Vapor Intrusion Risk Pathway: Practical & Cost Effective Assessment Strategies

Transcription

1 Vapor Intrusion Risk Pathway: Practical & Cost Effective Assessment Strategies Presented by: Dr. Blayne Hartman July 2006 Dr. Blayne Hartman H&P Mobile Geochemistry 2470 Impala Drive Carlsbad, CA Mark Jerpbak TEG Northern California Monier Park Place Rancho Cordova, CA

2 Vapor Intrusion Risk Pathway: Practical & Cost Effective Assessment Strategies July 2006 Blayne Hartman H&P Mobile Geochemistry Carlsbad, CA This presentation is a condensed version of the vapor intrusion training that Dr. Hartman has been presenting to Federal & State regulatory agencies, DOD facilities, consulting groups, and stakeholders around the country. As of July 2006, Dr. Hartman has given vapor intrusion or soil gas training to over 20 State Regulatory agencies, to regulators from all 50 states at the ASTSWMO national meeting, at the National UST conference in 2006, at the British Brownfields conference in May 2006, and to many RPs and stakeholders such as Exxon/Mobil, BP/ARCO, Dept. of Navy, & the Electrical Power Research Institute (EPRI). Lecture notes are at the bottom of each slide so that if played out as a hardcopy, the presentation can be a useful reference document.

3 Seminar Overview Overview of Vapor Intrusion Brief Review of EPA & CA Guidances Methods to Assess Vapor Intrusion Soil Gas Sampling/Analytical Issues Supplemental Tools/Data to Use Very Brief Comments on Mitigation Dos & Don ts for Assessing the Pathway Recommended VI Approach/Case History This presentation consists of an overview of the vapor intrusion risk pathway, a brief review of the new Federal EPA & CA vapor intrusion guidance, with special emphasis on methods to assess the VI pathway, primarily soil gas sampling and analysis. Practical and cost saving strategies will be emphasized throughout the presentation.

4 Evidence of residual LNAPL? National Enquirer Vapor intrusion cases making headlines around the country even the National Enquirer!

5 Newspaper articles slamming the Johnson-Ettinger model.

6 Vaporgate!

7 The Da Vapor Code (Newest Box-Office Blockbuster) AEHS 2006, 2005, AWMA Conf (9/06 LA, 1/06) Workgroups Everywhere (ASTM, ITRC, EPA-OSWR, API) EPA Seminars (2003 & 2004) Requests for Training from >25 States Vapor intrusion is the hot topic right now and, in movie lore, is a box-office blockbuster. Recent conferences on the topic have all been heavily attended and numerous workgroups are currently drafting policy. Many state agencies and EPA regions are requesting training on the topic.

8 ITRC Survey Results 39 of 43 states say vapor intrusion is a current concern being actively addressed VI concerns in every program (RCRA, FUDs CERCLA, brownfields, UST, dry-cleaning, Most preferred methods for evaluating vapor intrusion: shallow soil gas/subslab sampling followed by indoor air measurements 9 states allow for biodegradation of petroleum hydrocarbons Interstate Technology Regulatory Council (ITRC) conducted a survey of all States re vapor intrusion in late The results showed that nearly all States are worried about this pathway in most of their programs and that soil gas measurements are preferred over indoor air measurements.

9 What Is Vapor Intrusion? Key Assumptions: Risk level (1 in 10,000? 100,000? 1,000,000?) Toxicity of Compounds Exposure Factors (time, rates, ventilation) Vapor intrusion refers to the upward migration of contaminants in the vapor phase from groundwater, soil, or soil gas contamination sources. Key assumptions to the risk determination are the risk level, the toxicity of the contaminant, and the exposure factors. These parameters are often much more important than model parameters such as soil porosity and pressure gradients.

10 Why Are Indoor Air RBSLs So Low? Benzene: CA: ug/m3, EPA: 0.30 ug/m3 TCE: CA: 1.22 ug/m3, EPA: or 1.0 PCE: CA: 0.41 ug/m3, EPA: 0.41 ug/m3 Values Assume: 24 hr, 350 days/yr, 30 years Ultra Conservative Assumptions Lower Allowed Levels and Bring in More Sites Allowable indoor air concentrations are so low because of the ultra conservative assumptions that are used, especially in regards to exposure time.

11 Why Are Indoor Air RBSLs So Much Lower than GW? Typical Breathing Rate: 20 L/min = 28,800 L/d Typical Drinking Volume/day: 4 L/day 28,800/4 = 7,200 1 ug/l /7,200 = ug/l = 0.14 ug/m3 The reason indoor air allowable concentrations are so low is because of the large volume of air we breathe per day.

12 Why Do You Care About VI? (Risk Often More Perceived Than Real) Health & Safety of Occupants EPA RCRA/CERCLA: Draft VI Guidance Exists CA-EPA/DTSC: Guidance Exists Individual Counties: SF, SD ASTM New Phase 1 Standard Attorneys & Citizen Groups In some cases, there is a real threat to occupants. But in the majority of cases, the risk to occupants is exaggerated, hence the perception is greater than the real risk. Nevertheless, you need to worry about it because the EPA has identified it as a risk pathway, numerous states have their own guidance or policies, and citizen groups and of course, attorneys are making it an issue.

13 Why Do You Care About It? (Risk Often More Perceived Than Real) Which one is the famous attorney and who is it?

14 When to Worry About VI? If VOC Contamination & Structures Exist Laterally within 100 (EPA & DTSC) Vertically Within 100 (EPA & DTSC) NY: No Limits!!! Complaining Occupants Structures With Odors, Wet Basements Sites With Contamination & Future Use Attorneys & Communities Even Animals, Fruits, Vegetables The EPA various State guidances use the distance criteria listed above to screen sites needing to assess the pathway. At sites with existing contamination but no current buildings, the pathway will need to be assessed when development is proposed. Attorneys and community activist groups can expand these criteria beyond the EPA limits. In some recent cases, concern about the safety of burrowing animals, and fruits & vegetables has been the reason to assess the vapor intrusion pathway.

15 What Compounds? VOCs: Hydrocarbons (benzene, aliphatics) Chlorinated HCs (TCE, TCA, PCE, VC) Methane, Dioxane, Oxygenates Semi-VOCs: Naphthalene & PAHs (not NJ or EPA) PCBs & Pesticides DDT, DDE, Acrylates The list of compounds that are in the EPA VI guidance and some State guidances include VOCs and semi-vocs. Naphthalene is particularly problematic because existing GC/MS methods (TO-15 & 8260) have problems reaching low levels. The semi-vocs are problematic because the risk-based screening levels (RBSL) are typically very low (eg., for PCBs, the RBSL is 10 to 100 times lower than benzene) and this creates sampling and analytical headaches.

16 What Types of Sites? Petroleum Hydrocarbons Service Stations, USTs, Pipelines Oil Furnaces (naphthalene) Chlorinated Hydrocarbons Vapor Degreasers (TCE, TCA, CCl 4 ) Dry Cleaners (PCE, DCE) Circuit Boards (VC, TCE, CCl 4 ) Semi-Volatiles MGP Sites (PAHs) Electrical Power (PCBs) Common sites that may be susceptible for vapor intrusion problems are any locations containing VOCs. Most commonly, USTs, tanks, piping, and refueling operations associated with petroleum hydrocarbons. In the colder climates, homes with internal oil tanks are potential candidates. Common sources for chlorinated compounds are dry cleaners (PCE), engine & parts cleaning areas with vapor degreasers (TCE, TCA) and any circuit board manufacturing facility. Semi-volatile sites include MGP sites and any sites with electrical power facilities. Contamination may exist in the soil, groundwater, or as vapor clouds. Structures overlying or near these sources may be at risk.

17 Low RBSLs Mean More Sites (benzene 1e-6 risk, default values) Depth Water (ug/l) Soil (ug/kg)* Soil Gas (ug/l) * Federal EPA version Some are Below or Near Lab DLs! This table gives a summary of the value at which the VI pathway exceeds a 1 in 1 million risk for benzene using the DTSC version of the J-E spreadsheet. The default vapor intrusion criteria currently used by EPA, DTSC, OEHHA, and many other agencies are so conservative that few sites are screened out in the screening evaluation step. Some of the values are below laboratory detection levels meaning that even the non-detects fail. Further assessment requires more data which means more expense. ratio of the allowed soil gas value for benzene for workplace vs. residential settings for three California agencies published RBSLs. The OEHHA & SF ESL values have been reduced by a factor of two to take out the effect of the different ventilation rate between residential and commercial settings that is incorporated in their tabulated values. The ratio assuming workplace exposure times of 8 hours/day, 250 days/year, for 25 years should be 5. The agency values are about 2.5 times too conservative.

