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Modeling Vapor Attenuation WorkshopA Study of Vapor Intrusion Modeling in
the Context of EPA’s Guidance
Modeling Vapor Attenuation WorkshopA Study of Vapor Intrusion Modeling in
the Context of EPA’s Guidance
The 20th Annual International Conference on Soils, Sediments and WaterOctober 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
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:Steering Committee Members:
ORD Technical SupportORD Technical Support
Site Characterization and Data Acquisition
Regional Technical Assistance
OSWER Guidance Document Development
Technology Transfer
Indoor Air Vapor Intrusion Technology Transfer Activities
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
BackgroundBackground
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
BackgroundBackground
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
How does vapor intrusion occur?How does vapor intrusion occur?
• 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)
Typical VOC ContaminantsFound at IAVI Sites
Typical VOC ContaminantsFound at IAVI Sites
Why not just sample indoor air?
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
How can we use groundwater or soil gas data to evaluate the vapor
intrusion pathway?
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:
ionconcentrat vapor subsurface
ionconcentratair indoor α
cHxα
ionconcentratair indoor target ionconcentratrgroundwatetarget
Groundwater Sampling IssuesGroundwater 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.
Basement Slab on grade
CrawlspaceSampling Considerations
Location of screen
Screened interval
Water table fluctuations
Recharge
Soil Gas Sampling IssuesSoil Gas Sampling Issues
Least reliable samples (using traditional methods)
Temporal and spatial variabilityBasement Slab on gradeCrawlspace
Sources of VariabilityBarometric pressure
fluctuationsSurface cover, preferential
pathways Soil moisture content &
permeabilityBuilding depressurizationBiodegradation
Sources of Sampling Error
Sampling equipmentProtocols
How is the vapor intrusion pathway evaluated in EPA’s
guidance?
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
Basic Layout of GuidanceBasic Layout of Guidance
GuidanceI. I. IntroductionII. II. Explanation of Vapor IntrusionIII. III. Summary of GuidanceIV. IV. Use of Guidance
Discussion on specific tiers (V through VII) Tables 1-3
Appendices A. A. Data Quality Assurance ConsiderationB. B. Development of Conceptual Site ModelC. C. Detailed Flow DiagramsD. D. Development of TablesE. E. Relevant Methods and TechniquesF. F. Empirical Attenuation Factors and Reliability AssessmentG. G. Considerations for the Use of the J & E Vapor Intrusion
ModelH. H. Community Involvement GuidanceI. I. Consideration of Background