Modeling Vapor Attenuation Workshop

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Attenuation Workshop • A Study of Vapor Intrusion Modeling in the Context of EPA’s Guidance • USEPA’s (OSWER) Nov. 2002 Draft Guidance for • Evaluating the Vapor Intrusion to Indoor Air Pathway • from Groundwater and Soils • Another VI event sponsored by: • Doug Grosse, US EPA, ORD-Cin.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 20th 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 … • San Diego, 3/05? • Overview of draft OSWER 2002 VI Guidance • Tiers 1, 2, & 3 • Workshop’s Purpose & Objectives • Improve Guidance • 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, 2, 3) • “Irresponsible to Ignore” • Web-site-specific model prediction-based screening w/ (undoc.?) 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-GW(Q4 & Q5) OSWER Vapor Intrusion Guidance Not usable for screening out if ‘Precluding Factors’ - Sources of vapors above the water table, or - Shallow sources (< 5ft below bldg foundation), or - Relatively shallow groundwater sources (<15 ft) and: - Crawlspace homes (w/o liners*) [*= keyed into foundation] - 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 so, 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 [Dawson (db)] • 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 mod. from H. Dawson

9. Semi-Site-Specific Screening (Q5)EPA Johnson & Ettinger spreadsheet Model-based Fig. 3 (a,b) • 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.= Sample-Measurement Based Approach • 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 new (& existing) evidence suggest: • we’re using the best Approaches & Methods? • e.g., use of Empirical db, Models & Measurements for screening • Time-composite (air, adsorbent) vs. Real-time tech. • 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-specificmodel predictions could improve screening?

12. Workshop Agenda • Review of Pre-Existing Data (Hers, Dawson, Truesdale) • New - Attenuation at Residential Sites (Goldman, Lund) • New - Attenuation at Non-Residential Attenuation Sites • (Berry-Spark, Lawless, Sharma, Goldberg-Day) • Real-time Tech. (Mickunas) 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 & Discussions • Evening Concluding Session • Public Perspectives (Siegal) • Summary of Recommendations for Guidance