Modeling Vapor Attenuation Workshop A Study of Vapor Intrusion Modeling in the Context of EPA’s Guidance USEPA’s (OSWER) Nov Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils Another VI event sponsored by: Doug Grosse, US EPA, ORD-Cin.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)] (703) For: Annual Int. Conf. on Soils, Sediments and Water October 18-19, Amherst, MA

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)

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

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

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: RCRA ( Indoor Air Vapor Intrusion database )iavi.rti.org Revisions due out next summer

Tier 1- Primary Screening OSWER ’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

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

Calculation of Soil Gas and Groundwater Generic (Q4) Empirical Target Screening Levels Select indoor air target screening level. AF = 0.1 AF = AF = 0.01 Shallow soil gas screening level (SGSL shallow ) is 10 times indoor air target screening level. SVSL shallow = IASL * 10 Deep soil gas screening level (SGSL deep ) is 100 times indoor air target level. SVSL deep = 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) Slide by Dr. H. Dawson Crawl- space air =1.0

Semi-Site-Specific Screening (Q5) EPA Johnson & Ettinger spreadsheet Model-based 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) /risk/airmodel/johnson_ettinger.htm Fig. 3

Tier 3 – Site-Specific Assess. OSWER ’s draft-Subsurface Vapor Intrusion Guidance 1-Modeling (site-specific) e.g., [via Superfund web-site] Only to 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-specific samples, 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”

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?

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