encourage and assist public participation in the development, revision, implementation, and enforcement of any regulation, guideline, or program under RCRA. 247 EPA RCRA Public Participation Manual: ww.epa.gov/osw /hazard/tsd/permit/pubpart/manual.htm 176

282 At sites with vapor intrusion issues, EPA recommends that the site planning team (i.e., the remedial project manager (RPM) or on-scene coordinator (OSC); community involvement coordinator (CIC); risk assessor; the enforcement case team; EPA contractor; state, tribal, or local agency staff; federal agency staff relevant to the site; or others) to consider the following: Develop a community involvement plan (CIP) or update the existing CIP. Learn about the site and the community to foster development of a CIP that highlights key community needs, concerns and expectations. Commit to ongoing, sustained communication activities throughout vapor mitigation and site cleanup efforts. Develop a communication strategy 248 and conduct outreach to inform stakeholders about the facts and findings pertaining to the site. Obtain written permission, if appropriate and necessary, for building/property access, and involve the property owner/occupant in identifying or removing potential indoor air contamination sources, including inspection of residence and completing an occupant survey. Fully communicate and interpret sampling results, and evaluate mitigation options, if any are warranted. Recognize preference of owners and occupants for confidentiality with regards to property-specific data. When considering the most effective community involvement strategies, EPA recommends that its previous involvement be considered, as well as the existence of community or neighborhood groups and the phase of the regulatory process in which vapor intrusion is being addressed. Additional resources for planning and implementing effective community involvement activities are discussed in Section 9.2: Communication Strategies and Conducting Community Outreach. 9.1 Developing a Community Involvement or Public Participation Plan A CIP is a site-specific strategy to enable meaningful community involvement throughout the cleanup process. 249 CIPs specify EPA-planned community involvement to address community needs, concerns, and expectations that are identified through community interviews and other means. A CIP will enable community members to understand the ways in which they can participate in decision-making throughout the cleanup process. That is, the CIP is a way for EPA to plan for informing and involving the community in the cleanup process and can be a powerful 248 A communication strategy can be one component of a CIP, but it addresses a specific event, issue, or concern, such as an emergency response to a release, or communicating risk at a site. The CIP, on the other hand, describes an overall strategy for conveying information throughout the cleanup process at a site. 249 Community involvement plans available at: w w.epa.gov/superfund/community/pdfs/toolkit/ciplans.pdf 177

283 way to communicate EPA s commitment to listening and responding to community concerns, and provide timely information and opportunities for community involvement. The CIP is intended to be a living document and is most effective when it is updated or revised as site conditions change. When developing the CIP document, EPA recommends that the site planning team consider the following steps: Describe the Environmental Setting and Cleanup Process Describe the release and affected areas (the site). This includes information about the site, its history, the key issues related to site contamination, and how vapor intrusion fits into EPA s overall cleanup effort at the site. Describe and Learn about the Community Describe the community. The community profile is a description of the affected community that summarizes demographic information and identifies significant subgroups in the population, languages spoken, and other important characteristics of the affected community, such as whether the site is located in an area with environmental justice concerns or includes sensitive populations. EPA recommends that the community profile also document information sources and describe how the profile was developed. Learn about community needs, concerns and expectations: Issues of concern to residents and business owners can be identified through community interviews, informal discussions and interactions, local media reports, and other insights about the affected community. Questions may include: What are public perceptions and opinions of EPA and the cleanup process? How do people want to be kept informed (i.e., mechanisms to deliver information)? How do people want to be included in the decision-making process? What are the perceived barriers to effective public participation? Are there other sources of pollution that affect the community? Have there been past experiences of mistrust or any unique concerns? This information can be used to recommend any special services to be provided, including technical assistance, formation of a Community Advisory Group, facilitation/conflict resolution, or translation services. Write and Compile the CIP Once the site planning team has learned about the community, it is time to put the information together in a way that will be useful to EPA and the community. In addition to the site description, community description, and community needs and concerns, the CIP also may include a reference listing of contacts (name, address, phone, ) useful for the 178

284 community or the site planning team. EPA recommends that the contact list generally include contact information for: The site planning team. Community groups and community leaders. Local elected officials. Local, state, tribal, and federal agency staff relevant to the site. Media contacts (including social media outlets and community journalists). Others, as appropriate. To ensure that the CIP is indeed informed by the community, EPA recommends that a draft of the CIP be shared with the community, and their input and feedback be invited as it evolves. Again, the CIP is intended to be a living document and is most effective when it is updated or revised as site conditions change. In some cases, particularly when the CIP is updated or revised for a FYR or where community interest is minimal, a short CIP outlining EPA s plan for community involvement may be all that is needed. For most sites, EPA recommends that the CIP be written to address the community directly, and their active involvement be invited at each stage of the cleanup process. 9.2 Communication Strategies and Conducting Community Outreach EPA recommends that community outreach activities be initiated as soon as possible after determining that vapor intrusion may exist at a particular site. Informing and educating the community includes distributing information and providing opportunities for EPA to listen to community concerns. EPA recommends community outreach activities be tailored to the community based on information gleaned from community interviews and other methods used in developing the CIP. Public health officials from state, tribal, or local agencies may be helpful in communicating risk information and answering questions from the community. Communication Strategies Communication strategies are plans for communicating information related to a specific issue, event, situation, or audience. They serve as the blueprints for communicating with the public, stakeholders, or even colleagues. EPA recommends that communication strategies: Outline the objective and goals of the communication. Identify stakeholders. Define key messages. Pinpoint potential communication methods and vehicles for communicating information and obtaining information from the community for a specific purpose. 179

285 When developing a communication strategy, the first step is to determine why the communication is necessary and define its desired objectives, and then to focus on defining the audiences and how to reach them. Keep in mind that the demographics, knowledge, and concerns of the audiences play an important role in defining the key messages. Once the key messages are defined, the outreach vehicle can be determined. Conducting Community Outreach The site planning team likely will use several different outreach techniques during the course of the cleanup process. When planning community outreach, EPA generally recommends that the site planning team collaborate with internal and external partners, such as local, state, and tribal officials and departments of health; faith-based organizations; and community groups. It is important to accommodate hearing-impaired or limited English proficiency (LEP) 250 persons in all outreach efforts by providing spoken or sign language interpreters at meetings and translating printed outreach materials. It also is important to ensure that the community understands the concept of vapor intrusion. Examples of community outreach techniques to consider are described below. Public Meetings/Gatherings Public meetings are a useful opportunity to explain environmental conditions at the site, potential health impacts, intended indoor air sampling, and remediation strategies. It may be helpful to hold meetings prior to and following key sampling events to describe sampling strategies and consequent results, respectively. EPA recommends that the meeting include a period to address specific questions from the public regarding sampling results or any other specific concerns, as well as visual aids and maps and spoken or sign language interpreters to facilitate communication and discussion. The use of a CSM, for example, is useful in public meetings to graphically reinforce the messages. It may be helpful to follow up with meeting participants to inquire about the effectiveness of the meeting and whether it met their needs. Other meeting follow-up activities could include responding to requests for information, distributing meeting notes, and creating a mailing list. Additional opportunities for the site planning team to communicate with the community in a group setting include public availability sessions and public forums or poster sessions at community group meetings or neighborhood board meetings. These options are a more informal way of interacting with community members and they allow a casual question and answer or discussion format as compared to the more formal presentation at a public meeting. Mass Media The media can be the best means of reaching a large audience quickly. Extending invitations to the media for important meetings, providing opportunities for media questions 250 Executive Order 13166, Improving Access to Services for Persons with Limited English Proficiency, directs federal agencies to examine the services they provide, identify any need for services to those w ith LEP, and develop and implement a system to provide those services so LEP persons can have meaningful access to them. 180

286 to be addressed in a timely manner, and recognizing that the media control the content of their publications all are important considerations when working with the media. The site planning team can work with the Agency s regional site press officer to foster a relationship with the media by sharing the Agency s rationale for its plans and actions. It is appropriate to use the media to publicize a site-related decision, an upcoming meeting, changes in schedule, or changes in activities or expectations. Press releases can be used to inform the media of major site-related milestones. Fact Sheets Communities appreciate concise, easy-to-understand, and technically accurate fact sheets on the history of the contamination, chemicals of concern, human health risk, planned cleanup activities, and the vapor intrusion assessment and response actions. Be sure to include who to contact for more information. Because sites involving vapor intrusion can be complex, it may be useful to include additional information in the fact sheets for home owners and renters, including information about household products that may be potential sources of indoor air contamination, as well as steps that can be taken to minimize these sources. EPA recommends preparing and distributing periodic status updates and fact sheets to concerned community members throughout the cleanup process. Letters Whenever there are plans to conduct indoor air sampling, EPA recommends sending a letter to each building owner and renter explaining plans to conduct indoor air sampling and requesting written permission for voluntary access to do so. In addition, a one-on-one meeting with the building owner or renter is generally recommended to discuss sampling efforts and access agreements in detail (see Section 9.3). EPA also recommends that letters be sent to each building owner and renter to report sampling results in a timely manner (see Section 9.4). These letters and meetings often are part of a larger effort that also includes use of other communication strategies, such as community meetings and in-person visits. In-person Visits EPA recommends individual, one-on-one communication with each property owner and renter whenever possible. Try to schedule in-person visits with individual property owners and renters. These visits also may include owners and renters of properties located outside the planned investigation area. The initial visit can be used to explain sampling plans in more detail, answer questions, and obtain written permission to sample. During the visit, the property owner or renter can be briefed about any instructions to follow during sampling activities (for example, keep doors and windows closed during sampling). A general survey of the building could be conducted to determine likely sources of indoor air contaminants. 181

287 EPA recommends the site planning team also describe to owners and renters the sampling devices that will be used, what they look like, where they will be located, and any restrictions or impediments to daily activities that may arise from the ongoing sampling activities. Information Repository An information repository can be established and maintained prior to, during, and following site activities, which is generally required for sites where remedial action or removal actions (where on-site action is expected to exceed 120 days) are undertaken pursuant to CERCLA. The information repository is intended to include the administrative record, fact sheets, question-and-answer sheets, and other site-related documents and be located reasonably near the site. However, given the tremendous change in information technology, it may also be appropriate to set up an Internet-based or digital repository (webpages) to share key information. This depends on the community s ability to access and utilize this technology. EPA recommends that community members be made aware of the information repository through the other public outreach mechanisms described above (e.g., local media, newsletters, and public meetings). Electronic Notification It also may be useful to establish a registration capability that allows interested community members to sign up for automatic alerts to updates posted on the site website or listserv. 9.3 Addressing Building Access for Sampling and Mitigation EPA recommends that all requests for access, as well as provision of access, be in writing in order to document EPA s due diligence to protect human health at the site. EPA recommends that the site planning team provide building owners and occupants with information about the sampling device(s)) being used, including what they look like, where they will be located and any restrictions or impediments to daily activities that may arise due to ongoing sampling. In the case of an initial refusal to provide access, additional attempts for access are generally recommended, although regional practices may vary. EPA recommends documenting all attempts to gain access, for example using telephone conversation records, s, or letters sent to home or building owners. Gaining access to owner-occupied residences for vapor intrusion sampling and mitigation may be handled differently than for commercial buildings or rental properties. Owner-Occupied Residences: Allowing EPA to sample or install mitigation systems in an owneroccupied residence is a voluntary action. EPA generally encourages owners to take advantage of an offer for an assessment and mitigation system, if necessary. Rental Properties: Access may be voluntary or involuntary. Site planning teams often deal with both owners and renters when there is a need to sample on, in, or under a rental property. There are different legal and communication issues for owners and renters. For example, the owner is responsible for granting access for sampling and for installation of mitigation measures, if they are necessary; however, if the owner grants access, logistics normally are 182

288 arranged with the renter. EPA recommends apprising both the owner and the renter of human health risk that may be posed by vapor intrusion, which includes providing building-specific sampling results to both parties when available. If the owner of a rental property refuses access, EPA may, nevertheless, pursue access, in the interest of protecting the occupants, for determining the need for response, choosing a response action, taking a response action, or otherwise enforcing CERCLA or RCRA (EPA 1986, 1987, 2010a). Notifying the owner of a rental property of this statutory authority may help to avoid the need for legal action. Nonresidential Buildings: Site managers also may need to sample on, in, or under nonresidential buildings, such as schools, libraries, hospitals, hotels, and stores. In these situations, broader outreach to the public may be appropriate in addition to maintaining direct contact with the property owner. Similar to rental properties, access for sampling and for implementation of mitigation methods, if they are necessary, may be voluntary or involuntary. If the owner of a nonresidential building refuses access, EPA may, nevertheless, pursue access, in the interest of protecting the occupants, for determining the need for response, choosing a response action, taking a response action, or otherwise enforcing CERCLA or RCRA (EPA 1986, 1987, 2010a). Property Ownership Changes: For owners of homes or buildings who did not provide access for assessment sampling or installation of a mitigation system, EPA recommends that the site planning team make reasonable attempts to track ownership changes, although the appropriate state, tribal, or local agency or PRP may be in a better position to track this information. For example, reasonable attempts to make contact can be done by annually conducting drive-bys or inspections and noting homes or buildings for sale, periodically checking on-line real estate sales or title insurance listings, or using other mechanisms. Homes that were initially targeted but not sampled can be reconsidered during the review or if there are major changes to the toxicity values for the site contaminants of concern. Annually mailing notifications to buildings not previously sampled is a means to foster reconsideration of testing with a change in ownership. If ownership changes are noted, appropriate follow-up can be conducted with the new home owner or building owner. Federal statutory authority to access private property to conduct investigations, studies and cleanups pursuant to CERCLA and RCRA is discussed in Section 1.2 of this Technical Guide. 9.4 Communication of Indoor Sampling Efforts and Results The community involvement plan or public participation plan is intended to address community concerns and participation regarding indoor air and sub-slab sampling. In addition to the general community involvement activities occurring throughout the cleanup process (see Section 9.2), the site planning team may choose to hold a community meeting to discuss indoor sampling efforts and results. EPA recommends sending a letter to each home or building owner and renter explaining plans to conduct sampling or providing sampling results. EPA recommends that this letter be in addition to a one-on-one meeting with the building or home owner to discuss access agreements, sampling efforts, and sampling results. Prompt communication of sampling results to building or home owners is important as some people may choose to make precautionary decisions prior to regulatory decisions on remediation or mitigation measures. EPA recommends the site planning team inquire about stakeholder preferences for confidentiality with regards to property-specific data. It may be appropriate to segregate data for private residential properties versus community properties (e.g., schools, daycare centers, 183

289 commercial buildings) or provide different types of property identifiers for these respective building types in reports and maps and tables displayed at public meetings or otherwise made available to the community. Letters Transmitting Sampling Results 251 EPA recommends that the site planning team provide validated sampling results and interpretations (e.g., chemicals of concern, associated risk assessment implications) in plain English (and translations, if necessary) to property owners and renters in a timely manner (e.g., within approximately 30 days of receiving the results). EPA also recommends the transmittal letter indicate what future actions (e.g., mitigation options), if any, are contemplated, 252 based on the sampling results, and contain additional site-specific and possibly building-specific information, including, but not limited to: Site and Home/Building Information. o Site name and location of contamination. o Date of sampling. o Address of sampled home or building. o Locations sampled (both indoor and outdoor). Sampling Results o Sampling results for site-related, vapor-forming chemical(s) and for any other chemicals, if detected, including an explanation of results believed to be attributable to background sources, if known. 253 o Risk-based screening levels (for example, VISLs described in Section 6.5) or other riskbased benchmarks used to explain and interpret the sampling results. o Explanation and interpretation of sampling results, if known, which may include a summary of the human health risk assessment, if available (see Section 7.4) Within the community of risk professionals, the phrase risk communication has come to mean communication that supplies lay people w ith the information they need to make informed independent judgments about human health risk or public safety (Morgan et al. 1992). In this case about vapor intrusion, the ultimate goal of risk communication is to assist stakeholders and the general public in understanding the investigation data and the rationale behind any risk-informed decision, so they may arrive at a balanced judgement that reflects the factual evidence in relation to their ow n interests and values. 252 This section may include an explanation of mitigation process and responsibilities and a timeline for further contact regarding system installation and options. If a building mitigation system is recommended on the basis of a human health risk assessment, EPA recommends that the site planning team explain that the risk calculation reflects conservative, health-protective factors. 253 With such information, EPA can help advise citizens about the environmental and public health threats they face that are w ithin their control (e.g., from indoor sources). In cases w here background contamination may pose a human health risk, but its remediation is beyond the authority of the applicable statute, risk communication to the public may be most effective w hen coordinated w ith public health agencies (EPA 2002e). The public may also be advised about the scope and limits of EPA s statutory authorities. 254 Assessment uncertainty is generally an important factor in deciding how to act (Frew er 2004); i.e., w hether to reduce risk through response action or reduce uncertainty (e.g., through additional monitoring and data collection). Risk professionals, therefore, generally recommend that risk communication to stakeholders and the general public characterize the sources of uncertainty, as w ell as the magnitude of uncertainty associated w ith a particular hazard (see, for example, Frew er (2004) and Markon and Lemyre 92013)). 184

290 o Simple tabulated and color-coded results (representing exceedances of human health risk levels or no exceedance). Diagrams/Illustrations o Diagrams and illustrations of sampling devices. o Diagrams and illustrations of sampling locations o Diagrams of specific mitigation systems (e.g., how a SSD system works and looks). Next Steps o Actions that property owners and occupants can take to reduce vapor intrusion exposure until mitigation systems are in place. Information Sources o Contact information for a person who can answer questions or supply further explanations. o The location of the site information repository or site website can be included as a resource for public access to more detailed information and site documents. 9.5 Transmitting Messages Regarding Mitigation Systems The initial notification to residents or building owners about mitigating vapor intrusion can be delivered in various ways. A primary mechanism is a face-to-face meeting with the building owner or occupant to explain the sampling results and discuss next steps, including installation of a vapor intrusion mitigation system. EPA recommends that this meeting include a member of the site planning team (RPM or OSC and risk assessor, for example), a representative from the local health department or the Agency for Toxic Substances and Disease Registry (ATSDR), and the mitigation contractor scheduler. This meeting could discuss topics such as: Sampling Results: Describe where samples were taken and the chemicals of concern, and explain the results as related to site action levels. Any questions related to human health risk can be answered by the risk assessor or public health representative at this time. For questions or concerns regarding personal health, EPA recommends that residents and building owners contact their medical professional. Mitigation System Details: Describe the need for a mitigation contractor to visit the residence to identify potential locations for the mitigation system. The property owner will need to be present for the visit and will have input about where the system is installed, if they agree to install such a system. Photos of a mitigation system (piping, system fan, number of holes drilled in the slab, height of the vent on the outside of the residence, etc.) may be helpful. EPA recommends that plans and schedules for periodic inspection, maintenance, and monitoring also be described. Access: EPA recommends advance planning to ensure building access to install, monitor and maintain any mitigation system. Arrangements could be made at this meeting to sign an additional access agreement for these activities, if needed. Cost of the Mitigation System: Identify which party will pay for installation of the mitigation system and anticipated property-owner costs. For example, EPA or a PRP may pay for the 185

291 system installation, and the property owner or PRP may take responsibility to pay for the monthly costs associated with the mitigation system. Project Schedule and Next Steps: The meeting may be concluded by giving an overview of the overall project timeline, including the appointment for the mitigation contractor visit and system installation. Notification also can be provided through the data transmittal letter. In many cases, however, the decision to install mitigation systems will not have been made prior to the transmittal of sampling results. In these situations, data transmittal letters can convey that EPA is reviewing all data results for the affected area and considering appropriate next steps. Once the decision document is signed, the site planning team can develop and mail a fact sheet to all community members in the affected area, followed by a community meeting. In addition, if a vapor intrusion mitigation system is installed, EPA recommends that the property owner or renter be informed that the system normally is designed to protect the home or building only against vapor-forming chemicals coming from the subsurface. A vapor intrusion mitigation system generally will not protect the home against continuing indoor sources because vapor intrusion mitigation systems typically are not indoor air filtration systems. EPA recommends that current owner-occupants be advised that if they decline or waive an offer to install a vapor mitigation system, they might be responsible for the costs of installing and maintaining their own system if they decide to do so at a later time. EPA also recommends documenting any declination or waiver. 9.6 Addressing Community Involvement at Legacy Sites Ongoing site activities with assessment components, such as remedial investigations and monitoring, allow EPA to continually evaluate site conditions and adjust cleanup actions as warranted. During periodic reviews or conducting other site activities, such as the FYR pursuant to CERCLA, EPA has evaluated vapor intrusion where appropriate. In some instances, EPA has newly identified vapor intrusion as an exposure pathway. These mature or legacy sites present a unique challenge to site planning teams. Conducting community involvement at legacy sites may be complicated by several factors including: A remedy for the control of exposure to volatile chemicals already has been installed, proposed, or is under construction as part of the cleanup plan. Ownership of properties previously exposed to VOCs has changed hands through resale, foreclosure, or assumption of the property by second-generation homeowners. These owners were not part of any original resolution of exposure issues and in many cases may not be aware that a remediation or treatment was put in place. Property owners and other community members who participated in prior cleanup efforts may be reluctant to fully engage with efforts to reopen lines of investigation at their properties. 186

292 In these and similar circumstances, the challenge for Agency representatives is to resume contact with communities who have put past difficulties behind them. In many cases, mailing lists are outdated, previous reliable contacts no longer are available, and elected officials may not have institutional memory of the events that prompted the remediation. Strategies for Revitalizing Community Involvement at Legacy Sites Every legacy re-entry will be a site-specific situation. Therefore, EPA recommends that events and activities be planned to acknowledge and accommodate the inevitable changes in the makeup of a community. In addition to the communication strategies and community involvement techniques described in Sections 9.1 through 9.5, additional suggestions to ease re-entry and revitalize community involvement at a legacy site include: Reassess the community and the site by revisiting the site and the surrounding areas and taking note of new construction. Reintroduce yourself and the Agency to current municipal staff and check previously used public venues for viability. Determine if new venues may be closer or more accessible to the community. If contacts within the community are still extant, reconnect; ask for updates on the growth and stability of the community. If no viable contacts exist, attempt to cultivate new ones. Revise and update mailing lists and fact sheets. As with all sites affected by vapor intrusion issues, be prepared to meet with property owners door to door and to hold public meetings or forums to explain the current investigation and its importance to protecting human health. 9.7 Property Value Concerns for Current and Prospective Property Owners EPA recognizes that vapor intrusion impacts may have implications for property values. In some instances, mitigation systems and other clean-up measures may help to restore property values. Nevertheless, property value issues are outside the scope of Agency authority. In general, if asked, EPA recommends that regional staff suggest that prospective buyers and sellers contact real estate professionals and lenders from the local area with questions about property values. If a home owner or renter has questions about vapor intrusion mitigation systems, EPA regions can provide information that explains how vapor intrusion systems are designed to reduce exposure to chemicals found in indoor air and to avert human health-related problems. 9.8 Additional Community Involvement Resources EPA s Superfund Community Involvement Program: EPA s Superfund Community Involvement website contains many resources that may be helpful for planning community involvement activities for other cleanup programs. This resource includes a list of regional Superfund community involvement points of contact, a list of technical 187

293 assistance and training resources, and descriptions and links to community involvement policies, guidance and publications (see EPA's Superfund Community Involvement Toolkit (CI Toolkit): While targeted to a Superfund Program audience, the CI toolkit may be helpful to a wide variety of users because it is a practical, easy-to-use aid for designing and enhancing community involvement activities and contains tips on how to avoid some of the pitfalls common to the community involvement process. The toolkit enables users to quickly review and adapt a variety of community involvement tools to engage the community during all stages of the cleanup process. Relevant tools include tips for conducting public availability and poster sessions and public meetings, developing fact sheets, working with the media, planning communication strategies, developing a Community Involvement Plan, and establishing an information repository (see EPA s Community Engagement Initiative: The OSWER CEI is designed to enhance OSWER and regional offices engagement with local communities and stakeholders to help them participate meaningfully in government decisions on land cleanup, emergency preparedness and response, and the management of hazardous substances and waste (see 188

294 10.0 GLOSSARY The following definitions are provided for purposes of this Technical Guide: accumulate... Increase gradually in amount as time passes. Note that there will be a finite maximum amount, which will be determined by site- and building-specific conditions and will reflect a balance among physical processes (e.g., soil gas entry, air exchange). active... Involving mechanical operations; Compare with passive. active depressurization technology... Vapor intrusion mitigation method that creates a driving force for air flow from the building into the subsurface by lowering the pressure below the slab, thereby reducing vapor intrusion (soil gas entry into a building). acute... Refers to repeated or single exposure for 24 hours duration or less. Compare with short-term and subchronic. advection... As it pertains to soil gas, refers to bulk movement in the vadose zone induced by spatial differences in soil gas pressure. The direction of advective vapor transport is always toward the direction of lower air pressure. aerobic... Describes a process or activity requiring oxygen. Compare with anaerobic. air exchange rate... Rate of air infiltration into a building through windows, doorways, intakes and exhausts, adventitious openings (e.g., cracks and seams that combine to form the building envelope), plus natural and mechanical ventilation. ambient air... The outdoor air surrounding a building or site. anaerobic... Describes a process or activity requiring the absence of oxygen. Compare with aerobic. analyte... A substance for which identification (of presence) and/or quantification (of amount, such as concentration) is/are sought by instrumental measurement. attenuation... Decrease in vapor concentration in soil gas emanating from a subsurface vapor source along the migration route towards and into a building (indoor air) attenuation factor... The ratio of the indoor air concentration arising from vapor intrusion to the soil gas concentration at the source or a depth of interest in the vapor migration route. background... Refers to a vapor-forming chemical(s) or location(s) that is(are) not influenced by the releases from a site, and is usually described (EPA 1989, 1995c, 2002e) as naturally occurring or anthropogenic: 1) Anthropogenic natural 189

295 and human-made substances present in the environment as a result of human activities and not specifically related to the site-related release in question; and, 2) Naturally occurring substances present in the environment in forms that have not been influenced by human activity. Background may include a vapor-forming chemical(s) present in indoor air due to human activities that is(are) not related to vapor intrusion or site-related contamination. background vapor concentration... This term may include the concentration of a vaporforming chemical in indoor air that fits within the definition of background above. Information on background concentrations of vapor-forming chemicals in indoor air is important to risk managers because generally EPA does not clean up to concentrations below natural or anthropogenic background levels (EPA 2002e). 255 background vapor source... The origin(s) and location(s) of a vapor-forming chemical(s), other than vapor intrusion, and not associated with or emanating from a site-related release(s) to the environment. Background vapor sources may include indoor or outdoor sources. See also indoor vapor source, outdoor vapor source, and background vapor concentration; compare to subsurface vapor source. biodegradation... Decomposition or breakdown of a substance through the action of microorganisms (such as bacteria or fungi). brownfield... A parcel of real estate that is abandoned or inactive or may not be operated at its fully beneficial use and on which expansion or redevelopment is contemplated or reasonably expected; distinguished from greenfield because expansion or redevelopment may be complicated by the presence of vapor-forming chemicals in the subsurface environment. building... a structure that is intended for human occupancy and use. This would include, for instance, homes, offices, stores, commercial and industrial buildings, etc., but would not normally include sheds, carports, pump houses, or other structures that are not intended for human occupancy. building survey... Refers generically to gathering -- by observation, interviews, reviewing documents and records or other means -- information about existing buildings, including, 255 It should, how ever, be noted that some EPA regulations (e.g., indoor radon standards under 40 CFR ) are inclusive of background. 190

296 but not limited to, location, use, occupancy, basic construction (e.g., foundation type), heating ventilation and cooling systems, potential indoor sources of vaporforming chemicals, and anticipated susceptibility to soil gas entry (e.g., presence of radon mitigation system). capillary fringe... The porous material just above the ground water table which may hold water by capillarity (a property of surface tension that draws water upwards) in the smaller void spaces. chlorinated hydrocarbon (CHC)... Compound comprised solely of the elements chlorine, hydrogen and carbon. Includes dry-cleaning solvents such as tetrachloroethylene (PCE) and degreasing solvents such as trichloroethylene (TCE) and 1,1,1- trichloroethane (TCA). chronic... Refers to repeated exposure for more than approximately 10% of the life span (approximately seven years) in humans. Compare with subchronic. concentration... Amount (mass) of a vapor-forming chemical contained in a unit quantity (e.g., volume) of a specific medium (e.g., air, soil gas). conceptual site model (CSM)... Narrative description of the current understanding of the site-specific conditions, which, in the case of vapor intrusion, include the nature, location, and spatial extent of the source(s) of vapor-forming chemicals in the subsurface and the location, use, occupancy, and basic construction of existing buildings. A CSM represents an adaptation of a general conceptual model to account for and reflect site- and/or building-specific conditions. See also model. crawl space... A type of basement in which one cannot stand up the height may be as little as one foot, and the bottom surface is often bare soil. complete (vapor intrusion) pathway... The vapor intrusion pathway is referred to as complete for a building or collection of buildings when five conditions are met under current conditions: (1) a subsurface source of vapor-forming chemicals is present underneath or near the building(s); (2) vapors form and have a route along which to migrate (be transported) toward the building(s); (3) the building(s) is (or are) susceptible to soil gas entry, which means openings exist for the vapors to enter the building(s) and driving forces exist to draw the vapors from the subsurface into the building(s); (4) one or more vapor-forming chemicals comprising the subsurface vapor source(s) is (or are) present in the indoor environment; and (5) the building(s) 191

297 is (or are) occupied by one or more individuals when the vapor-forming chemical(s) is (or are) present indoors. data objectivity... Refers to the accuracy, reliability, and absence of bias in the information; scientific information will generally attain this criterion when the original or supporting data are generated using sound research, investigatory, or statistical methods. data quality objective (DQO)... Performance and acceptance criteria that clarify study objectives, define the appropriate type of data, and specify tolerable levels of potential decision errors that will be used as the basis for establishing the quality and quantity of data needed to support decisions. data utility... Refers to the usefulness (e.g., relevance, importance) of the information to reaching a conclusion or judgment (e.g., is the vapor intrusion pathway complete or incomplete? Does the vapor-forming chemical in indoor air arise from background sources or vapor intrusion? Does vapor intrusion pose an unacceptable human health risk in a specific building?) diffusion... Random motion that affects the distribution of molecules when there are spatial differences in chemical concentrations in the fluid (e.g., soil gas, indoor air, groundwater). The net direction of diffusive transport is toward the direction of lower concentrations. driving force... refers to the combination of: (i) pressure differences between a building interior and the subsurface or ambient air, which foster vapor intrusion and infiltration, respectively, via advection; and (ii) concentration differences between a building interior and the subsurface or ambient air, which foster vapor transport via diffusion. early action... Refers to a response action undertaken early in the cleanup process to achieve prompt risk reduction. Also see response action and pre-emptive mitigation. evidence... A fact or other information (i.e., datum) ascertainable by direct observation, interviews, review of records and documents, instrumental analysis in a lab or field setting, research and testing, sampling of environmental media (e.g., indoor air, soil gas, groundwater), statistical analysis, or other means, which is useful for forming a conclusion or judgment; each distinguishable datum is referred to as a line of evidence, which may be categorized into scientific realms (e.g., geology, biology, physics) or investigatory objectives (e.g., characterization of subsurface vapor source, accounting for background sources) 192

298 exposure... Opportunity to come into contact with vapor-forming chemicals (via inhalation, in the case of vapor intrusion). exposure assessment... Process of characterizing the magnitude, frequency, and duration of exposure to a vapor-forming chemical, along with the characteristics of the population exposed. exposure control... Modification of a property or building intended to reduce or eliminate human exposure to hazardous vapors in buildings or explosive vapors in structures, which arise from the vapor intrusion; such controls may include engineered methods (e.g., active depressurization technologies, mechanical ventilation, indoor air treatment) or non-engineered methods (e.g., institutional controls, such as deed notices and land use restrictions) exposure pathway... The physical course a vapor-forming chemical takes from its source (e.g., groundwater) to the individual (in a building in the case of vapor intrusion). exposure route... The way in which a vapor-forming chemical enters a human body (i.e., inhalation in the case of vapor intrusion). flux... The rate of movement of mass through a unit crosssectional area per unit time in response to a concentration gradient or a driving force for advection. gas... A fluid (as air) that has neither independent shape nor volume but tends to expand indefinitely; a state of matter in which the matter concerned occupies the whole of its container irrespective of its quantity. grab sample... A sample of air collected over a short (practically instantaneous) duration. Compare with time-integrated sample. hazard index (HI)... The sum of hazard quotients for substances that affect the same target organ or organ system. Because different pollutants can cause similar adverse health effects, it is often appropriate to combine hazard quotients associated with different substances. hazard quotient (HQ)... The ratio of the potential exposure to the substance and the level at which no adverse effects are expected. If the HQ is calculated to be equal to or less than 1, then no adverse health effects are expected as a result of exposure. If the HQ is greater than 1, then adverse health effects are possible. hazardous... Involving or exposing one to threat of adverse health effects (due to toxicity) or loss of loss of life or welfare (due to explosiveness). 193

299 Henry s Law Coefficient or Constant... Ratio of a chemical s vapor pressure in air to its solubility in water. Generally reported for standard reference temperature, such as 25 C. human exposure pathway... A way that people may come into contact with environmental contaminants while performing their dayto-day indoor activities. human health risk assessment... The evaluation of scientific information on the hazardous properties of vapor-forming chemicals (hazard assessment and characterization), the dose-response relationship, and the extent of human exposure to those agents. The product of the risk assessment is a statement regarding the probability that populations or individuals so exposed will be harmed and to what degree and describing the principal technical uncertainties (i.e., risk characterization). hydrocarbon... Compound comprised solely of the elements hydrogen and carbon. See also chlorinated hydrocarbon and petroleum hydrocarbon. inclusion zone... Land area within which EPA recommends assessing the vapor intrusion pathway, which extends beyond the aggregate boundaries of the site-specific source(s) of vapor-forming chemicals. indoor vapor source... Refers to a vapor-forming chemical(s) in indoor air which originates within a building. Indoor sources of vaporforming chemicals may include, but are not limited to, use and storage of consumer or household products, use or storage of industrial materials or products, combustion processes, activities or operations within a building, and releases from interior building materials (e.g., off-gases from furniture or clothing); for example, operational use or storage of chemicals in an industrial building may represent an indoor vapor source separate from a siterelated release. Also see background vapor source; compare to subsurface vapor source. infiltration... Air leakage into a building through random cracks, interstices, and other unintentional openings in the building envelope. institutional control (IC)... Non-engineering measures intended to affect human activities in such a way as to prevent or reduce exposure to hazardous substances. For example, ICs may be used to restrict certain land uses, buildings, or activities that could otherwise result in unacceptable exposure to the vapor intrusion pathway. Generally, four categories of ICs are recognized: governmental controls; proprietary controls; enforcement tools; and informational devices. They are almost always used in conjunction with, or as a 194

300 supplement to, other cleanup measures such as treatment or containment. interim action... Refers to a response action that is undertaken to protect human health, but is limited in scope and objective (e.g., does not accomplish complete or final remediation of subsurface vapor sources). Also see response action. interzonal air flow... Movement or transport of air through doorways, ductwork, and service chaseways that interconnect rooms or zones within a building. lines of evidence... Data collected and weighed together in supporting assessments of the vapor intrusion pathway, which are identified and described throughout Sections 2 through 7 inclusive. See also evidence. lower explosive limit (LEL)... The lowest concentration at which a gas or vapor is flammable or explosive at ambient conditions. mitigation... Interim actions taken to reduce or eliminate human exposure to vapor-forming chemicals in a specific building arising from the vapor intrusion pathway; compare with remediation. model... Refers to a description of a system. In the case of vapor intrusion the system will generally consist of a subsurface source of vapors, one or more buildings potentially subject to soil gas entry, and the soil underlying the building(s). Conceptual models (i.e., models that are conceptual) are comprised of narrative descriptions that identify the primary physical elements and processes of the system and the interactions between and relationships among them; for example, Section 2 of this document provides a general conceptual model of how vapor intrusion can arise and why it may be variable over time and in space. A mathematical model is an expression of a conceptual model, which uses mathematical symbols and language to identify key elements (e.g., variables) and processes. Generally, mathematical models are highly idealized or simplified descriptions, compared to the complex systems they represent. For example, Johnson and Ettinger (1991) formulated an idealized mathematical model of vapor intrusion. In the case of a physical model, the description is provided using physical objects, which may or may not have full functionality; for example, a physical model of a construction project might differ from a planned system in its scale, but would necessarily show significant elements in relationship to each other. 195

301 near-source... Refers to a soil gas sample collected within a practically short distance from subsurface vapor source nonresidential building... Refers to a building other than a home; includes, but is not limited to, institutional buildings (e.g., schools, libraries, hospitals, community centers and other enclosed structures for gathering, gyms and other enclosed structures for recreation); commercial buildings (e.g., hotels, office buildings, many (but not all) day care centers, and retail establishments); and industrial buildings where vapor-forming chemicals may or may not be routinely used or stored. Compare with residential building; see also building. outdoor vapor source... Refers to a vapor-forming chemical(s) present in outdoor (ambient) air. Sources of vapor-forming chemicals in outdoor air may include, but are not limited to, releases from industrial facilities, vehicle exhaust, yard maintenance equipment, fuel storage tanks, paint or pesticide applications, agricultural activities, and fires, as well as site-related contamination, activities, and operations (e.g., emissions from remediation equipment). Also see background vapor source; compare to subsurface vapor source. passive... Not involving mechanical operations; Compare with active. petroleum hydrocarbon (PHC)... Hydrocarbons derived from petroleum and present in various refined products of petroleum (such as automotive gasoline, diesel fuel, lubricating oils). See also hydrocarbon. potentially complete (vapor intrusion.. pathway)... The vapor intrusion pathway is referred to as potentially complete for a building when: a subsurface source of vapor-forming chemicals is present underneath or near an existing building or a building that is reasonably expected to be constructed in the future; vapors can form from this source(s) and have a route along which to migrate (be transported) toward the building; and three additional conditions are reasonably expected to all be met in the future, which may not all be met currently (i.e., the building is susceptible to soil gas entry, which means openings exist for the vapors to enter the building and driving forces exist to draw the vapors from the subsurface through the openings into the building; one or more vapor-forming chemicals comprising the subsurface vapor source(s) is (or will be) present in the indoor environment; and the building is or will be occupied by one or more individuals when the vaporforming chemical(s) is (or are) present indoors. 196

302 preemptive mitigation (PEM)... Implementation of systems or control measures to mitigate the vapor intrusion pathway as an early action, even though all pertinent lines of evidence have not yet been completely developed to characterize the vapor intrusion pathway for the subject building(s). Also see early action and response action. preferential migration route... Naturally occurring subsurface feature (e.g., gravel lens, fractured rock) or anthropogenic (human-made) subsurface conduit (e.g., utility corridor or vault, subsurface drain) that is expected to exhibit little resistance to vapor flow in the vadose zone (i.e., exhibits a relatively high gas permeability) or groundwater flow (i.e., effectively exhibits a relatively high hydraulic conductivity), depending upon its location and orientation relative to the water table and ground surface, thereby facilitating the migration of vapor-forming chemicals in the subsurface and towards or into buildings pressure difference/differential pressure... Difference between the air pressure within a building and the subsurface environment or ambient air. Can promote advective flow of gas into or out of a building through pores, cracks, or openings in the building foundation or envelope. radon... A radioactive gas formed during the radioactive decay of radium, which occurs naturally in many geologic settings. reasonable maximum exposure (RME)... A semi-quantitative term, referring to the lower portion of the high end of the exposure distribution; conceptually, above the 90 th percentile exposure but less than the 98 th percentile exposure. reasonable worst case... A semi-quantitative term, referring to the upper portion of the high end of the exposure distribution, but less than the absolute maximum exposure. reference concentration (RfC)... An estimate of the continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without appreciable risk of deleterious effects during a lifetime. remediation... Refers to interim and final cleanups, whether conducted pursuant to RCRA corrective action, the CERCLA removal or remedial programs, or using EPA brownfield grant funds with oversight by state and tribal response programs. In addition to permanent remedies for subsurface vapor sources, site remediation may also entail implementation of institutional controls and construction and operation of engineered systems. 197

303 residential building... refers to a building used as or intended for use as a home; includes, but is not limited to, single-family detached homes with foundations, trailer homes, multiunit apartments and condominiums. Compare with nonresidential building; see also building. response action... any action taken to reduce or eliminate human exposure to or risk posed by hazardous vapors in buildings and structures, which arise from the vapor intrusion pathway; these actions may include engineered exposure controls in a specific building(s), non-engineered exposure controls, remediation of subsurface vapor sources, and associated monitoring to assess effectiveness and protectiveness. Also see remediation and mitigation. risk... Probability of an adverse human health effect (due to toxicity) or physical hazard (e.g., due to potential for explosion) caused under specific circumstances by a vapor-forming chemical. risk communication... The process of exchanging information about health threats and levels or significance of human health risk. risk management... The process of determining whether response action(s) is(are) warranted to protect human health and, if so, selecting response actions to implement. screening... Process of comparing concentrations of vapor-forming chemicals in a specific medium (e.g., indoor air, soil gas, crawl space air, groundwater) to screening levels to identify sites, buildings, or chemicals unlikely to pose a health concern through the vapor intrusion pathway versus those warranting further investigation or analysis. screening level... Risk-based concentrations derived from standardized equations combining exposure information and assumptions with toxicity values. short-term... Refers to repeated exposure for more than 24 hours, up to 30 days. Compare with acute and subchronic. significant opening... Refers to refer to an atypical form and amount of an opening in a building (e.g., a sump, an unlined crawl space, an earthen floor), which could facilitate greater amounts of soil gas entry, all else being equal. Forms of openings typically expected to be present in all buildings include cracks, seams, interstices, and gaps in basement floors and walls or foundations and perforations due to utility conduits. site... The geographical area where investigation and evaluation of the presence of vapor-forming chemicals is desired; in many situations, it includes areas surrounding 198

304 a facility where a release to the subsurface environment is known or suspected to have originated. soil gas... The gas present underground in the pore spaces between soil particles. soil gas concentration... Vapor concentration in a soil gas sample. Sub-slab soil gas is found immediately beneath a building. Nearsource or exterior soil gas samples are collected at other depths and typically outside the building footprint. source strength... Vapor concentration(s) of vapor-forming chemical(s) arising from a subsurface vapor source. stakeholder... A person, group, community, or corporate entity with an interest in activities at a site with subsurface contamination. subchronic... Refers to repeated exposure for more than 30 days, up to approximately 10% of the life span (approximately seven years) in humans. Compare with short-term and chronic. subsurface remediation... Response action that eliminates or substantially reduces the level of vapor-forming chemicals in the subsurface vapor source via treatment or physical removal. Compare with mitigation. subsurface vapor source... Refers to a vapor-forming chemical(s) present in the subsurface environment arising from a release(s) to the environment. A subsurface vapor source may occur as a non-aqueous-phase liquid (NAPL), adsorbed-phase contamination, or dissolved-phase contamination, which may be present in the vadose zone, in groundwater, or within sewers and other conduits. Information on subsurface vapor sources is important to risk managers because response actions are generally warranted when vapor intrusion is determined to pose unacceptable human health risks. Compare with background vapor source and background vapor concentration. termination criteria... Refers to numeric cleanup levels for each site-specific contaminant and narrative cleanup objectives that are to be attained by the response actions. time-integrated sample... Sample collected over an extended period of time to account for temporal variations in vapor concentrations. Compare with grab sample. toxicity value... Refers to an inhalation unit risk (IUR) for potential cancer effects or an inhalation reference concentration (RfC) for potential non-cancer effects of a vapor-forming chemical. 199

305 vadose zone... The soil zone between land surface and the groundwater table within which the moisture content is less than saturation (except in the capillary fringe). Soil pore spaces not occupied by moisture contain (soil) gas. Also referred to as the unsaturated zone. vapor... A substance in the gaseous state as distinguished from the liquid or solid state. vapor intrusion... The migration of potentially hazardous vapors from any subsurface contaminant source, such as contaminated soil or groundwater, through the vadose zone and into a building or structure. vapor source... The place and form of origin of chemical vapors. Also see background vapor source, indoor vapor source, outdoor vapor source, and subsurface vapor source. vapor-forming chemical... A volatile chemical that EPA recommends be routinely evaluated during a site-specific vapor intrusion assessment, when it is present as a subsurface contaminant. volatile chemical... Chemical with a vapor pressure greater than 1 milliliter of mercury (mm Hg), or Henry s law constant greater than 10 5 atmosphere-meter cubed per mole. volatility... The tendency of a substance to form vapors, which are molecules in a gaseous state, and escape from a liquid or solid source. This tendency is directly related to a substance s vapor pressure and Henry s law constant and is indirectly related to a substance s molecular weight (i.e., substances with lower molecular weights tend to volatilize more readily than substances with similar molecular structures that have higher molecular weights). water table... The water surface in an unconfined aquifer at which the fluid pressure in the pore spaces is at soil gas pressure. weight of evidence... Refers to a conceptual approach to data evaluation, in which each of several lines of evidence is critically appraised for its quality (e.g., utility, objectivity) and systematically assessed for its logical support for a particular conclusion, as well as alternative conclusions; the appraisals consider lines of evidence individually and in light of other lines of reliable evidence for purposes of determining whether a particular conclusion is supported by the preponderance of the evidence and is consistent with the conceptual site model; this weighing concept does not entail a quantitative (a priori) scheme to score or rank the individual lines of evidence. See also evidence. 200

306 work plan... A site-specific document that includes a project description, project objective(s), historical information about the site. worst case... A semi-quantitative term, referring to the absolute maximum plausible exposure (i.e., a bounding highimpact case). 201

307 11.0 CITATIONS AND REFERENCES Agency for Toxic Substances and Disease Registry (ATSDR) Evaluating Vapor Intrusion Pathways at Hazardous Waste Sites. Currently available online at: American Society for Testing and Materials (ASTM) E 1739: Standard Guide for Risk- Based Corrective Action Applied at Petroleum Release Sites. ASTM International E 2121: Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings. Association of State and Territorial Solid Waste Management Officials (ASTSWMO) Vapor Intrusion Pathway: A Guide for State and Territorial Federal Facilities Managers. ASTSWMO Policy and Technology Focus Group, Washington, D.C. July. Brenner, D Results of a Long-Term Study of Vapor Intrusion at Four Large Buildings at the NASA Ames Research Center. J. Air & Waste Manage. Assoc. 60: California Environmental Protection Agency (CalEPA) Vapor Intrusion Mitigation Advisory. Department of Toxic Substances Control. Revision 1. October. Currently available online at: California Environmental Protection Agency (CalEPA) Advisory: Active Soil Gas Investigations. Department of Toxic Substances Control. April. Currently available online at: City of Mandan Chapter 21-10: Environmental institutional control ordinance. City of Mandan Municipal Code, Title 21: Planning and Zoning. Currently available online at: Clements, W.E. and M.H. Wilkening Atmospheric pressure effects on 222 Rn transport across the Earth-air interface. Journal of Geophysical Research 79(33): Folkes, D.J. and D.W. Kurz Efficacy of sub-slab depressurization for mitigation of vapor intrusion of chlorinated organic compounds. Proceedings of Indoor Air 2002: The 9th International Conference on Indoor Air and Climate. June 30-July 5. Folkes, D.J., W. Wertz, J. Kurtz, and T. Kuehster Observed spatial and temporal distributions of CVOCs at Colorado and New York vapor intrusion sites. Groundwater Monitoring & Remediation 29(1): Frewer, L The public and effective risk communication. Toxicology Letters 149: Gorder, K.A. and E.M. Dettenmaier Portable GC/MS methods to evaluate sources of cvoc contamination in indoor air. Groundwater Monitoring & Remediation 31(4): Holden, P.A. and N. Fierer Microbial processes in the vadose zone. Vadose Zone Journal 4:

