Vapor Intrusion is The migration of volatile chemicals from the
subsurface into overlying buildings. 2 Dissolved contamination LTLT
Diffusion Vadose zone Building zone of influence Wind effects
Enclosed space Cracks Q soil Air streamlines Convection Top of
capillary zone Water Table Stack effects Mixing in indoor air and
inhalation Advection/ Convection Diffusion Phase partitioning C gw
to C soil gas
Slide 3
VI isnt. Ambient (background) On-site processes Indoor air
sources 3
Slide 4
History of VI Guidance Johnson and Ettinger (1991): Heuristic
Model for Predicting the Intrusion Rate of Contaminant Vapors into
Buildings - not updated since 2004; 1-D 2002 - OSWER Draft Guidance
for Evaluating the Vapor Intrusion to Indoor Air Pathway from
Groundwater and Soils (Still Draft!) 2005 3D VI model by Abreu and
Johnson 2005 - DERR TDC Methodology for Vapor Intrusion Assessment
2007 - ITRC Guidance 4
Slide 5
History of VI Guidance 2010 - Ohio EPA Guidance May 2010 - a
bit of OSWER 2002, ITRC, and CAL EPA, plus Ohio EPA specific
experience 2011 - Background Indoor Air Concentrations of Volatile
Organic Compounds in North American Residences (1990 2005): A
Compilation of Statistics for Assessing Vapor Intrusion. 2012 -
EPA's Vapor Intrusion Database: Evaluation and Characterization of
Attenuation Factors for Chlorinated Volatile Organic Compounds and
Residential Buildings. 2012 VISL calculator and users guide 5
Slide 6
More. 2012 - Conceptual Model Scenarios for the Vapor Intrusion
Pathway Indoor Air Vapor Intrusion Mitigation Approaches, FAQs,
etc. April 2013 - US EPA Office of Underground Storage Tanks Draft
Petroleum Vapor Intrusion Guidance April 2013 - U.S. EPA VI
guidance (super secret document available from Inside EPA for a
limited time only!) expected update .????? October, 2014 ITRC
Petroleum Vapor Intrusion Fundamentals of Screening, Investigation,
and Management 6
Slide 7
US EPA VISL calculator: Uses the RSL construct for indoor air
values Applies attenuation factors to calculate screening values
for soil gas and ground water (based on the 2012 US EPA VI
Database) Adjust for exposure scenario (C/I vs residential) 7
Slide 8
What is an attenuation factor? AF ( ) unitless ratio of the
indoor air concentration (C indoor ) to the subsurface contaminant
concentration VISL and OSWER: GW = C IA /(C GW *H*1000L/m 3 ) =.001
(vapor at source) soil gas = C IA /C SG =.1 crawl space = C IA /C
SG = 1 However soil gas =.03 (SG = 33 X IA) According to US EPA
draft comment 8
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Vapor Attenuation slab contaminated soil or groundwater subslab
vapors Ratio of Vapor Flux to Indoor Air Exchange Indoor Air
Exchange Rate (L/minute) Vapor Flux Rate (L/minute) Subslab AF =
Vapor Flux Rate IAER
Proposed Changes Include RCRA Clarify use of OSHA PELs COC List
Current (2010) Ohio EPA guidance: US EPA 2002 tables plus a few
Proposed: VISL calculator list plus H 2 S; special consideration
for cis-1,2 DCE Major change: Must have reliable inhalation
toxicity factors (no extrapolation) The source vapor concentration
< toxicity 14
Slide 15
Proposed Changes Use VISL as front line screening for further
evaluation More robust mitigation/remedy alternatives section
Sampling for remedy verification Frequency Site specific Update
sampling SOPs and forms 15
Slide 16
Special Consideration for Petroleum Releases 16
Slide 17
Challenges Direct user to stepwise empirical data collection
How much data are necessary to make a decision for evaluation and
remedy? Use VISL calculator only? Allow J&E? If so, defaults
only? When are building parameters engineering controls? Some other
AF calculation? 17