A&WMA Specialty Conference URS Understanding VI Screening Levels Sept 29, 2010 VI Conference 1
Screening Values URS EPA and various states use screening values to decide which sites merit further investigation Values may exist for groundwater, soil, shallow soil gas, deep soil gas, or indoor air The values vary, in part, due to differences in acceptable risk levels (e.g., 10-5 vs. 10-6 ) and/or differences in attenuation factors Sept 29, 2010 VI Conference 2
Example Residential Screening Values - Benzene URS Media EPA Calif. New Jersey Illinois Penn. Groundwater (μg/l) 5 46 15 360 3,500 Soil Gas (μg/m3) 3.1 36 16 41,000 NA Indoor Air 0.31 0.084 2 NA 2.7 Sept 29, 2010 (μg/m3) VI Conference 3
Example Residential Screening Values - PCE URS Media EPA Calif. New Jersey Illinois Penn. Groundwater (μg/l) 5 120 1 210 42,000 Soil Gas (μg/m3) 8.1 180 34 66,000 NA Indoor Air 0.81 0.41 3 NA 36 Sept 29, 2010 (μg/m3) VI Conference 4
Sources of Values Shown URS EPA Values are the 1E-06 values are from 2002 Draft Guidance, which also includes 1E-05 and 1E-04 values. U.S. Environmental Protection Agency, Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance), Federal Register, 67, Number 230, pp. 71169-71172, November 29, 2002. California Indoor air and soil gas values are from January 2005 CHHSLs. GW values are from May 2008 CRWQCB, San Francisco Bay Region document. California EPA. Use of California Human Health Screening Levels (CHHSLs) in Evaluation of Contaminated Properties. January 2005 California Regional Water Quality Control Board (CRWQCB). Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater. Interim Final November 2007 (Revised 2008) Sept 29, 2010 VI Conference 5
Sources of Values Shown URS New Jersey Vapor Intrusion Guidance NJDEP Mater Table, Table 1. Generic Vapor Intrusion Screening Levels. March 2007. Illinois Draft values from Section 742, Table G (Values currently under review by the Agency) Proposed Amendments to Tiered Approach to Corrective Action Objectives. September 3, 2008 Pennsylvania Values are from 2004 Guidance Department of Environmental Protection. Land Recycling Program Technical Guidance Manual Section IV-A.4 Vapor Intrusion into Buildings from Groundwater and Soil under the Act 2 Statewide Health Standard. January 24, 2004. Sept 29, 2010 VI Conference 6
Vapor Intrusion Screening Level Calculations Robert Ettinger Geosyntec Consultants AWMA Specialty Conference Vapor Intrusion 2010 Chicago, IL September 29-30, 2010
Vapor Intrusion Screening Levels Screening Level Calculation Needs Target Indoor Air Concentration Vapor Intrusion Attenuation Factor (α) 2 Decisions Receptor Scenario Target Risk / Hazard Level How to Address Background Model Selection Model Inputs Media for Screening Evaluation Model Uncertainty Screening levels should be considered a starting point for risk-based decision making. Corrective action decisions should not be limited to a comparison to default VI screening levels.
Risk Management Considerations Target Indoor Air Concentrations Variability in target indoor air concentrations due to : Toxicity assumptions Exposure assumptions Target risk level May also consider Occupational standards Background risks/concentrations Relative Risk Levels 3
Vapor Intrusion Models There are a variety of modeling options to consider Empirical Analytical Numerical USEPA Database Johnson and Ettinger (1991) VAPOURT (1989) Utah DEQ Little et al. (1991) Sleep & Sykes (1989) San Diego SAM RUNSAT (1997) VOLASOIL (1996) Abreu & Johnson (2005) Krylov and Ferguson (1998) VIM (2007) DLM - Johnson et al. (1999) Brown University (2007) DeVaull (2007) Screening levels typically based on empirical models or simple analytical models with conservative assumptions 4
USEPA Empirical Attenuation Factors Source Median 95%ile Crawl Space 0.5 0.7 NR Sub-Slab Soil Gas 0.005 0.1 Soil Gas 0.01 0.3 Groundwater 0.0001 0.001 From USEPA, 2008. Draft USEPA s Vapor Intrusion Database: Preliminary Evaluation of Empirical Attenuation Factors, Office of Solid Waste and Emergency Response, March. USEPA study shows range of empirical attenuation factors Some regulatory agencies are focusing on 95%ile values Consider flexibility for alternate values for site-specific specific application 5
Analytical Modeling Attenuation Factors Conservative assumptions typically used for modeled screening-level attenuation factors Soil type moderately sensitive Soil gas advection rate moderately sensitive, but can be significant if assumed to be zero Building ventilation rate moderately sensitive Biodegradation very significant for petroleum hydrocarbons if conditions conducive to degradation Typical screening-level estimates consistent with empirical data slab ~ 0.005 soil_gas ~ 0.002 soil_gas ~ 0.0005 6 sub-slab soil_gas soil_gas
Vapor Intrusion Screening Levels Panel AWMA Vapor Intrusion Specialty Conf. Chicago, IL Sept. 29, 2010 Presented by: Personal Observations by Henry Schuver, DrPH USEPA Office of Resource Conservation & Recovery See: http://epa.gov/oswer/vaporintrusion http://iavi.rti.org & www.envirogroup.com/vaporintrusion
Goal of VI Screening Levels Three (simultaneous) Ideals Sensitive Catch all (current or future) VI problems Specific Do not catch (current or future) buildings without (current or future) VI problems Communicable Be able to assure occupants of buildings overlying a vapor source they are not more exposed (via VI) than occupants of buildings not overlying a subsurface vapor source
VI Screening Levels (for Internal & External samples) Sreening Level = Risk Dose-Response Attenuation a 0.0001 cancer Health effect Source type (bio, +) b 0.00001 Age/life-stage effects Subsurface factors c 0.000001 Species Hum./Animal/cell Building factors d Non-Cancer Methods Atmospheric factors e Background Age of studies Modeled (a scenario) f Observed (Empirical) (Variability & %) Indoor Air samples External samples
Draft - AEHS Spring 2010 Significant Variability remains at the Site-Specific level (for sites with sufficient observations to see it) 1.0E+00 1.0E-01 Hopewell Precision (NY) site SCM Cortlandville (NY) site West Side Corp. (NY) site Max 95th% Groundwater AF 1.0E-02 1.0E-03 50th% 5th% Min 1.0E-04 1.0E-05 1.0E-06 AEHS Spring 1.0E-07 2010 H. Dawson US EPA 4
Median Attenuation Factor <1E-4 ~1E-3 ~1E-1 Building-Specific Attenuation Indoor Air Subslab Groundwater 1.0E+01 Billings Site Attenuation Factor 1.0E+00 1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 IA/GW IA/SS SS/GW Max 95th% 50th% 5th% Min One case study by H. Dawson illustrating the importance of Building Effects/Factors
Samples out here can t reflect building factors, or atmospheric effects Radon workers are ahead of us Building-specific factors are important; &
Only Indoor Air samples are: Building-Specific & Reflect the full (cumulative) effects of: Source type Subsurface migration factors Building factors (& indoor sources) Atmospheric factors External samples (& models, largely) can not or do not include the last two parts of the equation.