18 Low RBSLs Mean More Sites (PCE 1e-6 risk, default values) Depth Water (ug/l) Soil (ug/kg)* Soil Gas (ug/l) * Federal EPA version Some are Below or Near Lab DLs! This table gives a summary of the value at which the VI pathway exceeds a 1 in 1 million risk for PCE using the DTSC version of the J-E spreadsheet. The default vapor intrusion criteria currently used by EPA, DTSC, OEHHA, and many other agencies are so conservative that few sites are screened out in the screening evaluation step. Some of the values are below laboratory detection levels meaning that even the non-detects fail. Further assessment requires more data which means more expense.

19 Screen-Out More Sites By: Adopting More Realistic Exposure Times Workplace: 8 hrs/day, 250 days/yr, 25 yrs (5x) School: 8 hrs/day, 180 days/yr, 6 yrs (30x) Hospital: 24 hrs/day, 1 yr (30x) Adopt More Reasonable Distance Criteria 100 Spatial for HCs Much to Far Due to Bio 100 Vertical for Cl Much to Far 5-10 Vertical for HC if O2 Present More sites will be screened out if more realistic screening criteria are used such as more realistic exposure times, especially for schools and hospitals, and adopting more reasonable depth criteria.

20 Reasonable Exposure Times? (Benzene 1e-6 risk, 5 deep SG sample) Agency Residential Workplace Ratio OEHHA 36 61* 1.7 DTSC SF ESLs * 1.7 * Corrected for ventilation rate Note: Ratio Should be 5 This table gives a summary of the ratio of the allowed soil gas value for benzene for workplace vs. residential settings for three California agencies published RBSLs. The OEHHA & SF ESL values have been reduced by a factor of two to take out the effect of the different ventilation rate between residential and commercial settings that is incorporated in their tabulated values. The ratio assuming workplace exposure times of 8 hours/day, 250 days/year, for 25 years should be 5. The agency values are about 2.5 times too conservative.

21 A Few Principles of Vapor Movement Fick s Law Directions & Rates of Movement Contaminant Partitioning Attenuation (alpha) Factors There are a number of basic principles that need to be understood in order to understand and effectively manage the vapor intrusion pathway. Some of these principles you may not have had in school or have never really used them, so you are rusty. We will be using them throughout the rest of this seminar so we will review them now.

22 Which Way do Things Move? Movement (Flux) = K d?/dx where: K is a proportionality constant d?/dx is a gradient Property Equation Constant Momentum: Flux = K dh/dx hydraulic cond Heat (Poisson s): Flux = Φ dt/dx thermal cond Mass (Fick s): Flux = D dc/dx diffusivity Momentum, Heat, Mass ALL Move from High to Low The fundamental equation describing momentum, heat, and mass movement is the same. Movement or flux is equal to a proportionality constant times a gradient. For momentum (groundwater or balls), the equation is known as Darcy s Law. For heat, the equation is known as Poisson s Law. For mass, it is known as Fick s Law. The proportionality constant is known as the diffusivity or diffusion coefficient (D). Balls, heat, and mass all move the same way: downhill, hot to cold, high to low concentration. As you will see, people often tend to forget this fundamental concept and make incorrect decisions.

23 Common Vapor Profiles Concentration Depth Flux Surface Source Concentration Depth Flux Deep Source Concentration Depth Flux Flux Surface and Deep Sources Knowledge of Fick s Law enables one to determine the direction of soil gas movement, and hence the direction of the source, from vertical gradients of the soil gas. Three types of common profiles are shown for sources at different locations in the vadose zone. Note that the flux is down the concentration gradient even when the flux is going uphill with respect to depth in the vadose zone.

24 How Fast do Things Move? Distance = (2*D e *t) 1/2 where: D e is effective diffusivity, t is time Vapors through the Vadose Zone: D e = 0.01 cm 2 /sec Distance = (2*0.01*31,000,000) = 800 cm/yr Vapors through Liquid (into/out of GW): D e = cm 2 /sec Distance = (2* *31,000,000) = 8 cm/yr Transport in Vadose Zone 100 times faster than in GW An estimate of how fast contaminants move in the vadose zone can be obtained by a simple calculation based upon the diffusivity. Contaminants move through the vadose zone by molecular diffusion at a rate of 800 cm/yr, which is 8 m/yr, or approx. 25 ft/yr, or 1 inch a day. Contaminants move through liquid (into or out of) 100 times slower because the diffusion coefficient for liquids is 10,000 times lower. Thus, volatilization of contaminants out of an undisturbed water interface (e.g., groundwater) is glacially slow and typically orders of magnitude below equilibrium. This is a crucial concept when using groundwater data to calculate soil gas concentrations. Calculated soil gas values will always be over estimated.

25 Contaminant Partitioning Groundwater to Soil Gas (Henry s Constant): H = Csg/Cw, so, Csg = Cw * H Example: H benzene = 0.25 (dimensionless) For GW Conc = 10 ug/l Csg = 10 * 0.25 = 2.5 ug/l Assumes Equilibrium. Very Rarely Achieved (no mixers or blenders in the subsurface) Partitioning refers to the distribution of molecules between different phases. Partition coefficients are determined empirically by laboratory measurement. The partition coefficient for water to air partitioning (e.g., groundwater to soil gas) is called the Henry s Constant or Henry s Law. It simply is a ratio of the concentration in the air to the concentration in the water. It is simple to calculate the soil gas concentration from groundwater data or the reverse from the dimensionless Henry s constant. Henry s constants are based upon equilibrium being reached. The container was vigorously mixed. Mixers do not exist in the subsurface so equilibrium not reached and actual soil gas concentrations are far below calculated ones.

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27 Attenuation (alpha) Factors α sg = C indoor /C sg α gw = C indoor /(C gw *H) Lower alpha means higher attenuation Current VI guidances: EPA αsg = for 5, 0.1 for sub-slab DTSC αsg = for 5, 0.01 for sub-slab Hydrocarbon αsg likely < A common term in the vapor intrusion community is the attenuation factor also called the alpha factor. The soil gas alpha factor is a ratio of the indoor air concentration to the soil gas concentration. The groundwater alpha factor is a ratio of the indoor air concentration to the groundwater concentration times its Henry s constant. Since indoor air values are lower than subsurface values, alpha factors tend to be less than 1, hence lower numbers mean greater attenuation. Thus, inverse alpha factors are often easier to understand. The EPA draft guidance uses very stringent alpha factors, determined empirically from a limited data base or from the J-E model. More recent and larger data bases (IBM Endicott) are showing that the alphas should be orders of magnitude lower, especially for petroleum hydrocarbons.

28 Using Alpha Factors to Calculate Screening Levels For Soil Gas: C sg = C indoor /α sg For Groundwater: C gw = C indoor /(H*α gw ) Example: C in benzene = ug/m3 C sg (5 ) = 0.084/0.002 = 42 ug/m3 C gw = 0.084/(0.20* ) = 4.2 ug/l By using alpha factors, one can calculate target levels for soil gas and groundwater by knowledge of the acceptable indoor air concentration. This is the method the EPA guidance and many state guidances use to determine acceptable levels in the soil gas or groundwater. Many consultants are not familiar with using alphas or doing risk calculations, and often are chasing incorrect target values.

29 Acceptable Soil Gas Levels (Benzene 1e-6 risk, 5 deep sample) State Alpha 1/Alpha Fail Level (ug/m 3 ) DTSC S DTSC S6 Model ~ SD-DEH Model 11, SF ESL CHHSLs Model ~ EPA Q This table gives a summary of the acceptable soil gas level (the fail level ) for a 5 foot deep soil gas sample for different agencies. Note the large difference in the levels based upon the agency. The DTSC S5 refers to Step 5 in their guidance where a default alpha is used. The DTSC S6 refers to step 6 where a DTSC custom version of the J-E model is allowed. The CHHSLs refer to the screening levels developed by CA-EPA OEHHA. San Diego County is likely to close the gap in their guidance within the next year.

