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USEPA’s (OSWER) Nov. 2002 Draft Guidance for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

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. DPHHartford, Ill. case

Rumchev, et al., Thorax, 2004; 59:746 [Assoc. …VOCs w/ asthma]

1) VI is Real2) 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: http://www.epa.gov/correctiveaction/eis/vapor.htm http://www.epa.gov/edocket RCRA-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

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) EmpiricalTarget Screening Levels

Select indoor air target screening level.

AF = 0.1

AF = 0.001

AF = 0.01

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/HcGWSL = 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)

http://www.epa.gov/superfund/programs/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