Transcript RCRA National Meeting

Modeling Vapor
Attenuation Workshop
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A Study of Vapor Intrusion Modeling in the Context of EPA’s Guidance
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Evaluating the Vapor Intrusion to Indoor Air Pathway
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USEPA’s (OSWER) Nov. 2002 Draft Guidance for
from Groundwater and Soils
Another VI event sponsored by:
Doug Grosse, US EPA, ORD-Cin.
Henry Schuver, US EPA, OSWER-OSW
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[sponsor of 2-day ORD VI workshops R9, 6, & 4 in 2003)]
[1999 EI Guidance Indoor Air check-off (acute vs. chronic)]
[email protected]
(703) 308-8656
20th Annual Int. Conf. on Soils, Sediments and Water
October 18-19, 2004 - Amherst, MA
My Agenda
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Regulatory Context = Decision Time
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Interim-Final scheduled for next summer [but science is …?]
Unless there is evidence for better ideas …
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Overview of draft OSWER 2002 VI Guidance
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San Diego, 3/05?
Tiers 1, 2, & 3
Workshop’s Purpose & Objectives
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Improve Guidance
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Cost-effective exposure reductions (via screening)
i.e., less false positives (w/ min. false negatives)
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
Introduction and/or Reminder of:
EPA’s VI Guidance history
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States of MA, etc., pioneered VI [radon papers]
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Colorado documented unique tracer (1, 2, 3)
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“background” confounding the evidence for VI
“Irresponsible to Ignore”
Web-site-specific model prediction-based
screening w/ (undoc.?) inputs [for diss. VOCs]
Needed general pathway screening guidance
Status of OSWER’s (11/02) draft
Vapor Intrusion Guidance
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Signed Nov. 22, 2002 (for use)
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Intent of Guidance:
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By OSWER Assist. Admin. (AA) Marianne Horinko
“a tool to help … conduct a screening evaluation”
Guidance, Comments, & Training available at:
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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
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“quickly identify … any potential exists”
Q1 Volatiles?
Q2 Buildings?
Q3 Immediate concerns?
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May be due to a mixture and/or non-toxic
If … not … “incomplete” … proceed to
Secondary Screening
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
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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)
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Q4 Debatable, but Violations of Q5 model assumptions
Calculation of Soil Gas and
Groundwater Generic (Q4) Empirical
Target Screening Levels
[Dawson (db)]
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Crawlspace
air
=1.0
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Select indoor air target screening level.
Shallow soil gas screening level (SGSLshallow ) is 10 times
indoor air target screening level.
SVSLshallow = IASL * 10
AF = 0.1
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SVSLdeep = IASL * 100
AF = 0.01
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AF = 0.001
Deep soil gas screening level (SGSLdeep ) is 100 times indoor
air target level.
Groundwater screening level (GWSL) is the aqueous
concentration corresponding to a soil gas concentration 1000
times greater than the indoor air target level.
Slide mod. from H. Dawson
GWSL = IASL * 1000/Hc
GWSL = IASL/Hc
(with units of 1000 liters/m3)
Indoor Air = GW * Hc
(GW in ug/l & Hc unitless)
Semi-Site-Specific Screening (Q5)
EPA Johnson & Ettinger spreadsheet Model-based
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Q5: Do media concentrations
exceed semi-site specific
criteria? (Table 3 (a, b ,c))
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Fig. 3 (a,b)
Attenuation factor:
(SG & GW specific)
‘Canned’ J&E model-based
Conservative model input
parameters (all, but:)
Soil type: sand – loam
Depth to contamination:
1 – 30 meters
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Read Attenuation Factor off
Y-axis of chart
http://www.epa.gov/superfund/programs
/risk/airmodel/johnson_ettinger.htm
Tier 3 – Site-Specific Assess.
= Sample-Measurement Based Approach
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1-Modeling (site-specific)
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Only to identify ‘most-likely-to-be-impacted’ bldgs:
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For identifying sampling locations
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Combines complex factors, e.g., soil, depth, & building factors
If no problem predicted there –
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e.g., [via Superfund web-site]
Interim (EI) determinations don’t need samples; = not a priority
2-Measurement
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(confirmation, even if no problem expect)
Building-specific samples, foundation &/or indoor air from:
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(by approp. site-specific model)
Subset of potentially affected buildings
Before a Final decision for vapor intrusion
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If using indoor air – need more than one + “background”
Some Objectives for
Modeling Vapor Attenuation Wksp
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Does the new (& existing) evidence suggest:
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we’re using the best Approaches & Methods?
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semi-site-specific Fig. 3 curves could be improved?
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e.g., use of Empirical db, Models & Measurements for screening
Time-composite (air, adsorbent) vs. Real-time tech.
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
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Review of Pre-Existing Data (Hers, Dawson, Truesdale)
New - Attenuation at Residential Sites (Goldman, Lund)
New - Attenuation at Non-Residential Attenuation Sites
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(Berry-Spark, Lawless, Sharma, Goldberg-Day)
Real-time Tech. (Mickunas) and Discussions
Day 2 - Focus Groups & Posters
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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
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Public Perspectives (Siegal)
Summary of Recommendations for Guidance