30 Brief Review of EPA & CA VI Guidances In this part of the seminar, we will briefly review the new EPA OSWER draft vapor intrusion guidance (2006 version) and some of the CA agency s guidances.

31 Overview of Proposed Changes EPA OSWER VI Guidance Nov Fall 2006 Tier 1: Primary Screening Q1: VOCs present? Q2: Near buildings? Q3: Immediate concern? Tier 2: Secondary Screening Q4: Generic screening Q5: Semi-site specific screening (alphas from charts & tables) Tier 3: Site-Specific Pathway Assessment Q6: Indoor air (and/or subslab) Tier 1: Preliminary Screening Q1: VOCs present? Q2: Near buildings? Q3: Immediate concern? Tier 2: Generic Screening Q4: Generic residential and non-residential screening levels Tier 3: External Site-Specific Screening Q5: More site-specific parameters (alpha from spreadsheet) Tier 4: Internal Site-Specific Assessment Q6: Indoor air or subslab or both Multiple lines of evidence The EPA has proposed changes to the draft guidance that were supposed to go into effect in the summer of 2006 but have been delayed due to recent conflicting opinions within the agency. The same 6 questions exist, but they have been divided into 4 tiers instead of 3 tiers (Q4, Q5, & Q6 all get their own tier). This was primarily done to allow more flexibility under Q5. Q5 now allows more sampling options external to the structure and more freedom in using the J-E model before having to go inside. This will allow the more versed consultants to be creative. (Slide courtesy of Helen Dawson of EPA)

32 Targe t Indo or Air Co nc. Bas is Saturated Vapor Conc. Sufficiently To xic? x Acenaphthene 2.10E+02 NC 2.07E+04 No x Acetaldehyde 1.11E+00 C 2.14E+09 Yes x Acetone 3.50E+02 NC 7.19E+08 Yes x Acetonitrile 6.00E+01 NC 2.01E+08 Yes x cis-1,2-dichloroethylene 3.50E+01 NC 1.06E+09 Yes x ,1-Dichloroethane 5.00E+02 NC 1.21E+09 Yes x ,2-Dichloroethane 9.36E-02 C 4.20E+08 Yes x ,1-Dichloroethylene 2.00E+02 NC 3.13E+09 Yes x Tetrachloroethylene 4.12E-01 C 1.66E+08 Yes x trans-1,2-dichloroethylene 7.00E+01 NC 1.74E+09 Yes x ,1,2-Trichloroethane 1.52E-01 C 1.67E+08 Yes x ,1,1-Trichloroethane 2.20E+03 NC 8.88E+08 Yes x Trichloroethylene 1.11E+00 C 5.19E+08 Yes x Vinyl chloride (chloroethene) 2.77E-01 C 1.00E+10 Yes OSWER VAPOR INTRUSION GUIDANCE Table 1. Chemicals Sufficiently Toxic to Pose an Inhalation Risk via Vapor Intrusion Preliminary Screening View Selected Chemicals Check (x) Cia, target C = cancer Cv Cv.Cia,target? If Present CASN Chemical (ug/m 3 ) NC = noncancer (ug/m 3 ) (yes/no) Generic Screening Considering: NJ - Min. 1 boring / house - 75% soil as fine as - Near-slab 3 x 10 ft External Site- Specific Screening - I.C. if not Unrestricted - Delineate for future Internal Site- Specific Assessment Sub-Slab Conc. Indoor Air Conc. In-Building Concentrations < 0.1 TL > 0.01 TL to < TL > TL No Action or < 0.1 TL/AF No Action Investigate IA Sources Investigate IA Sources Resample SS Investigate IA Sources Investigate IA Sources > 0.1 TL/AF to < TL/AF or No Action or No Action and Monitor IA Monitor IA Monitor IA > TL/AF Mitigate or Mitigate or Mitigate No Subslab Data Resample IA or Investigate IA Sources No Action** Sample SS or Mitigate No Indoor Air Data No Action Resample SS or Sample IA Monitor IA or Mitigate Sample IA and/or SS By Helen Dawson (minor mod. 8/3/05) This summarizes the series of steps in the new guidance and the way the data from each step will be interpreted. The last step shows a decision matrix similar to the State of NY. This is NOT good news for RPs. Slide courtesy of Henry Schuver of EPA

33 CA Agencies With Policy/Guidance CA-DTSC Soil Gas Collection & Analysis Advisory Vapor Intrusion Guidance EPA Region 9 Follows the EPA Draft VI Guidance SF-RWQCB Has own ESLs ( fail levels ) San Diego DEH Current TWG Revising Existing Guidance Here is a summary of the vapor intrusion policy/guidances for some California regulatory agencies. San Diego County is reviewing their existing guidance. DTSC has soil gas collection & analytical guidance and has just issued a vapor intrusion guidance document. The San Francisco Water Board has issued their own ESLs (fail levels).

34 Office of Environmental Health Hazard Assessment Mandated to develop screening numbers for California per Senate Bill 32 SB 32 document contains screening numbers for vapor intrusion: (CHHSLs) OEHHA screening numbers can be used to estimate the degree of effort for site cleanup but the numbers are risk-based Cal-EPA recently published a user s guide for the screening numbers ( This slide is from a recent presentation (May 2005) by Dan Gallagher from DTSC and describes the OEHHA CHHSLs.

35 DTSC VI Guidance Step-Wise Approach (11 steps) Extensive COC List (VOCs & SVOCs) Naphthalene, dioxane, PCBs Cumulative Risk Drives DLs down to TO-15 levels OSHA PELs Rarely Apply Soil Gas Data Preferred Over Indoor Air The DTSC Draft guidance (posted February 2005) consists of 11 steps. It has an extensive COC list including both VOCs and SVOCs. It requires cumulative risk (addition of risk from all sources and compounds) which in turn drives fail levels lower. In most cases, OSHA PELs do not apply. Soil gas data preferred over indoor air.

36 DTSC VI Guidance Issues (That Affect Cost) If GW Contamination, Also Do GW Soil Data Not Preferred 5035 required if & when done Soil Gas Data from 2 Depths 1 Sample per ¼ Acre, 100 Clean Zone Passive & Flux Chambers Qualitative Bioattenuation Recognized Finite Source Model Allowed (lowers) Many issues in the DTSC guidance require additional work and drive up the costs. If groundwater is the contaminant source, you must determine risk from both the soil gas and groundwater, ie., you must measure both. If soil gas data can not be obtained, soil phase data can be used but only if analyzed by method Soil gas data must be collected at 2 depths at a density of 1 sample per quarter acre. Passive soil gas and flux chambers are not considered to give quantitative results and can t be used alone for closure. The document acknowledges that bioattenuation occurs and how to demonstrate it (using vertical profiles), but there is no provision for how to use the data. Flux chambers may be a way to support the bioattenuation argument. The agency allows a finite source model to be used if the contamination zone will defined. Since all risk calculations assume 20 to 30 year exposure

37 Spill / R elease Identified Site Characterization Step 1 Step 2 U n k n o w n Site C andidate for Vapor Intrusion? Step 3 N o Current In c o m p le te Exposure Pathway Y e s U n k n o w n Im m inent H azard in B u ild in g? Step 4 Y e s N o D oes the Site Pass a G eneric J&E evaluation? Step 5 Y e s Y e s N o Step 6 Is Additional Site D ata Needed? C o lle c t Additional S ite D a ta N o Step 7 Does the Y e s S ite P a s s a S ite -S p e c ific J&E evaluation? N o Step 8 C onduct Building Screening Step 9 Collect Indoor Air Sam ples / Evaluate D ata N o Further C o n s id e ra tio n For Indoor Air Risk Indoor Air C oncentrations Acceptable? Step 10 Y e s N o Step 11 M itigate Indoor Air Exposure / C onduct Long Term M onitoring Note: Shaded steps do not apply to future building scenarios Here s the flow chart from the DTSC guidance, squeezed to one page.