308 Holton, C., E. Luo, Y. Guo, P. Dahlen, P. C. Johnson, K. Gorder and E. Dettenmaier. 2013a. Multi-year monitoring of a house over a dilute CHC plume: Implications for pathway assessment using indoor air sampling and forced under-pressurization tests. 23rd Annual International Conference of the Association of Environmental Health Sciences, San Diego, CA, March 19. Holton, C., H. Luo, P. Dahlen, K. Gorder, E. Dettenmaier, and P. C. Johnson. 2013b. Temporal variability of indoor air concentrations under natural conditions in a house overlying a dilute chlorinated solvent groundwater plume. Environmental Science & Technology 47: Interstate Technology & Regulatory Council (ITRC) Petroleum Vapor Intrusion: Fundamentals of Screening, Investigation, and Management. Interstate Technology and Regulatory Council, Vapor Intrusion Team, Washington, D.C. October. Currently available online at: Interstate Technology & Regulatory Council (ITRC). 2007a. Vapor Intrusion Pathway: A Practical Guideline. ITRC Vapor Intrusion Team, Washington, D.C. VI-1. January. Currently available online at: Interstate Technology & Regulatory Council (ITRC). 2007b. Vapor Intrusion Pathway: Investigative Approaches for Typical Scenarios. ITRC Vapor Intrusion Team, Washington, D.C. VI-1A. January. Currently available online at: Izzo, V. J Drycleaners A Major Source of PCE in Ground Water. Sacramento: State of California Regional Water Quality Control Board Central Valley Region. March. Currently available online at: Jia, C., S.A. Batterman, and G.E. Relyea Variability of indoor and outdoor VOC measurements: An analysis using variance components. Environmental Pollution 169: Johnson, P.C. and R.A. Ettinger Heuristic model for predicting the intrusion rate of contaminant vapors into buildings. Environmental Science & Technology 25: Little, J.C., J.M. Daisey, and W.W. Nazaroff Transport of subsurface contaminants into buildings. Environmental Science & Technology 26(11): Lowell, P.S. and B. Eklund VOC emission fluxes as a function of lateral distance from the source. Environmental Progress 23(1): Lundegard, P.D., P.C. Johnson, and P. Dahlen Oxygen transport from the atmosphere to soil gas beneath a slab-on-grade foundation overlying petroleum-impacted soil. Environmental Science & Technology 42: Lundgren, R.E., and A.H. McMakin Risk Communication: A Handbook for Communicating Environmental, Safety, and Health Risks, Fifth Edition. John Wiley & Sons. Luo, H., P. Dahlen, P.C. Johnson, T. Peargin, and T. Creamer Spatial variability of soilgas concentrations near and beneath a building overlying shallow petroleum hydrocarbon impacted soils. Groundwater Monitoring & Remediation 29(1):

309 Ma, J., H. Luo, G.E. DeVaull, W.G. Rixey, and P.J.J. Alvarez Numerical model investigation for potential methane explosion and benzene vapor intrusion associated with highethanol blend releases. Environmental Science & Technology 48: Ma, J., W.G. Rixey, G. E. DeVaull, B.P. Stafford, and P.J.J. Alvarez Methane bioattenuation and implications for explosion risk reduction along the groundwater to soil surface pathway above a plume of dissolved ethanol. Environmental Science & Technology 46: Markon, M. L. and L. Lemyre Public reactions to risk messages communicating different sources of uncertainty: An experimental test. Human and Ecological Risk Assessment 19: Massachusetts Department of Environmental Protection (MADEP) Interim Final Vapor Intrusion Guidance. WSC# December. Currently available online at: Maupins, K. and D.T. Hitchins Reducing employee exposure potential using the ANSI/ASHRAE 110 "Method of Testing Performance of Laboratory Fume Hoods" as a diagnostic tool. American Industrial Hygiene Association Journal 59(2): McAlary, T.A., J. Provoost, and H.D. Dawson Vapor intrusion. Dealing with Contaminated Sites: From Theory Towards Practical Applications, Chapter 10. F.A. Swartjes [ed.], Springer Science. McBride, S.J., A.R. Ferro, W.R. Otto, P. Switzer, and L.M. Hildemann Investigations of the proximity effect for pollutants in the indoor environment. Journal of Exposure Analysis and Environmental Epidemiology 9: McCarthy, M.C., H.R. Hafner, L.R. Chinkin, and J.G. Charrier Temporal variability of selected air toxics in the United States. Atmospheric Environment 41: McDonald, G.J. and W.E. Wertz PCE, TCE, and TCA vapors in subslab soil gas and indoor air: A case study in upstate New York. Groundwater Monitoring & Remediation 27(4): McHugh, T.E., L. Beckley, and D. Bailey Influence of shallow geology on volatile organic chemical attenuation from groundwater to deep soil gas. Groundwater Monitoring & Remediation 33(3): McHugh, T.E., L. Beckley, D. Bailey, K. Gorder, E. Dettenmaier, I. Rivera-Duarte, S. Brock, and I.C. MacGregor Evaluation of vapor intrusion using controlled building pressure. Environmental Science & Technology 46: Morgan, M.G., A. Bostrom, L. Lave, and C.J. Atman Communicating risk to the public. Environmental Science & Technology 26(11): Moseley, C.L. and M.R. Meyer Petroleum contamination of an elementary school: A case history involving air, soil-gas, and groundwater monitoring. Environmental Science & Technology 26(11):

310 National Conference of Commissioners on Uniform State Laws Uniform Environmental Covenants Act. Currently available online at: National Research Council (NRC) Alternatives for Managing the Nation's Complex Contaminated Groundwater Sites. National Academies Press, Washington, D.C. Committee on Future Options for Management in the Nation's Subsurface Remediation Effort. National Research Council (NRC) Science and Decisions: Advancing Risk Assessment. National Academies Press, Washington, D.C. Committee on Improving Risk Analysis Approaches Used by the U.S. EPA. National Research Council (NRC) Contaminants in the Subsurface: Source Zone Assessment and Remediation. National Academies Press, Washington, D.C. Committee on Source Removal of Contaminants in the Subsurface. New Jersey Department of Environmental Protection (NJDEP) Vapor Intrusion Technical Guidance, Version 2.0. Site Remediation Program. Currently available online at: Odencrantz, J.E., S.C. Thornley, and H. O Neill An evaluation of the performance of multiple passive diffusion devices for indoor air sampling of VOCs. Remediation 19(4): Odencrantz, J.E., H. O Neill, S.J. Steinmacher, J.D. Case, and P.C. Johnson Residential vapor-intrusion evaluation: Long-duration passive sampling vs. short-duration active sampling. Remediation 18(4): Patterson, B. M. and G.B. Davis Quantification of Vapor Intrusion Pathways into a Slabon-Ground Building under Varying Environmental Conditions. Environmental Science & Technology 43(3): Patterson, B. M., R. Aravena, G.B. Davis, A.J. Furness, T.P. Bastow, and D. Bouchard Multiple lines of evidence to demonstrate vinyl chloride aerobic biodegradation in the vadose zone, and factors controlling rates. J. Contaminant Hydrology 153(1) Pennell, K.G., M.K. Scammell, M.D. McClean, J. Ames, B. Weldon, L. Friguglietti, E.M. Suuberg, R. Shen, P.A. Indeglia, and W.J. Heiger-Bernays Sewer gas: An indoor air source of PCE to consider during vapor intrusion investigations. Groundwater Monitoring & Remediation 33(3): Robinson, A.L. and R.G. Sextro Radon entry into buildings driven by atmospheric pressure fluctuations. Environmental Science & Technology 31(6): Rossner, A., J.P. Farant, P. Simon, and D.P. Wick Development of a Flow Controller for Long-Term Sampling of Gases and Vapors Using Evacuated Canisters. Environmental Science & Technology 36(22): Rossner, A. and D.P. Wick A field study to assess the long-term sampling feasibility of evacuated canisters and the development of a mathematical model to analyze potential sampling bias. J. Occupational Environmental Hygiene 2(9):

311 Rydock, J.P Reality-check your fume hoods. Today s Chemist at Work 10(06): Sihota, N.J., K. U. Mayer, M.A. Toso, and J.F. Atwater Methane emissions and contaminant degradation rates at sites affected by accidental releases of denatured fuel-grade ethanol. Journal of Contaminant Hydrology 151:1-5. Strategic Environmental Research and Development Program and Environmental Security Technology Certification Program (SERDP-ESTCP) SERDP and ESTCP Workshop on Vapor Intrusion into Indoor Air from Contaminated Groundwater (Summary Report). March. Currently available online at: Initiatives/Vapor-Intrusion Tilman, F.D. and J.W Weaver Temporal moisture content variability beneath and external to a building and the potential effects on vapor intrusion risk assessment. Science of the Total Environment 379:1-15. U.S. Department of Defense (DoD) DoD Vapor Intrusion Handbook. January. Currently available online at: 09.pdf?syspage=documents&id= U.S. Department of the Navy (DoN). 2011a. Guidance for Environmental Background Analysis, Volume IV: Vapor Intrusion Pathway. Naval Facilities Engineering Command, Washington, D.C. April. U.S. Department of the Navy (DoN). 2011b. Vapor Intrusion Mitigation in Existing Buildings Fact Sheet. Naval Facilities Engineering Command, Washington, D.C. May. U.S. Department of the Navy (DoN). 2011c. Vapor Intrusion Mitigation in Construction of New Buildings Fact Sheet. Naval Facilities Engineering Command, Washington, D.C. August. U.S. Environmental Protection Agency (EPA). 2015a. Vapor Intrusion Screening Level (VISL) Calculator, User s Guide. Currently available online at: U.S. Environmental Protection Agency (EPA). 2015b. Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites [EPA 510-R ]. Office of Solid Waste and Emergency Response, Office of Underground Storage Tanks. 206

312 U.S. Environmental Protection Agency (EPA). 2014a. Human Health Evaluation Manual, Supplemental Guidance: Update of Standard Default Exposure Factors. Memorandum from Dana Stalcup. Office of Superfund Remediation and Technology Innovation, Washington, D.C. February 6. Currently available online at: U.S. Environmental Protection Agency (EPA). 2014b. Compilation of Information Relating to Early/Interim Actions at Superfund Sites and the TCE IRIS Assessment. Memorandum from Robin Richardson. Office of Superfund Remediation and Technology Innovation, Washington, D.C. August 27. Currently available online at: U.S. Environmental Protection Agency (EPA). 2013a. Evaluation of Empirical Data to Support Soil Vapor Intrusion Screening Criteria for Petroleum Hydrocarbon Compounds. Office of Underground Storage Tanks, Washington, D.C. EPA-510-R January. Currently available online at: U.S. Environmental Protection Agency (EPA). 2013b. Consumer s Guide to Radon Reduction. EPA 402/K-10/005. Office of Radiation and Indoor Air (ORIA), Indoor Environments Division. Washington, DC. September. Currently available online at: U.S. Environmental Protection Agency (EPA). 2012a. EPA s Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings. EPA-530-R March. Currently available online at: _Final.pdf U.S. Environmental Protection Agency (EPA). 2012b. Conceptual Model Scenarios for the Vapor Intrusion Pathway. EPA-530-R February. Currently available online at: U.S. Environmental Protection Agency (EPA). 2012c. Assessing Protectiveness at Sites for Vapor Intrusion: Supplement to the Comprehensive Five-Year Review Guidance. OSWER Directive Currently available online at: 12.pdf U.S. Environmental Protection Agency (EPA). 2012d. Institutional Controls: A Guide to Planning, Implementing, Maintaining, and Enforcing Institutional Controls at Contaminated Sites. OSWER , EPA-540-R December. Currently available online at: pdf U.S. Environmental Protection Agency (EPA). 2012e. Institutional Controls: A Guide to Preparing Institutional Control Implementation and Assurance Plans at Contaminated Sites. OSWER # , EPA-540-R December. Currently available online at: % pdf 207

313 U.S. Environmental Protection Agency (EPA). 2012f. Fluctuation of Indoor Radon and VOC Concentrations Due to Seasonal Variations. National Exposure Research Laboratory, Las Vegas, Nevada. EPA/600/R-12/673. September. Currently available online at: e=pr&timstype=published+report&showcriteria=0&address=nerl/pubs.html&view=citation&s ortby=pubdateyear&count=100&datebeginpublishedpresented=01/01/2010 U.S. Environmental Protection Agency (EPA). 2011a. Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences ( ): A Compilation of Statistics for Assessing Vapor Intrusion. Office of Solid Waste and Emergency Response, Washington, D.C. EPA-530-R June. Currently available online at: pdf U.S. Environmental Protection Agency (EPA). 2011b. Exposure Factors Handbook 2011 Edition. Office of Research and Development, Washington, D.C. EPA/600/R-090/052F. September. Currently available online at: U.S. Environmental Protection Agency (EPA). 2011c. Recommended Evaluation of Institutional Controls: Supplement to the Comprehensive Five-Year Review Guidance. OSWER Directive September. Currently available online at: U.S. Environmental Protection Agency (EPA). 2010a. Clarification of CERCLA Entry Policy. Office of Enforcement and Compliance Monitoring. Washington, D.C. Memorandum from Kenneth Patterson. March 3. Currently available online at: U.S. Environmental Protection Agency (EPA). 2010b. Review of the Draft 2002 Subsurface Vapor Intrusion Guidance. Office of Solid Waste and Emergency Response, Washington, D.C. August. U.S. Environmental Protection Agency (EPA). 2010c. Considering Reasonably Anticipated Future Land Use and Reducing Barriers to Reuse at EPA-Lead Superfund Remedial Sites. OSWER Directive March. Currently available online at: U.S. Environmental Protection Agency (EPA). 2009a. Evaluation Report: Lack of Final Guidance on Vapor Intrusion Impedes Efforts to Address Indoor Air Risks. Report No. 10-P EPA Office of Inspector General, Washington, D.C. December. Currently available online at: U.S. Environmental Protection Agency (EPA). 2009b. Operational and Functional Determination and the Transfer of Fund-Lead Vapor Intrusion Mitigation Systems to the State. OSWER April. Currently available online at: U.S. Environmental Protection Agency (EPA). 2009c. Risk Assessment Guidance for Superfund (RAGS), Volume I: Human Health Evaluation Manual (Part F, Supplemental Guidance for Inhalation Risk Assessment). Office of Superfund Remediation and Technology Innovation, 208

314 Washington, D.C. OSWER , EPA-540-R January. Currently available on-line at U.S. Environmental Protection Agency (EPA). 2008a. Brownfields Technology Primer: Vapor Intrusion Considerations for Redevelopment. EPA-542-R March. Currently available online at: velopment%20epa%20542-r pdf U.S. Environmental Protection Agency (EPA). 2008b. Superfund Environmental Indicators Guidance: Human Exposure Revisions. Office of Superfund Remediation and Technology Assessment, Washington, D.C. March. Currently available online at: U.S. Environmental Protection Agency (EPA). 2008c. Engineering Issue: Indoor Air Vapor Intrusion Mitigation Approaches. EPA/600/R-08/115. October. Currently available online at: U.S. Environmental Protection Agency (EPA) Risk Communication in Action: The Risk Communication Workbook. EPA/625/R-05/003. August. Currently available online at: U.S. Environmental Protection Agency (EPA). 2006a. Guidance on Systematic Planning Using the Data Quality Objectives Process (EPA QA/G-4). Office of Environmental Information. Washington, D.C. EPA-240-B February. Currently available online at: U.S. Environmental Protection Agency (EPA). 2006b. Assessment of Vapor Intrusion in Homes near the Raymark Superfund Site Using Basement and Subslab Air Samples. EPA/600/R- 05/147. March. Currently available online at: U.S. Environmental Protection Agency (EPA). 2006c. In Situ Treatment Technologies for Contaminated Soil. Office of Solid Waste and Emergency Response, Washington, D.C. EPA- 542-F November. Currently available on-line at: U.S. Environmental Protection Agency (EPA) Guidance for Evaluating Landfill Gas Emissions from Closed or Abandoned Facilities. EPA/600/R-05/123a. September. Currently available online at: U.S. Environmental Protection Agency (EPA) Human Health Toxicity Values in Superfund Risk Assessments. OSWER Directive December 5. Currently available online at: U.S. Environmental Protection Agency (EPA). 2002a. Ground-Water Sampling Guidelines for Superfund and RCRA Project Managers. EPA-542-S May. Currently available online at: 209

315 U.S. Environmental Protection Agency (EPA). 2002b. Office of Inspector General Recommendations Concerning RCRA Corrective Action Environmental Indicators. Office of Solid Waste, Washington, D.C. Currently available online at: U.S. Environmental Protection Agency (EPA). 2002c. OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance). Office of Solid Waste and Emergency Response, Washington, D.C. EPA- 530-D November. U.S. Environmental Protection Agency (EPA). 2002d. Superfund Response Actions: Temporary Relocations Implementation Guidance. Office of Solid Waste and Emergency Response, Washington, D.C. OSWER Directive April. Currently available online at: U.S. Environmental Protection Agency (EPA). 2002e. Role of Background in the CERCLA Cleanup Program. OSWER Directive P. Office of Emergency and Remedial Response, Washington, D.C. May. Currently available online at: U.S. Environmental Protection Agency (EPA) Comprehensive Five-Year Review Guidance. OSWER B-P, EPA-540-R June. Currently available online at: U.S. Environmental Protection Agency (EPA). 2000a. Data Quality Objectives Process for Hazardous Waste Site Investigations: EPA QA/G-4HW. EPA/600/R-00/007. January. Currently available online at: U.S. Environmental Protection Agency (EPA). 2000b. Risk Characterization Handbook. Science Policy Council, Washington, D.C. EPA-100-B December. Currently available online at: U.S. Environmental Protection Agency (EPA). 1999a. Interim-Final Guidance for RCRA Corrective Action Environmental Indicators. Office of Solid Waste, Washington, D.C. February 5. Currently available online at: U.S. Environmental Protection Agency (EPA). 1999b. A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Documents. Office of Solid Waste and Emergency Response, Washington, D.C. EPA-540-R July. Currently available online at: U.S. Environmental Protection Agency (EPA). 1999c. Compendium Method TO-14A. Determination of volatile organic compounds (VOCs) in ambient air using specially prepared canisters with subsequent analysis by gas chromatography. Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Second Edition. Center for Environmental Research Information, Office of Research and Development, Cincinnati, Ohio. EPA/625/R-96/010b. January. Available online at 210

316 U.S. Environmental Protection Agency (EPA). 1999d. Compendium Method TO-15. Determination of volatile organic compounds (VOCs) in air collected in specially-prepared canisters and analyzed by gas chromatography/mass spectrometry (GC/MS). Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Second Edition. Center for Environmental Research Information, Office of Research and Development, Cincinnati, Ohio. EPA/625/R-96/010b. January. Available online at U.S. Environmental Protection Agency (EPA). 1999e. Compendium Method TO-17. Determination of volatile organic compounds in ambient air using active sampling onto sorbent tubes. Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Second Edition. Center for Environmental Research Information, Office of Research and Development, Cincinnati, Ohio. EPA/625/R-96/010b. January. Available online at U.S. Environmental Protection Agency (EPA). 1999f. Interim Policy on the Use of Permanent Relocations as Part of Superfund Remedial Actions. OSWER Directive P. Office of Solid Waste and Emergency Response Washington, DC. Currently available on-line at: U.S. Environmental Protection Agency (EPA) Technical Guidance Document: Compliance Assurance Monitoring, Revised Draft. Office of Air Quality Planning and Standards, Research Triangle Park, NC. August. Currently available online at: U.S. Environmental Protection Agency (EPA) Rules of Thumb for Superfund Remedy Selection. OSWER Directive August. Currently available online at: U.S. Environmental Protection Agency (EPA). 1995a. Land Use in CERCLA Remedy Selection Process. OSWER Directive May. Currently available online at: U.S. Environmental Protection Agency (EPA). 1995b. Guidance for Risk Characterization. Science Policy Council, Washington, D.C. February. Currently available online at: U.S. Environmental Protection Agency (EPA). 1995c. Engineering Forum Issue Paper. Determination of Background Concentrations of Inorganics in Soils and Sediments at Hazardous Waste Sites, EPA/540/S-96/500. Office of Research and Development, Office of Solid Waste and Emergency Response, Washington, DC. Currently available online at: 211

317 U.S. Environmental Protection Agency (EPA) RCRA Corrective Action Plan (Final). OSWER Directive A. Office of Solid Waste, Washington, DC. Currently available online at: U.S. Environmental Protection Agency (EPA). 1993a. Radon Reduction Techniques for Existing Detached Houses: Technical Guidance (Third Edition) for Active Soil Depressurization Systems. EPA-625-R October. Currently available online at: U.S. Environmental Protection Agency (EPA). 1993b. Presumptive Remedies: Site Characterization and Technology Selection for CERCLA Sites with VOCs in Soils. U.S. Environmental Protection Agency (EPA). 1993c. Air/Superfund National Technical Guidance Study Series: Options for Developing and Evaluating Mitigation Strategies for Indoor Air Impacts at CERCLA Sites. Office of Air Quality Planning and Standards. EP-451/R , September. Currently available on-line at: U.S. Environmental Protection Agency (EPA). 1992a. Guidance for Data Useability in Risk Assessment, Part A. Currently available online at: U.S. Environmental Protection Agency (EPA). 1992b. Early Action and Long-Term Action under SACM Interim Guidance. Office of Solid Waste and Emergency Response, Washington, D.C. Publication December. U.S. Environmental Protection Agency (EPA). 1992c. Guidance on Risk Characterization for Risk Managers and Risk Assessors. Memorandum from F. Henry Habicht II, Deputy Administrator, Washington, D.C. February 26. Currently available online at: U.S. Environmental Protection Agency (EPA). 1991a. Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions. Office of Solid Waste and Emergency Response. Washington, D.C. OSWER Directive April. Currently available online at: U.S. Environmental Protection Agency (EPA). 1991b. Risk Assessment Guidance for Superfund (RAGS), Volume I: Human Health Evaluation Manual (Part B, Development of Preliminary Remediation Goals), Interim. Office of Emergency and Remedial Response, Washington, D.C. EPA-540-R December. Currently available on-line at U.S. Environmental Protection Agency (EPA). 1991c. Risk Assessment Guidance for Superfund (RAGS), Volume I: Human Health Evaluation Manual (Part C, Risk Evaluation of Remedial Alternatives), Interim. Office of Emergency and Remedial Response, Washington, D.C. Publication C. October. Currently available on-line at 212

318 U.S. Environmental Protection Agency (EPA) Risk Assessment Guidance for Superfund, Volume I Human Health Evaluation Manual (Part A), Interim Final. Office of Emergency and Remedial Response, Washington, D.C. EPA December. Currently available online at: U.S. Environmental Protection Agency (EPA) Entry and Continued Access under CERCLA. Office of Enforcement and Compliance Monitoring, Washington, D.C. Publication June 5. Currently available online at: U.S. Environmental Protection Agency (EPA) Inspection Authority under Section 3007 of RCRA. Office of General Counsel, Washington, D.C. Memorandum from Francis Blake. April 17. Currently available online at: U.S. Environmental Protection Agency, Environmental Response Team (EPA-ERT) Standard Operating Procedures, Trace Atmospheric Gas Analyzer (TAGA) IIE Operation (SOP 1711). October 22. Currently available online at: r00.pdf U.S. Environmental Protection Agency, Environmental Response Team (EPA-ERT) Standard Operating Procedures, Construction and Installation of Permanent Sub-Slab Soil Gas Wells (SOP 2082). March 29. Currently available online at: U.S. Environmental Protection Agency, Environmental Response Team (EPA-ERT). 2001a. Standard Operating Procedures, Groundwater Well Sampling (SOP 2007). April 16. Currently available online at: U.S. Environmental Protection Agency, Environmental Response Team (EPA-ERT). 2001b. Standard Operating Procedures, Soil Sampling (SOP 2012). July 11. Currently available online at: U.S. Environmental Protection Agency, Environmental Response Team (EPA-ERT). 2001c. Standard Operating Procedures, Soil Gas Sampling (SOP 2042). April 18. Currently available online at: U.S. Environmental Protection Agency, Environmental Response Team (EPA-ERT) Standard Operating Procedures, Summa Canister Sampling (SOP 1701). July 27. Currently available online at: U.S. Environmental Protection Agency, Region 9 (EPA-Region 9) R9 s RARE Opportunity to Improve Vapor Intrusion Indoor Air Investigations. EPA Vapor Intrusion Forum. June 14. U.S. Environmental Protection Agency, Risk Assessment Forum (EPA-RAF) Framework for Human Health Risk Assessment to Inform Decision Making. Office of Science Advisor, Washington, D.C. April. Currently available online at: 213

319 U.S. Environmental Protection Agency (EPA-SPC) Peer Review Handbook, 3rd Edition. EPA/100/B-06/002. Science Policy Council, Washington DC. Currently available online at: U.S. Postal Service (USPS) Vapor Intrusion Guidance, Volume 1. September. Vroblesky, D.A., M.D. Petkewich, M.A. Lowery, and J.E. Landmeyer Sewers as a source and sink of chlorinated-solvent groundwater contamination, Marine Corps Recruit Depot, Parris Island, South Carolina. Groundwater Monitoring & Remediation 31(4):

320 APPENDIX A RECOMMENDED SUBSURFACE-TO-INDOOR AIR ATTENUATION FACTORS A.1 INTRODUCTION This Technical Guide includes recommended medium-specific (groundwater, soil gas, and indoor air) Vapor Intrusion Screening Levels (VISLs) that are intended to help identify those sites unlikely to pose a health concern from vapor intrusion and identify areas or buildings that may warrant further investigation of the vapor intrusion pathway. These VISLs are recommended for use in evaluating the concentrations of vapor-forming chemicals measured in groundwater, near-source exterior soil gas, and sub-slab soil gas in residential and nonresidential settings where the potential for vapor intrusion is under investigation. The subsurface VISLs are developed considering a generic conceptual model for vapor intrusion consisting of a groundwater or vadose zone source of vapor-forming chemicals that diffuse upwards through unsaturated soils towards the surface and enter buildings. The underlying assumption for this generic model is that subsurface characteristics will tend to reduce or attenuate soil gas concentrations as vapors migrate upward from the source and into structures. Section describes this conceptual model further. In general, EPA recommends considering whether the assumptions underlying the generic conceptual model are attained at each site. The Vapor Intrusion Screening Level (VISL) Calculator User s Guide (EPA 2015a) provides additional information about the technical basis for deriving the VISLs. Comparison of sampling results to medium-specific VISLs (see Section 6.5.4) comprises one line of evidence in the multiple-lines-of-evidence approach described in this Technical Guide (see, for example, Sections 7.1 and 7.2). The subsurface (groundwater and soil gas) VISLs (C VISL ) are calculated using risk-based, screening levels for indoor air (C target,ia ) and a mediumspecific, subsurface-to-indoor air attenuation factor (α VI ), as follows: Equation A.1 The risk-based, indoor air screening levels (C target,ia ) are calculated according to the guidance provided in Risk Assessment Guidance for Superfund (RAGS) Part F (EPA 2009) as implemented in EPA s Regional Screening Levels (RSLs) for Chemical Contaminants at Superfund Sites ( The medium-specific, attenuation factors (α VI ) recommended for calculating the subsurface VISLs are derived from information in EPA s Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings (EPA 2012a). This appendix describes the technical basis for the selection of the subsurface-to-indoor air attenuation factors (α VI ) that are recommended for use in calculating the VISLs for groundwater, sub-slab soil gas, near-source exterior soil gas, and crawl space air, according to Equation A.1. A-1

321 A.2 DEFINITION AND DESCRIPTION OF ATTENUATION FACTOR Vapor attenuation refers to the reduction in concentration of vapor-forming chemicals that occurs during vapor migration in the subsurface, coupled with the dilution that can occur when the vapors enter a building and mix with indoor air (Johnson and Ettinger 1991). The aggregate effect of these physical and chemical attenuation mechanisms can be quantified through the use of a subsurface-to-indoor air vapor intrusion attenuation factor (α VI ), which is defined as the ratio of the indoor air concentration arising from vapor intrusion (C IA-VI ) to the subsurface vapor concentration (C sv ) at the source or a depth of interest in the vapor migration route (EPA 2012a): Equation A.2 As defined here, the vapor attenuation factor is an inverse measurement of the overall dilution that occurs as vapors migrate from a point of measurement in the subsurface into a building; i.e., attenuation factor values decrease with increasing dilution of vapor concentration. Subsurface vapor concentrations (C SV ) may be measured directly under a building (often called sub-slab soil gas or just sub-slab), measured exterior to a building at any depth in the unsaturated zone (often called exterior soil gas), or derived from groundwater concentrations by converting the dissolved concentration to a vapor concentration assuming equilibrium conditions (i.e., by multiplying the groundwater concentration by the chemical s dimensionless Henry s law constant for the groundwater temperature in situ) (EPA 2001); also see Appendix C of this Technical Guide. Subfloor vapor concentrations may also be measured in building crawl spaces. Although crawl space samples are not strictly subsurface samples, they represent the vapor concentration underlying a building s living space. Thus, crawl space samples may be evaluated in a manner similar to subsurface vapor samples. A.3 RECOMMENDED ATTENUATION FACTORS This section summarizes the technical basis and rationale for EPA s recommended attenuation factors for groundwater, sub-slab soil gas, exterior soil gas, and crawl space air, as follows: Section A.3.1 summarizes EPA s database of empirical attenuation factor values and the results of analyzing that database. Section A.3.2 identifies the recommended empirically based attenuation factors for groundwater. Section A.3.3 identifies the recommended attenuation factor for sub-slab soil gas and presents a theoretical analysis that supports the selection of the recommended empirically based value. Section A.3.4 recommends a generic attenuation factor for exterior soil gas and discusses its basis, justification, and limited applications. A-2

322 Section A.3.5 identifies the recommended attenuation factor for crawlspace vapor. Section A.3.6 presents a reliability analysis of the recommended generic attenuation factors. A.3.1 EPA S VAPOR INTRUSION DATABASE (EPA 2012A) The information in EPA s Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings (EPA 2012a) is used to derive recommended attenuation factor values for use in evaluating subsurface sample concentrations collected as part of vapor intrusion investigations. EPA s vapor intrusion database consists of numerous pairings of concentrations in indoor air and subsurface samples (groundwater, sub-slab soil gas, exterior soil gas, and crawlspace vapor) from actual sites. It represents the most comprehensive compilation of vapor intrusion data for chlorinated hydrocarbons (CHCs) available at this time. EPA s vapor intrusion database was analyzed and screened to reduce the impacts of background sources to indoor air concentrations. The resulting data distributions are considered representative of vapor intrusion of CHCs from subsurface vapor sources into residential buildings for most conditions. These distributions serve as the basis for identifying the high-end (conservative) attenuation factors for those media. Table A-1 and Figure A-1 (Table 19 and Figure 34, respectively, in EPA (2012a)) present and compare the distributions of the attenuation factors (groundwater, exterior soil gas, sub-slab soil gas, and crawl space) that remain after applying the respective source strength and indoor air screens considered most effective at reducing the influence of background contributions to indoor air concentrations. These data demonstrate that the attenuation factor distributions obtained for groundwater, sub-slab soil gas, and crawl spaces for multiple buildings and sites are consistent with the conceptual model for vapor intrusion, which predicts that greater attenuation is expected with greater depths to the vapor sources or vapor samples. As shown in Table A-1 and Figure A-1, the paired groundwater indoor air data generally exhibit greater attenuation (lower attenuation factors) than the paired sub-slab soil gas indoor air data, which in turn exhibit greater attenuation than the paired crawl space-indoor air data. A.3.2 RECOMMENDED ATTENUATION FACTORS FOR GROUNDWATER To account for the inherent temporal and spatial variability in indoor air and subsurface vapor concentrations, the 95 th percentile value of the source-screened groundwater data subset in EPA 2012a is recommended as a reasonably conservative generic attenuation factor, after considering a range of values. Thus, for groundwater, the recommended generic attenuation factor (α gw ) is This value is considered to apply for any soil type in the vadose zone (excepting where preferential vapor pathways are present; see Section 5.4) in cases where the groundwater is greater than five feet below the ground surface. If the depth to groundwater is less than five feet below the building foundation, investigation of the indoor space is recommended, as there is potential for contaminated groundwater to contact the building foundation, either because the capillary fringe intersects the building foundation or groundwater fluctuations results in groundwater wetting the foundation. A-3

323 Table A-2 (Table 13 in EPA (2012a)) provides statistics and Figure A-2 (Figure 28 in EPA (2012a)) shows box-and-whisker plots for individual sites compared with the statistics for the combined set of screened groundwater attenuation factors. This table and figure show that the 95 th percentile value of the combined groundwater-indoor air measurements is considered appropriate for estimating reasonable maximum indoor air concentrations that might be observed at a site due to vapor intrusion. The majority of sites and buildings would be expected to exhibit lower indoor air concentrations. A factor that commonly results in greater attenuation (lower attenuation factors) is the presence of laterally extensive, unfractured fine-grained sediment in the vadose zone. Table A-3 (Table 14 in EPA (2012a)) provides selected statistics and Figure A-3 (Figure 29 in EPA (2012a)) shows the box-and-whisker plots for the groundwater attenuation factors for three soil types. Comparing each descriptive statistic (except for the 25th percentile values) indicates that the attenuation factor values for residences overlying soils classified as very coarse generally are larger than those for residences overlying soils classified as coarse, which are larger than those for soils classified as fine. This pattern is consistent with the conceptual model for vapor intrusion; smaller attenuation factors, which indicate greater reduction in vapor concentration, would be expected in vadose zones with finer-grained soils, when all other factors (e.g., depth to groundwater, biodegradability of the volatile chemicals) are the same. The 95 th percentile value of the coarse-grained soil is equal to the generic value, as expected, since coarse-grained soil provide low resistance to vapor transport and thus would be expected to yield high-valued attenuation factors. Where fine-grained sediments underlay buildings, however, more attenuation is expected and observed in the database. Thus, a semi-site-specific attenuation factor of may be used at sites where laterally extensive fine-grained sediment has been demonstrated through site-specific sampling to underlay buildings being investigated for vapor intrusion. A.3.3 RECOMMENDED GENERIC ATTENUATION FACTOR FOR SUB-SLAB SOIL GAS To account for the inherent temporal and spatial variability in indoor air and subsurface vapor concentrations, the 95 th percentile value of the source-screened sub-slab data subset in EPA (2012a) is recommended as a reasonably conservative generic attenuation factor, after considering a range of values. Thus, for sub-slab soil gas, the recommended generic attenuation factor (α ss ) is The selection of this value can be supported by theoretical analysis. Specifically, a simple mass balance analysis, assuming a well-mixed interior volume and steady-state conditions, indicates that the theoretical (true) sub-slab soil gas attenuation factor can be expressed as the ratio of the soil gas entry rate to the building ventilation rate (Song et al., 2011; EPA 2012a) for cases where there is no background contribution to the indoor air concentration. Using median values for residential building volume and air exchange rate (395 m 3 and 0.45 ACH, respectively) provided in the Exposure Factors Handbook 2011 Edition (EPA, 2011) and a mid-range value of 5 L/min for soil gas entry rate in sandy materials (EPA 2002, Appendix G), the central tendency value of the sub-slab soil gas attenuation factor (according to Equation 4a therein), is expected to be approximately Using upper-end (10th percentile) values for residential building volume and air exchange rate (154 m 3 and 0.18 ACH, respectively (EPA 2011)) and soil gas entry rate (10 L/min), an upper-end value of 0.02 for the sub-slab soil gas attenuation factor is obtained. These values agree well with the 95 th percentile and 50 th percentile (median) values A-4

324 (0.03 and 0.003, respectively) obtained from the source-screened data. These calculations buttress the conclusion that the sub-slab attenuation factor distributions summarized in EPA s vapor intrusion database report can be considered representative of vapor intrusion of CHCs into residential buildings for most conditions. Table A-4 (Table 10 in EPA (2012a)) provides statistics and Figure A-4 (Figure 25 in EPA (2012a)) shows box-and-whisker plots for individual sites compared with the statistics for the combined set of screened sub-slab attenuation factors. This table and figure show that the 95 th percentile value of the combined sub-slab-indoor air measurements is considered appropriate for estimating reasonable maximum indoor air concentrations that might be observed at a site due to vapor intrusion. The majority of sites and buildings would be expected to exhibit lower indoor air concentrations. A.3.4 RECOMMENDED ATTENUATION FACTOR FOR NEAR-SOURCE EXTERIOR SOIL GAS Based upon the conceptual model for vapor intrusion, the attenuation factors for exterior soil gas data would be expected to be less than those for sub-slab soil gas, because the former includes an additional contribution from attenuation through the vadose zone, and greater than those for groundwater vapors for a given building at a site where groundwater is the primary subsurface source of vapors. The distributions of exterior soil gas attenuation factors shown in Table A-1 and Figure A-1 do not exhibit this expected relationship. In addition, a comparison of exterior soil gas to sub-slab soil gas concentrations for buildings where both types of samples were collected, shown in Figure A-5 (see Figure 6 in EPA (2012a)), suggests that a substantial proportion of the exterior soil gas data in the database, particularly shallow soil gas data, may not be representative of soil gas concentrations directly underneath a building. On this basis, shallow exterior soil gas sampling data generally are not recommended for purposes of estimating indoor air concentrations and the exterior soil gas attenuation factors in Table A-1 are not recommended for use in deriving generic attenuation factors. Based upon the data in Figure A-5, deep exterior soil gas data appear to more reliably reflect sub-slab concentrations beneath buildings. On this basis, near-source soil gas sampling data (i.e., collected in the vadose zone immediately above each vapor source) generally are allowed for purposes of assessing vapor concentrations that may be in contact with the building s subslab, as discussed further in Section However, the same conservative attenuation factor value for sub-slab soil gas is recommended for use with near-source exterior soil gas data for this purpose. Thus, for near-source exterior soil gas, the recommended generic attenuation factor is A-5

325 A.3.5 RECOMMENDED ATTENUATION FACTOR FOR CRAWLSPACE VAPOR The distribution of attenuation factors presented in Figure A-1 show that attenuation between building crawlspaces and living spaces is limited. To account for the inherent temporal and spatial variability in indoor air and crawlspace vapor concentrations, the 95 th percentile value of the indoor air-screened crawlspace data subset in EPA (2012a) is recommended as a reasonably conservative generic attenuation factor, after considering a range of values. Thus, for crawl space vapor the recommended generic attenuation factor is 1.0 (0.9 rounded up to 1.0). A.3.6 RELIABILITY ANALYSIS OF THE RECOMMENDED SUBSURFACE-TO- INDOOR AIR GENERIC ATTENUATION FACTORS An analysis was performed to determine the reliability of these recommended attenuation factors for screening in residences in EPA s vapor intrusion data base with measured indoor air concentrations exceeding target levels corresponding to a cancer risk of 10-6 and a hazard quotient of 1. The reliability analysis was performed separately for each medium by determining the number of correct assessments and the number of false negatives for a range of attenuation factors. The potential incidence of false negatives is a critical criterion, because the primary objective of risk-based screening is to identify sites or buildings unlikely to pose a health concern through the vapor intrusion pathway (see Section 6.5.1). For the purposes of this analysis: A correct assessment is deemed to occur either: (1) when a chemical s measured indoor air concentration exceeds the target level and the measured subsurface vapor concentration also exceeds the appropriate medium-specific VISL calculated using the specified generic attenuation factor, or (2) when a chemical s measured indoor air concentration is below the target level and the measured subsurface vapor concentration also is below the appropriate medium-specific VISL calculated using the recommended generic attenuation factor. Correct assessments in this analysis represent a correct decision based on subsurface concentration data regarding the potential for vapor intrusion to pose indoor air concentrations that exceed target risk-based concentrations in affected buildings. A false negative is deemed to occur when a chemical s measured indoor air concentration exceeds the target level, but the measured subsurface vapor concentration does not exceed the appropriate medium-specific VISL calculated using the specified generic attenuation factor. False negatives in this analysis represent the potential for making an incorrect decision based on subsurface concentration data regarding the potential for vapor intrusion to pose indoor air concentrations that exceed target risk-based concentrations in affected buildings. This assessment uses the Data Consistency Subset of the EPA s vapor intrusion database for residential buildings (i.e., before screening to minimize the impacts of background contributions to indoor air as described in EPA (2012a)). This subset was chosen to allow for the possibility that background indoor air contributions were incorrectly identified and removed from further analysis in the source-screened data subsets presented in EPA (2012a). Thus, false negatives may appear if indoor or ambient (outdoor) sources of VOCs are present and they exceed the A-6

326 indoor air target level. This choice of datasets provides a conservative estimate of the frequency of false negatives identified by this reliability analysis. Even lower rates of false negatives would be obtained when considering the source-screened data subsets, described in EPA (2012a), in which the impacts of background contributions to indoor air are minimized. The results of this assessment are shown in Figures A-6 through A-8 for sub-slab soil gas, groundwater, and exterior soil gas. 256 The essential results are as follows: The recommended generic attenuation factors yield low rates of false negatives (< 2%) for all three media when individual pairs of samples are evaluated together. The recommended generic attenuation factors for groundwater, exterior soil gas, and sub-slab soil gas provide generally high rates of correct assessments when individual pairs of samples are evaluated together: 78% for groundwater; 76% for exterior soil gas; and 87% for sub-slab soil gas. Higher rates of correct assessments are expected for sub-slab soil gas than for the other subsurface media, likely due to the closer spatial correspondence of building sub-slab soil gas and indoor air samples. The rates of correct assessments appear to level off in Figure A-6 through A-8 at about the point on the x-axis where the recommended generic attenuation factors occur. The rates of false positives using the Data Consistency Subset can be inferred from Figure A-6 through A-8. This analysis indicates that use of ground water data or exterior soil gas data is more likely to incorrectly identify a site or building as warranting further investigation than is use of sub-slab soil gas data. Compared to the values estimated in Figures A-6 through A-8, significantly higher rates of a correct assessment (and, hence, lower rates of false negatives and false positives) are reasonably anticipated to be realized by following this Technical Guide. Specifically, collecting multiple samples to characterize spatial and temporal variability (see, for example, Section 6.4), collecting multiple lines of additional evidence (see, for example, Section 6.3 and 7.1), and weighing this information together (see, for example, Sections 6.3 and 7) are reasonably expected to significantly reduce the error rates estimated in this reliability analysis, which are based upon comparison of individual pairs of indoor air and subsurface sample concentrations. As previously stated, this Technical Guide includes subsurface VISLs that are intended to help identify those sites with the potential to pose a vapor intrusion concern. The reliability analysis described above suggests the recommended attenuation factors, on which the recommended VISLs are based, can reasonably be expected to provide an acceptably small probability of screening out sites that pose a vapor intrusion concern and a high probability of correctly identifying sites or buildings that may pose a vapor intrusion concern. 256 The reliability assessment w as not conducted for craw l space data, because the distribution of attenuation factors presented in Figure A-1 show that attenuation betw een building craw lspaces and living spaces is limited. A-7

327 A.4 CONSIDERATIONS FOR NONRESIDENTIAL BUILDINGS The recommended attenuation factors (see Sections B.3.2 through B.3.5) are proposed for use for nonresidential buildings as well as residential buildings. The rationale is that, in many geographic locations, some commercial enterprises have been established in converted residential buildings. Although used for commercial purposes, such buildings can reasonably be expected to exhibit similar susceptibility to vapor intrusion and similar interior mixing and dilution (and, hence, similar attenuation factors) as residential buildings represented in EPA s vapor intrusion database. In addition, McDonald and Wertz (2007) found that sub-slab attenuation factors for commercial and institutional buildings in Endicott, New York, which were not extraordinarily large, were not substantially different than those for residential buildings in the same area. There are theoretical considerations to support expectations that larger nonresidential buildings that are constructed on thick slabs will have lower attenuation factors than residential buildings. These considerations include: Given that the size (e.g., interior height and footprint area) and air exchange rate tend to be larger for many nonresidential buildings (see, for example, Table A-5), it is expected that building ventilation rates for many nonresidential buildings would be higher than those for residential buildings. A higher ventilation rate is expected to result in greater overall vapor dilution as vapors migrate from a subsurface vapor source into a building. On this basis, many nonresidential buildings would be expected to have lower attenuation factors than those for residential buildings, all else being equal. Comparing buildings with slab-on-grade construction, nonresidential buildings tend to have thicker slabs than residential buildings. With thicker slabs, a given amount of differential settling would be expected to lead to less cracking in the slab and would be less likely to create cracks that extend across the entire slab thickness. Buildings with thicker slabs would, therefore, be expected to exhibit lower soil gas entry rates, all else being equal. Where appropriate, EPA may consider appropriate building-specific data, information, and analysis when evaluating vapor intrusion into large nonresidential buildings. A.5 CITATIONS (APPENDIX A) Johnson, P.C., and R.A. Ettinger Heuristic model for predicting the intrusion rate of contaminant vapors into buildings. Environmental Science & Technology 25: McDonald, G.J. and W.E. Wertz PCE, TCE, and TCA vapors in subslab soil gas and indoor air: A case study in upstate New York. Groundwater Monitoring & Remediation 27(4): Song, S., F. C. Ramacciotti, B. A. Schnorr, M. Bock, and C.M. Stubbs Evaluation of EPA s empirical attenuation factor database. EM: The Magazine for Environmental Managers February: Currently available online at U.S. Environmental Protection Agency (EPA). 2015a. Vapor Intrusion Screening Level (VISL) Calculator, User s Guide. Currently available online at: A-8

328 U.S. Environmental Protection Agency (EPA). 2012a. U.S. EPA s Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings. EPA 530-R Currently available online at _Final.pdf U.S. Environmental Protection Agency (EPA). 2012b. Conceptual Model Scenarios for the Vapor Intrusion Pathway. EPA-530-R Currently available online at U.S. Environmental Protection Agency (EPA) Exposure Factors Handbook 2011 Edition. Office of Research and Development, Washington, D.C. EPA/600/R-090/052. Currently available online at U.S. Environmental Protection Agency (EPA) Risk Assessment Guidance for Superfund (RAGS), Volume I: Human Health Evaluation Manual (Part F, Supplemental Guidance for Inhalation Risk Assessment). Office of Superfund Remediation and Technology Innovation, Washington, D.C. EPA-540-R Currently available online at U.S. Environmental Protection Agency (EPA) OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance). Office of Solid Waste and Emergency Response, Washington, D.C. EPA-530-D November. Currently available online at: U.S. Environmental Protection Agency (EPA) Fact Sheet, Correcting the Henry s Law Constant for Soil Temperature. Office of Solid Waste and Emergency Response, Washington, D.C. Currently available online at A-9

329 TABLE A-1. DESCRIPTIVE STATISTICS SUMMARIZING ATTENUATION FACTOR DISTRIBUTIONS FOR GROUNDWATER, EXTERIOR SOIL GAS, SUB-SLAB SOIL GAS, AND CRAWL SPACE VAPOR AFTER APPLICATION OF THE DATABASE SCREENS CONSIDERED MOST EFFECTIVE AT MINIMIZING THE INFLUENCE OF BACKGROUND SOURCES ON INDOOR AIR CONCENTRATIONS. Statistic Groundw ater (GW > 1,000X Bkgd) Exterior Soil Gas (SG > 50X Bkgd) Sub-slab Soil Gas (SS > 50X Bkgd) Craw l Space (IA > Bkgd) Min 1.0E E E E-02 5% 3.6E E E E-01 25% 2.3E E E E-01 50% 7.4E E E E-01 75% 2.0E E E E-01 95% 1.2E E E E-01 Max 2.1E E E E-01 Mean 2.8E E E E-01 StdDev 1.0E E E E-01 95UCL 3.4E E E E-01 Count All Count >RL Count <RL No. of sites Note: The applied database screens are groundwater (vapor) concentrations > 1,000X background, exterior soil gas > 50X background, sub-slab soil gas > 50X background, and for crawl space, indoor air concentrations > 1X background. SOURCE: Table 19 in EPA (2012a).

