Modeling the Vapor Intrusion Pathway: Revisions to the MCP GW-2 Groundwater Standards Environmental Protection One Winter Street, Boston, MA 02108 http://mass.gov/dep Paul W. Locke Bureau Waste Site Cleanup (617) 556-1160 Paul.Locke@state.ma.us Andrew Friedmann, Ph.D. Office Research & Standards (617) 292-5841 Andrew.Friedmann@state.ma.us Focus Today s Discussion Indoor Air Preferential Pathway Groundwater Soil Soil Gas
The History Concerns with the Groundwater/Indoor Air Pathway Hillside School (Microwave Development Lab Site) DEP Publishes GW-2 Standards National Attention: Colorado sites RCRA EI Work Draft EPA Guidance J&E Model Published in ES&T DEP Regional Staff Evaluate Vapor Intrusion Pathway (Nancy Fitzpatrick & John Fitzgerald) Revision GW-2 Stnds (Proposed) 1989 1991 1992 1993 1996 1998 1999 2000 2001 2002 2003
1991- Johnson & Ettinger Heuristic Model Johnson, P.C., and R.A. Ettinger, 1991, Heuristic Model for Predicting the Intrusion Rate Contaminant Vapors into Buildings, Environ. Sci. & Technol., v 25, pp. 1445-1452 GW-2: Groundwater -> Indoor Air Noncancer Risk-based Indoor Air Concentration Cancer Risk-based Indoor Air Concentration 50% Odor Recognition Threshold Indoor Air Background Lowest These 3 Higher these as Target Indoor Air Target Concentration Model (Johnson & Ettinger) α air groundwater Calculated Source Concentration in Groundwater Ceiling Concentration Groundwater Background Lower These 2 Practical Quantitation Limit Highest These 3 Concentrations Adopted as MCP GW-2 Standard
GW-2 Derivation Attenuation Factor, α = 5 x 10-4, applied to all chemicals with an additional adjustment factor, d, applied by DEP: [OHM] gw = [OHM] air / (α x d x H x C) Fitzpatrick & Fitzgerald Studied 47 Sites: 55% chlorinated VOCs, 45% gasoline 52% residential 2% schools 46% commercial
Fitzpatrick & Fitzgerald, continued Conclusions: Significant differences appear to exist between the fate/transport and impacts chlorinated and non-chlorinated VOCs Attenuation Coefficients for chlorinated VOCs appear to be in the range 1E-1 to 1E-3, significantly higher than the 5E-4 value assumed by MADEP Observed levels non-chlorinated VOCs in the vadose zone are typically 1 to 2 orders magnitude lower, due apparently to biodegradation these non-chlorinated (BTEX) VOCs above the water table. 3. The Future FY2000 Revisions Method 1: GW-2 Standards Development Method 2: GW-2 Standards New/Modified Method 3: Site-specific Risk Assessment
FY2003 Revisions to Standards GW-2 evaluation to include chemical-specific modeling vapor intrusion using modified USEPA Johnson & Ettinger model spreadsheets. Regulations also to include consideration VOCs in soil in applicability Method 1 soil standards.
EPA Review Objectives Evaluate the reliability federal and state screening level approaches for assessing the vapor intrusion pathway. Provide a comprehensive assessment the correspondence between screening level approaches and actual measurements. Determine whether this pathway is concern even if groundwater meets drinking water standards.
(2002)
Fall 2002 (Public Comment Period ended last week.)
EPA Proposed 3 Stage Screening Process: = Method 1 = Method 2 = Method 3
DEP Proposed Values
Summary: We are not alone. Proposed DEP Method 1 GW-2 Standards will be generally protective, but NOT as conservative as EPA Q4 Screening Values. EPA building on state experiences to develop national guidance, helpful for Method 2 and Method 3 Risk Characterizations Groundwater-to-Indoor Air or Soil-to-Indoor Air Pathways: Assessing Risks Goals Convey what site-specific data needs to be collected Convey how to input site-specific data and chemical data into J & E model
Groundwater-to-Indoor Air or Soil-to-Indoor Air Pathways: Assessing Risks Must determine the Exposure Point Concentration (EPC) in air. 1. Direct Sampling Indoor Air 2. Model Pathway from Soil Gas Sampling 3. Last resort: Model Pathway from Groundwater or Soil Download Johnson and Ettinger Model Go to U.S. EPA website: http://www.epa.gov/oerrpage/superfund/programs/risk/airmodel/ johnson_ettinger.htm Scroll down to 3-Phase System Models and Soil Gas Models Double-click on Excel zip file to download Once downloaded, double-click on excel.zip to extract
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Select Appropriate Workbook Choose from eight workbooks depending upon the media from which the data was obtained: - GW-ADV - GW-SCREEN - NAPL-ADV - NAPL-SCREEN - SG-ADV - SG-SCREEN - SL-ADV - SL-SCREEN Workbooks versus Worksheets Workbook is a collection spreadsheets (or worksheets) Worksheet is a page a Workbook
Site-Specific Data Required Site-Specific Data Parameter Depth below grade to water table (cm) Soil gas sampling depth below grade (cm) Depth below grade to top soil contamination (cm) Depth below grade to bottom soil contamination (cm) Soil stratum SCS type Thickness Soil strata (cm) Values site-specific site-specific site-specific site-specific site-specific site-specific