38 Steps 8 through 10 are for indoor air sampling programs and Step 11 describes mitigation. DTSC Step-Wise Approach Steps 1-3: Is Site VI Candidate? Got Buildings? (If not now, in future?) Got COCs? Step 4: Imminent Risk (Headaches? Odors?) Step 5: Screening Using Alphas or CHHSLs Steps 6 & 7: Site Specific Risk Using J-E Soil Gas Data Preferred. Near & Sub-slab. Steps 8-10: Indoor Air Sampling Step 11: Mitigate A brief summary of the DTSC guidance goes like this: Steps 1 through 3 evaluate whether vapor intrusion is a possible concern at a given site. Because the criteria are so conservative, few sites are filtered out. Step 4 asks is there is an imminent risk (got headaches, odors, or attorneys?) that needs immediate action. Step 5 is a generic screening step to determine if the VI pathway might be an issue. You compare any existing site data to acceptable levels using DTSC determined alpha factors or California human health screening levels (CHHSLs) determined by OEHHA. You must also use the maximum concentration found on the site. Steps 6 & 7 is a site specific evaluation in which you collect additional site specific data and then use the DTSC version of the J-E model to determine if there is a risk. Soil gas data are the preferred type. Other model parameters such as ventilation rate, soil porosity, etc., may be used rather than model default values.

39 DTSC Vapor Intrusion Document Step 6: Collect Additional Field Data Collect air samples from crawl spaces Collect soil gas samples directly under the building foundation (subslab) Measure the physical properties of the soil, such as: porosity air permeability moisture content bulk density This slide is from a recent presentation (May 2005) by Dan Gallagher from DTSC and describes some of the additional types of data to collect when a site-specific vapor risk evaluation is being done under Step 6.

40 DTSC Vapor Intrusion Guidance Step 7: Conduct a Site-Specific Modeling Evaluation for the Building Use the Johnson and Ettinger Model (JEM) Use site-specific geotechnical and building input parameters for modeling Use appropriate contaminant concentrations Attenuation factors should be reasonable (< are probably unrealististic for shallow soil) This slide is from a recent presentation (May 2005) by Dan Gallagher from DTSC and describes some of the additional types of data to use when a sitespecific vapor risk modeling evaluation is being done. Other investigatory tools such as radon measurements, ventilation rate measurments, pressure measurements can be useful to this effort and will be discussed in the following section.

41 DTSC Vapor Intrusion Guidance Step 8 and 9: Building Pathway Evaluation and Indoor Air Sampling Building occupancy survey Identify sources of indoor contamination with field analytical equipment Sample indoor air twice to evaluate human exposure (autumn and spring) using TO-14A / TO- 15 [SIM] This slide is from a recent presentation (May 2005) by Dan Gallagher from DTSC and summarizes the indoor air sampling steps.

42 DTSC Vapor Intrusion Guidance Step 11: Mitigate Indoor Air Exposure Remediate the subsurface contamination Land use covenants to restrict property use Engineering controls to eliminate exposure Long-term monitoring may be required This slide is from a recent presentation (May 2005) by Dan Gallagher from DTSC and summarizes the final step in the VI process: mitigation

43 Methods to Assess VI Indoor Air Sampling Predictive Modeling Measure Flux Directly Soil Gas Sampling Supplemental Tools/Data In this part of the seminar, we will discuss the primary techniques used to assess the vapor intrusion pathway, including the pros & cons of each.

44 Indoor Air Measurement Pros: Actual Indoor Concentration Cons: Where From? Inside sources (smoke, cleaners) Outside sources (exhaust, cleaners) People activities Laborious Protocols, no control Snapshot, limited data points Expensive!! Measuring indoor air might seem to be the most direct and simplest approach, but it has its share of problems. The biggest problem is background sources of contaminants. Many commonly used household products contain some of the target compounds of concern. For example, benzene from gasoline, PCE from dry cleaned clothes, TCA from degreasing cleaners. In addition, the protocols are laborious, intrusive, offer little control, and are expensive. For these reasons, the EPA and many States shy away from this method. However, this method may still be the method of choice if the contaminant of concern is not one commonly found in household products (e.g., 1,1 DCE).

45 VOCs in Indoor Air From USEPA BASE study Minimum, maximum, 5, 25, 50, 75, 95th percentiles From: Girman, J. Air Toxics Exposure in Indoor Environments, EPA Workshop on Air Toxics Exposure Assessment, This plot shows the most common VOCs detected in indoor air and their concentration levels.

46 Modeling Pros: Can Use GW, Soil (?), Soil Gas Data Relatively Easy Cons: Not All States Allow Which Version to Use? Often Too Restrictive The use of models to calculate an indoor air concentration, and in turn a health risk, is commonplace. Existing models use groundwater, soil, or soil gas data and are relatively easy to use. In general, if default parameters are used, they tend to overcalculate the risk for most situations. Several versions currently exist with different default values for various parameters, so one must be careful to know what version they are using. Regulators must be careful with using modeling results for a number of reasons, one being that it is easy to try and change the values of some of the variables to get a passing value. As a result, some States will let you use the models as a screening tool, but not give complete closure.

47 Which One & Version to Use? Johnson-Ettinger Most Common GW, soil, soil gas spreadsheets Screen & advanced versions 2003 and 2001 versions differ in some defaults Hard to compare defaults vs actual values used New Version Being Written (2006) One spreadsheet for all matrices Summarizes defaults vs actual values used Others: Jury The most common model currently being used in the Johnson & Ettinger (J- E) model. The EPA has written a number of spreadsheets that are based upon the model parameters and allow the use of groundwater, or soil, or soil gas data. The spreadsheets were updated in 2003 and are available from the EPA website referenced previously. The EPA is currently rewriting the spreadsheets that will be very different in style from the existing ones. One spreadsheet will handle all matrices (groundwater & soil gas, but not soil phase data) rather than separate ones. The spreadsheet will show both default values and the user inputted values to facilitate recognition of what values were changed and by how much. Other models do exist, but the J-E model is by far the primary one being used around the country.

48 This on-line calculator is a handy way to get a feel for fail levels without getting into the J-E spreadsheets. It uses EPA Federal default parameters for toxicity info, ventilation rates, etc. It can be found at to:

49 How Well Does J-E Predict? (From GW & Soil Data) Hydrocarbons Calculated SG value too high by x No bioattenuation (10 to 1000x reduction) OVER PREDICTS IN ALMOST ALL CASES Chlorinated Solvents Deep Source Calculated SG value too high by x OVER PREDICTS IN MOST CASES Chlorinated Solvents Surface Source Calculated SG value too low by x UNDER PREDICTS IN MOST CASES If you are going to use the models/spreadsheets, you need to be aware of the limitations. If the groundwater or soil spreadsheets are being used, the spreadsheet calculates the soil gas concentration assuming equilibrium partitioning. This is likely to give a soil gas concentration orders of magnitude higher than actual values. Also, for hydrocarbons, there is no allowance for bioattenuation. So, the result is that the spreadsheet is likely to over predict risk for hydrocarbons in almost all cases, unless right at the surface. For chlorinated compounds, the spreadsheet is also likely to over predict, but not as much since bioattenuation is not as prevalent. But, if surface sources exist, then vapor clouds might exist and the actual soil gas concentration might be higher than calculated, so in turn, the risk will be underestimated. Because these models tend to over-predict the risk, especially from groundwater and soil data, you should be careful to verify the predicted risk if they show you are failing.

50 Direct Flux Measurement (Flux Chambers) Pros: Direct Measurement of Intrusion Cons: Proper Location? Protocols Debated How to Use Data? Unsophisticated Audience Regulatory Acceptance Limited Surface flux chambers are attractive because they give a direct measurement of the flux into the structure or out of the soil. This eliminates the need to know the effective diffusivity and the uncertainty inherent in the models. The biggest drawback with chambers is whether they can be placed in the proper locations in an existing structure. Also, few regulators, consultants, or vendors have used them, so they are unfamiliar of the protocols to use and how to interpret the data. As a result, regulatory acceptance is limited. On undeveloped lots or houses with crawl spaces, surface flux chambers may be the best method to use. Flux chambers are also useful to verify if bioattenuation is eliminating contaminant fluxes from shallow vadose zone contamination.

51 Static Flux Chamber Photo of a static flux chamber equipped with a LandTech GEM 2000 realtime oxygen, carbon dioxide, and methane analyzer used to collect data continuously.

52 Soil Gas Measurement Pros: Representative of Subsurface Processes Higher Fail Levels Relatively Inexpensive Can Give Real-time Results Cons: Mass Transfer Coefficient Unknown Overly Restrictive Default Criteria Protocols still debated Measurement of soil gas is by far the most preferred approach around the country. Actual soil gas data are reflective of subsurface properties, are less expensive than indoor air measurements, and allow real-time results. The fail levels are also higher so there is less chance to be chasing blanks. There are some drawbacks, including the lack of knowledge of the effective diffusivity, very restrictive fail levels for sub-slab data, and debate over how & where to collect samples.

