The document discusses a strategy to minimize indoor sampling disturbances by combining external soil-gas concentrations with indoor air testing in vapor intrusion investigations. It highlights the importance of understanding shallow and deep soil gas dynamics alongside building characteristics to target sampling effectively. The conclusion suggests that while this approach is promising, it requires further testing for validation.

1. Future Testing: Combining
External Soil‐Gas Concentrations
With Indoor ITS to Minimize
Indoor Sampling

2. Example Application Strategy – Combining
External (Soil‐gas Concentration) With Indoor ITS
Measurements to Target Sampling
• Objective – can we target sampling efforts to minimize the occupant
disturbance concerns of subslab/indoor sampling?
• Background on the problem – lots of evidence that VI impacts are spotty
across a plume
• Understanding the predictive value of shallow and deep external soil gas in
various release/transport scenarios – using the CSM
• Supplementing a shallow soil gas concentration map with an understanding
of shallow soil types and building characteristics
• Using surrogates and building science to target sampling and validate
inferences

3. “Outside‐In” Strategy of VI Site Investigation
Typical
• Starts with identification of a site, most often based on groundwater
data, sometimes based on a known release to soil
• Typically progresses next to external soil gas:
• Often favored because it is seen as less invasive
• At some sites <50% of homeowners allow access for indoor sampling
• Can be done along streets with only one access agreement
• But shallow soil gas known to underpredict subslab concentrations
• Most attenuation occurs across the building envelope, which soil gas doesn’t
tell you
• How to determine then if and where subslab and indoor air sampling
is then required

4. Example of Large Soil Gas Plume Delineation in a Small
Midwestern Town
Reprinted from Lutes and
Knoepfle, 2016 AEHS Rapid,
Efficient Delineation From VI
Potential of A Large Soil Gas
Plume Using HAPSITE and
Other Lines of Evidence

5. Example of
House to House
Heterogeneity
Reprinted from Dawson and
Wertz “Empriical VI
Database, Background Indoor
Air Review, Updated J&E
Spreadsheet Model”

6. Reprinted from
Schumacher et. all
“Field Observations
on Ground
Covers/Buildings”
AEHS 2010; data from
NAS Lemoore

7. External Soil Gas vs. Subslab, Model
Results; Various Deep Source Placements
(EPA 530‐R‐10‐003)

8. External Soil Gas vs. Subslab, Model Results;
Mixed Shallow and Deep Source Placement
(EPA 530‐R‐10‐003)

9. So Could This Strategy Work?
• Delineate site and sources with multi‐depth external soil gas for VOCs
and radon
• Measure attenuation factors between external soil gas and indoor air
for radon
• Draw inferences based on those attenuation factors of likely indoor
VOC concentrations?
• Validate with indoor and subslab samples in a smaller number of
buildings then otherwise would be required

10. Evidence from Indianapolis Duplex (EPA/600/R‐12/673 Chapter 8)

11. Evidence from Indianapolis Duplex (EPA/600/R‐12/673 Chapter 8)

12. Evidence from Indianapolis Duplex (EPA/600/R‐13/241 Chapter 8)

13. Conclusion ‐ External Sampling Plus ITS
• This particular application is an attractive concept
• Needs much more testing, and the sooner the better! Your
observations could add significantly to our understanding