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of Massachusetts Department
ENVIRONMENTAL PROTECTION
Modeling the Vapor Intrusion Pathway: Revisions to the MCP GW-2 Groundwater Standards
Massachusetts Department of Environmental ProtectionOne Winter Street, Boston, MA 02108
http://Mass.Gov/dep
Paul W. LockeBureau of Waste Site Cleanup(617) 556-1160Paul.Locke@state.ma.us
Andrew Friedmann, Ph.D.Office of Research & Standards(617) 292-5841Andrew.Friedmann@state.ma.us
of Massachusetts Department
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Focus of Today’s Discussion
Groundwater
Indoor Air
Soil Soil Gas
PreferentialPathway
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The History
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Concerns with the Groundwater/Indoor Air Pathway
20011989
Hillside School(Microwave Development Lab Site)
19921993
DEP PublishesGW-2 Standards
1996
DEP Regional StaffEvaluate Vapor Intrusion Pathway(Nancy Fitzpatrick & John Fitzgerald)
19981999
2000
Revision ofGW-2 Stnds(Proposed)
2002
J&E ModelPublished in
ES&T
19912003
National Attention:•Colorado sites•RCRA EI Work•Draft EPA Guidance
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1991-Johnson &Ettinger HeuristicModel
Johnson, P.C., and R.A. Ettinger, 1991, Heuristic Model for Predicting the Intrusion Rate of Contaminant Vapors into Buildings, Environ. Sci. & Technol., v 25, pp. 1445-1452
of Massachusetts Department
ENVIRONMENTAL PROTECTION
GW-2: Groundwater -> Indoor AirNoncancerRisk-basedIndoor Air
Concentration
Cancer Risk-basedIndoor Air
Concentration
50% Odor RecognitionThreshold
Lowest ofThese 3
Indoor AirBackground
Higher of theseas Target Indoor
Air Target Concentration
airgroundwater
Model(Johnson & Ettinger)
Calculated SourceConcentration in Groundwater
Ceiling Concentration
Lower of These 2
GroundwaterBackground
PracticalQuantitation
Limit
Highest of These 3Concentrations Adoptedas MCP GW-2 Standard
α
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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)
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Fitzpatrick & Fitzgerald
Studied 47 Sites:
– 55% chlorinated VOCs, 45% gasoline
– 52% residential– 2% schools– 46% commercial
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Fitzpatrick & Fitzgerald, continued
Conclusions:
• Significant differences appear to exist between the fate/transport and impacts of chlorinated and non-chlorinated VOCs
• Attenuation Coefficients for chlorinated VOCs appear to be in the range of 1E-1 to 1E-3, significantly higher than the 5E-4 value assumed by MADEP
• Observed levels of non-chlorinated VOCs in the vadose zone are typically 1 to 2 orders of magnitude lower, due apparently to biodegradation of these non-chlorinated (BTEX) VOCs above the water table.
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3. The Future
FY2000 Revisions • Method 1: GW-2 Standards Development• Method 2: GW-2 Standards New/Modified• Method 3: Site-specific Risk Assessment
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FY2003 Revisions to Standards
• GW-2 evaluation to include chemical-specific modeling of vapor intrusion using modified USEPA Johnson & Ettinger model spreadsheets.
• Regulations also to include consideration of VOCs in soil in applicability of Method 1 soil standards.
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EPA Review Objectives
• Evaluate the reliability of federal and state screening level approaches for assessing the vapor intrusion pathway.
• Provide a comprehensive assessment of the correspondence between screening level approaches and actual measurements.
• Determine whether this pathway is of concern even if groundwater meets drinking water standards.
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of Massachusetts Department
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(2002)
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Fall 2002
(Public Comment Period ended last week.)
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EPA Proposed 3 Stage Screening Process:
= Method 1
= Method 2
= Method 3
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DEP Proposed Values
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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
of Massachusetts Department
ENVIRONMENTAL PROTECTION
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
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Groundwater-to-Indoor Air or Soil-to-Indoor Air Pathways: Assessing Risks
Must determine the Exposure Point Concentration (EPC) in air.