53 Soil Gas Sampling Methods & Issues Soil Gas Methods Sampling & Analysis Issues Where & When to Collect Samples Bioattenuation Other Tools/Approaches This part of the training will focus specifically on soil gas sampling since it is currently the most preferred approach around the country and, if you have a vapor intrusion problem, the chances are high you will be required to oversee or work with soil gas data.

54 Which Soil Gas Method? Active? Passive? (limited use) Flux Chambers? (limited use) Active method most often employed for VI There are three types of soil gas methods. Active refers to actively withdrawing vapor out of the ground. It gives quantitative values. Passive refers to burying an adsorbent in the ground and letting the vapors passively contact and adsorb onto the collector. It does not give quantitative data and hence can not be used for risk applications, except for screening. Surface flux chambers were discussed previously. The active method is the one most applicable to risk assessments.

55 Passive Soil Gas Pros: Easy to Deploy Can Find Contamination Zones Low Permeability soils Cons: Does not Give Concentration No Less Expensive Considered as Screening Tool Passive soil gas methods consist of the burial of an adsorbant into the group for a period of time (typically 5 to 10 days) and the subsequent retrieval of the adsorbant for measurement. The contaminants passively diffuse and adsorb onto the collector over time. The method is easy to deploy and is proven to find contamination zones. However, the method does not yield concentration values and thus can t be used for risk-based applications. Ongoing efforts to calibrate the method to give concentration data are inconclusive. As a result, this method is considered by most regulatory agencies, including EPA, to be a screening method. It can be used to locate contamination zones on larger parcels where the contamination is not already defined.

56 VI Requires Much Lower DLs Typical Soil Gas Concentrations MTBE & Benzene near gasoline soil: >100 ug/l PCE under dry cleaner: >100 ug/l Soil Gas Levels a Threat to GW: MTBE: >10 ug/l BTEX/PCE: >100 ug/l Soil Gas Levels Failing DTSC VI Criteria Subslab: Benzene: ug/l, PCE: 0.04 ug/l At 5 : Benzene: ug/l, PCE: 0.20 ug/l The biggest difference between sampling soil gas for site assessments and for vapor intrusion is that we are measuring at concentration levels 1,000 to 10,000 times lower. So, the protocols require much greater care. At such low levels, the chances for false positives from equipment blanks are much greater.

57 Probe Installation Methods Driven Probe/Rod Methods Hand Equipment, Direct-Push Collect sample while probe in ground Vapor Mini-Wells/Implants Inexpensive & easy to install/remove Allow repeated sampling Near surface & deep (down auger flights) Can nest in same bore hole There are two common ways to collect active soil gas samples: collection through a probe or rod driven into the ground or collection through a vapor well buried into the ground. Both methods give reliable data. The vapor wells consist of small diameter, inert tubing and offer advantages when vertical profiles are desired or when repeated sampling events are likely. Multiple tubes can be nested in the same borehole.

58 Sampling Through Rod Collection through the probe rod is advantageous if only one sampling round is required. Seals at the base of the probe are advisable, especially if depths are shallow and larger volume samples (>1 liter) are collected.

59 Soil Vapor Implants Soil vapor implants nested in same borehole at three different depths. This method is advantageous if repeated sampling is anticipated.

60 Soil Gas Sampling Issues Sample Size Greater the volume, greater the uncertainty Smaller volumes faster & easier to collect Containers Canisters: More blank potential. Higher cost Tedlars: Good for ~2 days. Easier to collect Flow Rate Really not imp. But most agencies < 200 ml/min Tracer/Leak Compound Crucial for sub-slab & larger sample volumes Gases (He, SF6, Propane) & Liquids (IPA) Lower detection levels requires more careful protocols. Important sampling considerations include sample volume, container type, flow rate, and leak testing to ensure valid samples are collected. Smaller volumes require less complicated sampling systems and minimize the chances for leakage from the surface and desorption off soil. Recent studies have shown no difference in soil gas values regardless of whether small (0.5 L) or large (100 L) volumes are collected. Sample containers must be inert, clean, and handled properly (no cooling or heat). Canisters have longer holding times, but have the potential for blanks (carry-over from previous samples), cost more, and can be trickier to fill. Tedlar bags are good for ~2 days, are less expensive, and suitable for concentrations of 1 ppbv or higher. Sample flow rate is of concern to many agencies, but recent data are showing it not to be a factor. Tracer/leak compounds are generally required to ensure sample integrity because small leaks can create significant effects at such low concentrations. The larger the volume extracted and the more complicated the sampling system, the greater the potential for leaks.

61 The Key Sampling Issues (That Directly Affect the Bottom Line) Get Enough Data Near/Around/Under Simpler Collection Systems. HUGE!!! 20 to 30 samples/day ($50-$75 each) Less chances for goofs & leaks Simpler Analysis (8021, 8260, 8270) Experience of the Collector/Consultant Have they done this before? Quality/experience of field staff? Sr or Jr? Soil gas, like soil, is not homogenous in most cases. So you need enough data to give decent coverage near, around, or under the receptor. Simpler collection systems with small volumes are advantageous as there is less to go wrong and enable higher production per day (20+ samples per day). Less expensive analytical methods (8021, 8260) enable more analyses for reasonable cost. Real-time data can be extremely helpful to track soil gas contamination laterally and vertically. The last important ingredient for cost effective and efficient VI investigations is the experience of the person/firm doing the collection. Is the collection being done by a firm that has prior experience? Is it a routine part of their services or an occasional part? Do they put experienced people in the field who can think or junior staff who aren t well versed? This applies to the consultant and their subcontractors. All of these issues affect the investigation progress and hence the cost you end up paying (the ultimate bottom line).

62 Sample Volumes A 6-liter Summa can is about the size of a basketball. A 400 cc mini-can is about the size of a baseball. Lower volumes give more control on sample location, require less time to collect, and minimize chances of breakthrough from the surface or other sampling zones in nested wells. For soil gas samples, most labs only require 100 cc of sample, so small canisters (<1 liter) are sufficient volume.

63 Volume Doesn t Matter (So Why Waste Time & $) This slide shows soil gas results for different collection volumes ranging from 500 cc to 100 liters collected by EPA-ORD at a test site. There is no significant variation in concentration. Slide courtesy of Dr. Dominic DiGuilio, EPA-ORD

64 Purging A simple and fast procedure to purge soil vapor probes is to use a disposable gas-tight syringe. Volumes can be carefully measured, the collector can get a feel for the permeability of the sampling zone from the syringe resistance, low vacuums and flow are applied, and no bulky hardware or power is required.

65 Sample Collection Collection of a soil vapor sample in a mini-summas (400 cc). Leak/tracer is typically applied prior to sample collection.

66 Sample Collection Collection of a soil vapor sample in a tedlar using a syringe. No power required, no complicated fittings. Leak/tracer can be applied prior to sample collection.

67 Beware of the Hardware The tackle box on the left shows the required hardware to collect soil gas samples in Summas. The syringe to the right is the only collection device required for on-site analysis of soil gas.

68 Sample Collection A soil gas sample collection system used by a consulting firm. Extremely complex, lots of dead-volume for cross contamination, and numerous fittings for potential leaks. Why use such a complicated system?

69 What Analysis to Use? (TO-14/15 or 8260 or 8021) All Methods Give Reliable Results Some States Require TO-15 Detection Level Discriminator: TO Methods: <1 to 10 ug/m 3 ($200-$300) 8260: 10 to 50 ug/m 3 ($100-$150) 8021: 10 ug/m 3 ($75-$100) On-Site Analysis: Extremely Helpful for VI Minimizes False Positives A variety of analytical methods are available to measure soil gas samples, but no federal guidance document exists specifying any one. Methods 8021 and 8260 are soil & water methods but give accurate results for soil gas samples at detection levels above 10 ug/m3. The toxic organic methods (TO) are designed for ambient air samples, so they give accurate results for soil gas samples at much lower detection levels. The TO methods require extensive hardware and are far more expensive. The criteria for selection should be which method(s) reach the required detection limits. On-site data are extremely useful to ensure that the samples do not have tracer/leak levels above acceptable levels, provide real-time data for decision making, and to validate detections seen in the off-site data. If measured values are high, then the on-site methods (8021, 8260) are more appropriate to use than the ultra-sensitive TO methods. If on-site values are low or below detection, then the samples can be measured off-site by the TO methods.