330 1.E+01 1.E+00 Attenuation Factor 1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 Max 95th % 75th % 50th % 25th % 5th % Min 1.E-07 Groundwater (GW > 1000X Bkgd) Exterior Soil Gas (SG > 50X Bkgd) Subslab Soil Gas (SS > 50X Bkgd) Crawlspace (IA > Bkgd) Figure A-1. Box-and-whisker plots summarizing attenuation factor distributions for groundwater, exterior soil gas, sub-slab soil gas, and craw l space vapor after application of the database screens considered most effective at minimizing the influence of background sources on indoor air concentrations. SOURCE: Figure 34 in EPA (2012a).

331 TABLE A-2. DESCRIPTIVE STATISTICS SUMMARIZING GROUNDWATER ATTENUATION FACTOR DISTRIBUTIONS FOR INDIVIDUAL SITES COMPARED WITH THE COMBINED DATA SET AFTER SOURCE STRENGTH SCREEN (GROUNDWATER VAPOR CONCENTRATIONS > 1,000 TIMES BACKGROUND ). Statistic GW > 1,000 X Bkgd Allepo Alliant BillingsPCE CDOT Davis Eau Claire Endicott Grants Hamilton-Sundstrand Harcros/Tri State Hopewell Precision Jackson LAFB Lockwood MADEP 1 MADEP 2 Moffet Mountain View Rapid City Redfield SCM - Cortlandville Uncasville Wall West Side Corp. Min 1.0E E E E E E E E E E E E E E E E E E E E E E E-06 5% 3.6E E E E E E E E E E E E E-05 25% 2.3E E E E E E E E E E E E E E-05 50% 7.4E E E E E E E E E E E E E E E E E E E E E E-05 75% 2.0E E E E E E E E E E E E E E-04 95% 1.2E E E E E E E E E E E E E-03 Max 2.1E E E E E E E E E E E E E E E E E E E E E E E-02 Mean 2.8E E E E E E E E E E E E E E E E E E E E E E-03 StdDev 1.0E E E E E E E E E E E E E E E E E E E E-03 95UCL 3.4E E E E E E E E E E E E E E E E E E E E-03 Count All Count >RL Count <RL SOURCE: Table 13 in EPA (2012a).

332 1.E+00 1.E-01 Groundwater Attenuation Factor 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 Max 95th % 75th % 50th % 25th % 5th % Min 1.E-07 Figure A-2.Box-and-whisker plots summarizing groundwater attenuation factor distributions for individual sites compared with the combined data set after Source Strength Screen (groundwater vapor concentrations > 1,000 times background ). SOURCE: Figure 28 in EPA (2012a).

333 TABLE A-3. DESCRIPTIVE STATISTICS SUMMARIZING GROUNDWATER ATTENUATION FACTOR DISTRIBUTIONS FOR SPECIFIC SOIL TYPES AFTER SOURCE STRENGTH SCREEN. Soil Type Below Foundation Statistic Fine Coarse V.Coarse Min 1.0E E E-06 5% 2.3E E E-05 25% 1.9E E E-05 50% 4.6E E E-04 75% 1.4E E E-04 95% 4.5E E E-03 Max 2.4E E E-02 Mean 1.3E E E-04 StdDev 2.4E E E-03 95UCL 1.5E E E-03 Count All Count >RL Count <RL No. of sites SOURCE: Table 14 in EPA (2012a).

334 1.0E+00 Groundwater Attenuarion Factor 1.0E E E E E E-06 Max 95th % 75th % 50th % 25th % 5th % Min 1.0E-07 Fine Coarse V.Coarse Figure A-3.Box-and-whisker plots summarizing groundwater attenuation factor distributions for specific soil types after Source Strength Screen. SOURCE: Figure 29 in EPA (2012a).

335 TABLE A-4. DESCRIPTIVE STATISTICS SUMMARIZING SUB-SLAB ATTENUATION FACTOR DISTRIBUTIONS FOR INDIVIDUAL SITES COMPARED WITH THE COMBINED DATA SET AFTER SOURCE STRENGTH SCREEN (SUB-SLAB SOIL GAS CONCENTRATIONS > 50 TIMES BACKGROUND ). BillingsPCE DenverPCEBB Endicott Georgetown Harcros/Tri State SS > 50X Statistic Bkgd Mi n 2.5E E E E E E E E E E E E-04 5% 3.2E E E E E E E-03 25% 1.5E E E E E E E E E-04 50% 2.7E E E E E E E E E E E E E-03 75% 6.8E E E E E E E E E-03 95% 2.6E E E E E E E-01 Ma x 9.4E E E E E E E E E E E E-01 Mean 9.2E E E E E E E E E E E E E-02 StdDev 5.0E E E E E E E E E E E E-01 95UCL 1.3E E E E E E E E E E E E-01 No. of AFs No. of AFs > RL No. of AFs < RL Hopewell Precision Jackson LAFB Orion Park Raymark SCM-Cortlandville West Side Corporation SOURCE: Table 10 in EPA (2012a).

336 1.0E+00 Subslab Soil Gas Attenuation Factor 1.0E E E E-04 Max 95th % 75th % 50th % 25th % 5th % Min 1.0E-05 SS > 50X Bkgd BillingsPCE DenverPCEBB Endicott Georgetown Harcros/Tri State Hopewell Precision Jackson LAFB Orion Park Raymark SCM-Cortlandville West Side Corporation Figure A-4.Box-and-whisker plots summarizing sub-slab soil gas attenuation factor distributions for individual sites after Source Strength Screen (sub-slab soil gas concentrations > 50 times background ). SOURCE: Figure 25 in EPA (2012a).

337 TABLE A-5 COMPARISON OF SIZE CHARACTERISTICS FOR RESIDENTIAL AND SOME COMMERCIAL BUILDINGS Building Parameter and Units Value and Source for Residential Building Value and Source for Commercial Buildings, Other Than Warehouses and Enclosed Malls ACH Bldg (1/hr), 10 th percentile 0.18 (EPA 2011, Table 19-1) 0.6 (EPA 2011, Table 19-27) H Bldg (feet) 8-feet ceiling height (EPA 2011, assumed value) 12-feet ceiling height (EPA 2011, assumed value) Figure A-5. Exterior soil gas versus sub-slab soil gas concentrations for buildings with both types of data in EPA s vapor intrusion database differentiated qualitatively by horizontal distance to building and depth to the exterior soil gas sample. SOURCE: Figure 6 in EPA (2012a). A-18

338 Subslab Soil Gas - Indoor Reliability Analysis 100% 90% 87% 88% 90% 89% 90% Correct 80% 82% FN 72% 70% Percent of Total 60% 50% 40% 30% 20% 10% 0% 1% 0% % 3% 3% % 9% Subslab Soil Gas - Indoor Air Attenuation Factor Figure A-6.Reliability Predictions for Alternative Choices of the Sub-slab Attenuation Factor Based on a Comparison of Paired Data in the Data Consistency Screen Dataset [tabulated values shown below] Reliability Analysis: Subslab Soil Gas - Indoor Air Classification SS AF = 1 SS AF = 0.1 SS AF = 0.03 SS AF = 0.02 SS AF = 0.01 SS AF = SS AF = Correct FN Total SS AF Correct 72% 82% 87% 88% 90% 89% 90% FN 0% 1% 2% 3% 3% 7% 9% A-19

339 Groundwater - Indoor Air Reliability Analysis 100% Correct 90% 80% 78% 84% 87% 78% FN 70% Percent of Total 60% 50% 40% 39% 55% 30% 30% 20% 20.9% 10% 0.0% 0.2% 0.5% 0.7% 0% % 6.7% Groundwater - Indoor Air Attenuation Factor Figure A-7.Reliability Predictions for Alternative Choices of the Groundwater Attenuation Factor Based on a Comparison of Paired Data in the Data Consistency Screen Dataset [tabulated values shown below] Reliability Analysis: Groundwater -Indoor Air Classification GW AF = 1 GW AF = 0.01 GW AF = GW AF = GW AF = GW AF = GW AF = Correct FN Total GW AF Correct 30% 39% 55% 78% 84% 87% 78% FN 0.0% 0.2% 0.5% 0.7% 3.1% 6.7% 20.9% A-20

340 Exterior Soil Gas - Indoor Air Reliability Analysis 80% 72% 76% 75% 75% Correct 70% FN 60% 58% Percent of Total 50% 50% 40% 30% 51% 20% 10% 0% 0% 0% 1% 0% % 3% 9% 0.01 Exterior Soil Gas - Indoor Air Attenuation Factor Figure A-8.Reliability Predictions for Alternative Choices of the Exterior Soil Gas Attenuation Factor Based on a Comparison of Paired Data in the Data Consistency Screen Dataset [tabulated values shown below] Reliability Analysis: Exterior Soil Gas - Indoor Air Classification SG AF = 1 SG AF = 0.6 SG AF = 0.3 SG AF = 0.1 SG AF = 0.03 SG AF = 0.02 SG AF = 0.01 Correct FN Total SG AF Correct 50% 51% 58% 72% 76% 75% 75% FN 0% 0% 0% 1% 2% 3% 9% A-21

341 B.1 INTRODUCTION APPENDIX B DATA QUALITY ASSURANCE CONSIDERATIONS Site-specific investigations of the vapor intrusion pathway will generally entail the collection and evaluation of environmental data and possibly the use of modeling. As noted in Exhibit B-1, EPA generally recommends the use of a quality assurance project plan (QAPP) for the collection of primary (and existing or secondary) data. A QAPP is a tool for project managers and planners to document the type and quality of data needed to make environmental decisions and to describe the methods for collecting and assessing the quality and integrity of those data. A QAPP is a plan or roadmap intended to help a project team document how they plan, implement, and evaluate a project. It applies the systematic planning process and the graded approach for collecting environmental data for a specific intended use. EPA standards governing the collection of data are outlined in Exhibit B-1. Exhibit B-1. EPA Data Standards CIO 2105 (formerly EPA Order 5360; Policy and Program Requirements for the Agency-wide Quality System, May 2000) is intended to promote the organization collecting or using the data to (1) establish a Quality System and prepare and approve a QAPP for each project. For clarity, CIO 2105 will be replaced by the following two standards: CIO 2106-S-01 is the Quality Standard for Environmental Data Collection, Production, and Use by EPA Organizations, also called Internal Standard (EPA 2013a); and CIO 2106-S-02 is the Quality Standard for Environmental Data Collection, Production, and Use by Non-EPA (External) Organizations, also called External Standard (EPA 2013b). These standards conform to EPA Quality Policy, CIO , Quality Policy (EPA 2008a), Procedure for Quality Policy, CIO 2106-P-01.0, Quality Procedure (EPA 2008b), and the American National Standards Institute (ANSI) consensus standard, Quality Systems for Environmental Data and Technology Programs Requirements with Guidance for Use (ANSI/ASQ 2004). Two guidance documents accompany these standards: EPA Guidance on Quality Management Plans (EPA 2012b, CIO 2106-G02-QMP), documents the quality system of the organization conducting environmental data collection or using the data for EPA. EPA Guidance on Quality Assurance Project Plans (EPA 2012a, CIO 2106-G-05) focuses on projects requiring the collection of new data, projects using existing data, and projects involving modeling. B-1

342 EPA also encourages the use of the Uniform Federal Policy for Quality Assurance Project Plans (UFP-QAPP) (EPA/DoD 2005) as a collaborative approach to fulfill the purposes of a QAPP, especially for Federal Facilities. OSWER Directive , Implementation of the Uniform Federal Policy for Quality Assurance Project Plans (UFP-QAPP) at Federal Facility Hazardous Waste Sites (EPA 2005a) and OSWER Directive (EPA 2005b) state that QAPPs prepared and approved under the UFP conform to EPA s quality standards and are consistent with EPA Standards CIO 2106-S-0 and CIO 2106-S-02, EPA s Quality Policy (EPA 2008a), and ANSI/ASQ B.2 RECOMMENDATIONS This appendix provides two recommendations concerning the key components of QAPP development. These recommendations are not exhaustive, but are included as a starting point as considerations before studying or applying EPA or UFP QAPP guidance. Recommendation 1: Using the conceptual site model (CSM), develop the project plan and QAPP through a process that involves all key players and share these materials with interested parties in draft form so that potential study weaknesses can be addressed early. The CSM is developed to portray the current understanding of site conditions, the nature and extent of contamination, routes of contaminant transport, potential contaminant pathways, and potentially exposed human population. Developing the CSM is the first step in EPA s DQO process. Recommendation 2: Use systematic planning in developing project documents, including the QAPP. Systematic planning is a science-based, common-sense approach designed to ensure that the level of documentation and rigor of effort in planning is commensurate with the intended use of the information and available resources. DQOs are a key component of systematic planning and play a central role in the systematic planning process. DQOs generally are addressed within the QAPP and typically are a critical element in the planning for environmental investigations. Guidance on Systematic Planning Using the Data Quality Objectives Process (QA/G-4) (EPA 2006) provides guidance addressing implementation of DQOs and application of systematic planning to generate performance and acceptance criteria for collecting environmental data. Table B-1 summarizes the steps in the DQO process, the purpose of each step, and provides some examples of how plans could be structured. B-2

343 TABLE B-1. EXAMPLE OF STEPS IN THE DQO PROCESS DQO Step Purpose of the DQO Step Example Application for Vapor Intrusion 1. State the Problem 2. Identify the Decision 3. Identify the Inputs to the Decision 4. Define the Boundaries of the Study 5. Develop a Decision Rule 6. Specify Tolerable Limits on Decision Errors 7. Optimize the Design for Obtaining Data Summarize the problem (e.g., the monitoring hypothesis, the investigation objective(s)) for which new environmental data will be collected or modeling or analysis will be performed. Identify the decision that will be supported by the new data, modeling or analysis. Identify the information needed to support the decision, including data gaps that warrant collection of new information. Specify the spatial and temporal aspects of the environmental media or endpoints that the data are to represent to support the decision. Develop a logical if then statement that defines the conditions that will inform the decision-maker to choose among alternative decisions. Specify acceptable limits on decision errors, which are used to establish performance goals for limiting uncertainty in the analysis. Identify the most resourceeffective sampling and analysis design for generating the information needed to satisfy the DQOs. Indoor air in one or more buildings overlying a shallow plume of PCE-contaminated groundwater is (are) to be sampled to determine whether PCE is present. The original PCE release occurred at an industrial site approximately 1,000 feet away from the closest building. The data will be used to support decisions about whether additional indoor air sampling or preemptive vapor intrusion mitigation will be pursued in one or more buildings. Indoor air sampling data for one or more buildings, in conjunction with information about measured or interpolated concentrations in groundwater near or underneath the building(s). The boundaries of this initial study area extend a prescribed distance outside the lateral extent of the plume. Eventually, the boundaries of a vapor intrusion impact zone will be defined by the extent to which indoor air contamination can be associated with site-related contamination. Buildings with detectable concentrations of PCE in indoor air samples will be considered for additional indoor air sampling or preemptive vapor intrusion mitigation. EPA recommends analytical limits of detection be less than risk-based screening levels for PCE to ensure that a building s indoor air concentration is not misidentified. Time-integrated samples will be collected in basements and in the first above-ground level of each building. The sampling and analysis plan and approach will be documented in a QAPP. B-3

344 B.3 CITATIONS AND REFERENCES (APPENDIX B) ANSI/ASQ Quality Systems for Environmental Data and Technology Programs Requirements with Guidance for Use. E Currently available for purchase online at m=0&searchtermsarray=null ansi+e4 null U.S. Environmental Protection Agency (EPA) Policy and Program Requirements for the Agency-wide Quality System. CIO May. Currently available online at U.S. Environmental Protection Agency (EPA). 2005a. Implementation of the Uniform Federal Policy for Quality Assurance Project Plans (UFP-QAPP) at Federal Facility Hazardous Waste Sites. OSWER Directive June 7. Currently available online at U.S. Environmental Protection Agency (EPA). 2005b. Applicability of the Uniform Federal Policy for Quality Assurance project Plans. EPA A, OSWER Directive December 5. Currently available online at U.S. Environmental Protection Agency (EPA) Guidance on Systematic Planning Using the Data Quality Objectives Process (QA/G-4). EPA-240-B February. Currently available online at U.S. Environmental Protection Agency (EPA). 2008a. U.S. Environmental Protection Agency Quality Policy. CIO Currently available online at U.S. Environmental Protection Agency (EPA). 2008b. U.S. Environmental Protection Agency Procedure for Quality Policy. CIO 2106-P Currently available online at U.S. Environmental Protection Agency (EPA). 2012a. U.S. Environmental Protection Agency Guidance on Quality Assurance Project Plans. CIO 2106-G-05 QAPP. January 17. U.S. Environmental Protection Agency (EPA), 2012b. EPA Draft Final Guidance on Quality Management Plans. CIO 2106-G02-QMP. January 17. Currently available online at 12.pdf U.S. Environmental Protection Agency (EPA). 2013a. Quality Standard for Environmental Data Collection, Production, and Use by EPA Organizations. CIO 2106-S-01. B-4

345 U.S. Environmental Protection Agency (EPA). 2013b. Draft Final Quality Standard for Environmental Data Collection, Production, and Use by Non-EPA (External) Organizations. External Standard. CIO 2106-S-02. February 22. Currently available online at U.S. Environmental Protection Agency and U.S. Department of Defense (EPA/DoD) Uniform Federal Policy for Quality Assurance Project Plans (UFP-QAPP). Part 1: UFP-QAPP Manual. EPA-505-B A, DTIC ADA March. Currently available online at B-5

346 APPENDIX C CALCULATING VAPOR SOURCE CONCENTRATION FROM GROUNDWATER SAMPLING DATA Correcting the Henry s Law Constant for Groundwater Temperature In the case of groundwater as the vapor source, the subsurface source concentration (C sv ) is estimated assuming that the vapor and aqueous phases are in local equilibrium according to Henry s law such that: where: C = H C sv C sv = vapor concentration at the source of contamination (g/cm 3 -v), TS w Equation C.1 H' TS = Henry's law constant at the system (groundwater) temperature (dimensionless), and C w = concentration of volatile chemical in groundwater (g/cm 3 -w). The Henry s law constants generally are reported for a temperature of 25 degrees Celsius ( o C). Table C-1 provides these values for the chlorinated hydrocarbons (CHCs) in the vapor intrusion database. Average groundwater temperatures, however, are typically less than 25 o C. In such cases, use of the Henry s law constant at 25 o C may over-predict the volatility of the contaminant in water. As described in EPA s Soil Screening Guidance (EPA 1996), the dimensionless form of the Henry s law constant at the average groundwater temperature (H' gw ) may be estimated using the Clapeyron equation: H gw H exp R = v, gw c 1 T R T gw gw 1 T R H R Equation C.2 where: H v,gw = enthalpy of vaporization of the specific chemical at the groundwater temperature (cal/mol), T gw = groundwater temperature ( K = o C ), T R R C H R R = reference temperature for the Henry s law constant ( o K), = gas constant (= cal/mol- o K), = Henry s law constant for the specific substance at the reference temperature (atm-m 3 /mol), and = gas constant (= E-05 atm-m 3 /mol- o K). C-1

347 The enthalpy of vaporization at the groundwater temperature can be approximated from the enthalpy of vaporization at the normal boiling point, as follows: where: H v, gw = H v, b ( 1 T / T ) ( 1 T / T ) H v,gw = enthalpy of vaporization at the groundwater temperature (cal/mol), gw B C C η Equation C.3 H v,b = enthalpy of vaporization at the normal boiling point (cal/mol), T C = critical temperature for specific chemical ( o K), T B = normal boiling point for specific chemical ( o K), η = exponent (unitless), and all other symbols are as defined previously. Table C-1 provides the chemical-specific property values used for temperature corrections to the Henry s law constant. Table C-2 provides the value of η as a function of the ratio T B /T C. If site-specific data are not readily available for the groundwater temperature, then Figure 1 of the EPA fact sheet, Correcting the Henry s Law Constant for Soil Temperature (EPA 2001) can be used to generate an estimate. Citations (Appendix C) U.S. Environmental Protection Agency (EPA) Soil Screening Guidance: Technical Background Document. Office of Solid Waste and Emergency Response, Washington, D.C. EPA-540-R Currently available online at: U.S. Environmental Protection Agency (EPA) Fact Sheet, Correcting the Henry s Law Constant for Soil Temperature. Office of Solid Waste and Emergency Response, Washington, D.C. Currently available online at U.S. Environmental Protection Agency (EPA). Regions 3, 6, and Regional Screening Levels for Chemical Contaminants at Superfund Sites. Region 3, Philadelphia, PA. November. Currently available online at C-2

348 Lide, D.R. (Ed.) CRC Handbook of Chemistry and Physics, 79thEd. Boca Raton, FL. CRC Press. Mallard, W.G. and P.J. Linstrom (Eds.) NIST Chemistry WebBook: NIST Standard Reference Database Number 69. Gaithersburg, MD. National Institute of Standards and Technology. November. Currently available online at C-3

349 Table C-1. Chemical Specific Parameters for Adjusting Henry's Law Coefficients for Groundwater Temperature Chemical Abstracts Service Registry Number (CASRN) Alphabetized List of Compounds Henry's Law C Henry's Law C g Normal Boiling Point Critical Temperature Enthalpy of vaporization at the normal boiling point H R H' R T b T c H v,b (atm-m 3 /mol) source (unitless) ( o K) source ( o K) source (cal/mol) source Carbon tetrachloride 2.76E-02 a 1.13E E+02 b 5.57E+02 h 7.13E+03 h Chloroethane (ethyl chloride) 1.11E-02 a 4.54E E+02 b 4.60E+02 f 5.88E+03 f Chloroform 3.67E-03 a 1.50E E+02 b 5.36E+02 h 6.99E+03 h Dichloroethane,1,1-5.62E-03 a 2.30E E+02 b 5.23E+02 h 6.90E+03 h Dichloroethene, 1,1-2.61E-02 a 1.07E E+02 b 5.76E+02 h 6.25E+03 h Dichloroethene,cis-1,2-4.08E-03 a 1.67E E+02 b 5.44E+02 h 7.19E+03 h Dichloroethene,trans-1,2-4.08E-03 a 1.67E E+02 b 5.17E+02 h 6.72E+03 h Methylene chloride 3.25E-03 a 1.33E E+02 b 5.10E+02 h 6.71E+03 h Tetrachloroethylene 1.77E-02 a 7.23E E+02 b 6.20E+02 h 8.29E+03 h Trichloro-1,2,2- trifluoroethane,1,1,2-5.26e-01 a 2.15E E+02 b 4.87E+02 f 6.46E+03 f Trichloroethane, 1,1,1-1.72E-02 a 7.03E E+02 b 5.45E+02 h 7.14E+03 h Trichloroethylene 9.85E-03 a 4.03E E+02 b 5.44E+02 h 7.51E+03 h Vinyl chloride (chloroethylene) 2.78E-02 a 1.14E E+02 b 4.32E+02 h 5.25E+03 h Sources and Footnotes: a Based on values reported in the U.S. EPA Regional Screening Tables. November Available online at: b Experimental values. EPA Estimation Programs Interface Suite for Microsoft Windows, v U.S EPA, Washington, DC, USA. Available online at: f CRC Handbook of Chemistry and Physics, 76th Edition h EPA (2001). FACT SHEET Correcting the Henry's Law Constant for Soil Temperature. Attachment. g National Institute of Standards and Technology (NIST). Chemistry WebBook. Available online at

350 Table C-2. Values of Exponent η as a Function of T B /T C Chemical-specific ratio TB/TC Η < (TB/TC) > C-5

351 4

352 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C MEMORANDUM DEC OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE OSWER Directive SUBJECT: Transmittal of OSWER Directive , "Assessing Protectiveness at Sites for Vapor Intrusion. Supplement to the Compre±.:ensivFive-Year Review Guidance" FROM: James E. Woolford, Director (l_~ Office ofsuperfund Rem~a~lnnovation (5204P) Reggie Cheatham, Director I - > Federal Facilities Restoration an euse Office (5106P) TO: Superfund National Policy Managers, Regions 1-10 This memorandum transmits OSWER Directive , entitled "Assessing Protectiveness at Sites for Vapor Intrusion. Supplement to the Comprehensive Five-Year Review Guidance." This supplemental guidance provides recommendations for conducting five-year reviews for the vapor intrusion component ofremedies in a manner similar to the review ofengineering or other remedy components. This document is designed primarily for U.S. Environmental Protection Agency Remedial Project Managers. Ifyou have any questions, please contact David Cooper at (703) (cooper.davide@epa.gov) or have your staff contact Howard Fribush at (703) (fribush.howard@epa.gov). Attachments cc: OSRTI Managers Federal Facilities Leadership Council Suzanne Rudzinski, OSWER/ORCR Larry Stanton, OSWER/OEM Elliott Gilberg, OECA/OSRE Dave Kling, OECA/FFEO Brigid Lowery, OSWER/CPA John Michaud, OGC/SEWRLO Lisa Price, Superfund Lead Region Coordinator, US EPA Region 6 NARPM Co-Chairs OSRTI Documents Coordinator Internet Address (URL) Recycled/Recyclable Printed with Vegetable Oil Based Inks on 100% Postconsumer, Process Chlorine Free Recycled Paper

353 Assessing Protectiveness at Sites for Vapor Intrusion Supplement to the Comprehensive Five-Year Review Guidance OSWER Directive Purpose The purpose of this supplemental guidance is to provide recommendations for assessing the protectiveness of a remedy for vapor intrusion at private and federal facility Superfund sites during the five-year review process described in the Comprehensive Five-Year Review Guidance (EPA, 2001). It also provides recommendations for assessing protectiveness at sites where a vapor intrusion remedy has not been implemented and: 1) the vapor intrusion pathway was never adequately characterized; or 2) changes in site conditions since the last five-year review have potentially led to a complete vapor intrusion pathway. Scope This supplemental guidance 1 provides a recommended approach for assessing protectiveness associated with the vapor intrusion pathway and remedies. EPA plans to issue additional guidance on how to test for vapor intrusion and evaluate appropriate courses of action to address vapor intrusion exposure. Additionally, a site may have other contaminated media or exposure pathways to assess during the fiveyear review process. Regions should consult the Comprehensive Five-Year Review Guidance and other supplemental five-year review guidance for information specific to these media exposures and remedies prior to making a protectiveness determination for the site. Overview What Is Vapor Intrusion? For purposes of this supplemental guidance, vapor intrusion is the general term given to migration of hazardous vapors from any subsurface contaminant source, such as contaminated soil or groundwater, through the vadose zone and into the indoor air, usually of overlying buildings through openings in the building foundation (e.g., through cracks in the slab, gaps around utility lines, or elevator shafts). Contaminants that may result in vapor intrusion include volatile organic compounds (VOCs) and other vapor-forming chemicals, such as some semivolatile organic compounds, elemental mercury, and radionuclides. VOCs typically pose the most common vapor intrusion concerns. For purposes of this guidance, having a complete vapor intrusion pathway means that humans are exposed to vapors originating from site contamination. For CERCLA sites determined to have a complete pathway, the site typically is evaluated to determine whether the pathway poses a potential risk to human health. Typically at sites where this risk is found to exist, remedial action objectives (RAOs) are established for the vapor intrusion pathway, and a remedy is selected to address it, consistent with the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) and EPA Superfund guidance. 1 This document does not substitute for statutes that EPA administers or their implementing regulations, nor is it a regulation itself. Thus, it does not impose legally binding requirements on EPA, states, or the regulated community, and may not apply to a particular situation based upon the specific circumstances. Risk management issues should be evaluated by the site manager, with input from the site-specific teams, stakeholders, regional management, and legal staff, as appropriate. This document may be modified in the future. 1

354 Vapor migration from the subsurface to indoor air often is influenced by many variables, including the geology and hydrogeology of the site, building characteristics, and seasonal changes. A key concept of vapor intrusion normally is that the vapor concentrations attenuate (decrease) as the vapors migrate away from the contaminant source. The attenuation typically occurs as a result of the processes that control vapor migration in soil (e.g., diffusion, advection, sorption, and in some cases, degradation), coupled with the dilution that occurs when the vapors enter a building and mix with indoor air. Due to these many variables, EPA currently recommends the use of multiple lines of evidence to adequately evaluate the vapor intrusion pathway and the associated potential risks to human health. 2 For example, it is recommended that all available data (e.g., analytical results, building type, and ventilation rates) be used in determining whether vapor intrusion is occurring and whether potential health concerns may exist as a result (ITRC 2007). Also, it is generally agreed that the use of a single data set (e.g., one sampling event, limited sampling options) to evaluate the vapor intrusion pathway is typically inadequate to support site decision making (EPA 2008). Further, the development of a conceptual site model can provide an understanding of the site setting, contaminant properties, and potential exposure pathways. Purpose of the Five-Year Review. In general, a five-year review evaluates the implementation and performance of an overall site remedy in order to determine if the remedy is or will be protective of human health and the environment. Protectiveness is generally described in the NCP by reference to the cancer risk range and non-cancer hazard index. Evaluation of the remedy and the determination of protectiveness should be based on, and sufficiently supported by, data and observations included in the Administrative Record for the site. The Comprehensive Five-Year Review Guidance addresses sites at which a remedy has been selected and/or implemented. For sites at which a vapor intrusion remedy has not been selected or implemented, but new information raises the potential for a complete vapor intrusion pathway, the five-year review process may offer an appropriate opportunity to identify issues, review data, make recommendations, and develop a protectiveness determination for vapor intrusion. Establishing a Five-Year Review Site Team. Vapor intrusion remedy performance data, environmental data, and/or other relevant information should be assessed by the appropriate technical experts in the region. For some five-year reviews, a multi-disciplinary team is an effective way to adequately review data and evaluate the protectiveness of the vapor intrusion remedy. Key Concepts for Incorporating Vapor Intrusion into the Five-Year Review As discussed in the Comprehensive Five-Year Review Guidance, data for a review may be collected through document reviews, interviews, a site inspection, and supplemental sampling. If decision documents have identified the vapor intrusion pathway as a risk to human health at a site, the data collected should help assess whether the portion of the remedy that was designed to address the vapor intrusion pathway is operating as intended and is still ensuring protectiveness of human health. It is possible that the vapor intrusion pathway was not considered at the time site-related decision documents were issued or that new site information (discovered since the decision documents were 2 EPA s previously recommended approach to assessing the vapor intrusion pathway is documented in Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (EPA, 2002). This document recommended a tiered approach to assess the vapor intrusion pathway. 2

355 issued) suggests that vapor intrusion is now a potential pathway of concern at a site. At sites where a complete vapor intrusion pathway is suspected, the five-year review site team may consider whether there is adequate, appropriate data to evaluate the pathway prior to commencing the five-year review. If no or inadequate data are available, the five-year review document can make recommendations for gathering appropriate data relevant to potential vapor intrusion. Where there is adequate, appropriate data to evaluate the vapor intrusion pathway prior to commencing the five-year review, the Region may be able to minimize the need to defer a protectiveness determination if vapor intrusion is determined to be an issue. Site Characteristics and Data. Vapor migration from the source to indoor air may be influenced by a number of factors, including hydrogeology, anthropogenic conditions, outdoor air contaminants, preferential pathways (e.g., utility lines), characteristics of individual buildings that may affect the degree vapors enter from the subsurface (e.g., building foundation and ventilation conditions), and/or seasonal and meteorological influences. By considering these factors early, EPA can minimize the likelihood of deferring a protectiveness determination due to insufficient information to evaluate whether vapor intrusion is an issue. Factors that influence vapor migration Geology and hydrogeology Anthropogenic conditions Outdoor air contaminants Preferential pathways (e.g., utility lines) Characteristics of individual buildings (e.g., foundation, ventilation) Seasonal and meteorological influences The Region typically should review the site characteristics and other available information as part of the preliminary technical assessment to determine whether adequate data exist to identify an actual or potential vapor intrusion pathway. For those sites where a vapor intrusion pathway may represent a risk to human health, the Region should assess whether that portion of the remedy originally selected and designed to address the vapor intrusion pathway is operating as intended, and if so, assess whether the vapor intrusion remedy is still protective of human health, also taking into account sensitive populations (such as the very young, the elderly, pregnant women, and the immunocompromised). Particular attention should be given to identifying data in the potential or actual vapor intrusion receptor area, for example, presence of shallow wells present, or whether soils on or near the vapor intrusion properties of interest have been characterized. Information that may be useful in evaluating the site, and developing or updating the conceptual site model for the vapor intrusion pathway includes, but is not limited to, the following: Nature and Extent of Contamination: Depth and areal extent of VOCs and other vapor-forming chemicals Concentrations of these contaminants in groundwater, soil and soil gas (vertical and lateral extent), sub-slab soil gas, indoor air (including crawlspace), and outdoor air (e.g., ambient background, air in the immediate vicinity of building including the air intake system) Recent groundwater or soil-to-air modeling Laboratory data, location of drinking water or public water wells 3

356 Natural / Physical Characteristics: Geology types, distribution, and permeability of unconsolidated materials, bedrock, and subsurface materials Hydrogeology depth to groundwater, direction and rate of flow, recharge rates, presence or absence of preferential flow zones and low permeability lenses, hydraulic conductivity and gradient, vadose zone/aquifer material Seasonal changes effect of precipitation on water table levels, temperature fluctuations between summer and winter, barometric pressure. Building Characteristics and Property Use(s): Onsite structures design and construction (e.g., slab on grade, basement, crawl space), integrity of the bottom floor and foundation (e.g., cracks and other openings present, unfinished dirt floor), heating and building ventilation (including operation of heating, ventilation, and cooling (HVAC) systems), sumps, utility corridors, elevator shafts Land use for the area overlying subsurface contamination historic, current, and reasonably anticipated potential future uses (if known), operation of daycare facilities within onsite businesses Zoning for the area overlying subsurface contamination, as well as any institutional controls (ICs) that serve to limit future development Vapor Intrusion Remedy Performance (as related to the source): Pressure differential Mitigation system discharge performance (i.e., concentration of vapors being discharged) Operating fan Indoor air concentrations Document Review. In the five-year review process, it generally is important to review documents associated with the remedial action(s) to assess activities taken that may address or affect existing or potential vapor intrusion exposure pathways. Potentially useful information can include preliminary remediation goals (PRGs) and remedial action objectives (RAOs), contaminant cleanup levels, overall site remedy decision documents, site implementation documents, overall site remedy performance documents, and legal and enforcement documents. Additionally, if vapor intrusion-related data are mentioned in the list of Operations and Maintenance (O&M) requirements, these data reports can be highlighted for assessing potential vapor intrusion pathways. See the appropriate appendix of the Comprehensive Five-Year Review Guidance for specific information regarding the review of documents related to the five-year review process. Assessing the Protectiveness of the Vapor Intrusion Remedy The site characteristics and data collected during the literature review, interviews, site inspection, and supplemental sampling generally should be evaluated to assess the protectiveness of the selected response action. The three technical assessment questions (Questions A, B and C) described in the Comprehensive Five-Year Review Guidance and Frequently Asked Questions About Vapor Intrusion provide a recommended framework for organizing and evaluating the data and information to help 4

357 ensure all relevant issues can be considered when determining the protectiveness of the overall site remedy during the five-year review. Both existing and potential vapor intrusion exposure pathways generally should be assessed during the document review; the possible existence of a vapor intrusion pathway may not have been considered prior to the five-year review. When answering the three recommended technical assessment questions, the Region should be able to evaluate whether an actual or potential vapor intrusion exposure at the site affects the ability of the overall site remedy to ensure protectiveness of human health and the environment. Answering the three questions generally should allow the Region to reach appropriate conclusions for the five-year review report by identifying relevant issues, making follow-up recommendations, and assessing the protectiveness of the overall site remedy. These recommended steps are summarized in the following sections. Technical Assessment Questions. As indicated above, answering the following three recommended technical assessment questions should help the Region evaluate whether an actual or potential vapor intrusion exposure at the site might affect the ability of the overall site remedy (or the vapor intrusion component of the overall remedy) to ensure protectiveness of human health and the environment. The Region should include language clearly articulating what site characteristics, data, and lines of evidence the site team used to reach its protectiveness determination; supporting information should be included in the administrative record file for the site. The Comprehensive Five-Year Review Guidance describes a number of items to consider in answering Questions A, B, and C. This section lists additional items to consider when answering the questions in the context of a vapor intrusion remedy and pathway. Question A: Is the remedy functioning as intended by the decision documents? When you ask Question A: Is the remedy functioning as intended by the decision documents? For vapor intrusion, factors you should consider may include whether Can available data, such as periodic system monitoring, O&M, and physical changes in building construction, be used to assess the effectiveness of the vapor intrusion remedy? Specifically, Are performance standards being met? Are indoor air concentrations below action levels? Are new chemicals being used or detected in the facility or buildings? Are the groundwater and vapor plumes contained? Are O&M activities maintaining the effectiveness of the vapor intrusion remedy? Do exhaust fans operate continuously? Is the exhaust pipe still in place? Are broken components replaced or fixed as soon as possible? Have physical changes in buildings decreased the effectiveness of the vapor intrusion remedy? Have new cracks appeared in floors or basement walls? Have new utilities been connected? Have additions been constructed on buildings with mitigation systems? 5

358 Question A: Is the remedy functioning as intended by the decision documents? Have the institutional controls (ICs) for the vapor intrusion portion of the remedy been implemented? If so, are they helping to minimize the potential for exposure to vapor intrusion over the long term by, for example, restricting or preventing potential impacts from vapor intrusion? 3 Are ICs helping to protect the integrity of engineered controls? Do the ICs provide adequate notice to parties of the potential impacts from vapor intrusion? Are there problems with the vapor intrusion remedy that could ultimately lead to the overall site remedy not being protective or question the protectiveness of the overall site remedy? Do residents regularly turn the exhaust fans off? Is the groundwater plume not contained? Are other actions (e.g., additional response actions, including ICs) necessary to ensure that there are no exposure pathways that could result in unacceptable risks? Question B Are the exposure assumptions, toxicity data, cleanup levels, and RAOs used at the time of the remedy selection still valid? Question B normally is appropriate at sites where a remedy for vapor intrusion has been implemented, as well as: 1) sites where vapor intrusion was determined not to pose a risk to human health at the time of decision document signature; and 2) sites where the vapor intrusion pathway was never evaluated, but the presence of vapor-forming chemicals and potential receptors raise the possibility of a completed vapor intrusion pathway. The Region should evaluate remedy objectives and risk assessment assumptions to ensure that the vapor intrusion pathway has been adequately assessed and that the current overall site remedy selected in the decision document(s) is protective of human health and the environment. In cases where the vapor intrusion pathway has not been addressed, the response to this question should include an evaluation of available data and the collection of additional data to determine if a complete vapor intrusion exposure pathway exists, and if so, whether it results in an unacceptable risk which warrants use of CERCLA response authority. When you ask Question B: Are the exposure assumptions, toxicity data, cleanup levels, and RAOs used at the time of the remedy selection still valid? For vapor intrusion, factors you should consider may include whether Was vapor intrusion evaluated in the baseline human health risk assessment? Was the potential or actual vapor intrusion pathway adequately assessed, and is the vapor intrusion remedy (if 3 For additional information, see Institutional Controls: A Guide to Planning, Implementing, Maintaining, and Enforcing Institutional Controls at Contaminated Sites (Interim Final) (EPA-540-R / OSWER ; November 2010). 6

359 Question B: Are the exposure assumptions, toxicity data, cleanup levels, and RAOs used at the time of the remedy selection still valid? one is in place) protective of human health and the environment? Do the exposure assumptions made at the time of the overall site remedy decision remain unchanged? If the potential for a vapor intrusion pathway exists (e.g., vapor-forming chemicals remain in the subsurface and potential receptors are present), does assessment of available data confirm that the pathway is complete using the appropriate guidelines (e.g., EPA, 2002)? Does vapor intrusion present an unacceptable risk, including to sensitive populations, that warrants use of CERCLA response authority? Are there any environmental justice concerns? Have potential or actual vapor intrusion exposure pathways been identified at the site that had not been previously considered? Have site conditions changed (e.g., new buildings or building modifications, changes in land use or zoning, or additional upgradient sources) that may present a potential vapor intrusion risk? Do the RAOs adequately address potential risk, based on current land use and reasonably anticipated future land use? Are the toxicity values and algorithms used originally to estimate risk from exposure to indoor air still appropriate? Have new contaminants or contaminant sources been identified? Are there unanticipated toxic byproducts of the response action not previously addressed by the decision documents? If byproducts are as or more toxic than the contaminant(s) of concern, are they being addressed? Are the cleanup levels included in the decision documents to address vapor intrusion still valid, including cleanup levels for source materials and other calculated cleanup numbers (sub-slab, indoor air, etc.)? Do components of the existing overall site remedy, even if not specifically designed to eliminate a vapor intrusion exposure pathway, currently prevent a potential vapor intrusion pathway or provide protection under a future vapor intrusion scenario? 7

360 Question C Has any other information come to light that could call into question the protectiveness of the remedy? Question C normally is appropriate at sites where a remedy for vapor intrusion has been implemented as well as: 1) sites where vapor intrusion was determined not to pose a risk to human health at the time of decision document signature; and 2) sites where the vapor intrusion pathway was never evaluated, but the presence of vapor-forming chemicals and potential receptors raise the possibility of a completed pathway. When you ask Question C: Has any other information come to light that could call into question the protectiveness of the remedy? For vapor intrusion, factors you should consider may include whether Have potential or actual vapor intrusion exposure pathways been adequately addressed by an existing remedy (even if that remedy was not originally intended to address vapor intrusion)? Have new homes or other buildings been built at the site? Has the groundwater plume migrated or has the water table risen or changed substantially? Have any natural disasters, such as flooding or earthquakes, occurred, and if so, have they affected the integrity of buildings or impacted vapor intrusion remedies? Developing Conclusions for the Five-Year Review The conclusions of the five-year review generally should include: 1) an identification of issues; 2) recommendations and follow-up actions; and 3) a determination of whether the vapor intrusion component and the overall site remedy are, or are expected to be, protective of human health and the environment. These conclusions should be documented in the five-year review report as a technical assessment summary. Please refer to Section 4.4 in the Comprehensive Five-Year Review Guidance (EPA, 2001) for a more detailed discussion of identifying issues and developing recommendations. If issues are identified that may prevent the response action from being protective, now or in the future, these issues and the follow-up recommendations and actions generally should be documented in the corresponding sections of the five-year review report. The issues and recommendations sections typically provide a summary of items that could affect current or future protectiveness at the site, and normally include milestone dates for completion of actions to help ensure protectiveness. Where possible, recommendations for gathering additional information (e.g., lines of evidence to evaluate current or future vapor intrusion risks) should be specific about the type of data needed. For example, a recommendation to "Collect groundwater samples at the surface of the groundwater to better assess the uppermost lens of contamination" generally is more useful than a recommendation that just states "Conduct a vapor intrusion investigation." 8

361 Identify Issues Examples of vapor intrusion issues that may be identified include: Vapor intrusion risks have not yet been assessed, or additional lines of evidence are needed to assess vapor intrusion risks. Groundwater contaminated with VOCs is migrating towards offsite buildings and may present future vapor intrusion risk. ICs are not implemented or are inadequate to restrict or provide notice on land or building use over or near a plume of vapor-forming chemicals. Inadequate O&M of physical structures is occurring, such as the vapor exhaust pipe and fan. Inadequate monitoring activities to determine the protectiveness of the vapor intrusion remedy (e.g., scheduled air sampling or pressure differential monitoring is not being conducted according to decision documents) Develop Recommendations The following are types of recommendations that, depending on site-specific circumstances, generally are considered appropriate as part of a five-year review: Vapor intrusion risks need to be assessed. Additional lines of evidence are needed to accurately assess vapor intrusion risks. Monitor groundwater to ensure migration of VOCs do not reach offsite buildings. Improve O&M and monitoring activities to ensure vapor intrusion remedies continue to operate as planned in a manner that will meet RAOs (e.g., replace broken fans or broken exhaust pipes, patch new holes in floors or in vapor barriers). Implement ICs to provide conditions on risks from new construction in the area of a VOC plume. 9

362 Determine Protectiveness. The five-year review should take into account the protectiveness for the vapor intrusion remedy in addition to the protectiveness of the other components of the remedy when determining the overall protectiveness of the site or operable unit. The different protectiveness statement options for a five-year review are: 1) protective; 2) will be protective upon completion of the remedial action; 3) protective in the short term; 4) protectiveness deferred until further information is obtained; and 5) not protective. For the vapor intrusion component, as with other remedy components, the determination whether the vapor intrusion remedy remains protective of human health and the environment should be based generally on the answers to Questions A, B, and C and the information obtained in the process of answering them. At sites where vapor intrusion risks have not been assessed, Questions B and C can help evaluate whether response actions (e.g., collecting lines of evidence) are needed to assess vapor intrusion risks and ensure protectiveness at the site. The following table generically describes possible situations and how they may affect remedy protectiveness determinations. Site-specific vapor intrusion-related characteristics, available data, and remedy components normally should all be taken into account when evaluating protectiveness. For consistency, Regions are encouraged to use the recommended model protectiveness statements as described in the Comprehensive Five-Year Review Guidance. For operable unit (OU)-specific and sitewide protectiveness guidelines, please review the appropriate section of the Comprehensive Five-Year Review Guidance. Protective Protectiveness Determination Potential or Actual Vapor Intrusion Conditions at the Site Data collected and assessed show no potential or actual vapor intrusion exposure pathway exists, based on: - Data reviewed during the five-year review process which indicate that the current RAOs address vapor intrusion and are being met by the remedy; - The vapor intrusion remedy is functioning as intended to meet the RAOs; or - Other remedy components (that do not explicitly address the vapor intrusion pathway) effectively mitigate the vapor intrusion risk. Will be protective upon completion of the remedial action Data collected and assessed show implementation of remedy components that will prevent a potential or actual exposure pathway is underway and expected to be protective upon completion, and in the interim, exposure pathways that could result in unacceptable risks are being controlled. 4 4 The will be protective determination generally is appropriate for sites that have not yet met the construction completion milestone as per Exhibit 4-6 of the Comprehensive Five-Year Review Guidance. (EPA 540-R / OSWER B- P; June 2001). 10