Required Site-Specific Data (continued) Parameter Values Depth below grade to bottom site-specific or enclosed space floor (cm) use default (15 or 200) Average soil/groundwater site-specific or temperature ( o C) default (10) Vadose zone soil dry site-specific or bulk density (g/cm3) default (1.5) Vadose zone soil total site-specific porosity (unitless) default (0.43) Required Site-Specific Data (continued) Parameter Default Values Vadose zone soil water- site-specific or filled porosity (cm3/cm3) default (0.061) Enclosed Space Floor site-specific or Length (cm) default (961) Enclosed Space Floor site-specific or Width (cm) default (961) Enclosed Space site-specific or Height (cm) default (488)
How to Use the Model for Risk Assessment Input Site-Specific Data Obtain and Input Chemical-Specific Data
Influence Site-Specific Parameters on Exposure Point Concentration Parameter Change in Parameter Exposure Point Concentration Depth below grade to bottom enclosed floor space Depth below grade to contamination Vadose zone soil dry bulk density Vadose zone soil water- filled porosity Vadose zone soil total porosity Required Chemical-Specific Data Parameter Concentration in media Units site-specific Organic carbon partition coefficient (K oc ) cm 3 /g Diffusivity in air (D a ) cm 2 /s Diffusivity in water (D w ) cm 2 /s Henry's law constant at reference temperature (H) atm-m 3 /mol Henry's law constant reference temperature (T R ) o C
Required Chemical-Specific Data Parameter Units Normal boiling point (T B ) o K Critical temperature (T C ) Enthalpy vaporization at the normal boiling point (DH v,b ) o K cal/mol Chronic Inhalation Reference mg/m 3 Concentration (RfC) Inhalation Unit Risk Factor (URF) (µg/m 3 ) -1
Chemical-Specific Data For chemicals listed in EPA workbooks, this information is provided For chemicals not listed in EPA workbooks, sources for the data are shown in the next four slides
Sources Chemical Physical Parameters Hazardous Substances Databank (http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?hsdb) National Institute Standards and Technology (http://webbook.nist.gov/chemistry/) Figure 30 TAC 350.73(e) the Texas Risk Reduction Rule (Texas Natural Resource Conservation Commission, 1999). Kawatomoto, K. and Urano, K. 1989. Parameters for predicting fate organochlorine pesticides in the environment (I) octanol-water and air-water partition coefficients. Chemosphere, 18(9/10):1987-1996. Sources Chemical Physical Parameters (continued) "Chemfate" database (http://esc.syrres.com/efdb.htm) Montgomery, J.H., 2000. Groundwater chemicals desk reference. 3rd edition. Lewis Publishers. Warner, H.P., Cohen, J.M., and Ireland, J.C. 1987. Determination Henry's law constants selected priority pollutants. Office Science and Development, U.S. EPA Report-600/D-87/229. "Handbook Chemical Property Estimation Methods" by WJ Lyman, WF Reehl, and DH Rosenblatt. 1982.
Sources Chemical-Specific Dose-Response Values Non-Cancer Effects U.S. EPA s Integrated Risk Information System (IRIS) U.S. EPA s Health Effects Assessment Summary Tables (HEAST) Other dose-response values developed by ORS (http://www.state.ma.us/dep/ors/files/chemical.htm) Allowable Threshold Concentrations as described in the Draft Indoor Air Sampling and Evaluation Guide (http://www.state.ma.us/dep/ors/files/orspubs.htm) Minimum Risk Levels from the Agency for Toxic Substances and Disease Registry Calculation a dose-response value using toxicity information from the literature Sources Chemical-Specific Dose- Response Values (continued) Cancer Effects U.S. EPA s Integrated Risk Information System (IRIS) U.S. EPA s Health Effects Assessment Summary Tables (HEAST) Dose-response values developed by ORS (http://www.state.ma.us/dep/ors/files/chemical.htm) Cancer Potency Factors from California Environmental Protection Agency s Office Of Environmental Health Hazard Assessment (OEHHA) Calculation a dose-response value using toxicity information from the literature
Run the Model Groundwater data Soil gas data Soil data SIMPLE THREE-STEP PROCESS Enter site-specific data and chemical concentration in DATENTER worksheet Enter (if necessary) chemical-specific data in CHEMPROPS worksheet Use Infinite source bldg. conc. from INTERCALCS worksheet for the Exposure Point Concentration in the risk assessment
Exposure Point Concentration
Exposure Point Concentration
Exposure Point Concentration Calculate Risks Using U.S. EPA Workbook
Calculate Risks Using U.S. EPA Workbook (continued) Some Default Exposure Duration Assumptions Location/receptor Infant Child Adult Homebound Adult Duration Residence 24 hrs/day 20 hrs/day 16 hrs/day; 30 yrs 24 hrs/day; 30 yrs Child Adult Adult School 8 hrs/day; 5 days/wk; 9 mo/yr; 7 yrs 8 hrs/day; 5 days/wk; 9 mo/yr; 25 yrs Workplace 8 hrs/day; 5 days/wk; 25 yrs