1. Vapor Intrusion Guidance Proposed Updates
VAP CP Coffee
April 13, 2015
Audrey Rush

2. Mixing in indoor air and inhalation Dissolved contamination
Vapor Intrusion is… The migration of volatile chemicals from the subsurface into overlying buildings.
Stack effects
Mixing in indoor air and inhalation
Enclosed space
Wind effects
Advection/
Convection
Qsoil
Cracks
Air streamlines
Building zone of influence
Convection
Vadose zone
Diffusion
Top of capillary
zone LT
Diffusion
Water Table
Phase partitioning
Dissolved contamination
Cgw
to Csoil gas

3. VI isn’t….
Ambient (background)
On-site processes
Indoor air sources

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
OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Still Draft!)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
DERR TDC Methodology for Vapor Intrusion Assessment
ITRC Guidance

5. History of VI Guidance
Ohio EPA Guidance May a bit of OSWER 2002, ITRC, and CAL EPA, plus Ohio EPA specific experience
Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences (1990 – 2005): A Compilation of Statistics for Assessing Vapor Intrusion.
EPA's Vapor Intrusion Database: Evaluation and Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential Buildings.
2012 – VISL calculator and user’s guide

6. More….
Conceptual Model Scenarios for the Vapor Intrusion Pathway
Indoor Air Vapor Intrusion Mitigation Approaches, FAQs, etc.
April US EPA Office of Underground Storage Tanks – Draft Petroleum Vapor Intrusion Guidance
April 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

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)

8. What is an attenuation factor?
AF () – unitless ratio of the indoor air concentration (Cindoor) to the subsurface contaminant concentration
VISL and OSWER:
 GW = CIA/(CGW*H*1000L/m3) = .001 (vapor at source)
 soil gas = CIA/CSG= .1
 crawl space= CIA/CSG= 1
However…
soil gas = .03 (SG = 33 X IA)
According to US EPA draft comment
As an example a building with TCE concentrations of 2,000 μg/m in soil gas and 2 3μg/m in indoor air would have an attenuation factor of (2 / 2000), or Similarly, a building with TCE concentrations of 5 μg/L in groundwater and 32μg/m in indoor air and a Henry’s law constant of would have an attenuation factor of (2/[5*0.118*1000]), or As defined in the equations above, the value of the AF decreases as the level of attenuation between the subsurface and building increases.

11. Ratio of Vapor Flux to Indoor Air Exchange
Exchange Rate
(L/minute)
Vapor
Attenuation
Subslab AF =
Vapor Flux Rate
IAER
slab
subslab vapors
Vapor Flux Rate
(L/minute)
contaminated soil or groundwater

12. Vapor Flux Rate* (4.5 L/min)
Example: PCE (IA standard res = 42 g/m3
Method
CSG
(g/m3)
VISL (SG = 0.1)
420
VISL (SG =0.03)
1,400
J&E screen (SG = )
32,000
Vapor Flux Rate* (4.5 L/min)
IAER (1,016 L/min)
(SG =0.0045)
9,333
* Estimated for Ohio, Brewer, et.al.

14. Proposed Changes Include RCRA COC List Clarify use of OSHA PELs
Current (2010) Ohio EPA guidance: US EPA 2002 tables plus a few…
Proposed: VISL calculator list plus H2S; special consideration for cis-1,2 DCE
Major change:
Must have reliable inhalation toxicity factors (no extrapolation)
The source vapor concentration < toxicity

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

16. Special Consideration for Petroleum Releases

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?