363 Protective in the short term (List in the protectiveness statement the follow-up actions that need to be taken in order for the remedy to be protective in the long-term.) Data collected and assessed show: - A potential or actual vapor intrusion exposure pathway exists but current site conditions prevent exposure (e.g., buildings currently are unoccupied but land use may change, or the HVAC system is currently operating but a determination needs to be made if an operating HVAC is needed for long-term protectiveness); - A vapor intrusion exposure pathway does not currently exist but due to the potential for changes in site conditions, a future assessment could be deemed appropriate (e.g., future construction; development of foundation cracks; inadequate O&M plan) - Current engineering control is preventing exposure in the short term, but ICs are not in place to protect against future exposure; or - A potential or actual vapor intrusion exposure pathway is prevented because of existing engineering or administrative actions that are not in a decision document. Protectiveness deferred until further information is obtained (Provide a timeframe for when a protectiveness determination will be made.) Available data are insufficient to determine whether there is a potential or actual vapor intrusion exposure pathway, and further evaluations are necessary Not protective (List in the protectiveness statement the actions that must be taken to ensure protectiveness. Include an anticipated timeframe for completing the actions and when the remedy will be protective.) Data collected and assessed shows: - An actual vapor intrusion exposure pathway is causing unacceptable exposures to receptors, either because no existing remedy components are in place to address them or existing remedy components are not functioning as intended to meet the RAOs; or - The existing cleanup level in the original decision document is no longer protective. The vapor intrusion remedy cannot meet a new cleanup level (based on a new ARAR or IRIS value, for example), and the previous cleanup level is no longer protective. Technical Support. In order to assist with the protectiveness determination for five-year reviews at sites with potential or actual vapor intrussion exposure pathways, Regional and Headquarters members of the Vapor Intrusion Forum and the Five-Year Review Team are available to provide technical 11

364 assistance to site teams to develop optimal strategies for site investigation. Contacts for the Vapor Intrusion Forum can be found via EPA s Vapor Intrusion website at and contacts for the Five-Year Review Teams for specific sites can be found via EPA s Five-Year Review website at References EPA, A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents. (EPA 540/R-98/031 / OSWER P; July). Available at: EPA, Operation and Maintenance in the Superfund Program. (EPA 540-F / OSWER FS; May 2001). Available at: EPA, Comprehensive Five-Year Review Guidance. (EPA 540-R / OSWER B-P; June). Available at: EPA, Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils. (EPA530-D ; November). Available at: ITRC Vapor Intrusion Pathway: A Practical Guideline. Available at: EPA Brownfields Technology Primer: Vapor Intrusion Considerations for Redevelopment. (EPA 542-R ; March). Available at: EPA, Assessing Protectiveness for Asbestos Sites: Supplemental Guidance to Comprehensive Five-Year Review Guidance. (OSWER Directive # B-P; October). Available at EPA, Institutional Controls: A Guide to Planning, Implementing, Maintaining, and Enforcing Institutional Controls at Contaminated Sites (Interim Final). (EPA-540-R / OSWER ; November). EPA, Recommended Evaluation of Institutional Controls: Supplement to the Comprehensive Five-Year Review Guidance" (OSWER Directive , September). Available at: EPA Frequently Asked Questions About Vapor Intrusion. Available at: EPA, Comprehensive Five-Year Review Guidance. (in development). Will be available at: 12

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366 çç 0 s1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY Region 9 75 Hawthorne Street LPro1 San Francisco, CA MEMORANDUM July 9, 2014 Subject: EPA Region 9 Response Action Levels and Recommendations to Address Near- Term Inhalation Exposures to TCE in Air from Subsurface Vapor Intrusion From: Enrique Manzanilla Director Superfund Division / To: Region 9 Superfund Division Staff and Management At my request, Gerry Hiatt and Dan Stralka have prepared the attached memorandum with their technical assessment and recommendations regarding action levels, investigation approaches and response measures to address inhalation exposures to trichloroethylene (TCE) in indoor air from the subsurface vapor intrusion pathway. The memorandum contains a useful operational framework and point of departure for Region 9 Superfund staff and management, in particular for Remedial Project Managers (RPMs) and On-Scene Coordinators (OSCs). I am asking each of you to consider this technical assessment and the resulting recommendations in making site-specific decisions regarding the investigation of and response to TCE vapor intrusion. Addressing vapor intrusion at our Superfund sites is one of the top priorities for the Superfund Division. When a completed vapor intrusion pathway exists, current exposure can potentially result in risks to human health (both long term cancer risks and near term non-cancer hazards). The recommendations set forth in the attached memorandum address a particular concern for TCE focusing on protecting sensitive and vulnerable populations, especially women in the first trimester of pregnancy (because of the potential for cardiac malformations to the developing fetus). We have been in regular communication with OSWER regarding these issues and our toxicologists consulted with their peers in OSWER in developing their memorandum. Numerous resources are available within the Superfund Division to help RPM s and OSC s evaluate and manage the many issues arise when investigating or responding to vapor intrusion at a site. Our Technical Support Section, including Dan and Gerry, is available to provide assistance and advice. And the Division has established the Vapor Intrusion Core Team that can be an important resource that is available to all of you. Over the coming months, the VI Core Team will be sharing their recommendations and insights regarding investigation approaches/techniques, mitigation approaches and innovative pilots/treatability work building on our experience within Region 9 (e.g., MEW, Omega, SEMOU, Amco, the South Bay sites etc.). that

367 ,ç.o Sq 1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY Region9 75 Hawthorne Street PRO1 San Francisco, CA MEMORANDUM iune 30, 2014 Subject: EPA Region 9 Interim Action Levels and Response Recommendations to Address Potential Developmental Hazards Arising from Inhalation Exposures to TCE in Indoor Air from Subsurfac Vapor Intrusion From: Gerald Hiatt, Ph.D. L1-- ( Senior Regional Toxicologist f2 Through: John Kennedy Chief, Technical Suppo Angeles Herrera 2 ection j / Chief, Federal Facilities & Site Cleanup Branch To: Enrique Manzanilla Director, Superfund Division We recommend that the EPA Region 9 Superfund program establish health protective response action recommendations to address inhalation exposures to trichloroethylene (TCE) in indoor air from the subsurface vapor intrusion pathway. The purpose of these interim action levels and response action recommendations is to be protective of sensitive and vulnerable populations, especially women in the first trimester of pregnancy, because of the potential for cardiac malformations to the developing fetus. This approach is consistent with recommendations provided by Region 101 and with previous actions taken at Region 9 Superfund sites. Issue: EPA identifies an inhalation level of concern for non-cancer hazards based on the ratio of the exposure concentration in air to a reference concentration ( RfC, which includes a margin of safety such that at the RfC and below there is little chance of an adverse effect). 2 This ratio is Memo: OEA Recommendations Regarding Trichloroethylene Toxicity in Human Health Risk Assessments. ic Kelly, Office of Environmental Assessment, u.s. EPA Region 10, Dec The RfC represents an estimate of the continuous inhalation exposure (with uncertainty spanning perhaps an order of magnitude) to the human population (including sensitive sub-groups) that is likely to be without appreciable risk of deleterious effects during a lifetime. See on-line glossary at:

368 Interim Action Levels & Response Recommendations TCE Exposures From Vapor Intrusion defined as a Hazard Quotient and abbreviated HQ. EPA s Integrated Risk Information System (IRIS) 2011 toxicity assessment concluded that TCE exposure poses potential human health hazards for noncancer toxicity to multiple organs and systems and to the developing fetus, including fetal cardiac malformations. This and other findings in the IRIS assessment of TCE indicates that women in the first trimester of pregnancy are one of the most sensitive populations to TCE inhalation exposure. For fetal cardiac malformations, a specific developmental effect, the critical period for exposure is considered to be the approximate 3-week period in the first trimester of pregnancy during which the heart develops. The National Oil and Hazardous Substances Pollution Contingency Plan (NCP) and Superfund guidance provide for early or interim actions where warranted by the hazards posed by site-related contamination. 3 EPA Region 9 Interim TCE Indoor Air Response Action Levels - Residential and Commercial TCE Inhalation Exposure from Vapor Intrusion Accelerated Response Action Urgent Response Exposure Scenario Level (HQ=1) Action Level (HQ=3) Residential * 2 iig/m 6 iig/m Commercial/Industrial ** 8.ig/m 24 pg/m (8-hour workday) Commercial/Industrial ** 7 i.tg/m 21 iig/m (10-hour workday) * The residential HQ=1 accelerated response action level is equivalent to the inhalation reference concentration (RfC) since exposure is assumed to occur continuously. ** Commercial/Industrial accelerated response action levels are calculated as a time-weighted average from the RfC, based on the length of a workday and rounding to one significant digit (e.g., for an 8-hour workday: Accelerated Response Action Level = (168 hours per week/40 hours per week) x 2 hg/rn = 8 hg/rn Timeweighted adjustments can be made as needed for workplaces with longer work schedules. Note: Indoor air TCE exposures corresponding to these accelerated response action levels would pose cancer risks near the lower end of the Superfund target cancer risk range, considering the IRIS toxicity assessment; thus, the health protective risk range for both accelerated response actions and long-term exposures becomes truncated to: pg/m for residential exposures and 3 8 lag/rn for 8-hour/day commercial/industrial exposures ). The NCP preamble states (55 FR 8704): EPA expects to take early action at sites where appropriate...to eliminate, reduce, or control the hazards posed by a site...ln deciding whether to initiate early actions, EPA must balance the desire to definitively characterize site risks and analyze alternative remedial approaches for addressing those threats in great detail with the desire to implement protective measures quickly. Consistent with today s management principles, EPA intends to perform this balancing with a bias for initiating response actions necessary or appropriate to eliminate, reduce, or control hazards posed by a site as early as possible. Consistent with CERCLA and the NCP, early actions may be appropriate using CERCLA authority to carry out removal actions (emergency response, time critical response, or non-time critical response) or remedial actions based on the site-specific situation (see, for example, 40 CFR (b)(1)-(3) and (a)(1)(ii)(a)). See also U.S. EPA (2/14/2000), Use of Non-Time Critical Removal Authority in Superfund Response Actions (OSWER, OERR; OECA, OSRE). There is a need to identify those TCE exposures that exceed the RfC by a magnitude sufficient enough that a more urgent response is prudent; it is generally Region 9 practice to immediately initiate response action to address exposures at or above an HQ=3 level.

369 If Interim Action Levels & Response Recommendations TCE Exposures From Vapor Intrusion Based upon the above information from EPA s 2011 Toxicological Review of Trichioroethylene in Support of the Integrated Risk Information System (IRIS), we recommend Region 9 establish interim action levels and response action recommendations to protect against potential non-cancer outcomes, including developmental effects such as cardiac malformations. These recommendations identify women of reproductive age as the sensitive population of concern, rather than only pregnant women, because some women may not be aware of their pregnancy during the critical period of the first trimester. Recommendations for Assessment of TCE Inhalation Vapor Intrusion Exposure in Residential and Commercial/Industrial Buildings and Accelerated and Urgent Response Actions The following recommendations should be used for assessing and responding to inhalation exposures to TCE in residential and non-residential/commercial/industrial settings caused by subsurface vapor intrusion at Region 9 Superfund sites. We also recommend consultation with an EPA Regional Toxicologist for implementation of these recommendations. Sampling Considerations: Generally, EPA recommends time-integrated air sampling methods to account for temporal variability in vapor intrusion. Time-integrated samples provide a direct measurement of the average TCE concentration over a fixed period of time (e.g., 8 hours, 24 hours, 4 days, 1 week, 2 weeks, etc.), which should be compared to the accelerated and urgent response action levels. Considerations for When to Expedite Turn-around Time for TCE Analytical Results: In determining the advisability of contracting for rapid (eg., hour) turn-around time for TCE analytical results for indoor air samples, the following factors should be taken into consideration: Exposure of women of reproductive age Are women of reproductive age (or known pregnancy status) exposed or reasonably expected to be exposed? Existing data Are there any existing data (e.g., from subsurface media) which indicate or suggest that indoor air TCE concentrations can exceed the accelerated response action level? Multiple lines of evidence Are there other types of existing information, data or analytical results which indicate or suggest that indoor air TCE concentrations exceed or can exceed the accelerated response action level? Confirmation sampling - previous TCE indoor air concentrations exceeded the accelerated response action level, and early or interim mitigation measures were taken, rapid turn-around time of TCE analytical results should be considered to verify TCE concentrations have been reduced sufficiently to below HQ=1. Implementation of Early or Interim Measures to Mitigate TCE Inhalation Exposure: When selecting a response to reduce or avoid inhalation exposures to TCE, we recommend the following early or interim response actions (mitigation measures) be considered, along with how quickly they can be implemented: Increasing building pressurization and/or ventilation Sealing potential conduits where vapors may be entering the building Treating indoor air (carbon filtration, air purifiers)

370 Interim Action Levels & Response Recommendations TCE Exposures From Vapor Intrusion Installing and operating engineered exposure controls (sub-slab/crawlspace, depressurization systems) Temporarily relocating occupants Tiered Response Actions: TCE Indoor Air Concentration Accelerated Response Action Level (HQ=1): If indoor air TCE concentrations are observed to be equal to or less than the accelerated response action level, then we recommend routine periodic confirmatory sampling and/or monitoring be conducted as appropriate for conditions at the site, including evaluation of the potential for subsurface vapor intrusion into indoor air exceeding health-based screening levels for long-term exposure. TCE Indoor Air Concentration > Accelerated Response Action Level (HQ=1): In the event indoor air TCE concentrations are observed to be greater than the accelerated response action level, we recommend early or interim mitigation measures be evaluated and implemented quickly, and their effectiveness (defined as a reduction of the TCE indoor air concentration to below HQ=1 level) confirmed promptly (e.g., all actions completed and confirmed within a few weeks). TCE Indoor Air Concentration > the Urgent Response Action Level (HQ=3): In the event indoor air TCE concentrations are observed to be greater than the urgent response action level, we recommend mitigation measures be initiated immediately and their effectiveness (defined as a reduction of the indoor air TCE concentration to below HQ=1 level) confirmed before any additional exposure is allowed to occur (e.g., all actions completed and confirmed within a few days). Note that temporary relocation may be indicated under these circumstances because of the need to prevent additional exposure. Basis for Tiered Response Actions: The Toxicological Review of Trichioroethylene in Support of the Integrated Risk Information System (IRIS) (EPA 2011a) established an inhalation Reference Concentration (RfC) at 2 to be protective for sensitive populations, including the developing fetus with regard to the potential for congenital heart defects arising due to maternal TCE exposure during fetal development. Identification of this developmental effect as a critical toxic end-point and the method of calculation of the RfC were the subjects of peer review by the EPA Science Advisory Board, which supported both. 3 ig/m This RfC in the 2011 TCE IRIS Assessment applies to continuous (24 hours per day) exposures and is therefore directly relevant to a reasonable maximum exposure in a residential exposure scenario. We recommend health protective inhalation concentrations for less-than-continuous exposures, such as in a commercial/industrial setting, be adjusted based on the number of hours per day of exposure. Application of the RfC in the present context allows calculation of Hazard Quotient (HQ) concentrations for exposures equivalent to the RfC (HQ=1) and exceeding the RfC by a factor of 3- fold (HQ=3). Note: It is appropriate for the resultant HUto be adjusted to a time-weighted average for exposures are less than continuous. Thus: Indoor Air Exposure Concentrations HQ=1: Indoor air exposures equal to or below (less than) the relevant HQ=1 level are protective for inhalation exposure. that

371 Interim Action Levels & Response Recommendations TCE Exposures From Vapor Intrusion Indoor Air Exposure Concentrations> HQ=1: For some exposure above the HQ.=1 level, the non-cancer hazard begins to increase. This hazard generally increases as the exposure (considering concentration, time, and frequency) exceeds the HQ=1 level. Because of the increased potential risk of a developmental effect, we recommend reducing exposure to below HQ1 using an accelerated time-frame. Indoor Air Exposure Concentrations HQ=3: The HQ=3 level is the level of exposure at which the increased risk of developmental effects is high enough that Region 9 considers an urgent response is warranted to reduce exposure for sensitive population to below HQ=1. References: Agency of Toxic Substances Disease Registry (ATSDR) Addendum to the Toxicological Profile for Trichioroethylene. Currently available online at: addendum.pdf U.S. Environmental Protection Agency (EPA). 2011a. Toxicological Review oftrichloroethylene in Support of the Integrated Risk Information System (IRIS). EPA/635/R-09/O11F. National Center for Environmental Assessment. Washington, DC. Currently available online at: U.S. Environmental Protection Agency (EPA). 2011b. IRIS Toxicity Profile for Trichloroethylene (CASRN ). Washington DC, USEPA. U.S. Environmental Protection Agency, Science Advisory Board (EPA-SAB) Review of EPA s Draft Assessment entitled Toxicological Review of Trichloroethylene// (October 2009). EPA-SAB Office of the Administrator. Washington, DC. January 11. http ://yosem ite.epa.gov/sab/sabprod uct. nsf/b73d5d39a8f184bd a1988/$fiie/epa- SAB unsigned.pdf Abbreviations: HQ Hazard Quotient (HQ = Exposure Concentration / RfC) IRIS Integrated Risk Information System RfC Reference concentration (inhalation) TCE Trichloroethylene ig/m 3 micrograms per cubic meter

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377 Vol. 81 Monday, No. 39 February 29, 2016 Part II Environmental Protection Agency 40 CFR Part 300 Addition of a Subsurface Intrusion Component to the Hazard Ranking System; Proposed Rule srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4717 Sfmt 4717 E:\FR\FM\29FEP2.SGM 29FEP2

378 10372 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 300 [EPA HQ SFUND ; FRL OLEM] RIN 2050 AG67 Addition of a Subsurface Intrusion Component to the Hazard Ranking System AGENCY: Environmental Protection Agency (EPA). ACTION: Proposed rule. SUMMARY: The U.S. Environmental Protection Agency (EPA) is proposing to add a subsurface intrusion (SsI) component to the Hazard Ranking System (HRS) which is the principal mechanism that EPA uses to evaluate sites for placement on the National Priorities List (NPL). The subsurface intrusion component (this addition) would expand the number of available options for EPA and state and tribal organizations performing work on behalf of EPA to evaluate potential threats to public health from releases of hazardous substances, pollutants, or contaminants. This addition will allow an HRS evaluation to directly consider human exposure to hazardous substances, pollutants, or contaminants that enter regularly occupied structures through subsurface intrusion in assessing a site s relative risk, and thus, enable subsurface intrusion contamination to be evaluated for placement of sites on the NPL. The agency is not considering changes to the remainder of the HRS except for minor updates reflecting changes in terminology. DATES: Comments must be received on or before April 29, ADDRESSES: Submit your comments, identified by Docket ID No. EPA HQ SFUND , to the Federal erulemaking Portal: Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or withdrawn. The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (i.e. on the Web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit commenting-epa-dockets. FOR FURTHER INFORMATION CONTACT: Terry Jeng, phone: (703) , jeng.terry@epa.gov, Site Assessment and Remedy Decisions Branch, Assessment and Remediation Division, Office of Superfund Remediation and Technology Innovation (Mail Code 5204P), U.S. Environmental Protection Agency, 1200 Pennsylvania Avenue NW., Washington, DC 20460; or the Superfund Hotline, phone (800) or (703) in the Washington, DC metropolitan area. SUPPLEMENTARY INFORMATION: The information presented in this preamble is organized as follows: I. General Information A. What is EPA seeking comment on? B. How does this action apply to me? II. Statutory Authority III. Background A. Why is EPA proposing an addition to the HRS? B. What is the history of the HRS? C. What is the impact of this proposed rule? 1. Impact on Current Cleanup Programs, Resources and Cost 2. Children s Environmental Health and Environmental Justice IV. Hazard Ranking System A. Purpose B. Structure V. Approach to HRS Addition A. General Approach 1. What is the need for regulatory action on the HRS? 2. What alternative regulatory options to this action were considered by EPA? 3. What public outreach activities did EPA conduct? 4. What peer review process did EPA use? 5. How did EPA select the approach for including the addition in the HRS? B. Technical Considerations To Maintaining The Current HRS Structure and Algorithm 1. Maintaining the Current Ground Water, Surface Water, and Air Migration Pathways 2. Addition of the New Component to Restructure and Rename the Soil Exposure Pathway C. Supporting Materials VI. Discussion of the Proposed SsI Addition to the HRS A. Addition Within a Restructured Soil Exposure Pathway B. SsI Component Addition 1. New Definitions 2. Delineation of Areas of Subsurface Intrusion VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 a. Area of Observed Exposure (AOE) b. Area of Subsurface Contamination (ASC) c. Other Area of Subsurface Intrusion Considered: Potential Migration Zone 3. Likelihood of Exposure a. Observed Exposure b. Potential for Exposure c. Calculation of the Likelihood of Exposure Factor Category Value 4. Waste Characteristics a. Toxicity/Degradation b. Hazardous Waste Quantity c. Calculation of the Waste Characteristics Factor Category Value 5. Targets a. Identification of Eligible Targets b. Exposed Individual and Levels of Exposure c. Population d. Resources e. Calculation of the Targets Factor Category Value 6. Calculation and Incorporation of the SsI Component Score Into the HRS Site Score a. Calculation of the SsI Component Score b. Incorporation of the SsI Component Score Into the Soil Exposure and Subsurface Intrusion Pathway Score c. Incorporation of the Soil Exposure and Subsurface Intrusion Pathway Score Into a Site Score 7. Example Site Scoring Scenarios VII. Summary of Proposed Updates to the HRS VIII. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review B. Paperwork Reduction Act (PRA) C. Regulatory Flexibility Act (RFA) D. Unfunded Mandates Reform Act (UMRA) E. Executive Order 13132: Federalism F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments G. Executive Order 13045: Protection of Children From Environmental Health Risks and Safety Risks H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use I. National Technology Transfer and Advancement Act J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations K. Executive Order 12580: Superfund Implementation I. General Information A. What is EPA seeking comment on? EPA is proposing an addition of one new component to one part of the current Hazard Ranking System (HRS). No major structural changes to other parts of the HRS are proposed. EPA is seeking comments on the addition of the subsurface intrusion component to the HRS. Comments on unmodified parts of

379 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 the HRS are not being requested and will not be considered if submitted. B. How does this action apply to me? This action proposes an addition to the HRS. The HRS is used for evaluating the relative potential risk posed by the uncontrolled release, or potential release, of hazardous substances to human health or the environment. This addition will enable EPA to identify risks posed by subsurface intrusion of hazardous substances into regularly occupied structures for all populations who live and work in areas where the subsurface environment may create exposures. The agency considers that including the evaluation of subsurface intrusion in the HRS serves the public interest by widening EPA s ability to evaluate these threats. This proposed regulatory change expands the available options for EPA and organizations performing work on behalf of EPA (state and tribal partners) to evaluate potential threats to public health and the environment from subsurface intrusion contamination. State and tribal partners may receive financial assistance from EPA to evaluate sites through a Cooperative Agreement. EPA and states or tribes collaborate closely throughout the Cooperative Agreement process, particularly when identifying sites to be evaluated and establishing priorities for performing evaluations. As necessary, sites where subsurface intrusion threats exist may be evaluated using the HRS and, if warranted, proposed for placement on the NPL. EPA does not expect that this proposed change will result in additional site assessments being conducted per year or placement of more sites on the NPL per year. Rather, given potentially limited budgets and the possibility of increased costs for an SsI site assessment, EPA may conduct fewer assessments per year. The pipeline of sites will be reviewed to identify those sites that pose the highest risk and prioritized accordingly. This is not a change to how EPA currently evaluates and prioritizes sites for the NPL; EPA will simply have an additional mechanism to address sites that pose the greatest risk. Because assessing the worst sites first is a priority, EPA will continue to identify the sites posing the highest risk or potential risk and develop a strategy to assess those sites in a timely manner, while balancing their other site assessment needs. The addition of a subsurface intrusion component to the HRS affirms that EPA is fulfilling its regulatory requirements by ensuring to the maximum extent feasible, that the hazard ranking system accurately assesses the relative degree of risk to human health and the environment posed by sites and facilities subject to review. 42 U.S.C. 9605(c)(1), as mandated by the Superfund Amendments and Reauthorization Act (SARA) amendments to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). This proposed addition is necessary because no present authority consistently and comprehensively addresses subsurface intrusion contamination across all non-federal potential sites, particularly when subsurface intrusion is the key exposure pathway. While most states have identified sites with subsurface intrusion contamination issues, not all states have subsurface intrusion programs, and states with subsurface intrusion remediation programs vary in their authority, resources, and remediation criteria. A redirection of resources available through Cooperative Agreement funding is expected to provide for greater national consistency in the identification and evaluation of subsurface intrusion sites. Additionally, EPA finalized the OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air, in June This guide and this proposed addition to the HRS would further the agency s efforts to establish national consistency in evaluating vapor intrusion threats by enabling EPA to use remedial authority under CERCLA. This proposed regulatory change does not affect the status of sites currently on or proposed to be added to the NPL. II. Statutory Authority The authority for these proposed technical modifications to the HRS (40 CFR 300, Appendix A) is in section 105(a)(8)(A) of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) enacted in Under this law, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) (40 CFR 300) must include criteria for determining priorities among releases or threatened releases for the purpose of taking remedial or removal actions. In 1986, Congress passed the Superfund Amendments and Reauthorization Act (SARA) (Pub. L ), which added section 105(c)(1) to CERCLA, requiring EPA to amend the HRS to assure to the maximum extent feasible, that the hazard ranking system accurately assesses the relative degree of risk to human health and the VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 environment posed by sites and facilities subject to review. Furthermore, CERCLA section 115 authorizes EPA to promulgate any regulations necessary to carry out the provisions of CERCLA. III. Background EPA is proposing this addition to protect human health from the threat posed by subsurface intrusion. By adding this component to the HRS, EPA will be able to consider subsurface intrusion threats when evaluating sites for placement on the NPL and implement the requirements of CERCLA and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This proposed addition is a technical modification to the current HRS that will allow EPA and its partners to more comprehensively address the releases of hazardous substances into the environment. A. Why is EPA proposing an addition to the Hazard Ranking System? Contaminant subsurface intrusion 1 is defined as the migration of hazardous substances, pollutants, or contaminants 2 from the subsurface environment, or more specifically, the surficial ground water into overlying structures and/or the unsaturated zone. Subsurface intrusion can result in people being exposed to harmful levels of hazardous substances and cause negative health effects. While subsurface intrusion can take multiple forms, the most common form of subsurface intrusion is vapor intrusion. There are several reasons why EPA is proposing this addition to the HRS. First, the current HRS (40 CFR 300, Appendix A), promulgated December 14, 1990 (hereafter referred to as the current HRS), discussed in more detail in section IV of this preamble, does not consider the threat posed by subsurface intrusion in its evaluation of relative risk posed by a site; therefore, it does not provide a complete assessment of the relative risk that a site may pose to the public. The existing pathways used to evaluate threats posed by hazardous substances do not include those entering a regularly occupied structure from the subsurface. For example, the ground water migration pathway evaluates the threat posed by 1 Subsurface intrusion, for the purposes of this preamble, refers to the intrusion of hazardous substances from the subsurface into a structure. 2 For the purpose of this preamble, the term hazardous substances, pollutants or contaminants will be referred to simply as hazardous substances. See section 1.1, of the current HRS for the definition of a hazardous substance.

380 10374 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 contaminated ground water if there is an indication that ground water is being consumed. Similarly, the soil exposure pathway evaluates the threat posed by contaminated surfaces (e.g., surface soils) if there is an indication of human exposure. The air migration pathway considers the threat posed by hazardous substances released to atmospheric air (ambient air), but does not address indoor air, and has no subsurface component. The surface water migration pathway does not cover subsurface intrusion as it only considers the threat posed by contaminated surface water bodies. In fact, in a May 2010 report, 3 the Government Accountability Office (GAO) concluded that if vapor intrusion sites are not assessed and, if needed, listed on the NPL, some seriously contaminated hazardous waste sites with unacceptable human exposure may not otherwise be cleaned up. The GAO recommended that EPA consider vapor intrusion as part of the NPL process; EPA agreed with the GAO recommendation. With the addition of a subsurface intrusion component, a site with vapor intrusion may qualify for the NPL, whereas presently the site may not have qualified using the threats evaluated in the current HRS. Therefore, without this addition, EPA may not be identifying the sites that most warrant further investigation. Second, EPA is offering this proposal because of the substantial public support for this action. EPA conducted outreach activities to determine the level of interest and support from the public. This included a Notice of Opportunity for Public Input (76 FR 5370, January 31, 2011) and four public listening sessions held across the country. More than 40 written comments, from a diverse group of private citizens, businesses, states, American Indian tribes, environmental action groups, and other governmental agencies, were received during the public comment period. Of the public who attended the listening sessions and provided comments, the majority were supportive of the addition of a subsurface intrusion component to the HRS. In addition, five states and two tribes submitted comments all in support of the addition. The Association of State and Territorial Solid Waste Management Officials (ASTSWMO) compiled and presented input from 14 states all but one favoring the addition of subsurface intrusion to the HRS. The 3 EPA s Estimated Costs to Remediate Existing Sites Exceed Current Funding Levels, and More Sites are Expected to Be Added to the National Priorities List, GAO Report to Congressional Requesters, GAO , May comments opposing the HRS addition were, in general, from industry representatives. Third, to support development of this proposal, EPA evaluated the need for this proposed addition to the current HRS by identifying the scope of the subsurface intrusion contamination problem. These efforts to identify and classify sites that may pose a subsurface intrusion threat have resulted in the identification of 1,073 sites that may or may not qualify for the NPL but are suspected of having vapor intrusion issues. Many of the sites in this inventory are currently listed in EPA s Superfund Enterprise Management System 4 (SEMS). Of the 1,073 identified sites: 328 sites are identified as having a suspected subsurface intrusion threat based on SEMS and Agency for Toxic Substances and Disease Registry (ATSDR) key word searches, as well as EPA or state self-identification, but for which no sampling data were obtained 532 sites are identified as having characteristics or evidence that indicate subsurface intrusion (e.g., volatile hazardous substance in ground water) may have occurred or will occur. 202 sites are identified as having a subsurface intrusion threat documented by subslab, crawl space, or indoor air samples but insufficient HRS-required evaluation factors to qualify for the NPL. 11 sites are identified as having a subsurface intrusion threat with documented actual exposure of a sufficient number of targets and sufficient other HRS-required evaluation factors to suggest the site may qualify for the NPL. EPA is also considering sites with another form of subsurface intrusion, namely, intrusion of contaminated ground water into regularly occupied structures which is an emerging issue. For example, a site was discovered where shallow (surficial) ground water contaminated with chromium had intruded into residential basements and after the water receded, or evaporated, a precipitate of chromium remained as a residue. The presence of this residue posed a significant threat to public health; however, the site could not be evaluated under the current HRS due to the lack of a mechanism to evaluate human exposure resulting from intrusion of contaminated ground water (subsurface intrusion contamination). The only viable option to place the site on the NPL was to rely on ATSDR to 4 This information was previously stored in a predecessor database called the Comprehensive Environmental Response, Compensation and Liability Information System (CERCLIS). VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 make a determination that the exposure at the site posed a significant threat to public health. The decision to include sites on the NPL based on a determination by the ATSDR is made infrequently because the HRS is the primary mechanism for placing a site on the NPL. EPA regional site assessment programs have identified 7 additional sites where intrusion of contaminated ground water is a potential issue and the related threat cannot be evaluated using the current HRS. Under the proposed SsI addition, ground water intrusion would be evaluated using current conditions, which may involve situations where metals have precipitated from water or where volatile substances have entered a structure via infiltrating ground water. As EPA further explores this emerging issue, the agency considers it likely that other ground water intrusion sites requiring evaluation will be identified. The inventory of sites, identified by EPA, with a possible threat from contaminated vapor or ground water intruding into overlying regularly occupied structures is not representative of the magnitude of the potential scope of sites with subsurface intrusion contamination. EPA identified these sites based on currently available information to initially assess the subsurface intrusion problem. In the case of vapor intrusion, certain states undertook comprehensive efforts to identify and evaluate subsurface intrusion threats, which resulted in the identification of a proportionately higher number of sites with potential vapor intrusion problems in those states. In the case of ground water intrusion, the issue is still emerging. For these reasons, EPA recognizes that a degree of inherent uncertainty is associated with compiling an inventory of sites with potential subsurface intrusion problems and that additional analysis is necessary, especially in cases where little information exists. See Appendix A of the Technical Support Document for this proposed addition (Proposal TSD) for the inventory of vapor intrusion sites. As additional information is gathered and new sites are added to SEMS and undergo the site assessment process, the number of sites with subsurface intrusion threats is likely to change. Nevertheless, the aforementioned illustrates that there currently exists at least 1,073 sites that have significant actual or potential human exposure due to subsurface intrusion, but because of the shortcomings of the current HRS, cannot be evaluated to determine if they warrant addition to the NPL.

381 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 It is also important to emphasize that the inventory of sites compiled (where subsurface intrusion has been identified as a possible issue) does not represent a list of sites that will be placed on the NPL. EPA recognizes that, in many instances, additional information is needed to verify the presence, and to determine the nature/extent, of a subsurface intrusion problem. As such, the inventory should not be considered a list of NPL candidate sites. EPA notes that less than 5% of all sites evaluated through the site assessment process are actually added to the NPL. This percentage is not expected to change significantly with this addition to the HRS. Finally, EPA has concluded that for non-federal facilities no other national program is able to consistently and comprehensively evaluate and, if warranted, address subsurface intrusion contamination. This topic is further discussed in section V.A.2 of this preamble. B. What is the history of the hazard ranking system? In 1980, Congress enacted CERCLA (42 U.S.C et seq.), commonly called Superfund, in response to the dangers posed by uncontrolled releases of hazardous substances into the environment. To implement section 105 (a)(8)(a) of CERCLA and Executive Order (46 FR 42237, August 20, 1981), EPA revised the NCP on several occasions, with the most recent comprehensive revision occurring on March 8, 1990 (55 FR 8666). The NCP sets forth the guidelines and procedures needed for responding to releases, or potential releases, of hazardous substances. Section 105(a)(8)(A) of CERCLA required EPA to establish: [C]riteria for determining priorities among releases or threatened releases [of hazardous substances] throughout the United States for the purpose of taking remedial action and, to the extent practicable, taking into account the potential urgency of such action, for the purpose of taking removal action. Criteria and priorities... shall be based upon relative risk or danger to public health or welfare or the environment... taking into account to the extent possible the population at risk, the hazard potential of hazardous substances at such facilities, the potential for contamination of drinking water supplies, the potential for direct human contact [and] the potential for destruction of sensitive ecosystems.... To meet this requirement and provide criteria to set priorities, EPA adopted the HRS as Appendix A to the NCP (47 FR 31180, July 16, 1982). The HRS was last revised on December 14, 1990 (55 FR 51532) to include the evaluation of additional threats to ensure a complete assessment of the relative risk that a site may pose to the public. The HRS is a scoring system used to assess the relative risk associated with actual or potential releases of hazardous substances from a site based on the information that can be collected in a limited, typically one to two day site inspection (SI). The HRS is designed to be applied consistently to each site, enabling sites to be ranked relative to each other with respect to actual or potential hazards. As EPA explained when it originally adopted the HRS, the HRS is a means for applying uniform technical judgment regarding the potential hazards presented by a facility relative to other facilities. It does not address the feasibility, desirability, or degree of cleanup required. 5 (47 FR 31220, July 16, 1982). Section 105(a)(8)(B) of CERCLA requires that the statutory criteria described in section 105(a)(8)(A) be used to prepare a list of national priorities among the known releases, or threatened releases throughout the United States. The list, which is Appendix B of the NCP, is the NPL. The HRS is a crucial part of the agency s program to address the identification and cleanup of actual and potential releases of hazardous substances because the HRS score is the primary criterion for determining whether a site is to be included on the NPL. The NPL (Appendix B to 40 CFR 300) includes those sites that emerge as potentially posing the most serious threats to public health and the environment and may warrant remedial investigation and possible cleanup under CERCLA. Only sites on the NPL are eligible for Superfund-financed remedial actions. Removal and enforcement actions can be conducted at any site, whether or not it is on the NPL. In 1986, Congress passed the Superfund Amendments and Reauthorization Act (SARA) (Pub. L ), which added section 105(c)(1) to CERCLA, requiring EPA to amend the HRS to assure to the maximum extent feasible, that the hazard ranking system accurately assesses the relative degree of risk to human health and the environment posed by sites and facilities subject to review. The HRS was previously amended in This proposed action will amend the HRS to add a subsurface intrusion component to the evaluation. 5 Although the HRS is designed to assess the relative risk of a site compared to other sites, it is not designed to be used as a site-specific quantitative risk assessment. Such an assessment is conducted later in the Superfund process, as necessary. VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 C. What is the impact of this proposed rule? 1. Impact on Current Cleanup Programs, Resources and Cost This proposed addition to the HRS will have the most significant impact on EPA s Superfund cleanup program. The current HRS considers releases to the ground water, surface water and air, as well as direct exposure to contamination such as soil in identifying releases which warrant further investigation. If promulgated, this proposed rule will not impact the way the current HRS addresses these releases. However, in the course of present HRS assessments, sometimes subsurface intrusion issues are coincident with a ground water or soil contamination problem. The HRS presently does not consider the threat posed at sites by subsurface intrusion problems and direct human exposure, when ground water is not being used as a drinking water source or surficial soils are not contaminated. If promulgated, this proposed rule will for the first time allow the EPA site assessment program to address sites with only subsurface intrusion issues and no coincidental exposure. When hazardous substances are released and enter the subsurface environment, they can move from the subsurface into buildings as a gas, vapor, or liquid. The addition of a subsurface intrusion component to the HRS would enable EPA to directly evaluate at sites the relative degree of risk posed by human exposure to hazardous substances that enter regularly occupied structures through the subsurface environment. To the extent practicable, EPA attempts to score all pathways that pose significant threats. If the contribution of a pathway is minimal to the overall score, in general, that pathway will not be scored. This proposed regulatory change would expand available options for EPA and organizations performing work on behalf of EPA (state and tribal partners) to evaluate potential threats to public health and the environment from hazardous waste sites. This modification to the HRS, by itself, only augments the criteria for applying the HRS. EPA also does not expect this proposed rulemaking to affect the status of sites currently on or proposed to the NPL. Sites that are currently on or proposed to the NPL have already been evaluated under another pathway (i.e., ground water migration, air migration, surface water migration, or soil exposure) and, consistent with section 105(c)(3) of CERCLA, as amended, would not be re-evaluated. Proposal of

382 10376 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 this addition also will not disrupt EPA s listing of sites. Because federal agencies currently address subsurface intrusion issues as part of their environmental programs, it is unlikely that a significant number of sites will be added to the NPL. However, it could lead to an increase in site assessment activities and related costs. Executive Order delegates broad CERCLA authority to federal agencies for responding to actual and potential releases of hazardous substances where a release is either on, or the sole source of the release is from, any facility or vessel under the jurisdiction, custody, or control of the federal agency. Federal agencies are required to exercise this authority consistent with the requirements of CERCLA section 120, as amended, and implement regulations under the NCP, for both NPL and non-npl sites. Therefore, federal agencies are in a position to proactively identify and respond to risks posed by subsurface intrusion of hazardous substances into regularly occupied structures for all populations who live and work in areas where the subsurface environment may create exposures. If it is determined that releases of hazardous substances pose immediate threats to public health and the environment, EPA fully expects that the appropriate federal agency will continue to undertake response actions to address such threats. In fact, some federal agencies, including EPA, have developed or are developing new or updated agency-specific policy and guidance documents to address subsurface intrusion threats. This proposed addition will impact both resources and costs to federal cleanup programs. EPA does not expect that this proposed change will result in additional site assessments being conducted per year or placement of more sites on the NPL per year. Rather, given potentially limited budgets and the possibility of increased costs for a subsurface intrusion (SsI) site assessment, EPA may conduct fewer assessments per year. The pipeline of sites will be reviewed to identify those sites that pose the highest risk and prioritized accordingly. This is not a change to how EPA currently evaluates and prioritizes sites for the NPL; EPA will simply have an additional mechanism to address sites that pose the greatest risk. Because assessing the worst sites first is a priority, EPA will continue to identify the sites posing the highest risk or potential risk and develop a strategy to assess those sites in a timely manner, while balancing their other site assessment needs. The proposed addition, which could lead to the inclusion of a site on the NPL, does not itself impose any costs on outside parties; it does not establish that EPA will necessarily undertake response actions, nor does it require any action by a private party or determine liability for site response costs. Costs are limited to screening relevant sites for subsurface intrusion contamination during site inspections and the resulting HRS evaluation and documentation record preparation. Costs that arise from site remedial responses are the result of site-specific decisions made post-listing, not directly from the act of listing itself. Later decisions that consider information collected under the proposed addition could separately have specific economic costs and benefits (e.g., remediation costs and reduced risk), but these impacts are contingent upon a series of separate and sequential actions after listing a site on the NPL. The addition of subsurface intrusion to the HRS is several regulatory steps removed from imposing costs on private entities. The HRS addition may increase the costs to government agencies conducting assessments at subsurface intrusion sites because the scope of a typical site inspection may need to be expanded or may require more expensive sampling to collect information for an SsI evaluation. SsI sampling may require additional sampling and different sample types than those collected at other sites. This may result in an increase in some site assessment costs at some sites with possible subsurface intrusion issues. However, SsI site assessment costs at some other sites may be comparable to, or even less than, sites scored under the existing HRS. For example, a site assessment requiring sampling of deep ground water monitoring wells under the existing HRS may cost as much as, or more, than sampling conducted at sites with possible subsurface intrusion issues. The exact cost of any sampling at a site, including sites with possible SsI issues, varies greatly based on sitespecific factors (e.g., number and type of samples required, difficulty in establishing sources of contamination or attribution of releases, number of HRS pathways being evaluated, and availability of data from previous sampling events). Additionally, any newly increased costs to government agencies conducting assessments at SsI sites are expected to be minimal because federal agencies should already be identifying and addressing subsurface intrusion as part of their environmental programs. Any increase in the cost of site assessments conducted by EPA for VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 SsI sites will require EPA to realign and prioritize its site assessment budget to address sites with subsurface intrusion. The addition of an SsI component to the HRS is not expected to result in additional site assessment funding to account for any increase in site assessment costs. Instead, the pipeline of sites will continue to be reviewed under the current site assessment process. If it is found that SsIcontaminated sites potentially pose a greater risk than other sites, then these sites will be prioritized over other sites. EPA will develop a strategy to assess these sites in a timely manner, while balancing other site assessment needs. 2. Children s Environmental Health and Environmental Justice This rulemaking is not subject to Executive Order 13045, Protection of Children from Environmental Health Risks and Safety Risks because this rulemaking is expected to only have moderate costs 6 and this executive order only applies to significant rulemakings. EPA has also found that this rulemaking will have no direct impact on communities considered under Executive Order 12898, Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations. Although the rule will not have any direct impact on human health or risk within minority or low-income populations located near potential SsI sites, populations of concern under Executive Order 12898, EPA did consider whether the proposed action might have contingent impacts on these communities if future actions affect remediation of these sites. This analysis concluded that potentially affected sites are located in areas that have slightly higher concentrations of minority populations and populations below the poverty line than surrounding areas. Therefore, any future actions addressing risks in these communities would not contribute to disproportionate adverse impacts on human health. IV. Hazard Ranking System A. Purpose The current HRS serves as a screening tool to evaluate the potential for uncontrolled hazardous substances to cause human health problems or environmental damage at one site relative to other sites evaluated. The pre-remedial portion of the Superfund 6 The regulatory impact analysis (RIA) found this rulemaking will only have moderate costs and will not be a significant rulemaking. The RIA for this rulemaking can be found in the official Docket for this action.

