1. Modeling Vapor Attenuation Workshop A Study of Vapor Intrusion Modeling in the Context of EPA’s Guidance The 20 th Annual International Conference on Soils, Sediments and Water October 18-20, 2004, at the University of Massachusetts, Amherst MA Sponsored by: US EPA’s Office of Research and Development and Office of Solid Waste and Emergency Response Sponsored by: US EPA’s Office of Research and Development and Office of Solid Waste and Emergency Response

2.  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 Steering Committee Members:

3. ORD Technical Support  Site Characterization and Data Acquisition  Regional Technical Assistance  OSWER Guidance Document Development  Technology Transfer

4. Indoor Air Vapor Intrusion Technology Transfer Activities  Vapor Intrusion Seminars  San Francisco - December 3&4, 2002  Dallas - January 14&15, 2003  Atlanta - 25&26, 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

5. 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

6. 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

7. How does vapor intrusion occur?

8. 1,1,1-Trichloroethane 1,1-Dichloroethane 1,1-Dichloroethylene 1,2-Dichloroethane Cis-1,2-Dichloroethylene Tetrachloroethylene trans-1.2-Dichloroethylene Trichloroethylene Vinyl chloride (chloroethene) Typical VOC Contaminants Found at IAVI Sites

9. 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

10. 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:

11. Groundwater Sampling Issues  Most reliable samples, but farthest from receptors.  Alpha factor assumes Henry’s law partitioning into soil- gas.  Only upper-most water table concentration is important. BasementSlab on gradeCrawlspace Sampling Considerations Location of screen Screened interval Water table fluctuations Recharge

12. Soil Gas Sampling Issues  Least reliable samples (using traditional methods)  Temporal and spatial variability BasementSlab on gradeCrawlspace Sources of Variability Barometric pressure fluctuations Surface cover, preferential pathways Soil moisture content & permeability Building depressurization Biodegradation Sources of Sampling Error Sampling equipment Protocols

13. How is the vapor intrusion pathway evaluated in EPA’s 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

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