1. Direct Sampling of Indoor Air2. Model Pathway from Soil Gas Sampling3. Last resort: Model Pathway from
Groundwater or Soil
of Massachusetts Department
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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 WorkbookChoose 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
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Workbooks versus Worksheets
Workbook is acollection of spreadsheets (orworksheets)
Worksheet is a pageof a Workbook
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Site-Specific Data
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Required Site-Specific DataParameter Values
Depth below grade to water table (cm) site-specific
Soil gas sampling depth below grade (cm) site-specific
Depth below grade to top of site-specificsoil contamination (cm)
Depth below grade to bottom site-specificof soil contamination (cm)
Soil stratum SCS type site-specific
Thickness of Soil strata (cm) site-specific
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Required Site-Specific Data (continued)
Parameter Values
Depth below grade to bottom site-specific orof enclosed space floor (cm) use default (15 or 200)
Average soil/groundwater site-specific ortemperature (oC) default (10)
Vadose zone soil dry site-specific orbulk density (g/cm3) default (1.5)
Vadose zone soil total site-specificporosity (unitless) default (0.43)
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Required Site-Specific Data (continued)
Parameter Default Values
Vadose zone soil water- site-specific orfilled porosity (cm3/cm3) default (0.061)
Enclosed Space Floor site-specific orLength (cm) default (961)
Enclosed Space Floor site-specific orWidth (cm) default (961)
Enclosed Space site-specific orHeight (cm) default (488)
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How to Use the Model for Risk Assessment
• Input Site-Specific Data
• Obtain and Input Chemical-Specific Data
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Influence of Site-Specific Parameterson Exposure Point Concentration
Parameter Change in Parameter Exposure Point Concentration
Depth below grade to bottom ↓ ↓ ↓of 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 ↑ ↑ ↑
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Required Chemical-Specific DataParameter Units
Concentration in media site-specific
Organic carbon partition coefficient (Koc) cm3/g
Diffusivity in air (Da) cm2/s
Diffusivity in water (Dw) cm2/s
Henry's law constantat reference temperature (H) atm-m3/mol
Henry's law constant reference temperature (TR) oC
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of Massachusetts Department
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Required Chemical-Specific Data
Parameter Units
Normal boiling point (TB) oK
Critical temperature (TC) oK
Enthalpy of vaporization at the cal/molnormal boiling point (DHv,b)
Chronic Inhalation Reference mg/m3
Concentration (RfC)
Inhalation Unit Risk Factor (URF) (µg/m3)-1
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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
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of Massachusetts Department
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Sources of Chemical Physical Parameters
• Hazardous Substances Databank (http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB)
• National Institute of Standards and Technology (http://webbook.nist.gov/chemistry/)
• Figure 30 TAC §350.73(e) of the Texas Risk Reduction Rule (Texas Natural Resource Conservation Commission, 1999).
• Kawatomoto, K. and Urano, K. 1989. Parameters for predicting fate of organochlorine pesticides in the environment (I) octanol-water and air-waterpartition coefficients. Chemosphere, 18(9/10):1987-1996.
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Sources of 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 of Henry's law constants of selected priority pollutants. Office of Science and Development, U.S. EPA Report-600/D-87/229.
• "Handbook of Chemical Property Estimation Methods" by WJ Lyman, WF Reehl, and DH Rosenblatt. 1982.
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of Massachusetts Department
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Sources of 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 of a dose-response value using toxicity information from the literature
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Sources of 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 of a dose-response value using toxicity information from the literature
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of Massachusetts Department
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Run the Model
• Groundwater data• Soil gas data• Soil data
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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
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of Massachusetts Department
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Exposure PointConcentration
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Exposure PointConcentration
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Exposure PointConcentration
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Calculate Risks Using U.S. EPA Workbook
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Calculate Risks Using U.S. EPA Workbook(continued)
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Some Default Exposure Duration Assumptions
8 hrs/day; 5 days/wk; 25 yrsAdultWorkplace
8 hrs/day; 5 days/wk; 9 mo/yr; 25 yrsAdult8 hrs/day; 5 days/wk; 9 mo/yr; 7 yrsChild
School
24 hrs/day; 30 yrsHomebound Adult16 hrs/day; 30 yrsAdult
20 hrs/dayChild24 hrs/dayInfant
ResidenceDurationLocation/receptor
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