383 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules program the portion prior to placing sites on the NPL is intended to identify those sites which warrant further investigation and possible cleanup under CERCLA. (See Figure 1 for a general depiction of the Superfund Site Assessment process.) During Pre- CERCLA screening, which is the first step of the pre-remedial process, EPA determines if there is indication of a possible significant release. If so, EPA determines if a substance in the release is regulated by CERCLA, whether it is already being addressed, and whether any statutorily mandated limitations on CERCLA response may exist. If EPA determines the release meets these requirements, then the suspected release is listed in EPA s Superfund Enterprise Management System (SEMS). Determining whether hazardous substances, pollutants, or contaminants can be addressed by CERCLA requires the application of site-specific facts to CERCLA statutory requirements and EPA policy. One such statutory requirement is CERCLA s limit on response actions to some naturally occurring substances. CERCLA expressly limits any response actions taken in response to a release, or threat of release, of a naturally occurring substance in its unaltered form from a location where it is naturally found, from products which are part of a structure, or into drinking water supplies due to deterioration of the system. (See CERCLA section 104(a)(3) and 104(a)(4) for additional guidance on limitations on response and exception to limitations). Therefore, even though a naturally occurring substance in its unaltered form may potentially be regulated by CERCLA, the response actions taken in response to these releases, or threat of releases, may be expressly limited by CERCLA. For example, although radon and asbestos may qualify as a CERCLA hazardous substance, CERCLA section 104(a)(3) may limit responses to releases of radon or asbestos in some situations where the release is from building products or occurs from in situ natural sources, but section 104(a)(4) identifies specific circumstances that, if present, would allow CERCLA response in such situations. (See also EPA OSWER Directive , Response Actions at Sites with Contamination Inside Buildings, August 12, 1993). If EPA finds an eligible release of a CERCLA eligible substance and response actions are permissible under CERCLA, then EPA proceeds to address the release under CERCLA. This may include a preliminary assessment. A preliminary assessment uses readily available data to determine if there is evidence of an unacceptable potential threat. If based on the results of a preliminary assessment, EPA determines that a site warrants further screening under the CERCLA remedial program, the agency initiates a site inspection as specified in the NCP (40 CFR ). The site inspection usually includes the collection of samples for chemical analysis. Such samples aid in ascertaining what substances are present at the site and whether they are being released. The purpose of the site inspection is to determine if there is an actual or potential threat to human health or the environment, to determine if there is an immediate threat to people or the environment in the area, and to collect sufficient data to enable the site to be scored using the HRS. srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4725 E:\FR\FM\29FEP2.SGM 29FEP2 EP29FE16.022</GPH>

384 10378 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules EPA has designed the Superfund program to focus its resources on sites that warrant further investigation. Consequently, the initial studies, the preliminary assessment and site inspection, which are performed on a large number of sites, are relatively modest in scope and cost compared to the remedial investigations and feasibility studies subsequently performed on NPL sites. Because of the need to carry out the initial studies expeditiously, EPA elected to place certain constraints on the data requirement for an HRS evaluation. The required HRS data should be information that, for most sites, can be collected during a screening level site inspection or that are already available. Thus, the HRS does not rely on data that require extensive sampling or repeated sampling over a long period of time. The HRS has also been designed so that it can be applied consistently to a wide variety of sites. The HRS is not a tool for conducting quantitative risk assessment and was designed to be a measure of relative risk among sites rather than absolute risk at an individual site. The narrow technical modifications being proposed reflect the agency s actions to encompass additional risks posed by releases of hazardous substances and to address the SARA statutory requirement that EPA amend the HRS to assure to the maximum extent feasible, that the HRS accurately assesses the relative degree of risk to human health and the environment posed by sites subject to review. Thus, the fundamental purpose and structure of the HRS approach will not be changed when the HRS is amended to include consideration of subsurface intrusion. B. Structure The current HRS (40 CFR 300, Appendix A) evaluates four pathways in projecting the relative threat a site poses: The ground water migration pathway evaluates the likelihood that hazardous substances will migrate to ground water and contaminate aquifers and drinking water wells that draw on those aquifers. The surface water migration pathway evaluates the likelihood that hazardous substances can enter surface water and affect people or the environment. Threats to human health and the environment included in this pathway include drinking water (DW), the human food chain (HFC) (i.e., hazardous substances accumulate in the aquatic organisms that humans in turn consume), and sensitive environments (ENV). The surface water migration pathway is also divided into two components reflecting different mechanisms for contaminant transport within each component (i.e., overland/ flood migration to surface water component and ground water to surface water migration component). The air migration pathway evaluates the likelihood of release of hazardous substances into the atmosphere and the number of people and sensitive environments actually or potentially exposed to hazardous substances carried in the ambient (outdoor) air, including gases and particulates. The air migration pathway does not evaluate releases to indoor air originating from the subsurface. The soil exposure pathway evaluates the potential threats to humans and terrestrial environments posed by direct, physical contact with, and subsequent ingestion of, hazardous substances. This pathway includes threats to people living on property where hazardous substances are present in the surface/subsurface, including contaminated soils (resident population threat), and to people living nearby with access to the contaminated area (nearby population threat). Figure 2 illustrates the general structure of the current HRS. srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2

385 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 The scoring system for each pathway is based on a number of individual factors associated with risk-related conditions at the site. These factors are grouped into three factor categories as discussed below. These categories include factors that are used to characterize the relative risk at the site. 1. Likelihood of release/exposure (i.e., likelihood that hazardous substances have been released or potentially could be released from a source into the environment, or that people or sensitive environments could come into contact with hazardous substances). 2. Waste characteristics (i.e., toxicity, mobility, and/or persistence of the substances in the environment and the quantity of the hazardous substances that have or could be released). 3. Targets (i.e., people or sensitive environments actually or potentially exposed to the release). An HRS score is determined for a site by summing the score for the four pathways. Specifically, the score for each pathway is obtained by evaluating a set of factors that characterize the potential of the release to cause harm via that pathway. The factors, which represent toxicity of the hazardous substance, or substances, at a site, waste quantity, and population are multiplied by a weighting factor, yielding the factor value; the factor values are used to assign factor category values. The factor category values are then multiplied together to develop a score for the pathway being evaluated. Finally, the pathway scores are combined according to the root-mean-square equation presented below to determine the HRS score for the site. See also Table 2 1 of the proposed addition (section 2.1.2) for additional discussion regarding the method for calculating an HRS site score. S = site score Sgw = ground water migration pathway score Ssw = surface water migration pathway score Sse = soil exposure pathway score Sa = air migration pathway score By using this formula to assign a site score, the HRS score will be low if all pathway scores are low. However, the final score can be relatively high if one VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 pathway score is high. This approach was chosen to ensure that the site scores do not deemphasize single-pathway problems, underestimating their importance. EPA considers this an important requirement for the HRS scoring methodology because some extremely dangerous sites pose threats through only one pathway. For example, leaking drums of hazardous substances can contaminate drinking water wells, but if the drums are buried deeply enough and the hazardous substances are not very volatile, they may not release any hazardous substances to the air or to surface water. It should be emphasized that the existing pathways can address subsurface contamination if it enters into ground water (in the ground water migration pathway), if it enters into surface water (in the surface water migration pathway), if it enters into ambient air (in the air migration pathway) from the soil surface or if it leads to surface soil contamination (in the soil exposure pathway). However, none of these scenarios address intrusion from the subsurface into regularly occupied structures. EP29FE16.023</GPH> EP29FE16.024</GPH>

386 10380 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 Finally, it should also be emphasized that the HRS score does not represent a specific level of risk at a site. Rather, the score serves as a screening-level indicator of the relative risk among sites reflecting the hazardous substance releases or potential releases at sites based on the criteria identified in CERCLA. V. Approach to HRS Addition The following sections detail EPA s comprehensive approach to the consideration of exposures to hazardous substances due to subsurface intrusion and the relevant scientific and technical considerations in developing this proposed rule. A. General Approach 1. What is the need for regulatory action on the HRS? Without an evaluation of threats posed by subsurface intrusion contamination, the HRS is not a complete assessment and omits a known pathway of human exposure to contamination. EPA considers the addition of subsurface intrusion to the HRS to be consistent with CERCLA section 105 because it will improve the agency s ability to identify sites for further investigation and will enhance EPA s ability, in dialogue with other federal agencies and the states and tribes, to determine the most appropriate state or federal authority to address sites. As is currently the case, EPA often defers to other state and federal cleanup authorities based on the site assessments and HRS evaluations. While some states/tribes have programs to address subsurface intrusion contamination, they often have limited authority and resources, and variable remediation criteria. The availability of the federal remedial authority and the more comprehensive site assessment program should complement and strengthen these programs. Other EPA programs such as the Resource Conservation and Recovery Act (RCRA) and the Brownfields program have limited authority and ability to address all subsurface intrusion threats. The RCRA Corrective Action/Enforcement is only applicable at sites subject to RCRA permitting or sites reachable by RCRA s enforcement activities. Furthermore, RCRA is a state delegated program and not all states recognize subsurface intrusion as a significant issue, and those that do may have variable remediation criteria. RCRA sites with subsurface intrusion issues may not be addressed in all states. Also, governmental entities with site-specific Brownfields assessment and/or revolving loan fund cleanup may only use grant funds on the selected eligible property. While subsurface intrusion sites may be eligible for Brownfields cleanup grants, site or property-specific limitations may not allow for permanent remediation where multiple properties may be involved or where Brownfields grant funds, as limited by statute, may not be adequate to fund long-term cleanups. 7 EPA s removal program has the ability to quickly respond to immediate threats to public health and the environment from the release of hazardous substances, such as subsurface intrusion into a structure through a removal action. A removal action can be implemented regardless of NPL status to eliminate or reduce the threat of a release, or a potential release, of hazardous substances, pollutants or contaminants that pose an imminent and substantial danger to public health. However, removal actions are not intended to necessarily serve as a method for dealing with long term issues such as ground water contamination. Generally, EPA considers vapor intrusion mitigation systems as interim or early response actions to promptly reduce threats to human health. Installation of vapor intrusion mitigation systems addresses temporary human health problems, but fails to address the source of the problem. The NCP expresses the preference for response actions that eliminate or substantially reduce the level of contamination in the source medium to acceptable levels, thereby achieving a permanent remedy. U.S. EPA, OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air, OSWER Publication , June OSWER s VI guidance states: The preferred long-term response to the intrusion of vapors into buildings is to eliminate or substantially reduce the level of contamination in the subsurface vapor source (e.g., groundwater, subsurface soil, sewer lines) by vapor-forming chemicals to acceptable-risk levels, thereby achieving a permanent remedy. Remediation of the groundwater plume or a source of vaporforming chemicals in the vadose zone will eventually eliminate potential exposure pathways and can include the following actions, among others: removal of contaminated soil via excavation; removal of contaminated groundwater with pump-andtreat approaches; decontaminating and/or 7 EPA s Estimated Costs to Remediate Existing Sites Exceed Current Funding Levels, and More Sites are Expected to Be Added to the National Priorities List, GAO Report to Congressional Requesters, GAO , May VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 rehabilitating sewer lines that harbor vaporforming chemicals; and, treatment of contaminated soil and groundwater in situ, using technologies such as soil vapor extraction, multiphase extraction, and bioremediation, or natural attenuation. In the case of vapor intrusion resulting from a subsurface contaminant plume, failing to address the source of contamination and the resulting plume may result in an increased exposure to individuals due to migration and expansion of the plume over time. In this instance, individuals in regularly occupied structures that were previously unaffected by the plume may become negatively impacted by subsurface intrusion. Additionally, a subsurface contaminant plume in a lesser-developed area has the potential to impact future development if left untreated. There are several other concerns related to only addressing subsurface intrusion problems with a vapor mitigation system. The first concern is that vapor mitigation systems require ongoing monitoring and maintenance throughout the life of the system. Periodic inspections of the vapor mitigation system are necessary to make sure it is operating as designed. Over time the system can degrade, and maintenance will also be necessary, such as replacing the fan in an active sub-slab depressurization system. Nonmechanical failures of the system can occur as well, such as, electric power failure, turning off the fan or ignoring a damaged system. A vapor intrusion mitigation system is a tool for protecting human health, but may not contribute to the Superfund program s goal of cleaning up uncontrolled hazardous waste sites. Furthermore, EPA still lacks a mechanism to assess human health hazards from vapor intrusion in the current HRS model, and therefore cannot currently evaluate the threat of vapor intrusion as part of its ranking of sites for placement on the NPL. Under the Superfund remedial program for NPL sites, subsurface intrusion is only addressed at sites placed on the NPL based on threats from other pathways. That is, subsurface intrusion issues are addressed later in the remedial process after placement on the NPL. For example, this may be done as part of EPA s five-year review process. Sites with only subsurface intrusion issues are not being included on the NPL due to the lack of a subsurface intrusion component in the HRS. Therefore, many sites, especially those not evaluated under another HRS pathway or those not scoring high enough under another HRS pathway,

387 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 may not be addressed for threats due to subsurface intrusion because they may not qualify for placement on the NPL. As the Government Accountability Office (GAO) states in its May 2010 report: EPA may not be listing some sites that pose health risks that are serious enough that the sites should be considered for inclusion on the NPL. While EPA is assessing vapor intrusion contamination at listed NPL sites, EPA does not assess the relative risks posed by vapor intrusion when deciding which sites to include on the NPL. By not including these risks, states may be left to remediate those sites without federal assistance, and given states constrained budgets, some states may not have the ability to clean up these sites on their own... However, if these sites are not assessed and, if needed, listed on the NPL, some seriously contaminated hazardous waste sites with unacceptable human exposure may not otherwise be cleaned up. EPA proposes the addition of the subsurface component to ensure the HRS does not omit this known pathway of human exposure to contamination and provides a mechanism for complete assessment of SsI threats to human health and the environment. 2. What alternative regulatory options to this action were considered by EPA? EPA considered alternatives to this proposed regulatory action for addressing the need to evaluate subsurface intrusion threats as discussed below. Specifically, EPA considered whether existing programs adequately address the risks associated with subsurface intrusion at contaminated sites, as discussed in the previous section. If one or more programs were in place to adequately address concerns from subsurface intrusion, this could obviate the need for EPA action. However, no other authority consistently and comprehensively addresses subsurface intrusion across all potential nonfederal sites, particularly when subsurface intrusion is the key exposure route. In particular, state programs vary significantly in addressing subsurface intrusion. In fact, not all states have subsurface intrusion programs, and states with programs vary in their authority, resources, and remediation criteria. The 2004 Interstate Technology and Regulatory Council s (ITRC) Vapor Intrusion Team developed and conducted an on-line survey of state, federal, and tribal agencies regarding vapor intrusion regulations, policy, and guidance. Ninety-six percent (96%) of survey respondents consider vapor intrusion a concern; however, only 11% have a procedure for evaluating vapor intrusion codified into law, while a larger number of states have developed, or are developing, guidance for addressing vapor intrusion issues. A majority of the states that responded to the survey expressed that their processes for addressing vapor intrusion were only informally adopted by their agencies, and most defer to EPA. The 2009 Vapor Intrusion Pathway: A Guide for State and Territorial Federal Facilities Managers study also surveyed state and territorial subsurface intrusion programs. According to this study, there were no states with a statute directly addressing vapor intrusion or identifying requirements for assessing the risk. Nine states had regulations that address vapor intrusion specifically; three states had regulations under development. Thirty-four states either have guidance for addressing vapor intrusion or are in the process of developing guidance. In addition, the Association of State and Territorial Solid Waste Management Officials (ASTSWMO) has expressed support for the proposed rule and has requested that EPA take leadership on this issue. Since vapor intrusion is projected to be the most significant component of subsurface intrusion, these responses would apply to subsurface intrusion as well. As previously discussed in section V.A.1 of this preamble, other federal programs were reviewed; while some programs could address subsurface intrusion at some sites, they cannot comprehensively address all sites (federal and non-federal). Two other mechanisms currently exist to place sites on the NPL. First, each state can designate a single site to the NPL as a state top priority site regardless of its HRS score; this can be done only once. (see NCP, 40 CFR (c)(2)). This state-designated sites option has been implemented for 44 states/territories, and the remaining state options would not be sufficient to address the subsurface intrusion issue nationally and comprehensively, given the projected number of sites with subsurface intrusion problems. Second, sites may be added in response to a health advisory from the ATSDR. (See NCP, 40 CFR (c)(3)). However, the ATSDR mechanism was designed to be used only when the Agency for Toxic Substances and Disease Registry (ATSDR) designated the threat found to warrant immediate dissociation from the release and other criteria are met. This is not a mechanism that can be used uniformly and consistently. It is highly resource intensive and may not comprehensively address all chronic threats. Furthermore, CERCLA section 105 clearly mandates that EPA implement VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 the HRS to take into account to the extent possible the population at risk, the hazard potential of hazardous substances..., the potential for contamination of drinking water supplies and the potential for direct human contact. When the HRS was last revised in 1990, the technology to detect and evaluate subsurface intrusion threats was not sufficiently developed. For example, there were no health-based benchmark concentration values for residences or standardized technologies for sampling indoor air, precision of analytical equipment prior to computerization was limited, and associations between contaminated ground water and soil vapors were not well understood. However, it is now possible for subsurface intrusion threats to be evaluated comprehensively. Therefore, it is now appropriate, given the potential that subsurface intrusion presents for direct human contact, to add to the HRS the consideration of threats due to subsurface intrusion. 3. What public outreach activities did EPA conduct? Before making the decision to issue this proposed rulemaking, EPA conducted outreach activities to determine interest and support from the public. Thus, on January 31, 2011, EPA published a Notice of Opportunity for Public Input (76 FR 5370, January 31, 2011) soliciting stakeholder comment on whether to include a subsurface intrusion component in the HRS. Additionally, EPA sent letters to all federally recognized tribes, asking for their comments on the FR document. During the 75-day public comment period on this action, four listening sessions were held throughout the country (Arlington, VA; San Francisco, CA; Albuquerque, NM; and Edison, NJ). The comments made by a majority of speakers, including members of the public, at the listening sessions were supportive of the potential addition of a subsurface intrusion component into the HRS. Of the 43 written comments received during the public comment period, 35 were in support of adding a vapor intrusion component to the HRS, 6 comments (generally from industry representatives) were opposed to this addition, and 2 comments were neutral. The comments received during the public listening sessions and in response to the Notice of Opportunity for Public Input have been reviewed and considered in the development of this proposed rulemaking. EPA has also established a public Web site, providing background information on

388 10382 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 why this addition to the HRS is being considered. 4. What peer review process did EPA use? This proposed rule consists of narrow technical modifications and is an expansion of the current HRS, which was peer reviewed by the agency s Science Advisory Board (SAB). The 1988 SAB review was comprehensive and addressed the basic structure and concepts of the HRS. This proposed addition adheres to the basic structure and concepts of the current HRS, and thus, is consistent with the recommendations of the SAB. The 1988 SAB report focused on the following issues: The overall algorithm for the HRS; The inclusion of exposure in the HRS; How the HRS could be evaluated in the future; Work that could be done to provide better documentation for the next revision of the HRS; The types of toxicity the HRS should address and how it should do so; Distances from an uncontrolled hazardous waste site that are relevant when considering air pollutants from sites; and The feasibility of including waste concentration in the HRS and whether large volume waste sites had been treated differently than others in the HRS. The 1988 SAB report is available in the public docket for this proposed rulemaking. During development of this proposed HRS update, EPA determined that several subsurface intrusion-specific issues warranted external independent scientific peer review. As a result, EPA has identified elements that have undergone peer review including: Consideration of potential for subsurface exposure (intrusion) into regularly occupied structures; Determination of hazardous waste quantity for the subsurface intrusion component; Population scoring; Evaluating populations in multistory and multi-subunit structures; and Evaluation of target values for workers. The results of the 2011 peer review of the proposed addition are discussed in the Summary of Peer Review Comments and Suggested Responses on the Addition of a Subsurface Intrusion Component to the HRS, which is available in the public docket for this proposed rulemaking. This proposed addition reflects modifications made as a result of EPA s peer review process. 5. How did EPA select the approach for including the addition in the HRS? The following six concepts were used as the basis for evaluating possible approaches to the HRS addition and the selection of a preferred approach: 1. Limit the proposed addition to the existing HRS structure to avoid confusion by minimizing the portions of the present HRS that would need to be revised. 2. Utilize the existing HRS basic structure and scoring algorithm, and maintain the relative weighting of the different pathways. 3. Base technical decisions on sound and proven science. 4. Ensure the HRS acts as an effective screening tool and minimizes unnecessary resource expenditures, while also minimizing the erroneous inclusion or exclusion of sites for possible NPL placement. 5. Assemble and utilize conceptual site models, case studies, and sensitivity analyses to test the model. 6. Ensure that an HRS scoring evaluation of the soil exposure and subsurface intrusion pathway can be completed using the information and level of effort that are typical of a site inspection or expanded site inspection (ESI). In the process of developing the proposed rule, EPA identified multiple options that are consistent with the above concepts. Based on literature reviews and agency experience, EPA projected the range of conditions at which the proposed addition might be applied. Using the basic structure of the current HRS, EPA tested each option by simulating the scores for typical scenarios. Using the results of these studies, EPA selected the option that best met the above criteria. To verify that the selected option would provide comparable results at actual sites, EPA tested the scoring algorithm using existing subsurface intrusion data from actual sites. The results of these studies demonstrate that the proposed addition functioned as expected. See section 8.0 of the Technical Support Document for this proposed addition (Proposal TSD) for supplemental information regarding EPA s testing efforts. B. Technical Considerations to Maintaining the Current HRS Structure and Algorithm 1. Maintaining the Current Ground Water, Surface Water, and Air Migration Pathways The current approach for scoring the ground water, surface water, and air migration pathways is not being altered by the proposed addition of a subsurface VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 intrusion component. Therefore, EPA is not soliciting comments on these pathways and will not respond to comments that are submitted on these pathways. 2. Addition of the New Component to the Soil Exposure Pathway EPA is proposing to add the subsurface intrusion threat to the present soil exposure pathway, which already considers direct exposure to receptors. This pathway is proposed to be restructured and renamed the soil exposure and subsurface intrusion pathway. The restructured pathway will retain unchanged the existing two soil exposure threats (resident population and nearby population) in the pathway as one component. The threat posed by subsurface intrusion is proposed to be added as a new component. The internal structure of the soil exposure component, including the two soil exposure threats within that component, remains unchanged. Therefore, EPA is not soliciting comments on the soil exposure component of the proposed soil exposure and subsurface intrusion pathway, nor will it respond to comments that are submitted on the soil exposure component. The soil exposure pathway was selected for modification because its structure already focuses on populations actually coming into or potentially coming into direct contact with hazardous substances. The present soil exposure pathway addresses direct contact with contamination outside of structures. The new subsurface intrusion component also addresses direct contact with contamination that has already been demonstrated to have entered into regularly occupied structures or where the contamination is present beneath the regularly occupied structures and is likely to enter into regularly occupied structures. See section VI.A of this preamble for further discussion. C. Supporting Materials The proposed addition to the HRS is discussed in the following primary documents: (1) The proposed rule, (2) this preamble, (3) the Proposal TSD (including all supporting appendices), (4) the regulatory impact analysis (RIA). The proposed rule identifies the proposed changes to the NCP and focuses on the specific mechanics of scoring sites with the new component. This preamble provides an overview of the proposed HRS addition, along with an explanation of any modifications and the supporting justification. The Proposal TSD contains a more detailed

389 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules explanation of the technical basis for the proposed additions to the HRS, along with descriptions of the options considered, analyses that were used to evaluate the performance of the new subsurface intrusion component, and technical literature that was used in the development of the addition. The Proposal TSD is available to help guide the evaluation of subsurface intrusion sites. The Proposal TSD follows the same general outline as the preamble, with one section describing the necessary narrow technical modifications that affect multiple pathways, and the remaining sections describing the addition of the subsurface intrusion component to the current soil exposure pathway. The Proposal TSD contains a description of the current HRS, the options considered, and the technical justifications for the option chosen. In addition, the Proposal TSD references other supporting documents that provide an even greater level of detail on the proposed additions. These four documents are available to the public in the Docket for this rulemaking. To facilitate public review, EPA has prepared an index to the proposed rule, the preamble to the proposed rule, and the Proposal TSD with detailed cross referencing of issues. This index is available in the public Docket. See the ADDRESSES section of this preamble for further information. VI. Discussion of the Proposed SsI Addition to the HRS This section first discusses why the evaluation of the relative risk posed by subsurface intrusion has been added as a component to the same HRS pathway as for soil exposure. It then discusses how the evaluation will be performed using a structure consistent with the other threats, components, and pathways in the HRS, but taking into account the unique parameters impacting the probability of exposure to subsurface intrusion. A. Addition Within a Restructured Soil Exposure Pathway EPA is proposing to add the evaluation of the relative risk posed by subsurface intrusion of hazardous substances into regularly occupied structures by restructuring the soil exposure pathway in the current HRS to include subsurface intrusion. As noted previously, no changes are being proposed for the other three pathways in the present HRS. The restructured soil exposure pathway is proposed to be renamed the soil exposure and subsurface intrusion pathway to reflect both components of the restructured pathway. See Figure 3 for a depiction of how the proposed addition fits into the HRS structure. srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4725 E:\FR\FM\29FEP2.SGM 29FEP2 EP29FE16.025</GPH>

390 10384 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 The threat posed by subsurface intrusion is proposed to be added to the soil exposure pathway because both consider the relative risk posed by direct contact with existing contamination areas. As identified in the preamble to the 1988 Federal Register document proposing the current HRS (53 FR , December 23, 1988), the soil exposure pathway, proposed in 1988 to be named the onsite exposure pathway, was added to the HRS to address the threat posed by direct contact with existing contamination and focused on ingestion of contaminated soil. This is in contrast with the other existing HRS pathways, which evaluate the relative risk posed by actual or potential migration of contamination from an original release location (called a source in HRS terminology) via ground water, surface water, or ambient air to other locations where exposure may occur. Given that the relative risk posed by subsurface intrusion is also due to direct contact with contamination already present in, or likely to be intruding into, regularly occupied structures and no further migration away from the existing contamination areas need occur, EPA considers it appropriate to incorporate the subsurface intrusion threat in the same direct exposure pathway that includes the soil exposure relative risk. See section 6.0 of the 1988 Revised HRS Technical Support Document (1988 Revised HRS TSD) for supplemental information (originally referred to as the onsite exposure pathway). The existing soil exposure pathway will be retained as one component of the restructured pathway, with the two threats within the present soil exposure pathway, resident and nearby populations, being retained as threats within the soil exposure component. The scoring of the soil exposure component will remain unaltered, but the score will be assigned as the soil exposure component score, not the pathway score. (See section 5.1 of the Proposed HRS Addition.) The proposed subsurface intrusion component will be added as a new component of the restructured soil exposure and subsurface intrusion pathway. As discussed in greater detail below, it will have the same basic structure, scoring, and weighting as other parts of the HRS. The score for the restructured pathway is based on a combination of the two component scores soil exposure and subsurface intrusion. The soil exposure component score is added to the subsurface intrusion component score to determine the pathway score. The two component scores are proposed to be additive because the populations may be subjected to exposures via both routes: The soil exposure component reflects exposures to people when outside a structure and focuses on ingestion and the subsurface intrusion component reflects exposures inside a structure and focuses on inhalation. Hence, the addition of the two component scores reflects the potential cumulative risk of multiple exposure routes and is not double counting the relative risk. A maximum pathway score is not contingent on scoring both the soil exposure and subsurface intrusion components. It is possible for a site to have only one component evaluated and still reach the maximum pathway score. Because the scoring of the soil exposure component is not being altered, this component would contribute the same score to the overall site score absent the addition of subsurface intrusion. B. Subsurface Intrusion Component Addition The structure of the current HRS is basically the same for all individual pathways, components, and/or threats. This structure was first used in the original HRS (47 FR 31220, 1982) and was only slightly altered when the HRS was revised in 1990 (55 FR 51532, December 14, 1990) to fit pathwayspecific parameters and to address comments on the proposed rule. See also section 2.2 of the 1988 Revised HRS TSD for supplemental information. The design of the HRS reflects a conceptual understanding of how hazardous substance releases from CERCLA sites can result in risks to public health and welfare and the environment. The risk scenario at these sites is a function of: The probability of exposure to (or releases to a medium in a migration pathway of) hazardous substances, The expected magnitude and duration of the releases or exposures, The toxicity or other potential adverse effects to a receptor (target) from the releases, The probability that the release will reach a receptor and the expected change in the concentration of hazardous substances during the movement from the location of the contamination to the receptors, The expected dose to the receptor, and The expected number and character of the receptors. The above considerations are addressed in three factor categories: likelihood of exposure (or release), waste characteristics, and targets. The following subsections describe the structure of the proposed subsurface VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 intrusion component and how this structure is consistent conceptually with the existing structure of the other HRS pathways and components: (1) New definitions, (2) delineation of areas of subsurface intrusion, (3) likelihood of exposure, (4) waste characteristics, (5) targets, and (6) calculating and incorporating the subsurface intrusion component score into the HRS site score. For background on why this structure was selected by EPA and peer reviewed by the SAB, see section 2.0 of the 1988 Revised HRS TSD. 1. New Definitions See Section 1.1 of the Proposed HRS Addition 8 EPA is proposing that 14 new definitions be added to the HRS, section 1.1, with additional modifications to existing definitions. EPA is adding these new definitions to aid the site evaluator in establishing the environmental boundaries that are being evaluated in this component (e.g., contamination in or above the surficial aquifer), in identifying factors unique to the subsurface intrusion component (e.g., channelized flow through which soil gas transports with no resistance), and to ensure consistent application of the HRS. 2. Delineation of Areas of Subsurface Intrusion See Section of the Proposed HRS Addition EPA is proposing to include in the subsurface intrusion component evaluation two areas in which exposure due to subsurface intrusion contamination exists or is likely to exist: (1) Areas of observed exposure areas in which contaminant intrusion into regularly occupied structures has been documented, and (2) areas of subsurface contamination areas in which subsurface contamination underlying regularly occupied structures (such as in surficial ground water or soil vapor) has been documented, but at which either sampling of indoor air has not documented that subsurface contamination has entered a regularly occupied structure or no sampling of indoor air has been undertaken. See Figure 4 for an illustration of the two areas. Additionally, special considerations are given to buildings with multiple subunits and multiple levels (e.g., apartment buildings) when establishing areas of subsurface intrusion. For a more detailed discussion on the selection of these areas, see section 6.0 of the Proposal TSD. 8 For references to a specific section of the proposed HRS addition, please refer to the regulatory text of the proposed rulemaking.

391 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules a. Area of Observed Exposure (AOE) See Section of the Proposed HRS Addition EPA is proposing to identify an area (or areas) of observed exposure at a site based on the location of regularly occupied structures with documented contamination resulting from subsurface intrusion attributable to the site being evaluated. The area encompassed by such structures constitutes the area of observed exposure (AOE). Other regularly occupied structures within this encompassed area (or areas) will also be inferred to be in the AOE unless available information indicates otherwise. Populations occupying structures within the AOE are considered exposed to subsurface contamination for HRS scoring purposes, and thus, are included in the HRS evaluation. See section 6.0 of the Proposal TSD for further discussion on the delineation of an AOE and the rationale for the inclusion of this area in an HRS evaluation. b. Area of Subsurface Contamination (ASC) See Section of the Proposed HRS Addition EPA is proposing to also identify an area (or areas) of subsurface contamination as an area outside that of the AOE, but for which subsurface contamination has been documented at levels meeting observed release criteria (contamination at levels significantly above background and the significant increase can be attributed at least in part to the site). The contamination would be present either in surficial ground water samples, in subslab or semi-enclosed or enclosed crawl space samples, in subsurface soil samples, or in soil gas samples in the unsaturated zone. An ASC may also include regularly occupied structures where indoor air sampling has not documented that an observed exposure has occurred. (See current HRS section 2.3 for observed release criteria.) In addition, EPA is proposing to limit the delineation of an ASC based on the location of subsurface volatile hazardous substances. However, non-volatile hazardous substances may be used to establish an ASC if they have also been documented in an observed exposure. Populations in regularly occupied structures within an ASC are considered potentially contaminated, but are weighted less in the HRS evaluation than those populations in an AOE. The populations in an ASC are assigned a weighting value ranging from 0.1 to 0.9 depending on such factors as the distance of subsurface contamination to a regularly occupied structure s foundation and the sample media (see section of the Proposed HRS Addition). The ASC is included in the HRS evaluation because there is currently contamination below regularly occupied structures in the ASC, and although a sampling event has not documented intrusion into these structures, based on previous studies, it is likely that intrusion has occurred or could occur when suitable climatic and lifestyle conditions were or are present. The populations in the ASC are weighted less to reflect the relatively lower demonstrated risk in the ASC in comparison to the AOE. See section 6.0 of the Proposal TSD for further discussion on the delineation of an ASC and the rationale for inclusion of this area in an HRS evaluation. srobinson on DSK5SPTVN1PROD with PROPOSALS2 c. Other Area of Subsurface Intrusion Considered: Potential Migration Zone In the three current HRS migration pathways (ground water, surface water, and air migration pathways), a projected present and future migration distance called the target distance limit is assigned based on studies performed when the HRS was revised in VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 Targets (receptors) within that distance are considered either actually or potentially exposed and the values assigned to these receptors are weighted based on the level of contamination, the EP29FE16.026</GPH>

392 10386 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 distance from a source, and the possible amount of hazardous substance dilution. As a result, EPA considered including within the subsurface intrusion component an approach for incorporating populations subject to future migration (outside the ASC) similar to that used for the ground water migration pathway. The approach included a standard 4-mile distance (modified if site-specific geologic information indicates otherwise) radiating either in all directions or only in the probable downgradient direction from each source at a site to establish this future migration zone. This approach could account for the possibility of future horizontal migration of either volatile substances in contaminated ground water or as a soil gas beyond the demonstrated boundaries of the subsurface contamination and subsequently into regularly occupied structures (i.e., a potential future migration zone). This might happen, for example, if hazardous substance plumes expand or migrate due to the additional release of hazardous substances, shift side-to-side due to ground water gradient changes resulting from seasonal variations or tidal influences, or change direction due to the sequencing of dry and wet years or pumping at municipal water supply or other well fields. Additionally, natural and anthropogenic influences, such as utility corridors, fracture patterns, karst features, or buried stream channels or other geologic heterogeneity may alter or enhance hazardous substance migration. However, EPA s confidence in the present science to accurately project hazardous substance migration through both the ground water and the unsaturated zone is limited. Several fate and transport models, many based on the Johnson and Ettinger Model, currently exist and are used to project vapor migration and predict contaminant vapor intrusion into a structure. The ability of a site assessor to accurately evaluate the potential future migration of subsurface hazardous substances would rely heavily on the ability to gather sitespecific data in all areas of future migration in the relatively short time period and with minimal resources available when data collection for an HRS evaluation is performed (i.e., during the site inspection). EPA s review of existing models indicate that in most instances, to obtain acceptable projections, extensive site-specific data collection efforts and often multiple rounds of site investigations are required to develop an accurate model for projecting the future extent of vapor migration, especially in the unsaturated zone. As discussed in section 2.5 of the 1988 TSD, the... misapplication of a model or the use of incomplete data would, of course, result in less accuracy... [and] a very conservative model may also increase the frequency with which sites that do not pose significant risks are placed on the NPL. Therefore, after thorough review of this option, the agency has chosen not to include the consideration of future subsurface contaminant migration in the proposed subsurface intrusion component. The possibility of placing sites on the NPL based on speculative projections with no demonstrated risk of actual exposure is too significant. The exclusion of this option in the proposed HRS addition does not directly prevent a site from being considered for listing on the NPL based on demonstrated intrusion, nor does it restrict future investigations from expanding the site boundaries or re-evaluating a site if further studies indicate that the extent of contamination at a site may have increased due to future migration. Please refer to section 6.0 of the Proposal TSD for supplemental information regarding consideration of a potential migration zone. 3. Likelihood of Exposure See Section of the Proposed HRS Addition A key factor considered in the HRS relative risk ranking is whether any exposure has occurred and if not, whether there is a probability that exposure could occur. This is termed the likelihood of exposure for the subsurface intrusion component. For purposes of an exposure assessment, not only must subsurface intrusion have occurred, but the structure must be regularly occupied. Consistent with other HRS pathways and components, likelihood of exposure is evaluated in two ways within the proposed subsurface intrusion component. The first step is to determine whether contamination has entered a regularly occupied structure; if this has occurred, observed exposure is established. If an observed exposure can be demonstrated in at least one structure, the likelihood of exposure category value is assigned the highest possible score. If observed exposure has not been documented, the second step is to evaluate the potential for exposure. The potential for exposure factor is assigned a score lower than that given when an observed exposure has been documented. How to evaluate the likelihood of exposure is discussed below. See section 4.0 of the Proposal VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 TSD for supplemental information regarding likelihood of exposure. a. Observed Exposure See Section of the Proposed HRS Addition For HRS purposes, an observed exposure is established if it can be documented that a hazardous substance from the site being evaluated has moved through the subsurface and has entered at least one regularly occupied structure. When it can be documented that subsurface intrusion has occurred, the likelihood of exposure is assigned its maximum value. The HRS identifies for all the pathways a consistent approach for establishing observed exposure (or observed release in migration pathways) and is discussed in section 2.3 of the current HRS. Also, the requirements for establishing observed exposure (or observed releases) are equivalent to those used to establish releases throughout the HRS. See section 2.6 of the 1988 Revised HRS TSD for supplemental information. Consistent with the current HRS structure, EPA is proposing to establish observed exposure in the subsurface intrusion component by any of the following methods: i. Observed Exposure by Direct Observation See Section of the Proposed HRS Addition The identification of an observed exposure by direct observation can be based on a solid, liquid, or gaseous hazardous substance attributable to the site being observed or known to have entered a regularly occupied structure from the subsurface. This finding will generally require the observation that a solid, liquid, or gas is entering the structure, and can be documented from a sample of the material that shows the hazardous substance is present due to the release from the site being evaluated. For example, this type of direct exposure could be documented if: (1) Contaminated vapors are found in a sample from a sump open to the regularly occupied structure, and (2) the same hazardous substances are found in subsurface samples collected beneath the regularly occupied structure or otherwise can be demonstrated as having emanated from known contamination underlying the structure. Another example would be if chromium precipitate is found in basements subject to ground water flooding and it is known that a chromium contaminant plume is present, and its presence is not from indoor sources. In neither example would a significant increase above a background contaminant level be required. For exposures to intruded ground water, EPA is proposing

393 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules documented observed exposure by direct observation as the only method for establishing likelihood of exposure. Figure 5 below depicts an additional example of documenting observed exposure by direct observation through collection of a contaminated water sample taken from the sump of an occupied structure that is known to be subject to flooding. Other methods may also be used to establish direct observation depending on site-specific conditions. See section 4.0 of the Proposal TSD for further information. srobinson on DSK5SPTVN1PROD with PROPOSALS2 ii. Observed Exposure by Chemical Analysis See Section of the Proposed HRS Addition Observed exposure by chemical analysis is established by comparing hazardous substance concentrations in background and release samples that have been chemically analyzed. The concentration of one or more hazardous substance in one or more indoor air sample taken from a regularly occupied structure (termed the release sample ) is compared to the concentration at appropriate background locations and under appropriate background conditions. If the chemical analyses document a significant increase over background levels and if at least part of the significant increase can be shown to be attributable to a release from the site being evaluated, then observed exposure by chemical analysis has been documented. This option for establishing observed exposure differs from observed exposure by direct observation in that comparison of the hazardous substance concentration in a release sample to a background level is required. This method for establishing observed exposure by chemical analysis is outlined in detail below. Background levels for this situation, in some cases, may be determined by chemical analysis of samples from similar environments collected from outside the area impacted by the release, or releases, from the site being evaluated. While the appropriate sample locations to be used to establish this background level will vary based on site-specific conditions, an appropriate background level needs to account for both outdoor air concentrations and indoor air concentrations in structures of similar construction type (e.g., basement, slab-on-grade) within the vicinity. This is to ensure that the background level represents the concentration of a hazardous substance in the absence of the subsurface intrusion. In some cases it may be possible to use published studies on typical background concentrations in establishing an appropriate background level. See section 4.0 of the Proposal TSD for further discussion on background levels. VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 The first step in determining if observed exposure by chemical analysis has occurred is to document that the magnitude of the difference between the background level concentration and the release sample concentration is sufficient to rule out the possibility that neither the difference nor the similarity is due to variation in site conditions; and to ensure the sampling and analytical procedures are precise and can be replicated. The magnitude of this significant increase was established for all HRS pathways based on studies peer reviewed by the Science Advisory Board when the HRS was last revised in See section 2.6 of the 1988 Revised HRS TSD for supplemental information. A significant increase is generally identified to have occurred if the release sample hazardous substance concentration is above quantification limits and at least three times the background level, provided the background sample concentrations for the hazardous substance are found at or above appropriate detection limits. If the hazardous substance background EP29FE16.027</GPH>

394 10388 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules level is below the appropriate detection limit, any quantifiable level of the hazardous substance detected in the targeted structure is considered to have a concentration significantly above background. The second step in determining if observed exposure by chemical analysis has occurred is to document that at least part of the significant increase can be attributed to a release from the site being evaluated. This step is required for establishing observed releases or observed exposures in all HRS pathways. See section 2.3 of the current HRS and section 2.6 of the 1988 Revised HRS TSD for supplemental information. This step is conducted to ensure that the increase is due to the release being evaluated and not from other potential contaminant sources located in the vicinity. (See section 4.0 of the Proposal TSD for further discussion.) For the proposed subsurface intrusion component, establishing significant increase over background is particularly critical because many of the projected intrusion contaminants are solvents and, in particular, chlorinated solvents. Chlorinated solvents are commonly found in multiple household and commercial cleaning products and in various consumer goods found in regularly occupied structures. These products present a substantial challenge for discerning the contribution from the environmental release that is being evaluated. Therefore, it is critical that a significant increase in these hazardous substances be documented as coming from the subsurface and not simply emanating from these products. It is suggested that the evidence to support this determination include multiple lines of evidence, including determining outdoor air hazardous substance concentrations; finding the hazardous substance at the source facility, site, or release being investigated; and finding the hazardous substance in subsurface samples. (See section 4.0 of the Proposal TSD regarding lines of evidence.) In addition, actions should be taken to ensure that sources of the hazardous substances inside a structure (e.g., household chemicals) have been removed from the structure prior to sampling. Establishing attribution to the site in some situations, however, may be straightforward to document, such as when the hazardous substance is manmade, unique, and not used in consumer products and thus, there would be no need to follow all the steps identified above to establish attribution. EPA expects that future advancement in methods for establishing the source of indoor contamination will be helpful for drawing conclusions about attribution. In summary, if it is demonstrated that there is a significant increase in hazardous substance levels in a regularly occupied structure and it is demonstrated that the significant increase in the contamination is in part due to the release from subsurface intrusion being evaluated, then an observed release by chemical analysis has been established. b. Potential for Exposure See Section of the Proposed HRS Addition When an observed exposure has not been established, EPA is proposing to evaluate the potential for exposure within structures located in an ASC using the subsurface intrusion component. Given that within an ASC, contamination has been demonstrated to be below or in the subsurface encompassing regularly occupied structures, it is probable that exposure to the intruding hazardous substance has occurred but that sampling has not been performed at the time the exposure took place. As explained in section 4.0 of the Proposal TSD, the factors affecting when intrusion will occur and the rate of subsurface intrusion are extremely time-, site-, and climatespecific. Sampling may not have been performed in these structures for a number of reasons, or, even if performed during the limited time period (due to resource limitations, site inspections are conducted over a limited period of time, usually 1 to 2 days) of a site inspection, the sampling may have been conducted during conditions in which the subsurface intrusion was not occurring, or occurring at levels not detectable or differentiable from that in background sources of the hazardous substance. Therefore, it is important that the potential for exposure be included as a consideration when evaluating subsurface intrusion threats, especially when volatile substances are documented in the subsurface below regularly occupied structures. As also explained in section 4.0 of the Proposal TSD, EPA is proposing to evaluate the potential for exposure for the subsurface intrusion component using the same concept and framework used to estimate the potential to release in other pathways. (See section 2.3 of current HRS.) As depicted in Figure 6 below, this involves predicting the probability of exposure in an area of subsurface contamination based on structural containment features of the regularly occupied structure and the route characteristics in the subsurface, including hazardous substance physical and chemical properties and physical subsurface properties that influence the probability that intrusion is occurring. srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2

395 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 i. Structure Containment See Section of the Proposed HRS Addition Containment within the current HRS is used to consider barriers that restrict the movement of hazardous substances. See the preamble to the 1988 Revised HRS (53 FR 51985, December 23, 1988) for supplemental information. For the proposed subsurface intrusion component, the containment features considered represent structural features that block the movement of hazardous substances so as to minimize or prevent indoor exposures resulting from subsurface intrusion into a regularly occupied structure. As is consistent with the current HRS, EPA is proposing containment factor values that range from zero to ten where a low containment factor value indicates a low chance for exposure. For example, in Table 5 12 of the proposed HRS addition, a structure with no visible open preferential pathways from the subsurface has a lower containment value than a structure with documented open preferential pathways because open preferential pathways (e.g., sumps, foundation cracks) represent a situation in which a greater probability for subsurface intrusion to occur is present. Populations in structures that show no possible SsI intrusion route are not evaluated in this new component. Supplemental information regarding containment and the factor values specified in Table 5 12 is provided in section 4.0 of the Proposal TSD. ii. Route Characteristics See Section of the Proposed HRS Addition The HRS uses route characteristics to index the relative degree to which hazardous substances move into or have already moved into specific areas, such as from a source into ground water, or for the subsurface intrusion component into a regularly occupied structure (see the 1988 TSD and section 4.0 of the Proposal TSD for supplemental information). These characteristics represent the physical and chemical properties of the specific hazardous substances and the media in which they must have moved through or could move through. To determine which route characteristics are appropriate for evaluating potential exposure to subsurface hazardous substances, EPA examined the literature to identify the modeling methods that are currently used to estimate the levels of hazardous substance exposure. Numerous route characteristics and the relationship of these and site-specific input requirements were identified. EPA also VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 gave careful consideration to ensure that route characteristic factors may be measured or calculated on a site-specific basis in a manner appropriate with current HRS evaluations. See section 4.0 of the Proposal TSD for supplemental information evaluated as part of this process. EPA reviewed existing sensitivity analyses and performed further analyses to evaluate the intrinsic relationships among the examined route characteristics to identify those that have the greatest impact on potential for exposure. Based on the agency s analysis, three factors represented the greatest impact on potential for exposure and for which sufficient sitespecific information could be collected during a site inspection: (1) Depth to contamination, (2) vertical migration, and (3) vapor migration potential. These three factors are described in the following sections. a. Depth to Contamination See Section of the Proposed HRS Addition The depth to contamination factor represents the vertical distance between contamination (either in soil, soil gas, or surficial ground water) and the lowest horizontal point of an overlying regularly occupied structure (e.g., a EP29FE16.028</GPH>

396 10390 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 basement floor). This distance represents how far a hazardous substance would have to travel through the subsurface to intrude into that structure. Based on available data, the probability of exposure decreases as the depth to contamination increases. In addition, as part of EPA s sensitivity analysis in developing route characteristics, at depths greater than 150 feet it became increasingly unlikely that exposure would occur. This is reflected in Table 5 13 (section of the Proposed HRS Addition). EPA is proposing depth to contamination factor values ranging from zero to ten, where increasing depth results in a lower factor value. EPA is also proposing to give special consideration in two situations in which it is likely that exposure has occurred. One situation is when subsurface profiles may be impacted by channelized flow features, such as fractured bedrock or karst. The other situation is at locations where the contamination is measured directly below the structure (e.g., in subslab or enclosed/semi-enclosed crawl space samples). These features reflect a situation with a high probability of exposure to intruded hazardous substances because of limited resistance to migration of the substances into the structure. See section 4.0 of the Proposal TSD for supplemental information on how the depths to contamination were weighted when assigning the factor values to different distances. b. Vertical Migration See Section of the Proposed HRS Addition The vertical migration factor considers the geologic makeup of materials between a regularly occupied structure and the hazardous substance plume and the rate at which substances are likely to have moved through the materials. EPA is proposing to index vertical migration based on two factors: Effective porosity (or equivalently, the permeability) of geologic materials and the thickness of the lowest porosity layer. Factor values for effective porosity (as it relates to permeability) of geologic materials range from one to four and are based solely on the typical range of porosity of subsurface materials (e.g., gravel, sand, silt and clay). These factor values are used in conjunction with the thickness of the lowest porosity layer (greater than 1 foot thickness) to establish a vertical migration factor value, ranging from one to fifteen. As part of the vertical migration factor, EPA identified soil moisture content to potentially be a significant route characteristic variable. Thus, to incorporate soil moisture in EPA s assessment of potential for exposure, the agency used published average soil moisture content values for specific soil types. These averages were used to develop effective porosity/permeability factor values. See section 4.0 of the Proposal TSD for supplemental information. c. Vapor Migration Potential See Section of the Proposed HRS Addition The vapor migration potential factor is based on hazardous substancespecific chemical properties, including both the vapor pressure and Henry s constant values for hazardous substances associated with the site. This factor evaluates the volatile nature of these hazardous substances and is projected to be the most influential route characteristic factor on calculating potential for exposure based on a sensitivity analysis using subsurface migration modeling. When calculating the vapor migration potential, a factor value is determined only for the most volatile hazardous substance based on vapor pressure and Henry s constant values. Those values are used to establish the vapor migration potential factor value. See section 4.0 of the Proposal TSD for supplemental information on this topic. iii. Calculation of the Potential for Exposure Factor Value See Section of the Proposed HRS Addition Consistent with potential to release determinations in the HRS, the potential for exposure for this component is calculated by summing all route characteristic factor values and multiplying the sum by the containment factor value to determine a potential for exposure factor value. c. Calculation of the Likelihood of Exposure Factor Category Value See Section of the Proposed HRS Addition As in all HRS pathways and components, the likelihood of exposure factor category value is assigned based on the higher of the observed exposure (or release) value or the potential for exposure (or release) value. The maximum value assigned for the likelihood of exposure factor category is 550 and is assigned if observed exposure is documented. If observed exposure is not documented, the value assigned when evaluating potential for exposure ranges between 0 and 500. This approach is consistent with the current HRS structure. See sections 2.2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 of the 1988 Revised HRS TSD for supplemental information regarding this approach. 4. Waste Characteristics See Section of the Proposed HRS Addition The waste characteristics factor category is based on factors that are related to the relative risk considerations included in the basic HRS structure: (1) The toxicity or other potential adverse effects to a receptor from the releases, (2) the potential to degrade in the subsurface prior to intruding into a regularly occupied structure, and (3) the expected magnitude and duration of the exposure. The factors considered in determining the waste characteristics factor category value are the toxicity of the hazardous substances, the ability of the hazardous substance to degrade, and an estimate of the quantity of the hazardous substances to which occupants could be exposed. Consistent with the soil exposure component, the assigned factor values are multiplied together to determine this category value for the subsurface intrusion component. (See sections 2.2 and 2.4 of the 1988 Revised HRS TSD for further discussion on the structure of this factor category and how it fits within the overall HRS structure.) How and why these factors are proposed to be included in this factor category is discussed below. a. Toxicity/Degradation See Section of the Proposed HRS Addition The combined toxicity/degradation factor includes consideration of both the toxicity and the possibility for degradation of hazardous substances being evaluated for HRS purposes. The toxicity factor in the overall HRS structure reflects the toxicity of a hazardous substance associated with a release or exposure, and is assigned the same factor value for all the pathways and components in the current HRS. As in all HRS pathways and components, it is proposed to be assigned the same corresponding factor value as for other parts of the HRS. The rationale for the assignment of the factor value is discussed in the section 2.3 of the 1988 Revised HRS TSD. This toxicity factor is based on the toxicity of the substances present at a site. In the HRS addition, a different factor value is proposed to be assigned to each hazardous substance that an occupant has been or is potentially exposed to. The factor value is driven by the magnitude of each hazardous substance s acute and chronic toxicity to humans. The toxicity factor value is directly related to the concentration at which the hazardous

