Modeling Vapor Attenuation Workshop A Study of Vapor Intrusion Modeling in the Context of EPA

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Modeling Vapor Attenuation WorkshopA Study of
Vapor Intrusion Modeling inthe Context of EPAs
Guidance
The 20th Annual International Conference on
Soils, Sediments and Water October 18-20, 2004,
at the University of Massachusetts, Amherst MA
Sponsored by US EPAs Office of Research and
Development and Office of Solid Waste and
Emergency Response
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Steering Committee Members

• Doug Grosse, US EPA, ORD
• Henry Schuver, US EPA, OSW
• Robert Truesdale, RTI International
• Helen Dawson, US EPA Region 8
• Todd McAlary, Geosyntec Consultants
• Ian Hers, Golder Associates
• Paul Johnson, Arizona State University

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ORD Technical Support

• Site Characterization and Data Acquisition
• Regional Technical Assistance
• OSWER Guidance Document Development
• Technology Transfer

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Indoor Air Vapor Intrusion Technology Transfer
Activities

• Vapor Intrusion Seminars
• San Francisco - December 34, 2002
• Dallas - January 1415, 2003
• Atlanta - 2526, 2003
• CDROM U.S.EPA Seminars on Indoor Air Vapor
  Intrusion EPA/625/C-03/004
• Specialty Workshop AEHS 14th Annual West Coast
  Conference on Soils, Sediments and Water, San
  Diego - March 15-18, 2004
• Modeling Vapor Attenuation Workshop The Annual
  International Conference on Soils, Sediments and
  Water, University of Massachusetts at Amherst -
  October 18-19, 2004

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Background

• 1st One Program Guidance
• 3 programs - similar but each slightly different
• Diverse Team Worked Together
• OSW, OERR, OUST, ORD, Regions, States,
  Contractors
• Shared resources and people between offices

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Background

• What is the intent of this guidance
• To help the user screen out sites not needing
  further consideration and, on the remaining
  sites, provide guidance on how to make the
  determination that this pathway does or does not
  pose a significant risk to human health
• It is not intended to provide guidance on how to
  delineate the extent of risk or how to eliminate
  the risk, only to determine if there is a
  potential for an unacceptable risk

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How does vapor intrusion occur?
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Typical VOC ContaminantsFound at IAVI Sites

• 1,1,1-Trichloroethane
• 1,1-Dichloroethane
• 1,1-Dichloroethylene
• 1,2-Dichloroethane
• Cis-1,2-Dichloroethylene
• Tetrachloroethylene
• trans-1.2-Dichloroethylene
• Trichloroethylene
• Trichloroethylene
• Vinyl chloride (chloroethene)

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Why not just sample indoor air?

• Indoor Air Sampling Issues
• Temporal and spatial variability
• Indoor air sources
• Consumer products (cleaners, paints, glues)
• Occupant activities (craft hobbies, smoking)
• Dry cleaned garments
• Construction materials
• Background
• Ambient air in urban areas

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How can we use groundwater or soil gas data to
evaluate the vapor intrusion pathway?

• Is existing groundwater and/or soil gas data
  adequate?
• How is indoor air concentration related to
  subsurface concentration? Attenuation
  factor Subsurface screening level

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Groundwater Sampling Issues

• Most reliable samples, but farthest from
  receptors.
• Alpha factor assumes Henrys law partitioning
  into soil-gas.
• Only upper-most water table concentration is
  important.

Sampling Considerations Location of
screen Screened interval Water table
fluctuations Recharge
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Soil Gas Sampling Issues

• Least reliable samples (using traditional
  methods)
• Temporal and spatial variability

• Sources of Variability
• Barometric pressure fluctuations
• Surface cover, preferential pathways
• Soil moisture content permeability
• Building depressurization
• Biodegradation
• Sources of Sampling Error
• Sampling equipment
• Protocols

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How is the vapor intrusion pathway evaluated in
EPAs guidance?

• Multiple lines of evidence approach
• Groundwater
• Soil gas
• Subslab or crawlspace vapor
• Indoor air
• Home survey for household products
• Outdoor air sampling
• Spatial relationship of indoor air contamination
  to
• subsurface contamination
• Johnson-Ettinger (or other) Model

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Basic Layout of Guidance

• Guidance
• I. Introduction
• II. Explanation of Vapor Intrusion
• III. Summary of Guidance
• IV. Use of Guidance
• Discussion on specific tiers (V through
  VII)
• Tables 1-3
• Appendices
• A. Data Quality Assurance Consideration
• B. Development of Conceptual Site Model
• C. Detailed Flow Diagrams
• D. Development of Tables
• E. Relevant Methods and Techniques
• F. Empirical Attenuation Factors and Reliability
  Assessment
• G. Considerations for the Use of the J E Vapor
  Intrusion Model
• H. Community Involvement Guidance
• I. Consideration of Background