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Modeling Vapor Attenuation Workshop

Modeling Vapor Attenuation Workshop. A Study of Vapor Intrusion Modeling in the Context of EPA’s Guidance USEPA’s (OSWER) Nov. 2002 Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils Another VI event sponsored by:

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Modeling Vapor Attenuation Workshop

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  1. Modeling Vapor Attenuation Workshop • A Study of Vapor Intrusion Modeling in the Context of EPA’s Guidance • USEPA’s (OSWER) Nov. 2002 Draft Guidance for • Evaluating the Vapor Intrusion to Indoor Air Pathway • from Groundwater and Soils • Another VI event sponsored by: • Doug Grosse, US EPA, ORD-Cin. [sponsor of 2-day ORD VI workshops R9, 6, & 4 in 2003)] • Henry Schuver, US EPA, OSWER-OSW [1999 EI Guidance Indoor Air check-off (acute vs. chronic)] • Schuver.henry@epa.gov • (703) 308-8656 For: Annual Int. Conf. on Soils, Sediments and Water October 18-19, 2004 - Amherst, MA

  2. My Agenda • Regulatory Context = Decision Time • Interim-Final scheduled for next summer [but science is …?] • Unless there is evidence for better ideas … • Overview of draft OSWER 2002 VI Guidance • Tiers 1, 2, & 3 • Workshop’s Purpose & Objectives • Improve Guidance • More cost-effective exposure reductions (via screening) • i.e., less false positives (w/ min. false negatives)

  3. 1) VI is Real 2) Worst cases are easiest to detect 3) Health impacts are possible Rumchev, et al., Thorax, 2004; 59:746 [Assoc. …VOCs w/ asthma] Photo from: Dave Webb, Ill. DPH Hartford, Ill. case

  4. Introduction and/or Reminder of: EPA’s VI Guidance history • States of MA, etc., pioneered VI [radon papers] • “background” confounding the evidence for VI • Colorado documented unique tracer (1-3) • “Irresponsible to Ignore” • Site-specific model prediction-based screening w/ (undocumented?) inputs [for diss. VOCs] • Needed general pathway screening guidance

  5. Status of OSWER’s (11/02) draft Vapor Intrusion Guidance • Signed Nov. 22, 2002 (for use) • By OSWER Assist. Admin. (AA) Marianne Horinko • Intent of Guidance: • “a tool to help … conduct a screening evaluation” • Guidance, Comments, & Training available at: • http://www.epa.gov/correctiveaction/eis/vapor.htm • http://www.epa.gov/edocketRCRA-2002-033 • http://www.clu-in.org/conf/tio/vapor_021203/ • http://iavi.rti.org (Indoor Air Vapor Intrusion database) • Revisions due out next summer

  6. Tier 1- Primary ScreeningOSWER’s draft-Subsurface Vapor Intrusion Guidance • “quickly identify … any potential exists” • Q1 Volatiles? • Q2 Buildings? • Q3 Immediate concerns? • May be due to a mixture and/or non-toxic • If … not … “incomplete” … proceed to Secondary Screening

  7. Before Secondary Screening (Q4 & Q5) OSWER Vapor Intrusion Guidance Not applicable if ‘Precluding Factors’: - Shallow sources (< 5ft below bldg foundation), or - Relatively shallow groundwater sources (<15 ft) and: - Crawlspace homes (w/o liners*) - Very permeable geology - Significant preferential pathways - Sources in unsaturated zone (above the water table fringe?) - Mobile gas plumes (Landfill gas, ‘vapor clouds’) - Very low air exchange rates or v. high (neg.) pressure differential If there are: Proceed to Tier 3 (Q6 Site-Specific Pathway) • Q4 Debatable, but Violations of Q5 model assumptions

  8. Calculation of Soil Gas and Groundwater Generic (Q4) EmpiricalTarget Screening Levels • Select indoor air target screening level. • Shallow soil gas screening level (SGSLshallow ) is 10 times indoor air target screening level. SVSLshallow = IASL * 10 • Deep soil gas screening level (SGSLdeep ) is 100 times indoor air target level. SVSLdeep = IASL * 100 • Groundwater screening level (GWSL) is the aqueous concentration corresponding to a soil gas concentration 1000 times greater than the indoor air target level. GWSL = IASL * 1000/Hc GWSL = IASL/Hc(with units of 1000 liters/m3) Indoor Air = GW * Hc (GW in ug/l & Hc unitless) Crawl-space air =1.0 AF = 0.1 AF = 0.01 AF = 0.001 Slide by Dr. H. Dawson

  9. Semi-Site-Specific Screening (Q5)EPA Johnson & Ettinger spreadsheet Model-based Fig. 3 • Q5: Do media concentrations exceed semi-site specific criteria? (Table 3 (a, b ,c)) • ‘Canned’ J&E model-based • Conservative model input parameters (all, but:) • Soil type: sand – loam • Depth to contamination:1 – 30 meters • Read Attenuation Factor off Y-axis of chart • Attenuation factor: (SG & GW specific) http://www.epa.gov/superfund/programs/risk/airmodel/johnson_ettinger.htm

  10. Tier 3 – Site-Specific Assess.OSWER’s draft-Subsurface Vapor Intrusion Guidance • 1-Modeling (site-specific) e.g., [via Superfund web-site] • Onlyto identify‘most-likely-to-be-impacted’ bldgs: • For identifying sampling locations • Combines complex factors, e.g., soil, depth, & building factors • If no problem predicted there – (by approp. site-specific model) • Interim (EI) determinations don’t need samples; = not a priority • 2-Measurement(confirmation, even if no problem expect) • Building-specificsamples, foundation &/or indoor air from: • Subset of potentially affected buildings • Before a Final decision for vapor intrusion • If using indoor air – need more than one + “background”

  11. Some Objectives for Modeling Vapor Attenuation Wksp • Does the evidence suggest: • we’re using the best approaches & methods? • e.g., use of Empirical, Models & Measurements • Time-composite vs. Real • semi-site-specific Fig. 3 curves could be improved? • Why do the data plot above or below? • Do we need all Precluding Factors? Or more?, or Modifying? • Should we adjust Fig. 3 curves and/or limit conditions? • site-specific model predictions could improve screening?

  12. Workshop Agenda • Review of Pre-Existing Data (Hers, Dawson, Truesdale) • Residential Attenuation (Goldman, Lund) • Non-Residential Attenuation • (Berry-Spark, Lawless, Sharma, Goldberg-Day) • Wrap-up and Discussions • Day 2 - Focus Groups & Posters • Approaches and Methods Influencing Observation Data, McAlary • Fig. 3 Predictions & Observational Data, Hers • Site-Specific Modeling and Observation Data, Johnson • Expert Panel - Charge Questions • Day 2 - Evening Concluding Session • Summary of Recommendations for Guidance

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