It appears that: External Screening Levels Can be used: To identify a generic Vapor Source Area With potential to cause unacceptable VI under some conditions i.e., be Sensitive Catch all (current or future) VI problems Specific [screen out sites w/ < generic source #] Communicable Be able to assure occupants of buildings overlying a vapor source they are not expected to be more exposed (via VI) than occupants of buildings not overlying a subsurface vapor source
It appears that: External Screening Levels Can NOT be: Modified to be more site-specific i.e., have Not yet been demonstrated to reliably: Predict non-generic migration Predict non-generic exposure point concentrations (indoor air)
APPLICATION OF SCREENING LEVELS AWMA Specialty Conference Vapor Intrusion 2010 Chicago, IL September 29-30, 2010 Site Characterization Risk Assessment Environmental Policy & Regulation (EP & R) Risk Management & Risk Communication Atul M. Salhotra, PhD asalhotra@ramgp.com 1
Two Options to Evaluate Vapor Intrusion 1. Measure representative point of exposure (POE), indoor air - Compare measured POE concentrations with indoor air screening levels - Compare measured POE concentrations with background concentrations 2. Measure non-exposure point concentrations (sub slab vapor, soil vapor, soil, and/or groundwater concentrations) - Compare measured concentrations with respective screening levels, - Use the measured concentrations to calculate risk Option 2 necessarily requires calculation of POE concentration Calculation of POE concentrations uses the attenuation factor. The attenuation factor can be calculated using a model or an empirical value. 2
Screening level/risk Calcualtion Issues The process of developing screening levels and the underlying science of vapor movement is well known So where lies the problem? Temporal and spatial variability in the factors that affect vapor migration and vapor intrusion Enough tools are available to account for uncertainty and variability Primary Issue: Efforts to force fit an inherently stochastic process within a conservative deterministic regulatory program 3 3
Factors that affect Vapor Accumulation and Vapor Intrusion Variability in daily, weekly and seasonal life style Variability in climatic factors (rainfall, barometric pressure, water table, pore water content) Spatial variability in geology 4 4
What Needs to Change Extreme risk aversion of regulatory process Management of sites based on a worst case scenario For a stochastic process, decisions based on worst case is not prudent At many sites, evaluation and management of VI causes huge amounts of waste and flies in the face of our stated goal of Green Remediation. 5 5
Indoor (Basement, First Floor) & Exterior Concentrations 6 6
Isopentane Attenuation Factor in a Home Sub-Slab ID All Attenuation Factors Attenuation Factors <1 N Min. Max. Avg. N Min. Max. Avg. SS-1 40 4.0E-06 5.4 1.2 24 4.0E-06 1 0.3 SS-2 22 3.3E-02 11.8 2.3 12 3.3E-02 0.9 0.4 SS-3 10 6.5E-05 4.9 2.5 3 6.5E-05 0.8 0.3 SS-Avg. 40 5.0E-06 6.7 1 29 5.0E-06 0.9 0.2 7 7
Sub-Slab Concentrations 8 8
Barometric Pressure Fluctuation 9 9
A&WMA Specialty Conference Ohio EPA VI Screening Levels for Ohio Cleanup Programs Sept 29, 2010 VI Conference 1
VI Guidance Issued May 2010 Ohio EPA Two Programs Voluntary Action Program (VAP) Semi-private Remedial Response Program (RRP) CERCLA/NCP Sept 29, 2010 VI Conference Both programs OSWER - Apply attenuation factor of 0.1 for soil gas or.001 for ground water J&E modeling for soil, gw, soil gas Allow the use of RAGS F for nonresidential exposures 2
RRP Screening Levels Ohio EPA OSWER Guidance or RSLs ELCR 1 E-06; HI = 0.1 COCs screened out of baseline risk assessment Ground water may or may not default to MCL Sept 29, 2010 VI Conference 3
VAP Ohio EPA No screening out of COCs Risk contribution from each carried forward in adjusting for multiple chemicals ELCR 1 E-05; HI = 1 Ground water defaults to MCL Sept 29, 2010 VI Conference 4