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