70 On-Site 8021 Analysis vs. Off-site TO-15 Analysis 1000 Tedlar Bag - On-Site GC Summa Canister - TO-15 This slide shows a comparison of on-site analysis of TCE by 8021 out of a tedlar vs. off-site analysis by TO-15 out of a Summa canister collected by EPA-ORD at a test site. Correlation is excellent down to values as low as 2 ppbv. Slide courtesy of Dr. Dominic DiGuilio, EPA-ORD

71 TO-15 for Soil Gas Samples Typical Soil Gas Concentrations Benzene near gasoline soil: >100,000 ug/m3 TPH vapor: >1,000,000 ug/m3 PCE under dry cleaner: >100,000 ug/m3 TO-15 Maximum Conc: 2,000 ug/m3 Must do large dilutions, DL goes up False positives from hot samples TO Method & Hardware Not Designed For This Concentration Range Typical soil gas concentrations at leaky UST, dry cleaner, and industrial solvent sites are in the 100,000s to 1,000,000 of ug/m3. But, for 1 in 1 million risk, the risk-based screening levels are less than 10 to 100 ug/m3. This large concentration range creates a number of analytical headaches. The TO-methods and hardware (canisters, flow chokes) are not designed for such high concentrations. System carryover, large dilutions, and contaminated canisters increase the potential for false positives, raises reporting levels, and gives air labs logistical fits which limits the utility of these methods. The 8260 and 8021 methods can t get lower than 10 to 100 ug/m3 so they may not reach required DLs. In practice, a combination of these methods is the best approach. If expected values are high, then the 8021 & 8260 are advantageous to use than the ultra-sensitive TO methods. If expected values are low, then the TO methods offer advantages.

72 Not All TO-15s Are Alike Standard Method QA/QC Poor & Does Not Meet Many States Requirements (CA-EPA, NJ, NY) Can use standard for a year!! No second source standard No surrogates Wider calibration acceptance windows Beware the Wal-Mart TO-15 Only use labs that have upgraded method Only use lab that has a certification The TO-15 analytical method has been advertised as the Gold Standard, but actually, the QA/QC is very poor and does not match the requirements of many State agencies. Further, it may have difficulty meeting the legal challenge. Incredibly, most State regulatory personnel don t realize this. Some States, like NJ, have published a more exacting method than the standard method. The higher-quality labs have upgraded the method to meet more exacting requirements required by the EPA SW-846 methods or any specific State regulatory requirements, such as second source standards & surrogates. Beware the Wal-Mart TO-15. To ensure that you are getting a quality analysis, only use labs that can show they have upgraded the method QA/QC and have a certification from some NELAC or a State agency.

73 On-Site/Off-Site Analysis ( TO15 Combo) Allows Purge/Sample Volume Test Allows Measure of Leak Compound Ensures valid samples Real-Time Results to Guide Program Validates Off-site Data Minimizes false positives Allows Optimal Method to Be Used 8260 if > 1 ug/l, TO-15 if < 1 ug/l On-site data are extremely useful to ensure that the samples do not have tracer/leak levels above acceptable levels, allow the DTSC required purge volume test, provide real-time data for decision making, and to validate detections seen in the off-site data. If measured values are high, then the on-site methods (8021, 8260) are more appropriate to use than the ultrasensitive TO methods. If on-site values are low or below detection, then the samples can be measured off-site by the TO methods.

74 What Method for Naphthalene? On 8021, 8260 & 8270 Target Lists Not on TO-15 or TO-17 Standard List Can be analyzed with custom standard Cold spots in system a problem Storage Likely to be Critical Variable Comparative Data Close 8260 if > ug/m3 TO-15 if < ? Naphthalene is a target compound on the 8021, 8260 (volatiles) and 8270 (semi-volatiles) method compound lists. While methods 8021& 8260 are commonly used for vapor samples, 8270 is not. Naphthalene is not a target compound by TO-15 or TO-17 and is not included in the calibration standard. But it can be analyzed by the method if a custom calibration standard is ordered. Be sure your lab is doing this. The compound is considered sticky due to it s low vapor pressure and hence all these methods have to be careful with carryover from hot samples and loss of low concentrations. Storage of the soil gas sample is also likely to be a critical variable. Comparative data to date show agreement within a factor of 2 by the two methods.

75 Where to Sample Spatially Source Not Immediately Below Collect on side towards source Collect on other sides of structure Preferential pathways at edges & conduits Source Below Collect around structure before sub-slab Get decent coverage Representativeness Need enough points. What algorithm? There is currently much debate on where to collect samples and no existing protocols or guidance. So, common sense comes into play. If source not directly below, collect samples between the structure and the source at a depth that is deep enough to give repeatable results. Collect in any known preferential pathways, such as utility lines. If the source is below, collect around the structure before going inside the structure. Spatial averaging allows a better representation of what s below the structure. One approach is to collect samples on all sides of the house and use an averaging method to get a value under the structure footprint. If real-time data exist, add additional points depending upon the results. If not, collect extra samples spatially and analyze if necessary.

76 Where to Sample Vertically Initially Deep Enough for Stable Data If contamination not deeper, how can it be shallower? For HCs, 3 to 5 below structure For Cl-HCs, at GW or mid-way to GW Work Within the VI Dead Zone Zone of Most Bioattenuation Zone of Surface Reaeration Vertical Profiles Determine direction of source Can aid in documenting bioattenuation The closer you get to the surface, the greater the chance that surface processes such as atmospheric pumping, precipitation, & advective flow from structures will affect the soil gas. So, initially, sample 5 bgs to get below this zone if the source is below. Collect samples within the draft VI guidance s dead zone, from 5 feet to the surface to document that the concentrations are attenuating. Vertical profiles also will aid in determining the direction of the source.

77 Sub-Slab vs. Near-Slab Profiles? Are sub-slab samples the best to collect? Slide courtesy of Dr. Paul Lundegard, Unocal/Chevron

78 Sub-Slab vs. Near-Slab EPA & Some States Prefer Sub-slab Ponding effect under slab? Balls don t run uphill Good Comparison Database Lacking Very Intrusive. Attorney Time. If O 2 High Around Slab, Near-slab OK For Cl-HCs, at GW or mid-way to GW The draft VI guidance strongly advocates sub-slab samples and some State agencies agree. Some are fearful that the contaminants build-up under the slab ( ponding effect ). But, sub-slab sampling is intrusive and often leads to legal complications. By Fick s law, the sub-slab concentration can be no higher than the source concentration, so if the source below, collection of samples at the source depth or midway to the source will give useful data and not create as many legal headaches. If high oxygen levels exist all around the slab at a shallow depth, and the slab small, there is a good chance that reaeration under the slab is occurring and sweeping contaminants clear.

79 Effect of Source Concentration [λ = 0.18 h -1 ] Results suggest that there may be source vapor concentrations that are of little concern if soil gas beneath the foundation is welloxygenated (e.g., groundwater plume sources) α = 7.1 x 10-5 α = 7.2 x 10-8 α = 5.6 x Recent modeling by Dr. Lilian Abreau (Geosyntec Consultants) and Dr. Paul Johnson (Arizona State University) has shown that for hydrocarbons sources in the soil vapor less than 20 mg/l, there is unlikely to be any vapor intrusion risk. The benzene vapor concentration in equilibrium with gasoline is only 7.8 mg/l and data from 100 sites show maximum benzene vapor concentrations of less than 1 mg/l! So, unless the source very close to the receptor, there is no need to worry. Slide courtesy of Dr. Lilian Abreau & Dr. Paul Johnson

80 How Often to Sample? Depth Below Surface 3 to 5 bgs generally considered stable Temporal Studies Ongoing Seasonal Effects How Important? Most studies show less than 5x Extreme Conditions? Heavy rain Extreme heating/cooling Why Spend the $? The closer to the surface, the more the potential temporal variation. Depths of 3 to 5 below the surface are generally considered deep enough to get repeatable data and resampling is not required by most agencies. Historical radon data around houses show variations less than a factor of 7 in cold climates. Recent VOC data from Endicott show soil gas variations less than a factor of 4 over 15 months. Larger variations may be likely in areas of extreme temperature variation (northern climates), during heavy periods of precipitation, and when the structure s heating or ventilation systems are operative. In general, if the soil gas concentrations are below allowed levels by a factor of 10, there should be no need to repeat sampling. If conditions suggest that temporal variations may be significant and if the measured values are close to the fail level, then repeated sampling may be appropriate and vapor implants are a good approach.