397 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 substance is known to have a health effect: The more toxic the chemical, the higher the toxicity value. Any hazardous substance identified in an observed exposure within the AOE or meeting the observed release criteria in either the AOE or ASC will be assigned a toxicity factor value. The method for assigning this value is contained in section of the current HRS (40 CFR 300, Appendix A) and is discussed in section 2.3 of the 1988 Revised HRS TSD. The degradation factor represents the possibility for a substance to degrade in the subsurface prior to intruding into a regularly occupied structure. The potential of a substance to degrade has been identified as a significant factor in numerous studies evaluating the potential for intrusion by a vapor. The possibility that a substance may degrade is both a substance- and locationspecific evaluation that is influenced by factors such as molecular structure, makeup of the immediate subsurface geology, and the presence or absence of oxygen within intervening unsaturated soils. Because many of the site-specific characteristics impacting the rate of degradation are considered beyond the scope of a typical site investigation, EPA is proposing to evaluate degradation based on the substance being evaluated, the depth to contamination, and if appropriate environmental conditions are present to ensure that sufficient degradation will occur to diminish the threat. Based on EPA s review of the current literature and research on this topic, the assigned degradation factor is limited to three possible factor values, two for substances that are readily degradable and the appropriate environmental factors are present, and one for when either of these parameters are not present. EPA seeks public input on the following question regarding the degradation factor: Is there a way to determine the presence and extent of biologically active soil at a site during a limited site investigation? If so, what soil characteristics should EPA consider to determine whether biologically active soil is documented to be present? EPA proposes the degradation factor also be based on the half-life of a substance, with the half-life being determined by biodegradation and hydrolysis rates. If this information is not available then a hazardous substance s estimated half-life will be based on the substance s chemical structure, unless available information indicates otherwise. Substances with relatively low structural complexity, such as petroleum and petroleum-like substances (having straight carbon chain or simple ring structures), have the greatest potential to degrade in the subsurface while halogenated and polyaromatic ringed substances (e.g., tetrachloroethylene, PCBs) are less likely to significantly degrade as result of subsurface microbial activity. If it has been documented that a hazardous substance has been found to have entered a regularly occupied structure, regardless of the substance or the site conditions, the degradation value is assigned to reflect the likelihood that the substance is not significantly degrading in the subsurface. Also, if the substance is a daughter, or degradation product, of a parent substance that is also present, then the degradation factor will reflect this relationship. Parent and daughter substances are assigned values to reflect that the daughter substance will be continuously created by degradation of the parent substance. See also section 5.0 of the Proposal TSD for additional discussion regarding the inclusion of a degradation factor. The toxicity and degradation factors are multiplied together to assign a combined factor value. If multiple substances are present, the highest combined factor value is selected for use in determining the waste characteristics factor category value, as discussed below. b. Hazardous Waste Quantity See Section of the Proposed HRS Addition In the basic HRS structure used in all pathways and components, the hazardous waste quantity factor reflects the risk consideration related to the magnitude and duration of either the release for a migration pathway or the exposure for an exposure pathway. In other words, for an exposure pathway, the risk posed by a release of hazardous substances is directly related to the amount of hazardous substances to which receptors (targets) are exposed and the length of the exposure. As explained in the preamble to the 1990 HRS and in the 1988 Revised HRS TSD, an estimate of the waste quantity associated with a site was the best surrogate for the amount of hazardous substances that receptors were exposed to and that the duration of the exposure was probably correlated to the magnitude of the exposure. In the current three migration pathways (ground water, surface water, air), the hazardous waste quantity factor reflects the total amount of hazardous substances in sources at the site to take into account not only where contamination has already migrated to, VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 but also future migration of contamination to other locations. For the soil exposure pathway, however, the estimate does not include the total amount in or released from the site sources, but only the amount of hazardous substance in the top two feet of contaminated soils sources and in the surface portions of other source types in an area of observed contamination. (See section of the current HRS.) EPA is proposing that since the subsurface intrusion component also focuses on exposure and not the amount of hazardous substances that might migrate to targets in the future, the waste quantity factor value for this component should also reflect only the amount of hazardous substances that people currently are exposed to, that is, the amount in regularly occupied structures. EPA is proposing a fourtiered hierarchical approach consistent with the current HRS (see section III.C of the preamble of the current HRS (55 FR 51542, December 14, 1990)) as well as minimum waste quantity factors (see section of the current HRS). The minimum waste quantity factors are included because of insufficient information at many sites to adequately estimate waste quantity with confidence, as discussed in section I of the preamble to the current HRS (55 FR 51533, December 14, 1990). The current HRS establishes a minimum waste quantity factor value of 10 for each pathway or component at sites with no actually contaminated targets and a waste quantity factor value of 100 for the migration pathways if observed exposure has been documented. (See section of the current HRS.) It is proposed for the estimation of waste quantity for the subsurface intrusion component, that regularly occupied structures within the AOE and ASC be considered. For sites at which the component waste quantity (the sum waste quantities for all occupied structures in the AOE and ASC) is below 10, it is proposed that a minimum factor of 10 should apply the same as in other pathways and components. This minimum factor reflects that in a limited site inspection, it is likely that information on the actual waste quantity at a site may not be available and a lower value would likely underestimate the actual conditions. Furthermore, if any target is subject to Level I or II contaminant concentrations a minimum hazardous waste quantity factor value of 100 could be assigned. EPA seeks public input on the following question regarding the calculation of hazardous waste quantity: How could EPA further take into account the differences in dilution and

398 10392 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 air exchange rates in large industrial buildings as compared to smaller residential and commercial structures when calculating the hazardous waste quantity for the HRS SsI Addition? The component waste quantity is the sum of all the waste quantities for all the regularly occupied structures found in both the AOE and ASC. The component waste quantity factor value assigned is then based on the magnitude of this sum, subject to minimum values. See section 5.0 of the Proposal TSD for supplemental information regarding this topic. c. Calculation of the Waste Characteristics Factor Category Value See Section of the Proposed HRS Addition As in all HRS pathways and components, the waste characteristics category value is the product of the toxicity/degradation factor value (or the functional equivalent) and the hazardous waste quantity factor value, scaled so as to be weighted consistently in all pathways. Similar to the likelihood of exposure factor category, the waste characteristics factor category is subject to a maximum value to maintain the balance between factor categories. This approach is consistent with the current HRS structure. See sections 2.2 and 2.4 of the 1988 Revised HRS TSD for supplemental information regarding this approach. 5. Targets See section of the Proposed HRS Addition The targets factor is based upon estimates of the expected dose to each receptor and the number and type of receptors present. In a human health risk assessment, it is critical to understand the nature and extent of exposure to individuals, populations, and resources. The relative risk assessment embodied within the current HRS uses the targets factor as an index of the nature and extent of exposure to individuals, populations, resources, if appropriate for the migration or exposure route being evaluated, sensitive environments. This will remain the same in the proposed HRS addition, except sensitive environments will not be considered an eligible target. a. Identification of Eligible Targets See Section of the Proposed HRS Addition. The target factors evaluated by all pathways under the current HRS include the following: The most exposed individual (i.e., nearest well for ground water migration, nearest intake for drinking water threat, food chain individual for human food chain threat, resident individual for resident population threat, and nearest individual for nearby population threat and air migration), Populations (including residents, workers, students, and those in daycare), Resources (including economic and cultural uses of contaminated resources), Sensitive environments (except for the ground water migration pathway). (Examples of sensitive environments include government designated protected areas (e.g., national wildlife refuge), wetlands and critical habitat known to be used by a State or Federally-designated threatened or endangered species.) See sections 2.5 and of the current HRS for supplemental information on how eligible targets are identified. Given that the subsurface intrusion component is proposed to be included as an exposure component within the modified soil exposure and subsurface intrusion pathway, the agency is proposing to use the same target categories used in the current soil exposure pathway, including exposed individual, resident populations, workers, and resources. However, unlike the current soil exposure pathway, workers are proposed to be evaluated as exposed individuals and as part of the population within an area of subsurface contamination instead of being evaluated under a separate worker factor value. See section and its subsections of the proposed HRS addition. Additionally, sensitive environments are not being considered as eligible targets because exposures related to subsurface intrusion are limited to indoor areas and it is unlikely that sensitive environments would be exposed. See section of the proposed HRS addition. EPA seeks public input on the following question regarding subsurface source strength: The HRS SsI Addition considers source strength in delineating ASCs and AOEs, in scoring likelihood of exposure, in assigning waste quantity specifically when estimating hazardous constituent quantity and in weighting targets in an ASC. The HRS algorithm for all pathways incorporates the consideration of source strength in determining an HRS site score. Could EPA further take into account source strength in performing an HRS evaluation? VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 b. Exposed Individual and Levels of Exposure See Section of the Proposed HRS Addition This section introduces the methods used to identify and establish the levels of contamination and benchmarks proposed to be used within the subsurface intrusion component. Additionally, the exposed individual factor is discussed, as well as how to apply a factor value based on the benchmarks and the resulting levels of exposure. i. Identifying Levels of Exposure and Benchmarks for Subsurface Intrusion See Section of the Proposed HRS Addition For all current HRS pathways, the magnitude of the values assigned to the individual and population factors depend on the concentration of the contamination to which the receptors (targets) are exposed. If receptors are exposed to hazardous substance levels that meet observed release criteria, they are identified as actually contaminated; however, if the receptors are not exposed to hazardous substances that meet the observed release criteria but are within the target area being evaluated, they may be considered potentially contaminated. Potential targets are evaluated because a typical site inspection may not identify the extent of contamination. A site inspection typically includes 1 to 3 days of sampling and investigation activities. These limited investigations may not adequately characterize the annual or longer term indoor exposure levels (see page 4 of the 1988 SAB report and section 6.0 of the Proposal TSD), especially in the case of subsurface intrusion where seasonal and temporal fluctuations can significantly impact the rate of subsurface intrusion. Actually contaminated targets are further divided into two categories based on whether the hazardous substance concentrations are above standard health-based benchmarks (or for environmental receptors, ambient water quality criteria). If so, they are identified as Level I; if they are not, they are identified as Level II. See section of the current HRS for a discussion of applicable benchmarks. EPA is proposing to use a similar target weighting structure in the subsurface intrusion component. (See sections and of the proposed HRS addition.) Those targets in the AOE are considered actually contaminated, whereas, those in the ASC are considered potentially contaminated. The targets in an AOE are further divided into Level I and II, based

399 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 on whether the hazardous substance concentrations are at or above identified health-based benchmarks. EPA is proposing to use the following benchmarks for the subsurface intrusion component: Screening concentrations for cancer Screening concentrations for noncancer toxicological responses Targets associated with an observed exposure by direct observation are only considered subject to Level II contamination in all parts of the HRS and EPA is proposing that this remains consistent in the subsurface intrusion component. Furthermore, because intrusion by contaminated ground water is documented by direct observation only, targets residing within a structure subject to intrusion by contaminated ground water are also proposed to be evaluated as Level II (see section 2.5 of the proposed HRS addition). The targets within an ASC are also further divided based on the type of sample (e.g., gas, soil, water) and the distance of the sample from the targets (e.g., the depth of the sample below the structure). Weighting factors ranging from 0.1 to 0.9 are then assigned accordingly as discussed below in section 5.c.ii. See also section III.H. of the preamble to the current HRS (55 FR 51547, December 14, 1990) for supplemental information. ii. Exposed Individual See Section of the Proposed HRS Addition The standard HRS approach for scoring targets includes a measure reflecting the maximum level of exposure to individuals. The evaluation of exposed individuals is proposed to include individuals living, attending school or day care, or working in a regularly occupied structure. The reasonably maximally exposed individuals are those individuals in the eligible target population that are expected to be exposed to the highest concentration of the hazardous substance in question for a significant time. See section V.C.9 of the preamble to the proposed 1988 HRS (53 FR 51978, December 28, 1988) for supplemental information. EPA is proposing to retain the basic scoring approach used throughout the current HRS for evaluating the exposed individual factor. As is consistent with all pathways, a value of 50 points is assigned if there is any individual exposed to Level I concentrations or 45 points if there is any individual exposed to Level II concentrations. If there are no individuals exposed to Level I or Level II concentrations, but at least one individual is living, attending school or day care, or working in a regularly occupied structure within an ASC, EPA proposes to assign a value of 20. See section 2.5 of the current HRS for supplemental information as to how EPA addresses exposed individuals within the HRS structure. c. Population See Section of the Proposed HRS Addition The population factor is evaluated using media-specific, health-based benchmarks as discussed above. EPA proposes the population factor include all populations qualifying as exposed individuals, including residents, students, workers and those attending day care. However, workers are weighted slightly differently than other exposed individuals to reflect that a worker s exposure is limited to the time present in a workplace. Additionally, as workers may be employed on a full-time or part-time basis, the number of workers present in a structure or subunit is proposed to be adjusted by an appropriate factor reflecting this difference in exposure durations. EPA is proposing to retain the current scoring methodology for weighting populations used throughout the HRS, with actual exposure more heavily weighted than those potentially exposed. The proposed subsurface intrusion component will evaluate populations based on the number of individuals located within an identified AOE (i.e., those populations exposed to Level I and Level II concentrations) and the number of individuals located within an ASC (i.e., potential contamination as determined based on subsurface sampling), which is further subdivided as described in subsection ii below. i. Weighting of Targets in the Area of Observed Exposure (AOE) See Sections and of the Proposed HRS Addition EPA is proposing to establish an AOE based on documented contamination meeting observed exposure criteria (either by direct observation or chemical analysis). Consistent with the weighting of populations throughout the HRS (see section 2.5 of the current HRS), the proposed subsurface intrusion component will weight targets subject to Level I contaminant concentrations by a factor of 10 and weight targets subject to Level II contaminant concentrations by a factor of 1. As noted previously, eligible populations also include individuals working in regularly occupied structures. However, the number of workers present in a regularly occupied structure will be adjusted to reflect that their exposure is limited to the time they are in a VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 workplace. Therefore, the number of full- and part-time workers in a structure or subunit will be identified and divided by an appropriate factor prior to being summed with the number of other individuals present. If information is unavailable to classify a worker as full- or part-time, that worker will be evaluated as full-time. For example, if a single residence occupied by a family of four was observed to be exposed to hazardous substance concentrations above a media-specific, health-based benchmark, the number of residents would be multiplied by 10 for a factor value of 40. However, if that same family was exposed to a hazardous substance and the hazardous substance concentration was below the applicable benchmark but met the criteria for observed exposure, the number of residents would be multiplied by 1 for a factor value of 4. To ensure the entire population within an AOE is included in the HRS evaluation, both Level I and Level II factor values are counted and summed together. Within the AOE, EPA is proposing to consider as actually contaminated those populations in regularly occupied structures for which observed exposures have not been established but the structures are surrounded by regularly occupied structures in which observed exposures have been identified, unless evidence indicates otherwise. This action is proposed because it is considered likely that if these structures were sampled during the correct conditions, observed exposures would be identified at levels similar to those in surrounding structures. Targets inferred to be exposed to this contamination will be weighted as Level II as there are no actual sample results to compare against benchmarks. However, EPA has included an exception to allow for situations where site-specific conditions clearly document that there may be no observed exposures in these structures. The rule language states that targets can be inferred to have observed exposures in these situations unless available information indicates otherwise. This concept of inferred exposure is also included in the existing soil exposure pathway and in the air migration pathway. In the case of multi-story/multisubunit structures, all regularly occupied subunits on a level with an observed exposure and all levels below are considered to be within an AOE, unless available information indicates otherwise. For multi-story/multisubunit structures located within an AOE, but where an observed exposure has not been documented, only those

400 10394 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 regularly occupied spaces on the lowest level are considered to be within an AOE, unless available information indicates otherwise. (See sections and 6.3 of the current HRS.) ii. Weighting of Targets in the Area of Subsurface Contamination (ASC) See Section of the Proposed HRS Addition EPA is proposing to establish an ASC as defined by documented ground water, subslab, soil, semi-enclosed or enclosed crawl space, or soil gas contamination meeting observed release criteria. These areas are included in the subsurface intrusion component due to the potential that limited sampling conducted during a site inspection may not identify that subsurface intrusion is occurring because of the high temporal and spatial variability associated with detecting subsurface intrusion. Temporal and spatial differences can significantly impact the rate at which volatile hazardous substances enter a structure. However, when an ASC has been defined, that area represents a location where subsurface hazardous substances have the potential to intrude into a structure. EPA is limited in its extent of preliminary screening activities, and a single indoor air sampling event is unlikely to identify the full threat posed by subsurface intrusion. As is consistent with the 1990 HRS, EPA is proposing to weight these potentially exposed targets at a value less than those targets that have been identified to be actually exposed. Due to the variability in subsurface intrusion rates, the potential weighting factor values for targets within an ASC range from 0.1 to 0.9 and depend on where the subsurface contamination has been found. Using EPA s vapor intrusion attenuation factors published in 2012 and basic subsurface contaminant transport concepts, EPA developed a relatively proportional weighting for potential targets based on the sampling media being considered. This range of weighting factors represents the proportional probability of a target to be exposed as a result of contaminant intrusion from the subsurface in a variety of likely sampling scenarios. The potential target weighting factors presented in the proposed addition do not directly correspond to attenuation factors in themselves. Instead, the relative weighting between these values is based on the published attenuation factors. These weighting factors are presented in this manner to project that contaminants found in a crawl space sample, for example, are more likely to attenuate less before entering into an overlying structure, and thus more likely to pose a threat, as opposed to those found in a shallow ground water sample. EPA is proposing that the weighting of potential targets also reflect the distance to or the depth at which contamination is found. For any contamination found at a horizontal or vertical distance of five feet or less from a regularly occupied structure s foundation, EPA is proposing to assign a minimum weighting factor of 0.4 regardless of the sample medium. Similarly, EPA is proposing to assign a weighing factor of 0.1 to any contamination found or inferred at depths greater than 30 feet regardless of sampling medium. These minimum weighting values are in response to an analysis of the data used in deriving published attenuation values. The attenuation values were published based on real-world sampling data collected from numerous sites across the United States. The majority of sampling data collected as part of this effort came from sites where contamination was generally found at depths less than 30 feet. Therefore, EPA considers the attenuation factors and relative weightings between them to only be appropriate for shallower depths. The minimum value for the upper five feet allows consideration of sites where contamination is found at extremely shallow depths and therefore has a minimal vertical distance to travel before intruding into a regularly occupied structure. In the case of multi-story/multisubunit structures, all regularly occupied subunits on a level above one where an observed exposure has been documented or inferred, or where a gaseous indoor air sample meeting observed release criteria is present, are considered to be located within an ASC, unless available information indicates otherwise. For multi-story/multisubunit structures located only within an ASC, only those regularly occupied subunits within the lowest level are considered in an HRS evaluation. EPA proposes eligible populations include individuals living in, or attending school or day care in the structure, and workers in regularly occupied structures. The number of workers is adjusted to reflect that their exposure is limited to the time they are in a workplace. Therefore, the number of full- and part-time workers in a structure or subunit will be divided by an appropriate factor prior to being summed with the number of other individuals present. If information is unavailable to classify a worker as full- VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 or part-time, that worker will be evaluated as full-time. The proposed weighting factors for exposed individuals in any structure within an ASC are based on the probability of contamination entering into occupied structures from the subsurface. The weighting factors reflect depth to contamination, sample type, and media. The magnitude of the factor is also based on attenuation factors from current scientific literature including EPA s 2012 vapor intrusion attenuation factors publication. Additional information regarding this analysis is presented in section 6.0 of the Proposal TSD. d. Resources See Section of the Proposed HRS Addition The resources target factor is evaluated in all pathways under the current HRS. A factor value of five is assigned if at least one resource is present and a factor value of zero if no resource is present. Eligible resources are pathway-, component-, or threatspecific. These resources represent uses of a contaminated medium or area where exposures occur and are not covered by the other identified targets. For example, resources within the air migration pathway include commercial agriculture or silviculture and major/ designated recreation areas. The resident population threat also includes commercial livestock production or grazing. See section III.I of the preamble to the current HRS (55 FR 51549, December 14, 1990) for supplemental information. Because subsurface intrusion is limited to indoor spaces, EPA is proposing to include regularly occupied structures that are located within a defined AOE or ASC (as previously discussed in section VI.B.2 of this preamble) and in which populations, not including those already counted as exposed individuals, may be exposed to contamination due to subsurface intrusion. For example, libraries, recreational facilities, and religious or tribal structures used by individuals, may qualify as eligible resources. e. Calculation of the Targets Factor Category Value See Section of the Proposed HRS Addition As is done throughout the HRS, EPA is proposing to sum all of the target factor values together to establish a target factor category value in calculating the proposed subsurface intrusion component score. Unlike the likelihood of exposure and waste characteristics factor category values in all HRS pathways, which are subject to maximum values, the target factor

401 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 category is not limited in the current HRS. This is to ensure that all individuals, populations, resources, and sensitive environments are included; thereby, representing the full relative risk associated with the identified threat. It is also consistent with the direction of CERCLA section 105 to amend the HRS to the maximum extent feasible to address the relative degree of risk to human health and the environment by putting the emphasis on the number of receptors exposed to contamination. 6. Calculation and Incorporation of the SsI Component Score Into the HRS Site Score The following subsections summarize the calculation of the subsurface intrusion component score, how the component score is then used in the calculation of the soil exposure and subsurface intrusion pathway score, and how, in turn, the pathway score is subsequently incorporated into the HRS site score. a. Calculation of the SsI Component Score See Section of the Proposed HRS Addition EPA is proposing to calculate the subsurface intrusion component score using the same algorithm as in other components and pathways of the HRS. (See section 2.2 of the 1988 Revised HRS TSD.) This involves multiplying the likelihood of exposure factor category value times the waste characteristics factor category value times the targets factor category value and dividing that value by a weighting factor so that it has equal magnitude to other component scores (subject to a maximum value). The values are multiplied to reflect that it is the product of these values that represents a relative risk level. In a relative risk (or in a site-specific risk) assessment, the use of the product of the factor category values is considered appropriate because the magnitude of each of the factor category values reflects the probability of exposure occurring: Likelihood of releases reflects the probability of exposure actually occurring, waste characteristics reflects the probable quantity and duration of the exposure, and targets reflect the probable number of receptors at risk. Thus, since each factor category value reflects a probability in a series of events, the overall probability associated with the series is the product of the individual probabilities. For example, if any factor category value is zero, such as when there are no targets exposed or potentially exposed to subsurface intrusion, the component score is zero, consistent with there being no risk due to subsurface intrusion. b. Incorporation of the SsI Component Score Into the Soil Exposure and Subsurface Intrusion Pathway Score See Section 5.3 of the Proposed HRS Addition The score for this restructured pathway is proposed to be a combination of two component scores. The subsurface intrusion component score is added to the soil exposure component score (subject to a maximum value) to determine the pathway score. The two component scores are proposed to be additive because the populations may be subjected to exposures separately via both routes: The soil exposure component reflects exposures to people when outside a structure and focuses on ingestion, while the subsurface intrusion component reflects exposures to people when inside a structure and focuses on inhalation. Hence, the addition of the two component scores reflects the cumulative potential risk and is not double counting the relative risk. In addition, a pathway score can be assigned without scoring both the soil exposure and subsurface intrusion components using this approach. It is possible for a site to have only one component evaluated and still reach the same pathway score as under the current HRS. It should be observed that because the scoring of the soil exposure component is not being altered, the soil exposure component would contribute the same score to the overall site score as it would if the subsurface intrusion component is not added. c. Incorporation of the Soil Exposure and Subsurface Intrusion Pathway Score Into a Site Score See Section of the Proposed HRS Addition EPA is not proposing any changes to the methodology used to assign an overall site score due to the addition of the subsurface intrusion component to the soil exposure pathway and renaming that pathway the soil exposure and subsurface intrusion pathway. The overall site score remains a function of four pathway scores and the same weighting is given to each pathway score as in the current HRS. See section 2.2 of the 1988 Revised HRS TSD for supplemental information on why the existing methodology was chosen. 7. Example Site Scoring Scenarios To evaluate the proposed subsurface intrusion component and factor category weighting, EPA developed three conceptual site scenarios: One that VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 would not qualify for the NPL (score below 28.50); one that would qualify marginally for the NPL (score of about 28.50); and one that should clearly qualify for the NPL (site score considerably above 28.50). The first scenario consists of a ground water plume contaminated with a hazardous substance with moderate toxicity that underlies approximately 3 acres of a residential neighborhood comprised of single-family detached homes. Indoor air samples have been collected from inside two homes and have reported hazardous substance concentrations above background, but below the applicable benchmarks. Additionally, several other occupied structures were sampled for indoor air and subslab contaminant concentrations; however, no other detections of hazardous substances were observed. This site would not qualify for the NPL based on available information (i.e., score below 28.50). The second scenario also consists of a ground water plume contaminated with a hazardous substance with moderate toxicity as in the first scenario, but it has a considerably larger plume and more targets. The ground water plume underlies approximately 20 acres of a residential neighborhood and commercial area comprised of single-family detached homes, a daycare facility, and a single-story office building. Indoor air samples collected inside 19 homes, the daycare facility, and office building have hazardous substance concentrations above the applicable benchmark. Indoor air samples in 5 homes, the daycare facility with approximately 25 children enrolled and 6 full-time and 2 part-time workers, and the office building with 18 full-time workers have hazardous substance concentrations above background, but below the applicable benchmark. The homes and daycare facility were checked for indoor sources of hazardous substances prior to sampling and such sources were removed if found. This site would likely qualify for the NPL based on available information (i.e., score of about 28.50). The third scenario consists of a ground water plume contaminated with a highly toxic hazardous substance and a larger number of targets than the second scenario. The plume underlies approximately 25 acres of a residential neighborhood and hazardous substance concentrations above a benchmark were detected in indoor air samples from 25 homes and one daycare with approximately 25 children enrolled and 5 full-time workers. Hazardous substance concentrations above background but below benchmarks were

402 10396 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 detected within 15 homes. The homes and daycare facility were checked for indoor sources of hazardous substances prior to sampling and such sources were removed if found. Based on available information, this site would qualify for the NPL and would likely achieve the maximum HRS score for a single component and pathway (i.e., 50.00). Further evaluation of the varying factor values and resulting HRS site scores, along with further discussion of these three scenarios is presented in section 8.1.c of the Proposal TSD. VII. Summary of Proposed Updates to the HRS (Sections 2, 5, 6, and 7) A. Addition of an SsI Component to the HRS (Sections 2, 5, and 7) 1. Chapter 5 The proposed addition of a subsurface intrusion component is proposed to be added to the existing Soil Exposure pathway as section 5.2 in Chapter 5 to the current HRS. The new pathway name is proposed as the Soil Exposure and Subsurface Intrusion Pathway. The existing method for evaluating the soil exposure threat will remain unchanged. 2. Chapter 2 Evaluations Common to All Pathways is proposed to be updated to reflect the addition of the subsurface intrusion component to the existing soil exposure pathway. The evaluations for the current four pathways remain unchanged and a comparable evaluation will be added for the subsurface intrusion component. 3. Chapter 7 Sites Containing Radioactive Substances currently reflects how radioactive substances are evaluated in the context of the four current HRS pathways. Updates will be made to reflect how radioactive substances are evaluated using the proposed subsurface intrusion component. B. Terminology Updates Affecting Specific Sections of the HRS (Sections 2, 5 and 6) During the development of this proposed addition to the HRS, the agency determined that the following terms should be updated to reflect current terminology and procedures used by EPA in performing risk assessments. 1. Ambient Water Quality Criteria Ambient Water Quality Criteria (AWQC) are now identified also as National Recommended Water Quality Criteria (NRWQC). In addition, the acute AWQC are now identified as the Criterion Maximum Concentration (CMC) and the chronic criteria are referred to as the Criterion Continuous Concentration (CCC). (See section 1.1 of the proposed HRS addition.) These criteria are used to determine the level of threat to environmental targets. 2. Reference Concentrations For inhalation exposures, EPA is adopting the use of Reference Concentrations (RfCs) instead of Reference Doses (RfDs) when determining non-cancer related risk levels. RfCs are used in determining the level of threat to human targets due to possible inhalation and when determining the toxicity of the substances. 3. Cancer Unit Risk For inhalation exposures, EPA is adopting the use of Inhalation Unit Risk (IUR) instead of cancer slope factors in determining cancer-related risk levels. IURs are used in determining the level of threat to human targets due to possible inhalation and when determining the toxicity of the substances. 4. Weight-of-Evidence Groupings The 2005 EPA weight-of-evidence groupings supporting the designation of a substance as a human carcinogen have been incorporated into the HRS algorithm for determining the toxicity factor value. (The former EPA weight-ofevidence categories included as part of the 1990 HRS have been retained as EPA has not yet completed assigning all substances to the revised categories and are doing so at the time the EPA substance literature reviews are updated.) VIII. Statutory and Executive Order Reviews Additional information about these statutes and Executive Orders can be found at A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review This action is a significant regulatory action that was submitted to the Office of Management and Budget (OMB) for review. This action may raise novel legal or policy issues arising out of legal mandates, the President s priorities, or the principles set forth in the EO. Any changes made in response to OMB recommendations have been documented in the docket. EPA prepared an analysis of the potential costs and benefits associated VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 with this action. This analysis, Addition of a Subsurface Intrusion (SsI) Component to the Hazard Ranking System (HRS): Regulatory Impact Analysis is available in the docket for this action. B. Paperwork Reduction Act (PRA) This action does not impose any new information collection burden under the PRA. OMB has previously approved the information collection activities contained in the existing regulations and has assigned OMB control number This proposed regulatory change will only affect how EPA and organizations performing work on behalf of EPA (state or tribal partners) conduct site assessments and HRS scoring at sites where certain environmental conditions exist. This proposed regulatory change will result in data collection at these types of sites to allow evaluation under the HRS. EPA expects that the total number of site assessments performed and the number of sites added to the NPL per year will not increase, but rather expects that there will be a realignment and reprioritization of its internal resources and state cooperative agreement funding. C. Regulatory Flexibility Act (RFA) I certify that this action will not have a significant economic impact on a substantial number of small entities under the RFA. This action will not impose any requirements on small entities. This proposed regulatory change enables the HRS evaluation to directly consider human exposure to hazardous substances that enter building structures through subsurface intrusion. This addition to the HRS would not impose direct impacts on any other entities. For additional discussion on this subject see section 4.9 of the Regulatory Impact Analysis (see the docket for this action). D. Unfunded Mandates Reform Act (UMRA) This action does not contain any unfunded mandate as described in UMRA, 2 U.S.C , and does not significantly or uniquely affect small governments. The action imposes no enforceable duty on any state, local, or tribal governments or the private sector. E. Executive Order 13132: Federalism This action does not have federalism implications. It will not have substantial direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and

403 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 responsibilities among the various levels of government. F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments This action does not have tribal implications, as specified in Executive Order EPA s evaluation of a site using the HRS does not impose any costs on a tribe (except those already in a cooperative agreement relationship with EPA). Thus, Executive Order does not apply to this action. Although Executive Order does not apply to this action, EPA consulted with tribal officials through meetings and correspondence, including a letter sent to all federally recognized tribes asking for comment on the Notice of Opportunity for Public Input that was published in the Federal Register on January 31, 2011 (76 FR 5370), and public listening sessions regarding the decision to proceed with the development of this action. All tribal comments indicated support for this action. EPA specifically solicits additional comment on this proposed action from tribal officials. G. Executive Order 13045: Protection of Children From Environmental Health Risks and Safety Risks EPA interprets Executive Order as applying only to those regulatory actions that concern environmental health or safety risks that EPA has reason to believe may disproportionately affect children, per the definition of covered regulatory action in section of the Executive Order. This action is not subject to Executive Order because it does not concern an environmental health risk or safety risk. H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use This action is not a significant energy action because it is not likely to have a significant adverse effect on the supply, distribution, or use of energy. The site assessment activities affected by this rule are limited in scope and number and rely on existing energy distribution systems. Further, we have concluded that this proposed rule would not significantly expand the energy demand for site assessments, and would not require an entity to conduct any action that would require significant energy use, that would significantly affect energy supply, distribution, or usage. Thus, Executive Order does not apply to this action. I. National Technology Transfer and Advancement Act This rulemaking does not involve technical standards. J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations EPA believes the human health or environmental risk addressed by this action will not have potential disproportionately high and adverse human health or environmental effects on minority, low-income or indigenous populations. The results of this evaluation are contained in section III.C.4 of this preamble and section 4.3 (and all subsections) and Appendix C of the Regulatory Impact Analysis for this proposed rulemaking. A copy of the Addition of a Subsurface Intrusion (SsI) Component to the Hazard Ranking System (HRS): Regulatory Impact Analysis is available in the docket for this action. K. Executive Order 12580: Superfund Implementation Executive Order 12580, section 1(d), states that revisions to the NCP shall be made in consultation with members of the National Response Team (NRT) prior to publication for notice and comment. Revisions shall also be made in consultation with the Director of the Federal Emergency Management Agency (FEMA) and the Nuclear Regulatory Commission (NRC) to avoid inconsistent or duplicative requirements in the emergency planning responsibilities of those agencies. Executive Order delegates responsibility for revision of the NCP to EPA. The agency has complied with Executive Order to the extent that it is related to the addition of a new component to the HRS, through consultation with members of the NRT. List of Subjects in 40 CFR Part 300 Environmental protection, Air pollution control, Chemicals, Hazardous substances, Hazardous waste, Intergovernmental relations, Natural resources, Oil pollution, Penalties, Reporting and recordkeeping requirements, Superfund, Water pollution control, Water supply. Dated: February 3, Gina McCarthy, Administrator. For the reasons set out in the preamble, Title 40, Chapter 1 of the Code of Federal Regulations is proposed to be amended as follows: VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 PART 300 NATIONAL OIL AND HAZARDOUS SUBSTANCES POLLUTION CONTINGENCY PLAN 1. The authority citation for part 300 continues to read as follows: Authority: 33 U.S.C et seq. 2. Amend Appendix A to Part 300: a. In section 1.1 by: i. Amending by removing the definition heading Ambient Water Quality Criteria (AWQC) and adding Ambient Water Quality Criteria (AWQC)/National Recommended Water Quality Criteria, in its place; and removing the text maximum acute or chronic toxicity and adding maximum acute (Criteria Maximum Concentration or CMC) or chronic (Criterion Continuous Concentration or CCC) toxicity. in its place; ii. Adding in alphabetical order the definitions Channelized flow and Crawl space ; iii. Revising the definitions Distance weight and Half-life ; iv. Amending the definition HRS pathway by removing the word soil, and adding soil exposure and subsurface intrusion, in its place; v. Adding in alphabetical order the definitions Indoor air, Inhalation Unit Risk (IUR), Occupied structures, Preferential subsurface intrusion pathways ; and Reference concentration (RfC) ; vi. Revising the definition Reference dose (RfD) ; Screening concentration, and Slope factor (also referred to as cancer potency factor) ; vii. Adding in alphabetical order the definitions Soil gas, Soil porosity ; Subslab, Subsurface Intrusion, Surficial ground water, Unit Risk, and Unsaturated Zone ; and viii. Revising the introductory text of the definition Weight-of-evidence. b. Revising section 2.0 to include sections 2.0 through 2.5.2; c. Revising section 5.0 to include sections 5.0 through 5.3; d. In section 6.0 by revising Table 6 14, entitled Health-Based Benchmarks for Hazardous Substances in Air ; and e. In section 7.0 by: i. Revising the table entitled Table 7 1. HRS Factors Evaluated Differently For Radionuclides ; ii. Under Table 7 1, the second undesignated paragraph, revising the third sentence ; iii. Revising sections 7.1, 7.1.1, and 7.1.2; 7.2.3; 7.2.4; , through ; ; ; 7.3, 7.3.1, and 7.3.2; and iv. Adding section The revisions and additions read as follows:

404 srobinson on DSK5SPTVN1PROD with PROPOSALS Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Appendix A of Part 300 Hazard Ranking System * * * * * 1.1 Definitions * * * * * Channelized flow: Natural geological or manmade features such as karst, fractures, lava tubes, and utility conduits (e.g., sewer lines), which allow ground water and/or soil gas to move through the subsurface environment more easily. * * * * * Crawl space: The enclosed or semienclosed area between a regularly occupied structure s foundation (e.g., pier and beam construction) and the ground surface. Crawl space samples are collected to determine the concentration of hazardous substances in the air beneath a regularly occupied structure. * * * * * Distance weight: Parameter in the HRS air migration pathway, ground water migration pathway, and the soil exposure component of the soil exposure and subsurface intrusion pathway that reduces the point value assigned to targets as their distance increases from the site. [unitless]. * * * * * Half-life: Length of time required for an initial concentration of a substance to be halved as a result of loss through decay. The HRS considers five decay processes for determining surface water persistence: Biodegradation, hydrolysis, photolysis, radioactive decay, and volatilization. The HRS considers two decay processes for determining subsurface intrusion degradation: Biodegradation and hydrolysis. * * * * * Indoor air: The air present within a structure. Inhalation Unit Risk (IUR): The upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent (i.e., hazardous substance) at a concentration of 1mg/m3 in air. * * * * * Occupied structures: Structures with enclosed air space, either where people are present on a regular basis or that were previously occupied but vacated due to a site-related hazardous substance(s). * * * * * Preferential subsurface intrusion pathways: Subsurface features such as animal burrows, cracks in walls, spaces around utility lines or drains through which a hazardous substance moves more easily into a regularly occupied structure. * * * * * Reference concentration (RfC): An estimate of a continuous inhalation exposure to the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime. Reference dose (RfD): An estimate of a daily oral exposure to the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime. * * * * * Screening concentration: Mediaspecific benchmark concentration for a hazardous substance that is used in the HRS for comparison with the concentration of that hazardous substance in a sample from that media. The screening concentration for a specific hazardous substance corresponds to its reference concentration for inhalation exposures or reference dose for oral exposures, as appropriate, and, if the substance is a human carcinogen with either a weightof-evidence classification of A, B, or C, or a weight-of-evidence classification of carcinogenic to humans, likely to be carcinogenic to humans or suggestive evidence of carcinogenic potential, to that concentration that corresponds to its 10 6 individual lifetime excess cancer risk for inhalation exposures or for oral exposures, as appropriate. * * * * * Slope factor (also referred to as cancer potency factor): Estimate of the probability of response (for example, cancer) per unit intake of a substance over a lifetime. The slope factor is typically used to estimate upper-bound probability of an individual developing cancer as a result of exposure to a particular level of a human carcinogen with either a weight-of-evidence classification of A, B, or C, or a weightof-evidence classification of carcinogenic to humans, likely to be carcinogenic to humans or having suggestive evidence of carcinogenic potential. [(mg/kg-day) 1 for nonradioactive substances and (pci) 1 for radioactive substances]. Soil gas: The gaseous elements and compounds in the small spaces between particles of soil. Soil porosity: The degree to which the total volume of soil is permeated with pores or cavities through which fluids (including air or gas) can move. It is typically calculated as the ratio of the pore spaces within the soil to the overall volume of the soil. * * * * * VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 Subslab: The area immediately beneath a regularly occupied structure with a basement foundation or a slabon-grade foundation. Subslab samples are collected to determine the concentration of hazardous substances in the soil gas beneath a home or building. Subsurface Intrusion: The migration of hazardous substances from the unsaturated zone and/or the surficial ground water into overlying structures. Surficial ground water: The uppermost saturated zone, typically unconfined. * * * * * Unit Risk: The upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent (i.e., hazardous substance) at a concentration of 1 mg/l in water, or 1 mg/m 3 in air. Unsaturated Zone: The portion of subsurface between the land surface and the zone of saturation. It extends from the ground surface to the surficial water table (excluding localized or perched water). * * * * * Weight-of-evidence: EPA classification system for characterizing the evidence supporting the designation of a substance as a human carcinogen. The EPA weight-of-evidence groupings, depending on the date EPA updated the profile, include either: * * * * * 2.0 Evaluations Common to Multiple Pathways 2.1 Overview. The HRS site score (S) is the result of an evaluation of four pathways: Ground Water Migration (S gw ). Surface Water Migration (S sw ). Soil Exposure and Subsurface Intrusion (S sessi ). Air Migration (S a ). The ground water and air migration pathways use single threat evaluations, while the surface water migration and soil exposure and subsurface intrusion pathways use multiple threat evaluations. Three threats are evaluated for the surface water migration pathway: Drinking water, human food chain, and environmental. These threats are evaluated for two separate migration components overland/flood migration and ground water to surface water migration. Two components are evaluated for the soil exposure and subsurface intrusion pathway: Soil exposure and subsurface intrusion. The soil exposure component evaluates two threats: Resident population and nearby population, and the subsurface

405 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules intrusion component is a single threat evaluation. The HRS is structured to provide a parallel evaluation for each of these pathways, components and threats. This section focuses on these parallel evaluations, starting with the calculation of the HRS site score and the individual pathway scores Calculation of HRS site score. Scores are first calculated for the individual pathways as specified in sections 2 through 7 and then are combined for the site using the following root-mean-square equation to determine the overall HRS site score, which ranges from 0 to 100: Calculation of pathway score. Table 2 1, which is based on the air migration pathway, illustrates the basic parameters used to calculate a pathway score. As Table 2 1 shows, each pathway (component or threat) score is the product of three factor categories : Likelihood of release, waste characteristics, and targets. (The soil exposure and subsurface intrusion pathway uses likelihood of exposure rather than likelihood of release.) Each of the three factor categories contains a set of factors that are assigned numerical values and combined as specified in sections 2 through 7. The factor values are rounded to the nearest integer, except where otherwise noted Common evaluations. Evaluations common to all four HRS pathways include: Characterizing sources. Identifying sources (and, for the soil exposure and subsurface intrusion pathway, areas of observed contamination, areas of observed exposure and/or areas of subsurface contamination (see sections and 5.2.0)). Identifying hazardous substances associated with each source (or area of observed contamination, or observed exposure, or subsurface contamination). Identifying hazardous substances available to a pathway. TABLE 2 1 SAMPLE PATHWAY SCORESHEET Factor category Maximum value Value assigned Likelihood of Release 1. Observed Release Potential to Release Likelihood of Release (higher of lines 1 and 2) Waste Characteristics 4. Toxicity/Mobility... ( a ) 5. Hazardous Waste Quantity... ( a ) 6. Waste Characteristics Targets 7. Nearest Individual:... 7a. Level I b. Level II c. Potential Contamination d. Nearest Individual (higher of lines 7a, 7b, or 7c) Population... ( b ) 8a. Level I... ( b ) 8b. Level II... ( b ) 8c. Potential Contamination... ( b ) 8d. Total Population (lines 8a+8b+8c). 9. Resources Sensitive Environments... ( b ) 10a. Actual Contamination... ( b ) 10b. Potential Environments... ( b ) 10c. Sensitive Environments (lines 10a+10b)... ( b ) 11. Targets (lines 7d+8d+9+10c)... ( b ) 12. Pathway Score is the product of Likelihood of Release, Waste Characteristics, and Targets, divided by 82,500. Pathway scores are limited to a maximum of 100 points. a Maximum value applies to waste characteristics category. The product of lines 4 and 5 is used in Table 2 7 to derive the value for the waste characteristics factor category. b There is no limit to the human population or sensitive environments factor values. However, the pathway score based solely on sensitive environments is limited to a maximum of 60 points. srobinson on DSK5SPTVN1PROD with PROPOSALS2 Scoring likelihood of release (or likelihood of exposure) factor category. Scoring observed release (or observed exposure or observed contamination). Scoring potential to release when there is no observed release. Scoring waste characteristics factor category. Evaluating toxicity. D Combining toxicity with mobility, persistence, degradation and/or bioaccumulation (or ecosystem bioaccumulation) potential, as appropriate to the pathway (component or threat). VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 D Evaluating hazardous waste quantity. Combining hazardous waste quantity with the other waste characteristics factors. D Determining waste characteristics factor category value. Scoring targets factor category. EP29FE16.029</GPH>

406 10400 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Determining level of contamination for targets. These evaluations are essentially identical for the three migration pathways (ground water, surface water, and air). However, the evaluations differ in certain respects for the soil exposure and subsurface intrusion pathway. Section 7 specifies modifications that apply to each pathway when evaluating sites containing radioactive substances. Section 2 focuses on evaluations common at the pathway, component and threat levels. Note that for the ground water and surface water migration pathways, separate scores are calculated for each aquifer (see section 3.0) and each watershed (see sections and ) when determining the pathway scores for a site. Although the evaluations in section 2 do not vary when different aquifers or watersheds are scored at a site, the specific factor values (for example, observed release, hazardous waste quantity, toxicity/ mobility) that result from these evaluations can vary by aquifer and by watershed at the site. This can occur through differences both in the specific sources and targets eligible to be evaluated for each aquifer and watershed and in whether observed releases can be established for each aquifer and watershed. Such differences in scoring at the aquifer and watershed level are addressed in sections 3 and 4, not section Characterize sources. Source characterization includes identification of the following: Sources (and areas of observed contamination, areas of observed exposure or areas of subsurface contamination) at the site. Hazardous substances associated with these sources (or areas of observed contamination, areas of observed exposure or areas of subsurface contamination). Pathways potentially threatened by these hazardous substances. Table 2 2 presents a sample worksheet for source characterization Identify sources. For the three migration pathways, identify the sources at the site that contain hazardous substances. Identify the migration pathway(s) to which each source applies. For the soil exposure and subsurface intrusion pathway, identify areas of observed contamination, areas of observed exposure, and/or areas of subsurface contamination at the site (see sections and 5.2.0). Table 2 2 Sample Source Characterization Worksheet Source:ll A. Source dimensions and hazardous waste quantity. Hazardous constituent quantity:ll Hazardous wastestream quantity:ll Volume:ll Area:ll Area of observed contamination:ll Area of observed exposure:ll Area of subsurface contamination:ll B. Hazardous substances associated with the source. srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2

407 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 Available to pathway Soil exposure/subsurface intrusion (SESSI) Subsurface intrusion Surface water (SW) Soil exposure Air Ground water (GW) Hazardous substance Area of subsurface contamination Area of observed Resident Nearby exposure GW to SW Gas Particulate Overland/ flood VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2

408 srobinson on DSK5SPTVN1PROD with PROPOSALS Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Identify hazardous substances associated with a source. For each of the three migration pathways, consider those hazardous substances documented in a source (for example, by sampling, labels, manifests, oral or written statements) to be associated with that source when evaluating each pathway. In some instances, a hazardous substance can be documented as being present at a site (for example, by labels, manifests, oral or written statements), but the specific source(s) containing that hazardous substance cannot be documented. For the three migration pathways, in those instances when the specific source(s) cannot be documented for a hazardous substance, consider the hazardous substance to be present in each source at the site, except sources for which definitive information indicates that the hazardous substance was not or could not be present. For an area of observed contamination in the soil exposure component of the soil exposure and subsurface intrusion pathway, consider only those hazardous substances that meet the criteria for observed contamination for that area (see section 5.1.0) to be associated with that area when evaluating the pathway. For an area of observed exposure or area of subsurface contamination (see section 5.2.0) in the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, consider only those hazardous substances that: Meet the criteria for observed exposure, or Meet the criteria for observed release in an area of subsurface contamination and has a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atm-m 3 /mol, or Meet the criteria for an observed release in a structure within, or in a sample from below, an area of observed exposure and has a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atm-m 3 /mol Identify hazardous substances available to a pathway. In evaluating each migration pathway, consider the following hazardous substances available to migrate from the sources at the site to the pathway: Ground water migration. Hazardous substances that meet the criteria for an observed release (see section 2.3) to ground water. Sample Measurement < Sample Quantitation Limit. a No observed release is established. All hazardous substances associated with a source with a ground water containment factor value greater than 0 (see section ). Surface water migration overland/ flood component. Hazardous substances that meet the criteria for an observed release to surface water in the watershed being evaluated. All hazardous substances associated with a source with a surface water containment factor value greater than 0 for the watershed (see sections and ). Surface water migration ground water to surface water component. Hazardous substances that meet the criteria for an observed release to ground water. All hazardous substances associated with a source with a ground water containment factor value greater than 0 (see sections and ). Air migration. Hazardous substances that meet the criteria for an observed release to the atmosphere. All gaseous hazardous substances associated with a source with a gas containment factor value greater than 0 (see section ). All particulate hazardous substances associated with a source with a particulate containment factor value greater than 0 (see section ). For each migration pathway, in those instances when the specific source(s) containing the hazardous substance cannot be documented, consider that hazardous substance to be available to migrate to the pathway when it can be associated (see section 2.2.2) with at least one source having a containment factor value greater than 0 for that pathway. In evaluating the soil exposure and subsurface intrusion pathway, consider the following hazardous substances available to the pathway: Soil exposure component resident population threat. All hazardous substances that meet the criteria for observed contamination at the site (see section 5.1.0). Soil exposure component nearby population threat. All hazardous substances that meet the criteria for observed contamination at areas with an attractiveness/accessibility factor TABLE 2 3 OBSERVED RELEASE CRITERIA FOR CHEMICAL ANALYSIS VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 value greater than 0 (see section ). Subsurface intrusion component. All hazardous substances that meet the criteria for observed exposure at the site (see section 5.2.0). All hazardous substances with a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atm-m 3 /mol that meet the criteria for an observed release in an area of subsurface contamination (see section 5.2.0). All hazardous substances that meet the criteria for an observed release in a structure within, or in a sample from below, an area of observed exposure (see section 5.2.0). 2.3 Likelihood of release. Likelihood of release is a measure of the likelihood that a waste has been or will be released to the environment. The likelihood of release factor category is assigned the maximum value of 550 for a migration pathway whenever the criteria for an observed release are met for that pathway. If the criteria for an observed release are met, do not evaluate potential to release for that pathway. When the criteria for an observed release are not met, evaluate potential to release for that pathway, with a maximum value of 500. The evaluation of potential to release varies by migration pathway (see sections 3, 4 and 6). Establish an observed release either by direct observation of the release of a hazardous substance into the media being evaluated (for example, surface water) or by chemical analysis of samples appropriate to the pathway being evaluated (see sections 3, 4 and 6). The minimum standard to establish an observed release by chemical analysis is analytical evidence of a hazardous substance in the media significantly above the background level. Further, some portion of the release must be attributable to the site. Use the criteria in Table 2 3 as the standard for determining analytical significance. (The criteria in Table 2 3 are also used in establishing observed contamination for the soil exposure component and for establishing areas of observed exposure and areas of subsurface contamination in the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, see section and section 5.2.0). Separate criteria apply to radionuclides (see section 7.1.1).

