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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

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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

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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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(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

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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

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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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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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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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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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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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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