81 Recent data collected over 15 months from Endicott NY show very low variations in deep soil gas (max variation less than factor of 2) and sub-slab soil gas concentrations (max variation less than factor of 4). Hence, in most cases, it is not necessary to collect samples more than once. Slide courtesy of Dr. William Wertz, NY-DEC

82 Bioattenuation of HCs Existing data suggest O 2 effective barrier Attenuation > 10,000 times Vertical profiles of COC & O 2 DNA can confirm presence of tropic bugs A vast number of studies have been performed clearly demonstrating that the bioattenuation of hydrocarbon vapors occurs in aerobic soils. In general, the studies show that when oxygen levels are 5% or greater and a couple feet of vadose zone exist between the source and receptor, that the hydrocarbons aren t escaping into the receptor. Attenuation factors can be as high as 10,000 times (alpha = ). Documention that this process is occurring is done by collecting vertical profiles of the soil gas for the hydrocarbons, oxygen, and carbon dioxide. If shown to occur, many agencies are conservatively allowing a factor of 10 to 100 reduction in the alpha factor.

83 Theoretical Bio Profile O 2 soil surface O 2 increasing depth flux VOCs CO 2 clean soil VOCs petroleum product This is the theoretical profile for hydrocarbon VOCs, CO2, and oxygen in the soil gas with depth where bioattenuation is active.

84 Sample Events and % Attenuation of Benzene and TPH Study Data Set Events: 102 Benzene, 71 TPH n=# vapor sample events n 60 98% 92% Benzene TPH % 8% Significant AF <0.1 Insignificant AF >0.1 SIGNATURE CHARACTERISTICS OF BIO-ATTENUATION - 5 feet clean coarse-grained or 2 feet of fine-grained soil overlies contaminant source - Vapor concentrations decrease significantly vertically away from source - O2 depleted and CO2 enriched near the source, O2 enriched and CO2 depleted with increasing distance from the source - O2 minimum range 3% to 5% An analysis of hydrocarbon sites from around the country has being performed by Robin Davis of the Utah DEP. Her analysis shows that 92% of TPH contaminated sites and 98% of benzene contamination have significant (>100 times) reduction in concentration due to bioattenuation. Slide courtesy of Robin Davis of Utah DEP

85 In the Future Depth BGS (m) E HC Depth BGS (m) Graphical Summary of Many Model Simulations and Actual Field Data (α-value vs. some sub-set of general site characteristics) Conceptual Vapor Intrusion Nomogram Incorporating Bio -attenuation x (m) O x (m) 3-D Numerical Model Results [sophisticated codes are needed to address the problem, but these codes are too complex for routine use..] (0.5 Building Width/LT ) No Concerns? 10-2? 10-3? 10-4? 10-5? ,000 10,000 Source Concentration (ug/m 3 ) Although bioattenuation is recognized to exist, it is still not clear how best to account for it. Some States (NJ, NH) have reduced the distance criteria to account for the fact that hydrocarbons won t travel as far from the source. Since source strength and distance are important, a better approach might be to generate some type of nomogram based upon depth from source and strength of source. Slide courtesy of Dr. Paul Johnson, ASU

86 Supplemental Tools/Data Site Specific Alpha Using Radon Factor of 10 to 100. $125/sample Indoor Air Ventilation Rate Factor of 2 to 10. Inexpensive. Real-Time, Continuous Analyzers Can sort out noise/scatter Pressure Measurements Can held interpret indoor air results Forensics Ratios? Isotopes? If the soil gas levels exceed the fail levels, there are some other inexpensive tools/data that can be applied to better evaluate some of the default model parameters. These tools/data have much more influence on the resulting risk than measurement of soil porosity and cost about the same. Radon can be used to determine a site-specific alpha that may be 10 to 100 times lower than the default alpha allowed. Tracers can be used to measure the room ventilation rates and may give values 2 to 10 times higher than the default value, especially for commercial sites. Real-time analyzers can be used to locate problem houses, preferential pathways into structures, or sort out background scatter. Pressure measurements are helpful with indoor air data to possibly show a background source. Forensic approaches using contaminant ratios and isotopes are still in development.

87 Building Ventilation Rates ANSI / ASHRAE Standard Ventilation for Acceptable Indoor Air Quality Building Type USEPA Default (Residential) Office Space Supermarket Classroom Restaurant Air Exchange Rate (# / day) High Building Ventilation KEY POINT: Buildings designed for high density use will have high air exchange rates. Building ventilation rates for non-residential structures are known to be much higher than the default value allowed by the EPA in their J-E spreadsheet. Using the proper ventilation rate can lower the risk by as much as a factor of 20. Slide courtesy of Dr. Thomas McHugh, GSI, Houston, TX

88 A Few Words on Mitigation

89 Overview of Mitigation Approaches Soil/Groundwater Cleanup Building mitigation (interim) Institutional controls (interim) Prevent buildings Require controls in new buildings Restrict occupancy or use X Some of the more common mitigation methods for subsurface vapors include cleaning up the source, passive and active venting of the soil gas below the home, increased circulation in the structure, or institutional controls.. Simple soil gas venting systems can cost less than $2,000 and rarely are less than several thousand. Slide Courtesy of David Folkes, Envirogroup.

90 Building Mitigation Approaches Sub-Slab Depressurization Sub-Membrane Depressurization Sub-Slab Pressurization Building Pressurization Indoor Air Treatment Passive Barriers Slide Courtesy of David Folkes, Envirogroup.

91 Long-Term Liability Issues for Mitigation Remedies Changes in exposure and risk Toxicological profiles (TCE, DCE) Land uses (urban infill and senior living) Subsurface environmental conditions Building deterioration and renovation Mitigation system failure Design defects Breach of containment, damage to system, failure to continue operating HVAC, etc. Although seemingly easy to do and inexpensive, many RPs are reluctant to install mitigation systems due to the long-term liability that a system carries with it. Slide courtesy of Gregory Bibler, Goodwin Proctor LLP

92 Long-Term Liability Issues for Mitigation Remedies Monitoring and O&M Allocation of monitoring, energy, maintenance and replacement costs Monitoring and enforcement of O&M duties Access, particularly after property transferred Continuing response obligations Communication of test results and evolving risk standards Response to fluctuating test results More long term liability concerns Slide courtesy of Gregory Bibler, Goodwin Proctor LLP

93 Practical & Cost-Effective Do s & Don ts

94 Practical & Cost Saving Dos Use Reasonable RBSLs (eg, ESLs) Have Reasonable Distance Criteria Use Simplier, Faster Sampling Systems Allow Less Expensive Methods (8260) HCs: Vertical Profiles Around Structure Use Radon for Slab-Specific Alpha Measure Ventilation Rate Have Competent Consultants & Subs These are things you want to do/allow to practically and cost effectively assess this risk pathway.

95 Practical & Cost Saving Don ts (Things Not to Do or Require) Don t Require a Detailed Site Conceptual Model Don t Require TO-Analytical Methods Don t Require SS Canisters (& Certified Clean) Don t Worry About Irrelevant SG Procedures Don t Require Repeated Analysis if Values <10x Don t Require All Soil Physical Properties Don t Require Sub-Slab or Indoor Air Don t Require Meterological Data Some things you don t want to do or require if you want to keep the assessment from getting too complicated or costly.

96 The Most Common Goof 1 ug/l Benzene equals: a) 1 ppbv b) 1 ppmv c) 330 ppbv d) None of the Above Vapor units is one of the most common mistakes being made by practitioners in this field. For groundwater, the correct answer is (a). Since most consultants are used to working with groundwater, this is the default answer in their minds. But for vapors, the answer is c. The difference is a factor of 300!!

97 Previews of the VI Future VI Likely to be a Concern at Your Sites Variable Regulatory Guidance & Unclear Science Makes Assessment Tricky Existing VI Guidances Ultra Conservative Which Increases Costs New EPA Guidance to be More Flexible, Less Strict, & User Friendly Hydrocarbons to be Less of a Concern Here are some predictions & previews of the vapor intrusion pathway for the next few years.