409 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules TABLE 2 3 OBSERVED RELEASE CRITERIA FOR CHEMICAL ANALYSIS Continued Sample Measurement Sample Quantitation Limit. a An observed release is established as follows: If the background concentration is not detected (or is less than the detection limit), an observed release is established when the sample measurement equals or exceeds the sample quantitation limit. a If the background concentration equals or exceeds the detection limit, an observed release is established when the sample measurement is 3 times or more above the background concentration. a If the sample quantitation limit (SQL) cannot be established, determine if there is an observed release as follows: If the sample analysis was performed under the EPA Contract Laboratory Program, use the EPA contract-required quantitation limit (CRQL) in place of the SQL. If the sample analysis is not performed under the EPA Contract Laboratory Program, use the detection limit (DL) in place of the SQL. srobinson on DSK5SPTVN1PROD with PROPOSALS2 2.4 Waste characteristics. The waste characteristics factor category includes the following factors: Hazardous waste quantity, toxicity, and as appropriate to the pathway or threat being evaluated, mobility, persistence, degradation, and/ or bioaccumulation (or ecosystem bioaccumulation) potential Selection of substance potentially posing greatest hazard. For all pathways (components and threats), select the hazardous substance potentially posing the greatest hazard for the pathway (component or threat) and use that substance in evaluating the waste characteristics category of the pathway (component or threat). For the three migration pathways (and threats), base the selection of this hazardous substance on the toxicity factor value for the substance, combined with its mobility, persistence, and/or bioaccumulation (or ecosystem bioaccumulation) potential factor values, as applicable to the migration pathway (or threat). For the soil exposure component of the soil exposure and subsurface intrusion pathway, base the selection on the toxicity factor alone. For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, base the selection on the toxicity factor value for the substance, combined with its degradation factor value. Evaluation of the toxicity factor is specified in section Use and evaluation of the mobility, persistence, degradation, and/or bioaccumulation (or ecosystem bioaccumulation) potential factors vary by pathway (component or threat) and are specified under the appropriate pathway (component or threat) section. Section identifies the specific factors that are combined with toxicity in evaluating each pathway (component or threat). A or Carcinogenic to humans Toxicity factor. Evaluate toxicity for those hazardous substances at the site that are available to the pathway being scored. For all pathways and threats, except the surface water environmental threat, evaluate human toxicity as specified below. For the surface water environmental threat, evaluate ecosystem toxicity as specified in section Establish human toxicity factor values based on quantitative dose-response parameters for the following three types of toxicity: Cancer Use slope factors (also referred to as cancer potency factors) combined with weight-of-evidence ratings for carcinogenicity for all exposure routes except inhalation. Use inhalation unit risk (IUR) for inhalation exposure. If an inhalation unit risk or a slope factor is not available for a substance, use its ED 10 value to estimate a slope factor as follows: Noncancer toxicological responses of chronic exposure use reference dose (RfD) or reference concentration (RfC) values as applicable. Noncancer toxicological responses of acute exposure use acute toxicity parameters, such as the LD 50. Assign human toxicity factor values to a hazardous substance using Table 2 4, as follows: If RfD/RfC and slope factor/ inhalation unit risk values are available for the hazardous substance, assign the substance a value from Table 2 4 for each. Select the higher of the two values assigned and use it as the overall toxicity factor value for the hazardous substance. If either an RfD/RfC or slope factor/ inhalation unit risk value is available, Carcinogenicity (Human) B or Likely to be carcinogenic to humans Weight-of-evidence a /Slope factor (mg/kg-day) 1 but not both, assign the hazardous substance an overall toxicity factor value from Table 2 4 based solely on the available value (RfD/RfC or slope factor/inhalation unit risk). If neither an RfD/RfC nor slope factor/inhalation unit risk value is available, assign the hazardous substance an overall toxicity factor value from Table 2 4 based solely on acute toxicity. That is, consider acute toxicity in Table 2 4 only when both RfD/RfC and slope factor/iur values are not available. If neither an RfD/RfC, nor slope factor/inhalation unit risk, nor acute toxicity value is available, assign the hazardous substance an overall toxicity factor value of 0 and use other hazardous substances for which information is available in evaluating the pathway. TABLE 2 4 TOXICITY FACTOR EVALUATION Chronic toxicity (Human) Assigned value Reference dose (RfD) (mg/kgday): RfD < , RfD < , RfD < RfD < RfD... 1 RfD not available... 0 Reference concentration (RfC) (mg/m 3 ): RfC < , RfC < , RfC < RfC < RfC... 1 RfC not available... 0 C or Suggestive evidence of carcinogenic potential Assigned value 0.5 SF b... 5 SF SF... 10,000 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 EP29FE16.030</GPH>

410 10404 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Carcinogenicity (Human) A or Carcinogenic to humans B or Likely to be carcinogenic to humans C or Suggestive evidence of carcinogenic potential Assigned value 0.05 SF < SF < SF < ,000 SF < SF < SF < SF < SF < Slope factor not available... Slope factor not available... Slope factor not available... 0 Weight-of-evidence a /Inhalation unit risk (µg/m 3 ) IUR c IUR IUR... 10, IUR < IUR < IUR < ,000 IUR < IUR < IUR < < IUR < Inhalation unit risk not available... Inhalation unit risk not available... Inhalation unit risk not available... 0 a A, B, and C, as well as Carcinogenic to humans, Likely to be carcinogenic to humans, and Suggestive evidence of carcinogenic potential refer to weight-of-evidence categories. Assign substances with a weight-of-evidence category of D (inadequate evidence of carcinogenicity) or E (evidence of lack of carcinogenicity), as well as inadequate information to assess carcinogenic potential and not likely to be carcinogenic to humans a value of 0 for carcinogenicity. b SF = Slope factor. c IUR = Inhalation Unit Risk. Acute Toxicity (Human) Oral LD 50 (mg/kg) Dermal LD 50 (mg/kg) Dust or mist LC 50 (mg/l) Gas or vapor LC 50 (ppm) Assigned value LD 50 < 5... LD 50 < 2... LC 50 < LC 50 < ,000 5 LD 50 < LD 50 < LC 50 < LC 50 < LD 50 < LD 50 < LC 50 < LC 50 <2, LD LD LC ,000 LC LD 50 not available... LD 50 not available... LD 50 not available... LD 50 not available... 0 srobinson on DSK5SPTVN1PROD with PROPOSALS2 If a toxicity factor value of 0 is assigned to all hazardous substances available to a particular pathway (that is, insufficient toxicity data are available for evaluating all the substances), use a default value of 100 as the overall human toxicity factor value for all hazardous substances available to the pathway. For hazardous substances having usable toxicity data for multiple exposure routes (for example, inhalation and ingestion), consider all exposure routes and use the highest assigned value, regardless of exposure route, as the toxicity factor value. For HRS purposes, assign both asbestos and lead (and its compounds) a human toxicity factor value of 10,000. Separate criteria apply for assigning factor values for human toxicity and ecosystem toxicity for radionuclides (see sections and 7.2.2) Hazardous substance selection. For each hazardous substance evaluated for a migration pathway (or threat), combine the human toxicity factor value (or ecosystem toxicity factor value) for the hazardous substance with a mobility, persistence, and/or bioaccumulation (or ecosystem bioaccumulation) potential factor value as follows: Ground water migration. Determine a combined human toxicity/mobility factor value for the hazardous substance (see section 3.2.1). Surface water migration overland/ flood migration component. Determine a combined human toxicity/persistence factor value for the hazardous substance for the drinking water threat (see section ). Determine a combined human toxicity/persistence/bioaccumulation factor value for the hazardous substance for the human food chain threat (see section ). Determine a combined ecosystem toxicity/persistence/bioaccumulation factor value for the hazardous substance for the environmental threat (see section ). Surface water migration ground water to surface water migration component. Determine a combined human toxicity/mobility/persistence factor value for the hazardous substance for the drinking water threat (see section ). Determine a combined human toxicity/mobility/persistence/ bioaccumulation factor value for the hazardous substance for the human food chain threat (see section ). Determine a combined ecosystem toxicity/mobility/persistence/ VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 bioaccumulation factor value for the hazardous substance for the environmental threat (see section ). Air migration. Determine a combined human toxicity/mobility factor value for the hazardous substance (see section 6.2.1). Determine each combined factor value for a hazardous substance by multiplying the individual factor values appropriate to the pathway (or threat). For each migration pathway (or threat) being evaluated, select the hazardous substance with the highest combined factor value and use that substance in evaluating the waste characteristics factor category of the pathway (or threat). For the soil exposure and subsurface intrusion pathway, determine toxicity and toxicity/degradation factor values as follows: Soil exposure and subsurface intrusion soil exposure component. Select the hazardous substance with the highest human toxicity factor value from among the substances that meet the criteria for observed contamination for the threat evaluated and use that substance in evaluating the waste characteristics factor category (see section

411 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS ). Soil exposure and subsurface intrusion subsurface intrusion component. Determine a combined human toxicity/degradation factor value for each hazardous substance being evaluated that: D Meets the criteria for observed exposure, or D Meets the criteria for observed release in an area of subsurface contamination and has a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atmm 3 /mol, or D Meets the criteria for an observed release in a structure within, or in a sample from below, an area of observed exposure and has a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atmm 3 /mol. Select the hazardous substance with the highest combined factor value and use that substance in evaluating the waste characteristics factor category (see sections and ) Hazardous waste quantity. Evaluate the hazardous waste quantity factor by first assigning each source (or area of observed contamination, area of observed exposure or area of subsurface contamination) a source hazardous waste quantity value as specified below. Sum these values to obtain the hazardous waste quantity factor value for the pathway being evaluated. In evaluating the hazardous waste quantity factor for the three migration pathways, allocate hazardous substances and hazardous wastestreams to specific sources in the manner specified in section 2.2.2, except: Consider hazardous substances and hazardous wastestreams that cannot be allocated to any specific source to constitute a separate unallocated source for purposes of evaluating only this factor for the three migration pathways. Do not, however, include a hazardous substance or hazardous wastestream in the unallocated source for a migration pathway if there is definitive information indicating that the substance or wastestream could only have been placed in sources with a containment factor value of 0 for that migration pathway. In evaluating the hazardous waste quantity factor for the soil exposure component of the soil exposure and subsurface intrusion pathway, allocate to each area of observed contamination only those hazardous substances that meet the criteria for observed contamination, for that area of observed contamination and only those hazardous wastestreams that contain hazardous substances that meet the criteria for observed contamination for that area of observed contamination. Do not consider other hazardous substances or hazardous wastestreams at the site in evaluating this factor for the soil exposure component of the soil exposure and subsurface intrusion pathway. In evaluating the hazardous waste quantity factor for the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, allocate to each area of observed exposure or area of subsurface contamination only those hazardous substances and hazardous wastestreams that contain hazardous substances that: Meet the criteria for observed exposure, or Meet the criteria for observed release in an area of subsurface contamination and has a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atm-m 3 /mol, or Meet the criteria for an observed release in a structure within, or in a sample from below, an area of observed exposure and has a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atm-m 3 /mol. Do not consider other hazardous substances or hazardous wastestreams at the site in evaluating this factor for the subsurface intrusion component of the soil exposure and subsurface intrusion pathway. When determining the hazardous waste quantity for multisubunit structures, use the procedures identified in section Source hazardous waste quantity. For each of the three migration pathways, assign a source hazardous waste quantity value to each source (including the unallocated source) having a containment factor value greater than 0 for the pathway being evaluated. Consider the unallocated source to have a containment factor value greater than 0 for each migration pathway. For the soil exposure component of the soil exposure and subsurface intrusion pathway, assign a source hazardous waste quantity value to each area of observed contamination, as applicable to the threat being evaluated. For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, assign a source hazardous waste quantity value to each regularly occupied structure within an area of observed exposure or VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 an area of subsurface contamination that has a structure containment factor value greater than 0. For determining all hazardous waste quantity calculations except for an unallocated source or an area of subsurface contamination, evaluate using the following four measures in the following hierarchy: Hazardous constituent quantity. Hazardous wastestream quantity. Volume. Area. For the unallocated source, use only the first two measures. For an area of subsurface contamination, evaluate nonradioactive hazardous substances using only the last two measures and evaluate radioactive hazardous substances using hazardous wastestream quantity only. See also section 7.0 regarding the evaluation of radioactive substances. Separate criteria apply for assigning a source hazardous waste quantity value for radionuclides (see section 7.2.5) Hazardous constituent quantity. Evaluate hazardous constituent quantity for the source (or area of observed contamination) based solely on the mass of CERCLA hazardous substances (as defined in CERCLA section 101(14), as amended) allocated to the source (or area of observed contamination), except: For a hazardous waste listed pursuant to section 3001 of the Solid Waste Disposal Act, as amended by the Resource Conservation and Recovery Act of 1976 (RCRA), 42 U.S.C et seq., determine its mass for the evaluation of this measure as follows: If the hazardous waste is listed solely for Hazard Code T (toxic waste), include only the mass of constituents in the hazardous waste that are CERCLA hazardous substances and not the mass of the entire hazardous waste. If the hazardous waste is listed for any other Hazard Code (including T plus any other Hazard Code), include the mass of the entire hazardous waste. For a RCRA hazardous waste that exhibits the characteristics identified under section 3001 of RCRA, as amended, determine its mass for the evaluation of this measure as follows: If the hazardous waste exhibits only the characteristic of toxicity (or only the characteristic of EP toxicity), include only the mass of constituents in the hazardous waste that are CERCLA hazardous substances and not the mass of the entire hazardous waste. If the hazardous waste exhibits any other characteristic identified under

412 10406 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules section 3001 (including any other characteristic plus the characteristic of toxicity [or the characteristic of EP toxicity]), include the mass of the entire hazardous waste. Based on this mass, designated as C, assign a value for hazardous constituent quantity as follows: For the migration pathways, assign the source a value for hazardous constituent quantity using the Tier A equation of Table 2 5. For the soil exposure and subsurface intrusion pathway soil exposure component, assign the area of observed contamination a value using the Tier A equation of Table 5 2 (section ). For the soil exposure and subsurface intrusion pathway subsurface intrusion component, assign the area of observed exposure a value using the Tier A equation of Table 5 18 (section ). If the hazardous constituent quantity for the source (or area of observed contamination or area of observed exposure) is adequately determined (that is, the total mass of all CERCLA hazardous substances in the source and releases from the source [or in the area of observed contamination or area of observed exposure] is known or is estimated with reasonable confidence), do not evaluate the other three measures discussed below. Instead assign these other three measures a value of 0 for the source (or area of observed contamination or area of observed exposure) and proceed to section If the hazardous constituent quantity is not adequately determined, assign the source (or area of observed contamination or area of observed exposure) a value for hazardous constituent quantity based on the available data and proceed to section TABLE 2 5 HAZARDOUS WASTE QUANTITY EVALUATION EQUATIONS Tier Measure Units Equation for assigning value a A... Hazardous constituent quantity (C)... lb... C B b... Hazardous wastestream quantity (W)... lb... W/5,000 C b... Volume (V). Landfill... yd 3... V/2,500 Surface impoundment... yd 3... V/2.5 Surface impoundment (buried/backfilled)... yd 3... V/2.5 Drums c... gallon... V/2.5 Tanks and containers other than drums... yd 3... V/2.5 Contaminated soil... yd 3... V/2,500 Pile... yd 3... V/2.5 Other... yd 3... V/2.5 D b... Area (A). Landfill... ft 2... A/3,400 Surface impoundment... ft 2... A/13 Surface impoundment (buried/backfilled)... ft 2... A/13 Land treatment... ft 2... A/270 Pile d... ft 2... A/13 Contaminated soil... ft 2... A/34,000 a Do not round to nearest integer. b Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1 cubic yard = 4 drums = 200 gallons. c If actual volume of drums is unavailable, assume 1 drum = 50 gallons. d Use land surface area under pile, not surface area of pile. srobinson on DSK5SPTVN1PROD with PROPOSALS Hazardous wastestream quantity. Evaluate hazardous wastestream quantity for the source (or area of observed contamination or area of observed exposure) based on the mass of hazardous wastestreams plus the mass of any additional CERCLA pollutants and contaminants (as defined in CERCLA section 101[33], as amended) that are allocated to the source (or area of observed contamination or area of observed exposure). For a wastestream that consists solely of a hazardous waste listed pursuant to section 3001 of RCRA, as amended or that consists solely of a RCRA hazardous waste that exhibits the characteristics identified under section 3001 of RCRA, as amended, include the mass of that entire hazardous waste in the evaluation of this measure. Based on this mass, designated as W, assign a value for hazardous wastestream quantity as follows: For the migration pathways, assign the source a value for hazardous wastestream quantity using the Tier B equation of Table 2 5. For the soil exposure and subsurface intrusion pathway soil exposure component, assign the area of observed contamination a value using the Tier B equation of Table 5 2 (section ). For the soil exposure and subsurface intrusion pathway subsurface intrusion component, assign the area of observed exposure a value using the Tier B equation of Table 5 18 (section ). Do not evaluate the volume and area measures described below if the source VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 is the unallocated source or if the following condition applies: The hazardous wastestream quantity for the source (or area of observed contamination) is adequately determined that is, total mass of all hazardous wastestreams and CERCLA pollutants and contaminants for the source and releases from the source (or for the area of observed contamination) is known or is estimated with reasonable confidence. If the source is the unallocated source or if this condition applies, assign the volume and area measures a value of 0 for the source (or area of observed contamination) and proceed to section Otherwise, assign the source (or area of observed contamination) a value for Hazardous wastestream quantity based on the available data and proceed to section

413 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS Volume. Evaluate the volume measure using the volume of the source (or the volume of the area of observed contamination, area of observed exposure, or area of subsurface contamination). For the soil exposure and subsurface intrusion pathway, restrict the use of the volume measure to those areas of observed contamination, areas of observed exposure, or areas of subsurface contamination as specified in sections and Based on the volume, designated as V, assign a value to the volume measure as follows: For the migration pathways, assign the source a value for volume using the appropriate Tier C equation of Table 2 5. For the soil exposure and subsurface intrusion pathway soil exposure component, assign the area of observed contamination a value for volume using the appropriate Tier C equation of Table 5 2 (section ). For the soil exposure and subsurface intrusion pathway subsurface intrusion component, assign the value based on the volume of the regularly occupied structures within the area of observed exposure or area of subsurface contamination using the Tier C equation of Table 5 18 (section ). If the volume of the source (or volume of the area of observed contamination, area of observed exposure, or area of subsurface contamination, if applicable) can be determined, do not evaluate the area measure. Instead, assign the area measure a value of 0 and proceed to section If the volume cannot be determined (or is not applicable for the soil exposure and subsurface intrusion pathway), assign the source (or area of observed contamination, area of observed exposure, or area of subsurface contamination) a value of 0 for the volume measure and proceed to section Area. Evaluate the area measure using the area of the source (or the area of the area of observed contamination, area of observed exposure, or area of subsurface contamination). Based on this area, designated as A, assign a value to the area measure as follows: For the migration pathways, assign the source a value for area using the appropriate Tier D equation of Table 2 5. For the soil exposure and subsurface intrusion pathway soil exposure component, assign the area of observed contamination a value for area using the appropriate Tier D equation of Table 5 2 (section ). For the soil exposure and subsurface intrusion pathway subsurface intrusion component, assign a value based on the area of regularly occupied structures within the area of observed exposure or area of subsurface contamination using the Tier D equation of Table 5 18 (section ) Calculation of source hazardous waste quantity value. Select the highest of the values assigned to the source (or areas of observed contamination, areas of observed exposure, or areas of subsurface contamination) for the hazardous constituent quantity, hazardous wastestream quantity, volume, and area measures. Assign this value as the source hazardous waste quantity value. Do not round to the nearest integer Calculation of hazardous waste quantity factor value. Sum the source hazardous waste quantity values assigned to all sources (including the unallocated source) or areas of observed contamination, areas of observed exposure, or areas of subsurface contamination for the pathway being evaluated and round this sum to the nearest integer, except: If the sum is greater than 0, but less than 1, round it to 1. Based on this value, select a hazardous waste quantity factor value for the pathway from Table 2 6. TABLE 2 6 HAZARDOUS WASTE QUANTITY FACTOR VALUES Hazardous waste quantity value Assigned value a to b 1 Greater than 100 to 10, Greater than 10,000 to 1,000, ,000 Greater than 1,000, ,000,000 a If the hazardous waste quantity value is greater than 0, but less than 1, round it to 1 as specified in text. b For the pathway, if hazardous constituent quantity is not adequately determined, assign a value as specified in the text; do not assign the value of 1. For a migration pathway, if the hazardous constituent quantity is adequately determined (see section ) for all sources (or all portions of sources and releases remaining after a removal action), assign the value from Table 2 6 as the hazardous waste quantity factor value for the pathway. If the hazardous constituent quantity is not adequately determined for one or more sources (or one or more portions of sources or releases remaining after a removal action) assign a factor value as follows: If any target for that migration pathway is subject to Level I or Level II VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 concentrations (see section 2.5), assign either the value from Table 2 6 or a value of 100, whichever is greater, as the hazardous waste quantity factor value for that pathway. If none of the targets for that pathway is subject to Level I or Level II concentrations, assign a factor value as follows: If there has been no removal action, assign either the value from Table 2 6 or a value of 10, whichever is greater, as the hazardous waste quantity factor value for that pathway. If there has been a removal action: D Determine values from Table 2 6 with and without consideration of the removal action. D If the value that would be assigned from Table 2 6 without consideration of the removal action would be 100 or greater, assign either the value from Table 2 6 with consideration of the removal action or a value of 100, whichever is greater, as the hazardous waste quantity factor value for the pathway. D If the value that would be assigned from Table 2 6 without consideration of the removal action would be less than 100, assign a value of 10 as the hazardous waste quantity factor value for the pathway. For the soil exposure component of the soil exposure and subsurface intrusion pathway, if the hazardous constituent quantity is adequately determined for all areas of observed contamination, assign the value from Table 2 6 as the hazardous waste quantity factor value. If the hazardous constituent quantity is not adequately determined for one or more areas of observed contamination, assign either the value from Table 2 6 or a value of 10, whichever is greater, as the hazardous waste quantity factor value. For the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, if the hazardous constituent quantity is adequately determined for all areas of observed exposure, assign the value from Table 2 6 as the hazardous waste quantity factor value. If the hazardous constituent quantity is not adequately determined for one or more areas of observed exposure, assign either the value from Table 2 6 or assign a factor value as follows: If any target for the subsurface intrusion component is subject to Level I or Level II concentrations (see section 2.5), assign either the value from Table 2 6 or a value of 100, whichever is

414 srobinson on DSK5SPTVN1PROD with PROPOSALS Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules greater, as the hazardous waste quantity factor value for this component. If none of the targets for the subsurface intrusion component is subject to Level I or Level II concentrations and if there has been a removal action, assign a factor value as follows: Determine the values from Table 2 6 with and without consideration of the removal action. If the value that would be assigned from Table 2 6 without consideration of the removal action would be 100 or greater, assign either the value from Table 2 6 with consideration of the removal action or a value of 100, whichever is greater, as the hazardous waste quantity factor value for the component. If the value that would be assigned from Table 2 6 without consideration of the removal action would be less than 100, assign a value of 10 as the hazardous waste quantity factor value for the component. Otherwise, if none of the targets for the subsurface intrusion component is subject to Level I or Level II concentrations and there has not been a removal action, assign a value from Table 2 6 or a value of 10, whichever is greater Waste characteristics factor category value. Determine the waste characteristics factor category value as specified in section for all pathways and threats, except the surface water-human food chain threat and the surface water-environmental threat. Determine the waste characteristics factor category value for these latter two threats as specified in section Factor category value. For the pathway (component or threat) being evaluated, multiply the toxicity or combined factor value, as appropriate, from section and the hazardous waste quantity factor value from section , subject to a maximum product of 1x10 8. Based on this waste characteristics product, assign a waste characteristics factor category value to the pathway (component or threat) from Table 2 7. TABLE 2 7 WASTE CHARACTERISTICS FACTOR CATEGORY VALUES Waste characteristics product Assigned value Greater than 0 to less than to less than 1x x10 2 to less than 1x x10 3 to less than 1x x10 4 to less than 1x x10 5 to less than 1x x10 6 to less than 1x TABLE 2 7 WASTE CHARACTERISTICS FACTOR CATEGORY VALUES Continued Waste characteristics product Assigned value 1x10 7 to less than 1x x10 8 to less than 1x x10 9 to less than 1x x10 10 to less than 1x x10 11 to less than 1x x , Factor category value, considering bioaccumulation potential. For the surface water-human food chain threat and the surface waterenvironmental threat, multiply the toxicity or combined factor value, as appropriate, from section and the hazardous waste quantity factor value from section , subject to: A maximum product of 1x10 12, and A maximum product exclusive of the bioaccumulation (or ecosystem bioaccumulation) potential factor of 1x Based on the total waste characteristics product, assign a waste characteristics factor category value to these threats from Table Targets. The types of targets evaluated include the following: Individual (factor name varies by pathway, component, and threat). Human population. Resources (these vary by pathway, component, and threat). Sensitive environments (included for the surface water migration pathway, air migration pathway, and soil exposure component of the soil exposure and subsurface intrusion pathway). The factor values that may be assigned to each type of target have the same range for each pathway for which that type of target is evaluated. The factor value for most types of targets depends on whether the target is subject to actual or potential contamination for the pathway and whether the actual contamination is Level I or Level II: Actual contamination: Target is associated either with a sampling location that meets the criteria for an observed release (or observed contamination or observed exposure) for the pathway or with an observed release based on direct observation for the pathway (additional criteria apply for establishing actual contamination for the human food chain threat in the surface water migration pathway, see sections and ). Sections 3 through 6 specify how to determine the targets associated with a sampling location or with an observed release VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 based on direct observation. Determine whether the actual contamination is Level I or Level II as follows: Level I: D Media-specific concentrations for the target meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway and are at or above media-specific benchmark values. These benchmark values (see section 2.5.2) include both screening concentrations and concentrations specified in regulatory limits (such as Maximum Contaminant Level (MCL) values), or D For the human food chain threat in the surface water migration pathway, concentrations in tissue samples from aquatic human food chain organisms are at or above benchmark values. Such tissue samples may be used in addition to media-specific concentrations only as specified in sections and Level II: D Media-specific concentrations for the target meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway, but are less than media-specific benchmarks. If none of the hazardous substances eligible to be evaluated for the sampling location has an applicable benchmark, assign Level II to the actual contamination at the sampling location, or D For observed releases or observed exposures based on direct observation, assign Level II to targets as specified in sections 3, 4, 5, and 6, or D For the human food chain threat in the surface water migration pathway, concentrations in tissue samples from aquatic human food chain organisms, when applicable, are below benchmark values. If a target is subject to both Level I and Level II concentrations for a pathway (or threat), evaluate the target using Level I concentrations for that pathway (or threat). Potential contamination: Target is subject to a potential release (that is, target is not associated with actual contamination for that pathway or threat). Assign a factor value for individual risk as follows (select the highest value that applies to the pathway or threat): 50 points if any individual is exposed to Level I concentrations. 45 points if any individual is exposed to Level II concentrations.

415 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 Maximum of 20 points if any individual is subject to potential contamination. The value assigned is 20 unless reduced by a distance or dilution weight appropriate to the pathway. Assign factor values for population and sensitive environments as follows: Sum Level I targets and multiply by 10. (Level I is not used for sensitive environments in the soil exposure component of the soil exposure and subsurface intrusion and air migration pathways.) Sum Level II targets. Multiply potential targets in all but the soil exposure and subsurface intrusion pathway by distance or dilution weights appropriate to the pathway, sum, and divide by 10. Distance or dilution weighting accounts for diminishing exposure with increasing distance or dilution within the different pathways. For targets within an area of subsurface contamination in the subsurface intrusion component of the soil exposure and subsurface intrusion pathway, multiply by a weighting factor as directed in section Sum the values for the three levels. In addition, resource value points are assigned within all pathways for welfare-related impacts (for example, impacts to agricultural land), but do not depend on whether there is actual or potential contamination Determination of level of actual contamination at a sampling location. Determine whether Level I concentrations or Level II concentrations apply at a sampling location (and thus to the associated targets) as follows: Select the benchmarks applicable to the pathway (component or threat) being evaluated. Compare the concentrations of hazardous substances in the sample (or comparable samples) to their benchmark concentrations for the pathway (component or threat), as specified in section Determine which level applies based on this comparison. If none of the hazardous substances eligible to be evaluated for the sampling location has an applicable benchmark, assign Level II to the actual contamination at that sampling location for the pathway (component or threat). In making the comparison, consider only those samples, and only those hazardous substances in the sample, that meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway, except: Tissue samples from aquatic human food chain organisms may also be used as specified in sections and of the surface water-human food chain threat. If any hazardous substance is present in more than one comparable sample for the sampling location, use the highest concentration of that hazardous substance from any of the comparable samples in making the comparisons. Treat sets of samples that are not comparable separately and make a separate comparison for each such set Comparison to benchmarks. Use the following media-specific benchmarks for making the comparisons for the indicated pathway (or threat): Maximum Contaminant Level Goals (MCLGs) ground water migration pathway and drinking water threat in surface water migration pathway. Use only MCLG values greater than 0. Maximum Contaminant Levels (MCLs) ground water migration pathway and drinking water threat in surface water migration pathway. Food and Drug Administration Action Level (FDAAL) for fish or shellfish human food chain threat in surface water migration pathway. EPA Ambient Water Quality Criteria (AWQC/National Recommended Water Quality Criteria) for protection of aquatic life environmental threat in surface water migration pathway. EPA Ambient Aquatic Life Advisory Concentrations (AALAC) environmental threat in surface water migration pathway. National Ambient Air Quality Standards (NAAQS) air migration pathway. National Emission Standards for Hazardous Air Pollutants (NESHAPs) air migration pathway. Use only those NESHAPs promulgated in ambient concentration units. Screening concentration for cancer corresponding to that concentration that corresponds to the 10 6 individual cancer risk for inhalation exposures (air migration pathway or subsurface intrusion component of the soil exposure and subsurface intrusion pathway) or for oral exposures (ground water migration pathway; drinking water and human food chain threats in surface water migration pathway; and soil exposure and subsurface intrusion pathway). Screening concentration for noncancer toxicological responses corresponding to the RfC for inhalation exposures (air migration pathway and subsurface intrusion component of the soil exposure and subsurface intrusion pathway) or RfD for oral exposures (ground water migration pathway; drinking water and human food chain threats in surface water migration VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 pathway; and soil exposure and subsurface intrusion pathway). Select the benchmark(s) applicable to the pathway (component or threat) being evaluated as specified in sections 3 through 6. Compare the concentration of each hazardous substance from the sampling location to its benchmark concentration(s) for that pathway (component or threat). Use only those samples and only those hazardous substances in the sample that meet the criteria for an observed release (or observed contamination or observed exposure) for the pathway, except: Tissue samples from aquatic human food chain organisms may be used as specified in sections and If the concentration of any applicable hazardous substance from any sample equals or exceeds its benchmark concentration, consider the sampling location to be subject to Level I concentrations for that pathway (or threat). If more than one benchmark applies to the hazardous substance, assign Level I if the concentration of the hazardous substance equals or exceeds the lowest applicable benchmark concentration. If no hazardous substance individually equals or exceeds its benchmark concentration, but more than one hazardous substance either meets the criteria for an observed release (or observed contamination or observed exposure) for the sample (or comparable samples) or is eligible to be evaluated for a tissue sample (see sections and ), calculate the indices I and J specified below based on these hazardous substances. For those hazardous substances that are carcinogens (that is, those having either a carcinogen weight-of-evidence classification of A, B, or C or a weightof-evidence classification of carcinogenic to humans, likely to be carcinogenic to humans, or suggestive evidence of carcinogenic potential), calculate an index I for the sample location as follows: Where: C i = Concentration of hazardous substance i in sample (or highest concentration of hazardous substance i from among comparable samples). SC i = Screening concentration for cancer corresponding to that concentration that corresponds to its 10 6 individual cancer risk for applicable exposure (inhalation or oral) for hazardous substance i. n = Number of applicable hazardous substances in sample (or comparable EP29FE16.031</GPH>

416 10410 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules samples) that are carcinogens and for which an SC i is available. For those hazardous substances for which an RfD or RfC is available, calculate an index J for the sample location as follows: Where: C j = Concentration of hazardous substance j in sample (or highest concentration of hazardous substance j from among comparable samples). CR j = Screening concentration for noncancer toxicological responses corresponding to RfD or RfC for applicable exposure (inhalation or oral) for hazardous substance j. m = Number of applicable hazardous substances in sample (or comparable samples) for which a CR j is available. If either I or J equals or exceeds 1, consider the sampling location to be subject to Level I concentrations for that pathway (component or threat). If both I and J are less than 1, consider the sampling location to be subject to Level II concentrations for that pathway (component or threat). If, for the sampling location, there are sets of samples that are not comparable, calculate I and J separately for each such set, and use the highest calculated values of I and J to assign Level I and Level II. See sections and for criteria for determining the level of contamination for radioactive substances. * * * * * 5.0 Soil Exposure and Subsurface Intrusion Pathway 5.0. Exposure components. Evaluate the soil exposure and subsurface intrusion pathway based on two exposure components: Soil exposure component (see section 5.1). Subsurface intrusion component (see section 5.2). Score one or both components considering their relative importance. If only one component is scored, assign its score as the soil exposure and subsurface intrusion pathway score. If both components are scored, sum the two scores and assign it as the soil exposure and subsurface intrusion pathway score, subject to a maximum of 100. srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 EP29FE16.032</GPH>

417 srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 5.1 Soil exposure component. Evaluate the soil exposure component based on two threats: Resident population threat and nearby population threat. Evaluate both threats based on three factor categories: Soil Exposure Component Subsurface Intrusion Component Resident Population + Nearby Population Figure 5-1 Overview of the Soil Exposure and Subsurface Intrusion Pathway Likelihood of Exposure (LE) Observed Contamination Area with Resident Targets Likelihood of Exposure (LE) Attractiveness/ Accessibility Area of Contamination Likelihood of Exposure (LE) Observed Exposure Potential for Exposure Structure Containment Depth to Contamination Vertical Migration Vapor Migration Potential X I X I X Waste Characteristics (WC) Toxicity Chronic Carcinogenic Acute Hazardous Waste Quantity Hazardous Constituent Quantity Hazardous Wastestream Quantity Volume Area Waste Characteristics (WC) Toxicity Chronic Carcinogenic Acute Hazardous Waste Quantity Hazardous Constituent Quantity Hazardous Wastestream Quantity Volume Area + Waste Characteristics (WC) Toxicity Chronic Carcinogenic Acute Degradation Hazardous Waste Quantity Hazardous Constituent Quantity Hazardous Wastestream Quantity Volume Area Targets (T) Resident Individual X I Resident Population Level I Concentrations Level II Concentrations Workers Resources Terrestrial Sensitive Environments Targets (T) Nearby Individual X I Population Within One Mile X Targets (T) Exposed Individual Population Level I Concentrations Level II Concentrations Population on ASC Resources Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules EP29FE16.033</GPH>

418 10412 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Likelihood of exposure, waste characteristics, and targets. Figure 5 1 indicates the factors included within each factor category for each type of threat. Determine the soil exposure component score (S se ) in terms of the factor category values as follows: Where: LE i = Likelihood of exposure factor category value for threat i (that is, resident population threat or nearby population threat). WC i = Waste characteristics factor category value for threat i. T i = Targets factor category value for threat i. SF = Scaling factor. Table 5 1 outlines the specific calculation procedure. TABLE 5 1 SOIL EXPOSURE COMPONENT SCORESHEET Factor categories and factors Resident Population Threat Maximum value Value assigned Likelihood of Exposure 1. Likelihood of Exposure Waste Characteristics 2. Toxicity... ( a ) Hazardous Waste Quantity... ( a ) Waste Characteristics Targets 5. Resident Individual Resident Population: 6a. Level I Concentrations ( b )... 6b. Level II Concentrations ( b )... 6c. Resident Population (lines 6a + 6b) ( b ) Workers Resources Terrestrial Sensitive Environments... (c) Targets (lines 5 + 6c )... ( b )... Resident Population Threat Score 11. Resident Population Threat (lines 1x4x10)... ( b )... Nearby Population Threat Likelihood of Exposure 12. Attractiveness/Accessibility Area of Contamination Likelihood of Exposure Waste Characteristics 15. Toxicity... ( a ) Hazardous Waste Quantity... ( a ) Waste Characteristics Targets 18. Nearby Individual Population Within 1 Mile... ( b ) Targets (lines )... ( b )... Nearby Population Threat Score 21. Nearby Population Threat (lines 14x17x20)... ( b )... Soil Exposure Component Score 22. Soil Exposure Component Score d (S se), (lines [11+21]/82,500, subject to a maximum of 100) a Maximum value applies to waste characteristics category. b Maximum value not applicable. c No specific maximum value applies to factor. However, pathway score based solely on terrestrial sensitive environments is limited to maximum of 60. d Do not round to nearest integer. srobinson on DSK5SPTVN1PROD with PROPOSALS General considerations. Evaluate the soil exposure component based on areas of observed contamination: Consider observed contamination to be present at sampling locations where analytic evidence indicates that: A hazardous substance attributable to the site is present at a concentration significantly above background levels for the site (see Table 2 3 in section 2.3 for the criteria for determining analytical significance), and This hazardous substance, if not present at the surface, is covered by 2 feet or less of cover material (for example, soil). Establish areas of observed contamination based on sampling locations at which there is observed contamination as follows: For all sources except contaminated soil, if observed contamination from the site is present at any sampling location within the source, consider VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 that entire source to be an area of observed contamination. For contaminated soil, consider both the sampling location(s) with observed contamination from the site and the area lying between such locations to be an area of observed contamination, unless available information indicates otherwise. If an area of observed contamination (or portion of such an area) is covered by a permanent, or otherwise maintained, essentially EP29FE16.034</GPH>

419 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules impenetrable material (for example, asphalt) that is not more than 2 feet thick, exclude that area (or portion of the area) in evaluating the soil exposure component. For an area of observed contamination, consider only those hazardous substances that meet the criteria for observed contamination for that area to be associated with that area in evaluating the soil exposure component (see section 2.2.2). If there is observed contamination, assign scores for the resident population threat and the nearby population threat, as specified in sections and If there is no observed contamination, assign the soil exposure component of the soil exposure and subsurface intrusion pathway a score of Resident population threat. Evaluate the resident population threat only if there is an area of observed contamination in one or more of the following locations: Within the property boundary of a residence, school, or day care center and within 200 feet of the respective residence, school, or day care center, or Within a workplace property boundary and within 200 feet of a workplace area, or Within the boundaries of a resource specified in section , or Within the boundaries of a terrestrial sensitive environment specified in section If not, assign the resident population threat a value of 0, enter this value in Table 5 1, and proceed to the nearby population threat (section 5.1.2) Likelihood of exposure. Assign a value of 550 to the likelihood of exposure factor category for the resident population threat if there is an area of observed contamination in one or more locations listed in section Enter this value in Table Waste characteristics. Evaluate waste characteristics based on two factors: Toxicity and hazardous waste quantity. Evaluate only those hazardous substances that meet the criteria for observed contamination at the site (see section 5.1.0) Toxicity. Assign a toxicity factor value to each hazardous substance as specified in section Use the hazardous substance with the highest toxicity factor value to assign the value to the toxicity factor for the resident population threat. Enter this value in Table Hazardous waste quantity. Assign a hazardous waste quantity factor value as specified in section In estimating the hazardous waste quantity, use Table 5 2 and: Consider only the first 2 feet of depth of an area of observed contamination, except as specified for the volume measure. Use the volume measure (see section ) only for those types of areas of observed contamination listed in Tier C of Table 5 2. In evaluating the volume measure for these listed areas of observed contamination, use the full volume, not just the volume within the top 2 feet. Use the area measure (see section ), not the volume measure, for all other types of areas of observed contamination, even if their volume is known. Enter the value assigned in Table 5 1. TABLE 5 2 HAZARDOUS WASTE QUANTITY EVALUATION EQUATIONS FOR SOIL EXPOSURE COMPONENT Tier Measure Units Equation for assigning value a A... Hazardous Constituent Quantity (C)... lb... C B b... Hazardous Wastestream Quantity (W)... lb... W/5,000 C b... Volume (V). Surface Impoundment c... yd 3... V/2.5 Drums d... gallon... V/500 Tanks and Containers Other Than Drums... yd 3... V/2.5 D b... Area (A). Landfill... ft 2... A/34,000 Surface Impoundment... ft 2... A/13 Surface Impoundment (Buried/backfilled)... ft 2... A/13 Land treatment... ft 2... A/270 Pile e... ft 2... A/34 Contaminated Soil... ft 2... A/34,000 a Do not round nearest integer. b Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1 cubic yard = 4 drums = 200 gallons. c Use volume measure only for surface impoundments containing hazardous substances present as liquids. Use area measures in Tier D for dry surface impoundments and for buried/backfilled surface impoundments. d If actual volume of drums is unavailable, assume 1 drum = 50 gallons. e Use land surface area under pile, not surface area of pile. srobinson on DSK5SPTVN1PROD with PROPOSALS Calculation of waste characteristics factor category value. Multiply the toxicity and hazardous waste quantity factor values, subject to a maximum product of Based on this product, assign a value from Table 2 7 (section ) to the waste characteristics factor category. Enter this value in Table Targets. Evaluate the targets factor category for the resident population threat based on five factors: Resident individual, resident population, workers, resources, and terrestrial sensitive environments. In evaluating the targets factor category for the resident population threat, count only the following as targets: Resident individual a person living or attending school or day care on a property with an area of observed contamination and whose residence, school, or day care center, respectively, is on or within 200 feet of the area of observed contamination. VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 Worker a person working on a property with an area of observed contamination and whose workplace area is on or within 200 feet of the area of observed contamination. Resources located on an area of observed contamination, as specified in section Terrestrial sensitive environments located on an area of observed contamination, as specified in section Resident individual. Evaluate this factor based on whether

420 10414 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules there is a resident individual, as specified in section , who is subject to Level I or Level II concentrations. First, determine those areas of observed contamination subject to Level I concentrations and those subject to Level II concentrations as specified in sections and Use the healthbased benchmarks from Table 5 3 in determining the level of contamination. Then assign a value to the resident individual factor as follows: Assign a value of 50 if there is at least one resident individual for one or more areas subject to Level I concentrations. Assign a value of 45 if there is no such resident individuals, but there is at least one resident individual for one or more areas subject to Level II concentrations. Assign a value of 0 if there is no resident individual. Enter the value assigned in Table Resident population. Evaluate resident population based on two factors: Level I concentrations and Level II concentrations. Determine which factor applies as specified in sections and 2.5.2, using the health-based benchmarks from Table 5 3. Evaluate populations subject to Level I concentrations as specified in section and populations subject to Level II concentrations as specified in section TABLE 5 3 HEALTH-BASED BENCHMARKS FOR HAZARDOUS SUBSTANCES IN SOILS Screening concentration for cancer corresponding to that concentration that corresponds to the 10 6 individual cancer risk for oral exposures. Screening concentration for noncancer toxicological responses corresponding to the Reference Dose (RfD) for oral exposures. Count only those persons meeting the criteria for resident individual as specified in section In estimating the number of people living on property with an area of observed contamination, when the estimate is based on the number of residences, multiply each residence by the average number of persons per residence for the county in which the residence is located Level I concentrations. Sum the number of resident individuals subject to Level I concentrations and multiply this sum by 10. Assign the resulting product as the value for this factor. Enter this value in Table Level II concentrations. Sum the number of resident individuals subject to Level II concentrations. Do not include those people already counted under the Level I concentrations factor. Assign this sum as the value for this factor. Enter this value in Table Calculation of resident population factor value. Sum the factor values for Level I concentrations and Level II concentrations. Assign this sum as the resident population factor value. Enter this value in Table Workers. Evaluate this factor based on the number of workers that meet the section criteria. Assign a value for these workers using Table 5 4. Enter this value in Table 5 1. TABLE 5 4 FACTOR VALUES FOR WORKERS Number of workers Assigned value to to 1, Greater than 1, Resources. Evaluate the resources factor as follows: Assign a value of 5 to the resources factor if one or more of the following is present on an area of observed contamination at the site: Commercial agriculture. Commercial silviculture. Commercial livestock production or commercial livestock grazing. Assign a value of 0 if none of the above are present. Enter the value assigned in Table Terrestrial sensitive environments. Assign value(s) from Table 5 5 to each terrestrial sensitive environment that meets the eligibility criteria of section Calculate a value (ES) for terrestrial sensitive environments as follows: where: S i=value(s) assigned from Table 5 5 to terrestrial sensitive environment i. n=number of terrestrial sensitive environments meeting section criteria. Because the pathway score based solely on terrestrial sensitive environments is limited to a maximum of 60, determine the value for the terrestrial sensitive environments factor as follows: TABLE 5 5 TERRESTRIAL SENSITIVE ENVIRONMENTS RATING VALUES Terrestrial sensitive environments Assigned value srobinson on DSK5SPTVN1PROD with PROPOSALS2 Terrestrial critical habitat a for Federal designated endangered or threatened species National Park Designated Federal Wilderness Area National Monument Terrestrial habitat known to be used by Federal designated or proposed threatened or endangered species National Preserve (terrestrial) National or State Terrestrial Wildlife Refuge Federal land designated for protection of natural ecosystems Administratively proposed Federal Wilderness Area Terrestrial areas utilized for breeding by large or dense aggregations of animals b Terrestrial habitat known to be used by State designated endangered or threatened species Terrestrial habitat known to be used by species under review as to its Federal designated endangered or threatened status State lands designated for wildlife or game management State designated Natural Areas Particular areas, relatively small in size, important to maintenance of unique biotic communities a Critical habitat as defined in 50 CFR VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 EP29FE16.035</GPH>