98 Existing Documents & Training (Available at Overview of SV Methods LustLine Part 1 - Active Soil Gas Method, 2002 LustLine Part 2 - Flux Chamber Method, 2003 LustLine Part 3 - FAQs October, 2004 LustLine Part 4 More Q&A, Summer 2006 New Regulatory Guidance ITRC Guidance Out for Public Review Revised EPA OSWER Guidance 2007? A summary of existing documents and training on the VI pathway and soil gas methods can be found at these locations:

99 Existing Documents & Training Soil Gas Sampling SOPs Soil Gas Sampling, Sub-slab Sampling, Vapor Monitoring Wells/Implants, Flux Chambers ( EPA-ORD Sub-slab SOP Draft, Dr. Dom DiGuilio ( Other API Soil Gas Document ( Robin Davis Lustline Article on Bioattenuation (Lustline June 2006, More documents.

100 Blayne Hartman, Ph.D Impala Dr. Carlsbad, CA (800)

101 How to Collect Reliable Soil-Gas Data for Risk-Based Applications Part 1: Active Soil-Gas Method October 2002 LUSTLine Bulletin 42 by Blayne Hartman In July 2002, I attended a conference held by the Indiana Department of Environmental Management (IDEM) in Indianapolis with special emphasis on the upward-vapor risk-assessment pathway. Issues raised repeatedly during the conference pertained to the advantages of using soil-gas data in making risk assessments and the need for having established protocols and guidance for soil-gas surveys to ensure high-enough quality data. After making a brief statement to the audience and then being swarmed by interested parties, it was clear to me that the environmental community would be well served by an article addressing this topic. Contrary to Popular Belief Before diving into the meat of the topic, let me make three points to address some of the misconceptions raised at the IDEM meeting: Contrary to popular belief, soil-gas techniques that yield reliable data have been in existence for many years, and published regulatory protocols do exist. (I list applicable Web sites later.) Contrary to the prevailing opinion that soil-gas data is so variable that it can not be trusted for riskassessment purposes, soil-gas data collected in a careful, consistent manner typically show reproducibility of +/- 25 percent. This margin of error is on the same order as indoor air measurements and is a much smaller error than that introduced by many of the assumptions in the Johnson- Ettinger (J-E) model using groundwater data. Contrary to popular belief, soil-gas data should be significantly less expensive (by at least a factor of two) than indoor air measurements. Why Use Soil-Gas Data for Upward-Vapor Risk Assessment? As was pointed out repeatedly at the Indianapolis conference, even by Dr. Paul Johnson himself, the use of actual soil-gas values, rather than values calculated from models, is preferred. The reason for this is that the measured values account for processes that are currently hard to quantify with risk models, such as volitalization from groundwater, transport across the capillary fringe, and bioattenuation. In addition, measured values will take into account the presence of vapors in the vadose zone from sources other than groundwater, such as contaminated soil or lateral vapor transport (i.e., vapor clouds). Experience has documented that the potential error in calculated soilgas values versus measured soil-gas values can be several orders of magnitude. If calculated soil-vapor values can differ from actual values by factors of 10 to 1,000, then the calculated vapor fluxes and in turn, the calculated room concentrations using any version of the J-E model, will be off by a similar factor. In other words, the error introduced by using calculated soil-vapor data is likely to be far greater than the errors introduced by all of the other parameters used in the model (e.g., porosity, advection, multi-layers). Some History and Current Status of Regulatory Soil-Gas Guidance Historically, soil-gas surveys have been used primarily for site assessment purposes to identify soil and groundwater contamination. Part of the motive for employing such surveys was that the methods were inexpensive and quick. In the absence of published U.S. EPA methods, soilgas surveys were conducted using a variety of protocols, depending on the operator. Indeed, in their simplest form, soil-gas surveys have been conducted by hammering a piece of galvanized water pipe into the ground and hooking up a hand-held meter. No wonder soil-gas methods got such a bad rap for data quality. In the early 1990s, the Los Angeles Regional Water Quality Control Board (L.A. Water Board), under contract to U.S. EPA Region 9, began investigating the sources of chlorinated solvent contamination in groundwater in parts of the Los Angeles Basin. The board preferred to use soil-gas surveys as its initial investigatory method on the basis that the technique had a greater chance of detecting vadose-zone contamination. Recognizing the lack of published protocols and noting a wide variability in techniques by firms offering the service, the L.A. Water Board, with input from many of the soil-gas firms, wrote a set of analytical guidelines for soil-gas surveys for the purpose of bringing some consistency to the data. The original document, written in 1992, has been revised several times by the L.A. Water Board (most recent version: February 1997), and adapted as recently as 2000 by the San Diego County Department of Environmental Health (DEH) for its site assessment manual ( sandiego.ca.us/deh/lwq/sam/pdf_ files/soilgas.pdf). As years passed, these protocols became the standard for most of southern California and parts of northern California. However, they focused primarily on the analysis of soil-gas samples and gave little information on the collection of these samples. Since collection methods are also extremely varied among operators and can introduce large errors, the San Diego County DEH decided that additional guidelines were needed to bridge this gap, especially continued on page 18 17

102 LUSTLine Bulletin 44 August 2003 How to Collect Reliable Soil-Gas Data for Upward Risk Assessments Part 2: Surface Flux-Chamber Method by Blayne Hartman Since Part 1 of this topic, Active Soil-Gas Method, was printed in October 2002, U.S. EPA has initiated a series of informational workshops/conferences that address the soil-gas upward-migration risk pathway. (See tio/vapor/resource.cfm for more information.) While the active soil-vapor method is discussed in detail during these workshops, there is little discussion on the surface flux-chamber method. Yet, based on some of the default approaches recommended by U.S. EPA, the surface flux-chamber method may be the best method to use in some situations. Why is the method not discussed in the guidance? Primarily because of a lack of familiarity, experience, and understanding by the environmental community, including regulators, consultants, and contractors. So, let s take a look at this field technique and see when and how it can aid in the assessment of this risk pathway. Let me start by making two important points concerning surface flux chambers: There is currently no published or official U.S. EPA method for surface flux chambers. There is a published study performed under contract with EPA that gives a recommended protocol, but it is not regulatory guidance. There is no one right way to perform a flux-chamber survey. Like any field technique, there are variations of the method the suitability of each depends on the project goals. History Direct measurement of compound fluxes has been commonly performed in the oceanographic, soil science, and natural resource exploration (i.e., petroleum and minerals) communities for many years. The approach has not been as readily applied to environmental risk assessment. In the mid 1980s, Radian Corporation, under contract to U.S. EPA, performed a series of testing programs on the method that were summarized in a users guide (Kienbusch, 1986). The method described in this document has often been incorrectly labeled as the official U.S. EPA flux - chamber method. While the document gives a thorough treatment of one flux-chamber approach, including a comprehensive treatment of statistical sampling, it is a recommended protocol only, has several limitations for risk-based applications as described further in this article, and is a difficult read for the inexperienced user. Subsequent documents by Radian for EPA on air emissions at Superfund sites contain more general discussions on flux chamber methods and applications (Eklund & Schmidt, 1990). 14 Why Use Flux Chambers? Currently, risk due to the upward flux of vapor-phase contaminants into an overlying structure is assessed either from direct measurements of indoor air or by the collection of groundwater and/or soil-gas data and the application of a predictive transport model or attenuation factor. Both approaches have limitations. The determination of upward contaminant flux from the measurement of indoor air is subject to such complications as contributions from the natural background of contaminants in ambient air (especially in urban locations), contributions from sources from within the structure, and temporal and spatial variations. Further, the process is often a logistical headache, especially when the measurements are performed in private residences. Surface-flux chambers installed on site. For these and other reasons, U.S. EPA currently recommends collecting subsurface groundwater or soilgas data prior to the measurement of indoor air concentrations (OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils, November 29, 2002, eis/vapor.htm). The determination of upward contaminant flux using groundwater or soil-gas data requires the application of a predictive model or attenuation factor to compute the contaminant concentration in an overlying room. Attenuation factors, commonly referred to as alpha factors (α), are defined as the concentration of indoor air to either measured soil-gas concentration (soil-gas alpha) or indoor air to a calculated soil-gas value from groundwater concentrations using the compound-specific Henry s Constant (groundwater alpha). At present, attenuation factors predicted by the models have yet to be thoroughly validated with field data. Until such time that a sufficient data base is accumulated to test the model-derived values, U.S. EPA is recommending the use of default attenuation factors in its vapor intrusion guidance that are conservative and may be overprotective by up to