421 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules b Limit to vertebrate species. Multiply the values assigned to the resident population threat for likelihood of exposure (LE), waste characteristics (WC), and ES. Divide the product by 82,500. If the result is 60 or less, assign the value ES as the terrestrial sensitive environments factor value. If the result exceeds 60, calculate a value EC as follows: Assign the value EC as the terrestrial sensitive environments factor value. Do not round this value to the nearest integer. Enter the value assigned for the terrestrial sensitive environments factor in Table Calculation of resident population targets factor category value. Sum the values for the resident individual, resident population, workers, resources, and terrestrial sensitive environments factors. Do not round to the nearest integer. Assign this sum as the targets factor category value for the resident population threat. Enter this value in Table Calculation of resident population threat score. Multiply the values for likelihood of exposure, waste characteristics, and targets for the resident population threat, and round the product to the nearest integer. Assign this product as the resident population threat score. Enter this score in Table Nearby population threat. Include in the nearby population only those individuals who live or attend school within a 1-mile travel distance of an area of observed contamination at the site and who do not meet the criteria for resident individual as specified in section Do not consider areas of observed contamination that have an attractiveness/accessibility factor value of 0 (see section ) in evaluating the nearby population threat Likelihood of exposure. Evaluate two factors for the likelihood of exposure factor category for the nearby population threat: Attractiveness/accessibility and area of contamination Attractiveness/ accessibility. Assign a value for attractiveness/accessibility from Table 5 6 to each area of observed contamination, excluding any land used for residences. Select the highest value assigned to the areas evaluated and use it as the value for the attractiveness/ accessibility factor. Enter this value in Table Area of contamination. Evaluate area of contamination based on the total area of the areas of observed contamination at the site. Count only the area(s) that meet the criteria in section and that receive an attractiveness/accessibility value greater than 0. Assign a value to this factor from Table 5 7. Enter this value in Table 5 1. TABLE 5 6 ATTRACTIVENESS/ACCESSIBILITY VALUES Area of observed contamination Assigned value Designated recreational area Regularly used for public recreation (for example, fishing, hiking, softball) Accessible and unique recreational area (for example, vacant lots in urban area) Moderately accessible (may have some access improvements, for example, gravel road), with some public recreation use Slightly accessible (for example, extremely rural area with no road improvement), with some public recreation use Accessible, with no public recreation use Surrounded by maintained fence or combination of maintained fence and natural barriers... 5 Physically inaccessible to public, with no evidence of public recreation use... 0 TABLE 5 7 AREA OF CONTAMINATION FACTOR VALUES Total area of the areas of observed contamination (square feet) Assigned value Less than or equal to 5, Greater than 5,000 to 125, Greater than 125,000 to 250, Greater than 250,000 to 375, Greater than 375,000 to 500, Greater than 500, Likelihood of exposure factor category value. Assign a value from Table 5 8 to the likelihood of exposure factor category, based on the values assigned to the attractiveness/ accessibility and area of contamination factors. Enter this value in Table 5 1. srobinson on DSK5SPTVN1PROD with PROPOSALS2 Area of contamination factor value TABLE 5 8 NEARBY POPULATION LIKELIHOOD OF EXPOSURE FACTOR VALUES Attractiveness/accessibility factor value VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 EP29FE16.036</GPH>

422 10416 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules TABLE 5 8 NEARBY POPULATION LIKELIHOOD OF EXPOSURE FACTOR VALUES Continued Area of contamination factor value Attractiveness/accessibility factor value Waste characteristics. Evaluate waste characteristics based on two factors: Toxicity and hazardous waste quantity. Evaluate only those hazardous substances that meet the criteria for observed contamination (see section 5.1.0) at areas that can be assigned an attractiveness/accessibility factor value greater than Toxicity. Assign a toxicity factor value as specified in section to each hazardous substance meeting the criteria in section Use the hazardous substance with the highest toxicity factor value to assign the value to the toxicity factor for the nearby population threat. Enter this value in Table Hazardous waste quantity. Assign a value to the hazardous waste quantity factor as specified in section , except: Consider only those areas of observed contamination that can be assigned an attractiveness/ accessibility factor value greater than 0. Enter the value assigned in Table Calculation of waste characteristics factor category value. Multiply the toxicity and hazardous waste quantity factor values, subject to a maximum product of Based on this product, assign a value from Table 2 7 (section ) to the waste characteristics factor category. Enter this value in Table Targets. Evaluate the targets factory category for the nearby population threat based on two factors: Nearby individual and population within a 1-mile travel distance from the site Nearby individual. If one or more persons meet the section criteria for a resident individual, assign this factor a value of 0. Enter this value in Table 5 1. If no person meets the criteria for a resident individual, determine the shortest travel distance from the site to any residence or school. In determining the travel distance, measure the shortest overland distance an individual would travel from a residence or school to the nearest area of observed contamination for the site with an attractiveness/ accessibility factor value greater than 0. If there are no natural barriers to travel, measure the travel distance as the shortest straight-line distance from the residence or school to the area of observed contamination. If natural barriers exist (for example, a river), measure the travel distance as the shortest straight-line distance from the residence or school to the nearest crossing point and from there as the shortest straight-line distance to the area of observed contamination. Based on the shortest travel distance, assign a value from Table 5 9 to the nearest individual factor. Enter this value in Table 5 1. TABLE 5 9 NEARBY INDIVIDUAL FACTOR VALUES Travel distance for nearby individual (miles) Greater than 0 to a 1 Greater than 1 4 to Assigned value a Assign a value of 0 if one or more persons meet the section criteria for resident individual Population within 1 mile. Determine the population within each travel distance category of Table Count residents and students who attend school within this travel distance. Do not include those people already counted in the resident population threat. Determine travel distances as specified in section In estimating residential population, when the estimate is based on the number of residences, multiply each residence by the average number of persons per residence for the county in which the residence is located. Based on the number of people included within a travel distance category, assign a distance-weighted population value for that travel distance from Table Calculate the value for the population within 1 mile factor (PN) as follows: Where: W i = Distance-weighted population value from Table 5 10 for travel distance category i. If PN is less than 1, do not round it to the nearest integer; if PN is 1 or more, round to the nearest integer. Enter this value in Table Calculation of nearby population targets factor category value. Sum the values for the nearby individual factor and the population within 1 mile factor. Do not round this sum to the nearest integer. Assign this sum as the targets factor category value for the nearby population threat. Enter this value in Table 5 1. srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 EP29FE16.037</GPH>

423 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 TABLE 5 10 DISTANCE WEIGHTED POPULATION VALUES FOR NEARBY POPULATION THREAT a Number of people within the travel distance category 300,001 to 1,000, ,001 to 300,000 30,001 to 100,000 10,001 to 30,000 3,001 to 10,000 1,001 to 3, to 1, to to to 30 1 to 10 0 Travel distance category (miles) Greater than 0 to ,303 4,081 13,034 Greater than 1 4 to ,041 6,517 Greater than 1 2 to ,020 3,258 a Round the number of people present within a travel distance category to nearest integer. Do not round the assigned distance-weighted population value to nearest integer. VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2

424 10418 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Calculation of nearby population threat score. Multiply the values for likelihood of exposure, waste characteristics, and targets for the nearby population threat, and round the product to the nearest integer. Assign this product as the nearby population threat score. Enter this score in Table Calculation of soil exposure component score. Sum the resident population threat score and the nearby population threat score, and divide the sum by 82,500. Assign the resulting value, subject to a maximum of 100, as the soil exposure component score (S se ). Enter this score in Table Subsurface intrusion component. Evaluate the subsurface intrusion component based on three factor categories: Likelihood of exposure, waste characteristics, and targets. Figure 5 1 indicates the factors included within each factor category for the subsurface intrusion component. Determine the component score (S ssi ) in terms of the factor category values as follows: Where: LE = Likelihood of exposure factor category value. WC = Waste characteristics factor category value. T = Targets factor category value. SF = Scaling factor. Table 5 11 outlines the specific calculation procedure. TABLE 5 11 SUBSURFACE INTRUSION COMPONENT SCORESHEET Factor categories and factors Subsurface Intrusion Component Maximum value Value assigned Likelihood of Exposure: 1. Observed Exposure Potential for Exposure: 2a. Structure Containment b. Depth to contamination c. Vertical Migration d. Vapor Migration Potential Potential for Exposure (lines 2a * (2b + 2c + 2d), subject to a maximum of 500) Likelihood of Exposure (higher of lines 1 or 3) Waste Characteristics: 5. Toxicity/Degradation... (a) 6. Hazardous Waste Quantity... (a) 7. Waste Characteristics (subject to a maximum of 100) Targets: 8. Exposed Individual Population:. 9a. Level I Concentrations... (b) 9b. Level II Concentrations... (b) 9c. Population within an Area of Subsurface Contamination... (b) 9d. Total Population (lines 9a + 9b + 9c)... (b) 10. Resources Targets (lines 8 + 9d + 10)... (b) Subsurface Intrusion Component Score: 12. Subsurface Intrusion Component (lines )/82,500 c (subject to a maximum of 100) Soil Exposure and Subsurface Intrusion Pathway Score: 13. Soil Exposure Component + Subsurface Intrusion Component (subject to a maximum of 100) a Maximum value applies to waste characteristics category. b Maximum value not applicable. c Do not round to the nearest integer. srobinson on DSK5SPTVN1PROD with PROPOSALS General considerations. The subsurface intrusion component evaluates the threats from hazardous substances that have or could intrude into regularly occupied structures via surficial ground water or the unsaturated zone. Evaluate the subsurface intrusion component based on the actual or potential intrusion of hazardous substances into a regularly occupied structures that has structure containment value greater than zero; or actual or potential intrusion of hazardous substances exists in the unsaturated zone or the surficial ground water below the regularly occupied structures. These structures may or may not have subunits. Subunits are partitioned areas within a structure with separate heating, ventilating, and air conditioning (HVAC) systems or distinctly different air exchange rates. Subunits include regularly occupied partitioned tenant spaces such as office suites, apartments, condos, common or shared areas, and portions of residential, commercial or industrial structures with separate heating, ventilating, and air conditioning (HVAC) systems. In evaluating the subsurface intrusion component, consider the following: Area(s) of observed exposure: An area of observed exposure is delineated by regularly occupied structures with documented contamination meeting observed exposure criteria; an area of observed exposure includes regularly occupied structures with samples VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 meeting observed exposure criteria or inferred to be within an area of observed exposure based on samples meeting observed exposure criteria (see section Observed Exposure). Establish areas of observed exposure as follows: For regularly occupied structures that have no subunits, consider both the regularly occupied structures containing sampling location(s) meeting observed exposure criteria for the site and the regularly occupied structure(s) in the area lying between such locations to be an area of observed exposure (i.e., inferred to be in an area of observed exposure), unless available information indicates otherwise. EP29FE16.038</GPH>

425 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 In multi-story, multi-subunit, regularly occupied structures, consider all subunits on a level with sampling locations meeting observed exposure criteria from the site and all levels below, if any, to be within an area of observed exposure, unless available information indicates otherwise. In multi-tenant structures, that do not have a documented observed exposure, but are located in an area lying between locations where observed exposures have been documented, consider only those regularly occupied subunits, if any, on the lowest level of the structure, to be within an area of observed exposure (i.e., inferred to be in an area of observed exposure, unless available information indicates otherwise. Area(s) of subsurface contamination: An area of subsurface contamination is delineated by sampling locations meeting observed release criteria for subsurface intrusion, excluding areas of observed exposure (see Table 2 3 in section 2.3). The area within an area of subsurface contamination includes potentially exposed populations. If the significant increase in hazardous substance levels cannot be attributed at least in part to the site and cannot be attributed to other sites, attribution can be established based on the presence of hazardous substances in the area of subsurface contamination. Establish areas of subsurface contamination as follows: Exclude those areas that contain structures meeting the criteria defined as an area of observed exposure. Consider both the sampling location(s) with subsurface contamination meeting observed release criteria from the site and the area lying between such locations to be an area of subsurface contamination (i.e., inferred to be in an area of subsurface contamination), unless available information indicates otherwise. Evaluate an area of subsurface contamination based on hazardous substances that: D Meet the criteria for observed exposure, or D Meet the criteria for observed release in an area of subsurface contamination and have a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atm-m 3 /mol, or D Meet the criteria for an observed release in a structure within, or in a sample from below, an area of observed exposure and has a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atm-m 3 /mol. See Section 7.0 for establishing an area of subsurface contamination based on the presence of radioactive hazardous substances. Evaluate all structures with no subunits to be in an area of subsurface contamination if they are lying between locations of subsurface intrusion samples meeting observed release criteria. Evaluate multi-subunit structures as follows: D If an observed exposure has been documented based on a gaseous indoor air sample, consider all regularly occupied subunit(s), if any, on the level immediately above the level where an observed exposure has been documented (or has been inferred to be within an area of observed exposure), to be within an area of subsurface contamination, unless available information indicates otherwise. D If observed release criteria have been met based on a gaseous indoor air sample collected from a level not regularly occupied, consider all regularly occupied subunit(s), if any, on the level immediately above the level where the observed release criteria has been documented, to be within an area of subsurface contamination, unless available information indicates otherwise. D If an observed exposure has been documented based on an intruded liquid or particulate sample, do not consider any regularly occupied subunit(s) above the level where an observed exposure has been documented to be within an area of subsurface contamination, unless available information indicates otherwise. D If any regularly occupied multisubunit structure is inferred to be in an area of subsurface contamination, consider only those regularly occupied subunit(s), if any, on the lowest level, to be within an area of subsurface contamination, unless available information indicates otherwise. If there is no area of observed exposure and no area of subsurface contamination, assign a score of 0 for the subsurface intrusion component Subsurface intrusion component. Evaluate this component only if there is an area of observed exposure or area of subsurface contamination: Within or underlying a residence, school, day care center, workplace, or VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 Within or underlying a resource specified in section Likelihood of exposure. Assign a value of 550 to the likelihood of exposure factor category for the subsurface intrusion component if there is an area of observed exposure in one or more locations listed in section Enter this value in Table Observed exposure. Establish observed exposure in a regularly occupied structure by demonstrating that a hazardous substance has been released into a regularly occupied structure via the subsurface. Base this demonstration on either of the following criterion: Direct observation: A solid, liquid or gaseous material that contains one or more hazardous substances attributable to the site has been observed entering a regularly occupied structure through migration via the subsurface or is known to have entered a regularly occupied structure via the subsurface, or When evidence supports the inference of subsurface intrusion of a material that contains one or more hazardous substances associated with the site into a regularly occupied structure, demonstrated adverse effects associated with that release may be used to establish observed exposure. Chemical analysis: Analysis of indoor samples indicates that the concentration of hazardous substance(s) has increased significantly above the background concentration for the site for that type of sample (see section 2.3). Some portion of the significant increase must be attributable to the site to establish the observed exposure. Documentation of this attribution should account for possible concentrations of the hazardous substance(s) in outdoor air or from materials found in the regularly occupied structure, and should provide a rationale for the increase being from subsurface intrusion. If observed exposure can be established in a regularly occupied structure, assign an observed exposure factor value of 550, enter this value in Table 5 11, and proceed to section If no observed exposure can be established, assign an observed exposure factor value of 0, enter this value in Table 5 11, and proceed to section Potential for exposure. Evaluate potential for exposure only if an observed exposure cannot be

426 10420 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules established, but an area of subsurface contamination has been delineated. Evaluate potential for exposure based only on the presence of hazardous substances with a vapor pressure greater than or equal to one torr or a Henry s constant greater than or equal to 10 5 atm-m 3 /mol. Evaluate potential for exposure for each area of subsurface contamination based on four factors: structure containment (see section ), depth to contamination (see section ), vertical migration (see section ) and vapor migration potential (see section ). For each area of subsurface No. contamination, assign the highest value for each factor. If information is insufficient to calculate any single factor value used to calculate the potential for exposure factor values at an identified area of subsurface contamination, information collected for another area of subsurface contamination at the site may be used when evaluating potential for exposure. Calculate the potential for exposure value for the site as specified in section Structure containment. Calculate containment for eligible hazardous substances within this component as directed in Table 5 12 and enter this value into Table TABLE 5 12 STRUCTURE CONTAINMENT Evidence of structure containment Assign each regularly occupied structure within an area of subsurface contamination the highest appropriate structure containment value from Table 5 12 and use the regularly occupied structure at the site with the highest structure containment value in performing the potential for exposure calculation. Assign a structure containment factor value of 10 to any regularly occupied structure located within an area of observed exposure that is established based on documented surficial ground water intrusion, unless available information indicates otherwise. Assigned value 1... Regularly occupied structure with evidence of subsurface intrusion, including documented observed exposure 10 or sampling of bio or inert gases, such as methane and radon Regularly occupied structure with open preferential pathways from the subsurface (e.g., sumps, foundation 10 cracks, unsealed utility lines) Regularly occupied structure with an engineered vapor migration barrier system that does not address all preferential 7 pathways Regularly occupied structure with an engineered passive vapor mitigation system without documented institutional 6 controls (e.g., deed restrictions) or evidence of regular maintenance and inspection Regularly occupied structure with no visible open preferential pathways from the subsurface (e.g., sumps, 4 foundation cracks, unsealed utility lines) Regularly occupied structure with an engineered passive vapor mitigation system (e.g., passive venting) with 3 documented institutional controls (e.g., deed restrictions) or evidence of regular maintenance and inspection Regularly occupied structure with an engineered, active vapor mitigation system (e.g., active venting) without 2 documented institutional controls (e.g., deed restrictions) and funding in place for on-going operation, inspection and maintenance Regularly occupied structure with unknown containment features Regularly occupied structure with a permanent engineered, active vapor mitigation system (e.g., active venting) 0 with documented institutional controls (e.g., deed restrictions) and funding in place for on-going oper- ation, inspection and maintenance. This does not include mitigation systems installed as part of a removal or other temporary response by federal, state or tribal authorities Regularly occupied structure with a foundation raised greater than 6 feet (e.g., structure on stilts) or structure that has been built, and maintained, in a manner to prevent subsurface intrusion. 0 srobinson on DSK5SPTVN1PROD with PROPOSALS Depth to contamination. Assign each area of subsurface contamination a depth to contamination based on the least depth to either contaminated crawl space or subsurface media underlying a regularly occupied structure. Measure this depth to contamination based on the distance between the lowest point of a regularly occupied structure to the highest known point of hazardous substances eligible to be evaluated. Use any regularly occupied structure within an area of subsurface contamination with a structure containment factor greater than zero. Subtract from the depth to contamination the thickness of any subsurface layer composed of features that would allow channelized flow (e.g., karst, lava tubes, open fractures). Based on this calculated depth, assign a factor value from Table If the necessary information is available at multiple locations, calculate the depth to contamination at each location. Use the location having the least depth to contamination to assign the factor value. Enter this value in Table TABLE 5 13 DEPTH TO CONTAMINATION Depth range 12 Depth to contamination assigned value 0 to 10 ft.(including subslab and semi-enclosed or enclosed crawl space contamination) >10 to 20 ft... 8 >20 to 50 ft... 6 >50 to 100 ft... 4 >100 to 150 ft... 2 >150 ft If any part of the subsurface profile has channelized flow features, assign that portion of the subsurface profile a depth of 0. VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 2 Measure elevation below any regularly occupied structure within an area of subsurface contamination at a site. Select the regularly occupied structure with the least depth to contamination below a structure Vertical migration. Evaluate the vertical migration factor for each area of subsurface contamination based on the geologic materials in the interval between the lowest point of a regularly occupied structure and the highest known point of hazardous substances in the subsurface. Use any regularly occupied structure either within an area of subsurface contamination or overlying subsurface soil gas or ground water contamination. Assign a value to the vertical migration factor as follows: If the depth to contamination (see section ) is 10 feet or less, assign a value of 15.

427 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Do not consider layers or portions of layers within the first 10 feet of the depth to contamination. If, for the interval identified above, all layers that underlie a portion of a regularly occupied structure at the site are karst or otherwise allow channelized flow, assign a value of 15. Otherwise: Select the lowest effective porosity/ permeability layer(s) from within the above interval. Consider only layers at least 1 foot thick. (If site-specific data is not available, use the layer with the highest value assigned in Table 5 14.) Assign a value for individual layers from Table If more than one layer has the same assigned porosity/permeability value, include all such layers and sum their thicknesses. Assign a thickness of 0 feet to a layer with channelized flow features found within any area of subsurface contamination at the site. Assign a value from Table 5 15 to the vertical migration factor, based on the thickness and assigned porosity/ permeability value of the lowest effective porosity/permeability layer(s). Determine vertical migration only at locations within an area of subsurface contamination at the site. If the necessary subsurface geologic information is available at multiple locations, evaluate the vertical migration factor at each location. Use the location having the highest vertical migration factor value to assign the factor value. Enter this value in Table TABLE 5 14 EFFECTIVE POROSITY/PERMEABILITY OF GEOLOGIC MATERIALS Type of material Assigned porosity/ permeability value Gravel; highly permeable fractured igneous and metamorphic rocks; permeable basalt; karst limestones and dolomites... 1 Sand; sandy clays; sandy loams; loamy sands; sandy silts; sediments that are predominantly sand; highly permeable till (coarse-grained, unconsolidated or compact and highly fractured); peat; moderately permeable limestones and dolomites (no karst); moderately permeable sandstone; moderately permeable fractured igneous and metamorphic rocks... 2 Silt; loams; silty loams; loesses; silty clays; sediments that are predominantly silts; moderately permeable till (fine-grained, unconsolidated till, or compact till with some fractures); low permeability limestones and dolomites (no karst); low permeability sandstone; low permeability fractured igneous and metamorphic rocks... 3 Clay; low permeability till (compact unfractured till); shale; unfractured metamorphic and igneous rocks... 4 TABLE 5 15 VERTICAL MIGRATION FACTOR VALUES a Assigned porosity/ permeability value 0 to 5 Greater than 5 to 10 Thickness of lowest porosity layer(s) b (feet) Greater than 10 to 20 Greater than 20 to 50 Greater than 50 to 100 Greater than 100 to a If depth to contamination is 10 feet or less or if, for the interval being evaluated, all layers that underlie a portion of the structure at the site are karst or have other channelized flow features, assign a value of 15. b Consider only layers at least 1 foot thick. srobinson on DSK5SPTVN1PROD with PROPOSALS Vapor migration potential. Evaluate this factor for each area of subsurface contamination as follows: If the depth to contamination (see section ) is 10 feet or less, assign a value of 25. Assign a value for vapor migration potential to each of the gaseous hazardous substances associated with the area of subsurface contamination (see section 2.2.2) as follows: Assign values from Table 5 16 for both vapor pressure and Henry s constant to each hazardous substance. If Henry s constant cannot be determined for a hazardous substance, assign that hazardous substance a value of 2 for the Henry s constant component. Sum the two values assigned to each hazardous substance. Based on this sum, assign each hazardous substance a value from Table 5 17 for vapor migration potential. Assign a value for vapor migration potential to each area of subsurface contamination as follows: Select the hazardous substance associated with the area of subsurface contamination with the highest vapor migration potential value and assign this value as the vapor migration potential factor for the area of subsurface contamination. Enter this value in Table TABLE 5 16 VALUES FOR VAPOR PRESSURE AND HENRY S CONSTANT Vapor pressure (Torr) Assigned value Greater than VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 TABLE 5 16 VALUES FOR VAPOR PRESSURE AND HENRY S CON- STANT Continued Vapor pressure (Torr) Assigned value 1 to Less than Henry s constant (atm-m 3 / mol) Assigned value Greater than Greater than 10 4 to to Less than

428 10422 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules srobinson on DSK5SPTVN1PROD with PROPOSALS2 TABLE 5 17 VAPOR MIGRATION PO- TENTIAL FACTOR VALUES FOR A HAZARDOUS SUBSTANCE Sum of values for vapor pressure and Henry s constant Assigned value or or or Calculation of potential for exposure factor value. For each identified area of subsurface contamination, sum the factor values for depth to contamination, vertical migration and vapor migration potential, and multiply this sum by the factor value for structure containment. Select the highest product for any area of subsurface contamination and assign this value as the potential for exposure factor value for the component. Enter this value in Table Calculation of likelihood of exposure factor category value. If observed exposure is established for the site, assign the observed exposure factor value of 550 as the likelihood of exposure factor category value for the site. Otherwise, assign the potential for exposure factor value for the component as the likelihood of exposure value. Enter the value assigned in Table Waste characteristics. Evaluate waste characteristics based on two factors: Toxicity/degradation and hazardous waste quantity Toxicity/degradation. For each hazardous substance, assign a toxicity factor value, a degradation factor value and a combined toxicity/ degradation factor value as specified in sections 2.2.3, and through Toxicity. Assign a toxicity factor value to each hazardous substance as specified in sections and Degradation. Assign a degradation factor value to each hazardous substance as follows: For any hazardous substance that meets the criteria for an observed exposure, assign that substance a degradation factor value of 1. For all hazardous substances at the site that meet subsurface intrusion observed release criteria but not observed exposure criteria, assign a degradation factor value of 1 if the depth to contamination below an area of subsurface contamination or area of observed exposure is less than 10 feet or if available evidence suggests that there is less than 10 feet of biologically active soil in the subsurface anywhere underneath a regularly occupied structure within an area of subsurface contamination or area of observed exposure. For all other situations first calculate the half-life for each hazardous substance that meets subsurface intrusion observed release criteria as follows: The half-life or a substance in the subsurface is defined for HRS purposes as the time required to reduce the initial concentration in the subsurface by onehalf as a result of the combined decay processes of two components: biodegradation and hydrolysis. Estimate the half-life (t 1/2 ) of a hazardous substance as follows: Where: h=hydrolysis half-life. b=biodegradation half-life. If one of these component half-lives cannot be estimated for the hazardous substance from available data, delete that component half-life from the above equation. If no half-life information is available for a hazardous substance and the substance is not already assigned a value of 1, unless information indicates otherwise, all straight-chain and simplering structure substances will be considered to have a half-life less than 30 days if not the hazardous substance will be assigned a half-life of greater than 100 days. Based on the hazardous substance s assigned half-life the degradation factor is assigned as follows: For all hazardous substances at the site that meet subsurface intrusion observed release criteria but not observed exposure criteria, assign a degradation factor value of 0.1, if: The depth to contamination at the site is greater than or equal to 10 feet, but not if available evidence suggests that at least 10 feet of biologically active soil is not present in the subsurface anywhere underneath a structure within an area of subsurface contamination or area of observed exposure, and The hazardous substance has a halflife of 30 days or less. For all hazardous substances at the site that meet subsurface intrusion observed release criteria but not observed exposure criteria, assign a degradation factor value of 0.5, if: The depth to contamination at the site is greater than 30 feet, but not if available evidence suggests that at least 30 feet of biologically active soil is not present in the subsurface VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 anywhere underneath a structure within an area of subsurface contamination or area of observed exposure, and The hazardous substance has a halflife equal to or less than 100 days. For all other situations assign a degradation factor of 1 for all hazardous substances at the site that meet subsurface intrusion observed release criteria. In addition, for hazardous substances that meet observed release criteria, have a parent-daughter degradation relationship, and the daughter substance is found only in samples with a depth greater than 10 feet, assign the daughter substance degradation factor value as follows: 1. Identify the shallowest subsurface sample that contains the daughter substance. 2. Determine if the selected sample or another sample from the same relative position in the media of concern, or in a shallower sample, contains the parent substance. 3. If the parent substance is not present in the identified samples, assign the degradation factor value for the daughter substance based on the halflife for the daughter substance. 4. If the parent substance is present in a sample from the same relative position in the subsurface or in a shallower sample, compare the half-life-based degradation factor value for the daughter substance to the degradation factor value assigned to the parent substance. Assign the greater of the two values as the degradation factor value for the daughter substance Calculation of toxicity/ degradation factor value. Assign each substance a toxicity/biodegradation value by multiplying the toxicity factor value by the degradation factor value. Use the hazardous substance with the highest combined toxicity/degradation value to assign the factor value to the toxicity/degradation factor for the subsurface intrusion threat. Enter this value in Table Hazardous waste quantity. Assign a hazardous waste quantity factor value as specified in section Consider only those regularly occupied structures with a non-zero structure containment value. In estimating the hazardous waste quantity, use Tables 2 5 and 5 18 and: For Tier A, hazardous constituent quantity, use the mass of constituents found in the regularly occupied structure(s) where the observed exposure has been identified. For multi-subunit structures, when calculating Tier A, use the mass of EP29FE16.039</GPH>

429 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules constituents found in the regularly occupied subunit space(s) where the observed exposure has been identified. For Tier B, hazardous wastestream quantity, use the flow-through volume of the regularly occupied structures where the observed exposure has been identified. For multi-subunit structures, when calculating Tier B, use the flowthrough volume of the regularly occupied subunit spaces where the observed exposure has been identified. For Tier C, volume, use the volume divisor listed in Tier C of Table Volume is calculated for those regularly occupied structures located within areas of observed exposure with observed or inferred intrusion and within areas of subsurface contamination. In evaluating the volume measure for these listed areas of observed exposure and areas of subsurface contamination based on a gaseous/ vapor intrusion or the potential for gaseous/vapor intrusion, consider the following: Calculate the volume of each regularly occupied structure based on actual data. If unknown, use a ceiling height of 8 feet. For multi-subunit structures, when calculating Tier C, calculate volume for those subunit spaces with observed or inferred exposure and all other regularly occupied subunit spaces on that level, unless available information indicates otherwise. If the structure has multiple stories, also include the volume of all regularly occupied subunit spaces below the floor with an observed exposure and one story above, unless evidence indicates otherwise. For multi-subunit structures within an area of subsurface contamination and no observed or inferred exposure, consider only the volume of the regularly occupied subunit spaces on the lowest story, unless available information indicates otherwise. In evaluating the volume measure for these listed areas of observed exposure and areas of subsurface contamination where intrusion of contaminated ground water has occurred, do not calculate the volume of each regularly occupied structure. Instead, consider only the volume of contaminated ground water known to have intruded into a regularly occupied structure. For Tier D, area, if volume is unknown, use the area divisor listed in Tier D of Table 5 18 for those regularly occupied structures within areas of observed exposure with observed or inferred intrusion and within areas of subsurface contamination. In evaluating the area measure for these listed areas of observed exposure and areas of subsurface contamination, calculate the area of each regularly occupied structure (including multi-subunit structures) based on actual footprint area data. If the actual footprint area of the structure(s) is unknown, use an area of 1,740 square feet for each structure (or subunit space). TABLE 5 18 HAZARDOUS WASTE QUANTITY EVALUATION EQUATIONS FOR SUBSURFACE INTRUSION COMPONENT Tier Measure Units Equation for assigning value a A Hazardous Constituent Quantity (C)... lb... C. B b Hazardous Wastestream Quantity (W)... lb... W/5,000. C bc Volume (V). Regularly occupied structure(s) in areas of observed exposure or subsurface contamination... yd 3... V/2.5. D bd Area (A). Regularly occupied structure(s) in areas of observed exposure or subsurface contamination... ft 2... A/13. a Do not round to the nearest integer. b Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1 cubic yard = 4 drums = 200 gallons. c Calculate volume of each regularly occupied structure or subunit space in areas of observed exposure and areas of subsurface contamination Assume 8-foot ceiling height unless actual value is known. d Calculate area of the footprint of each regularly occupied structure in areas of observed exposure and areas of subsurface contamination. If the footprint area of a regularly occupied structure is unknown, use 1,740 square feet as the footprint area of the structure or subunit space. srobinson on DSK5SPTVN1PROD with PROPOSALS2 For the subsurface intrusion component, if the hazardous constituent quantity is adequately determined for all areas of observed exposure, assign the value from Table 2 6 as the hazardous waste quantity factor value. If the hazardous constituent quantity is not adequately determined for one or more areas of observed exposure or if one or more areas of subsurface contamination are present, assign either the value from Table 2 6 or assign a factor value as follows: If any target for the subsurface intrusion component is subject to Level I or Level II concentrations (see section 2.5), assign either the value from Table 2 6 or a value of 100, whichever is greater, as the hazardous waste quantity factor value for this component. If none of the targets for the subsurface intrusion component is subject to Level I or Level II concentrations and if there has been a removal action that does not permanently interrupt target exposure from subsurface intrusion, assign a factor value as follows: Determine the values from Table 2 6 with and without consideration of the removal action. If the value that would be assigned from Table 2 6 without consideration of the removal action would be 100 or greater, assign either the value from Table 2 6 with consideration of the VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 removal action or a value of 100, whichever is greater, as the hazardous waste quantity factor value for the component. If the value that would be assigned from Table 2 6 without consideration of the removal action would be less than 100, assign a value of 10 as the hazardous waste quantity factor value for the component. Otherwise, if none of the targets for the subsurface intrusion component is subject to Level I or Level II concentrations and there has not been a removal action, assign a minimum value of 10. Enter the value assigned in Table 5 11.

430 10424 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Calculation of waste characteristics factor category value. Multiply the toxicity/degradation and hazardous waste quantity factor values, subject to a maximum product of Based on this product, assign a value from Table 2 7 (section ) to the waste characteristics factor category. Enter this value in Table Targets. Evaluate the targets factor category for the subsurface intrusion threat based on three factors: Exposed individual, population, and resources in regularly occupied structures. Evaluate only those targets within areas of observed exposure and areas of subsurface contamination (see section 5.2.0). In evaluating the targets factor category for the subsurface intrusion threat, count only the following as targets: Exposed individual a person living, attending school or day care, or working in a regularly occupied structure with observed exposure or in a structure within an area of observed exposure or within an area of subsurface contamination. Population exposed individuals in a regularly occupied structure within an area of observed exposure or within an area of subsurface contamination. Resources located within an area of observed exposure or within an area of subsurface contamination as specified in section If a former structure that has been vacated due to subsurface intrusion attributable to the site, count the initial targets as if they were still residing in the structure. In addition, if a removal action has occurred that has not completely mitigated the release, count the initial targets as if the removal action has not permanently interrupted target exposure from subsurface intrusion. For populations residing in or working in a multi-subunit structure with multiple stories in an area of observed exposure or area of subsurface contamination, count these targets as follows: If there is no observed exposure within the structure, include in the evaluation only those targets, if any, in the lowest occupied level, unless available information indicates otherwise. If there is an observed exposure in any level, include in the evaluation those targets in that level, the level above and all levels below, unless available information indicates otherwise. (The weighting of these targets is specified in Section ) Exposed individual. Evaluate this factor based on whether there is an exposed individual, as specified in sections 2.5.1, and , who is subject to Level I or Level II concentrations. First, determine those regularly occupied structures or partitioned subunit(s) within structures in an area of observed exposure subject to Level I concentrations and those subject to Level II concentrations as specified as follows (see section 5.2.0): Level I Concentrations: For contamination resulting from subsurface intrusion, compare the hazardous substance concentrations in any sample meeting the observed exposure by chemical analysis criteria to the appropriate benchmark. Use the healthbased benchmarks from Table 5 19 to determine the level of contamination. If the sample is from a structure with no subunits and the concentration equals or exceeds the appropriate benchmark, assign Level I concentrations to the entire structure. If the sample is from a subunit within a structure and the concentration from that subunit equals or exceeds the appropriate benchmark, assign Level I concentrations to that subunit. Level II Concentrations: Structures, or subunits within structures, with one or more samples that meet observed exposure by chemical analysis criteria but do not equal or exceed the appropriate benchmark; structures, or subunits, that have an observed exposure by direct observation; and structures inferred to be in an area of observed exposure based on samples meeting observed exposure, are assigned Level II concentrations. Æ For all regularly occupied structures, or subunits in such structures, in an area of observed exposure that are not assigned Level I concentrations, assign Level II concentrations. Then assign a value to the exposed individual factor as follows: Assign a value of 50 if there is at least one exposed individual in one or more regularly occupied structures subject to Level I concentrations. Assign a value of 45 if there are no Level I exposed individuals, but there is at least one exposed individual in one or more regularly occupied structures subject to Level II concentrations. Assign a value of 20 if there is no Level I or Level II exposed individual but there is at least one individual in a regularly occupied structure within an area of subsurface contamination. Enter the value assigned in Table Population. Evaluate population based on three factors: Level I concentrations, Level II concentrations, and population within an area of subsurface contamination. Determine which factors apply as specified in section , using the health-based benchmarks from Table Evaluate populations subject to Level I and Level II concentrations as specified in section 2.5. TABLE 5 19 HEALTH-BASED BENCHMARKS FOR HAZARDOUS SUBSTANCES IN THE SUBSURFACE INTRUSION COMPONENT Screening concentration for cancer corresponding to that concentration that corresponds to the 10 6 individual cancer risk using the inhalation unit risk. For oral exposures use the oral cancer slope factor. Screening concentration for noncancer toxicological responses corresponding to the reference dose (RfD) for oral exposure and the reference concentration (RfC) for inhalation exposures. srobinson on DSK5SPTVN1PROD with PROPOSALS2 Count only those persons meeting the criteria for population as specified in section In estimating the number of individuals in structures in an area of observed exposure or area of subsurface contamination if the actual number of residents is not known, multiply each residence by the average number of persons per residence for the county in which the residence is located Level I concentrations. Assign the population subject to Level I concentrations as follows: 1. Identify all exposed individuals regularly present in a structure, or if the structure has subunits, identify those regularly present in each subunit, located in an area of observed exposure VerDate Sep<11> :37 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2 subject to Level I concentrations as described in sections and Identify only once per structure those exposed individuals that are using more than one eligible subunit of the same structure (e.g., using a common or shared area and other parts of the same structure). 2. For each structure or subunit count the number of individuals residing in or

431 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules attending school or day care in the structure or subunit. 3. Count the number of full-time and part-time workers in the structure or subunit(s) subject to Level I concentrations. If information is unavailable to classify a worker as fullor part-time, evaluate that worker as being full-time. Divide the number of full-time workers by 3 and the number of part-time workers by 6, and then sum these products with the number of other individuals for each structure or subunit. 4. Sum this combined value for all structures, or subunits, within areas of observed exposure and multiply this sum by 10. Assign the resulting product as the combined population factor value subject to Level I concentrations for the site. Enter this value in line 9a of Table Level II concentrations. Assign the population subject to Level II concentrations as follows: 1. Identify all exposed individuals regularly present in an eligible structure, or if the structure has subunits, identify those regularly present in each subunit, located in an area of observed exposure subject to Level II concentrations as described in sections and Identify only once per structure those exposed individuals that are using more than one eligible subunit of the same structure (e.g., using a common or shared area and other parts of the same structure). 2. Do not include exposed individuals already counted under the Level I concentrations factor. 3. For each structure or subunit(s), count the number of individuals residing in or attending school or day care in the structure, or subunit, subject to Level II concentrations. 4. Count the number of full-time and part-time workers in the structure or subunit(s) subject to Level II concentrations. If information is unavailable to classify a worker as fullor part-time, evaluate that worker as being full-time. Divide the number of full-time workers by 3 and the number of part-time workers by 6, and then sum these products with the number of other individuals for each structure or subunit. 5. Sum the combined population value for all structures within the areas of observed exposure for the site. Assign this sum as the combined population value subject to Level II contamination for this factor. Enter this value in line 9b of Table Population within area(s) of subsurface contamination. Assign the population in area(s) of subsurface contamination factor value as follows, unless available information indicates otherwise (see sections and ): 1. Identify the regularly occupied structures with a structure containment value greater than zero and the eligible population associated with the structures or portions of structures in each area of subsurface contamination: For each regularly occupied structure or portion of a structure in an area of subsurface contamination, sum the number of all individuals residing in or attending school or day care, in the structure or portion of the structure in the area of subsurface contamination. Count the number of full-time and part-time workers regularly present in each structure or portion of a structure in an area of subsurface contamination. If information is unavailable to classify a worker as full- or part-time, evaluate that worker as being full-time. Divide the number of full-time workers by 3 and the number of part-time workers by 6. Sum these products with the number of individuals residing in or attending school or day care in the structure. Use this sum as the population for the structure. 2. Estimate the depth or distance to contamination at each regularly occupied structure within an area of subsurface contamination based on available sampling data, and categorize each eligible structure based on the depth or distance to contamination and sampling media as presented in Table Weight the population in each structure using the appropriate weighting factors in Table If samples from multiple media are available, use the sample that results in the highest weighting factor. 3. Sum the weighted population in all structures within the area(s) of subsurface contamination and assign this sum as the population subject subsurface contamination factor value. Enter this value in line 9c of Table TABLE 5 20 WEIGHTING FACTOR VALUES FOR POPULATIONS WITHIN AN AREA OF SUBSURFACE CONTAMINATION Eligible populations a in structures b within an area of subsurface contamination Population weighting factor srobinson on DSK5SPTVN1PROD with PROPOSALS2 Population in a structure with levels of contamination in a semi-enclosed or enclosed crawl space sample meeting observed release criteria or Population in a subunit of a multi-story structure within an area of subsurface contamination located directly above a level in an area of observed exposure or a gaseous indoor air sample meeting observed release criteria Population in a structure where levels of contaminants meeting observed release criteria are found in any sampling media at or within five feet horizontally or vertically of the structure foundation Population occupying a structure where levels of contaminants meeting observed release criteria are found or inferred based on any underlying non-ground water subsurface sample at a depth less than or equal to 30 feet or Population in a structure within an area of subsurface contamination where levels of contaminants meeting observed release criteria are inferred based on semi-enclosed or enclosed crawl space samples in surrounding structures Population in a structure where levels of contaminants meeting observed release criteria are found or inferred based on underlying ground water samples greater than five feet from the structure foundation or Population in a structure where levels of contaminants meeting observed release criteria are found or inferred based on any underlying sample at depths greater than 30 feet a Eligible populations include residents (including individuals living in, or attending school or day care in the structure), and workers in regularly occupied structures (see HRS Section ). b Eligible structures may include single- or multi-tenant structures where eligible populations reside, attend school or day care, or work. These structures may also be mixed use structures. VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2

432 10426 Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules Calculation of population factor value. Sum the factor values for Level I concentrations, Level II concentrations, and population in the area(s) of subsurface contamination. Assign this sum as the population factor value. Enter this value in line 9d of Table Resources. Evaluate the resources factor as follows: Assign a value of 5 if a resource structure (e.g., library, church, tribal facility) is present and regularly occupied within either an area of observed exposure or area of subsurface contamination. Assign a value of 0 if there is no resource structure within an area of observed exposure or area of subsurface contamination. Enter the value assigned in Table Calculation of targets factor category value. Sum the values for the exposed individual, population, and resources factors. Do not round to the nearest integer. Assign this sum as the targets factor category value for the subsurface intrusion component. Enter this value in Table Calculation of subsurface intrusion component score. Multiply the factor category values for likelihood of exposure, waste characteristics and targets and round the product to the nearest integer. Divide the product by 82,500. Assign the resulting value, subject to a maximum of 100, as the subsurface intrusion component score and enter this score in Table Calculation of the soil exposure and subsurface intrusion pathway score: Sum the soil exposure component score and subsurface intrusion component. Assign the resulting value, subject to a maximum of 100, as the soil exposure and subsurface intrusion pathway score (S sessi ). Enter this score in Table Air Migration Pathway * * * * * TABLE 6 14 HEALTH-BASED BENCHMARKS FOR HAZARDOUS SUBSTANCES IN AIR Concentration corresponding to National Ambient Air Quality Standard (NAAQS). Concentration corresponding to National Emission Standards for Hazardous Air Pollutants (NESHAPs). Screening concentration for cancer corresponding to that concentration that corresponds to the 10 6 individual cancer risk for inhalation exposures. Screening concentration for noncancer toxicological responses corresponding to the Reference Concentration (RfC) for inhalation exposures. * * * * * 7.0 Sites Containing Radioactive Substances * * * * * srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4702 E:\FR\FM\29FEP2.SGM 29FEP2

433 srobinson on DSK5SPTVN1PROD with PROPOSALS2 VerDate Sep<11> :14 Feb 26, 2016 Jkt PO Frm Fmt 4701 Sfmt 4725 E:\FR\FM\29FEP2.SGM 29FEP2 TABLE 7-1. HRS FACTORS EVALUATED DIFFERENTLY FOR RADIONUCLIDES Subsurface Soil Exposure Ground Water Surface Water Status Intrusion Status Pathway Pathway Component of Status Component of SESSI Pathway SESSI Pathway Status Air Pathway Status Likelihood of Likelihood of Likelihood of Likelihood of Likelihood of Release Release Exposure Exposure Release Observed Yes Observed Yes Observed Yes Observed Yes Observed Yes Release Release Contamination Exposure Release Potential to No Potential to No Attractiveness/ No Potential for Yes Gas Potential to No Release Release Accessibility to Exposure Release Nearby Residents Containment No Overland Flow No Area of No Structure No Gas No Containment Contamination Containment Containment Net Precipitation No Runoff No Depth to Yes Gas Source No Contamination Type Depth to Aquifer No Distance to No Vertical No Gas Migration No Surface water migration Potential Travel Time No Flood Frequency No Vapor Migration No Particulate No Potential Potential to Release Flood No Particulate No Containment Containment Particulate No Source Type Particulate No Migration Potential Waste Waste Waste Waste Waste Characteristics Characteristics Characteristics Characteristics Characteristics Toxicity Yes Toxicity/ Yes/Y Toxicity Yes Toxicity/ Yes Toxicity Yes Ecotoxicity es Degradation Mobility No Persistence/ Yes/N Hazardous Yes Hazardous Yes Mobility No Mobility 0 Waste Quantity Waste Quantity Hazardous Yes Bioaccumu- No Hazardous Yes Waste Quantity lation Potential Waste Quantity Hazardous Yes Waste Quantity Targets Targets Targets Targets Targets Nearest Well Yes b Nearest Intake Yes b Resident Yes b Exposed Yes b Nearest Yes b Federal Register / Vol. 81, No. 39 / Monday, February 29, 2016 / Proposed Rules EP29FE16.040</GPH>

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