Frequently Asked Questions

The following Q&A is a result of the questions posed during Drs. Hartman and Kram’s presentation.

The Vapor Intrusion Pathway

Land Science presented a webinar with vapor intrusion (VI) experts, Dr. Blayne Hartman of Hartman Environmental and Dr. Mark Kram of Groundswell Technologies. During this webinar presentation, Drs. Hartman and Kram discussed updates regarding VI pathway issues, as well as the use of continuous monitoring data. Vapor intrusion continues to be a hot topic among environmental practitioners and represents an opportunity in the industry for firms to expand in providing informed and proper VI guidance and best practices for their clients’ sites.


Blayne Hartman, PhD
President, Hartman Environmental Geoscience


Mark Kram, PhD
Founder and CTO, Groundswell Technologies

The Vapor Intrusion Pathway

Q. What are the key questions for most VI investigations and how are they addressed?

A. The following are the key questions for most VI investigations:

  1. Do I have an indoor exceedance?
  2. If “Yes”, is this from an indoor source or due to VI?
  3. If due to an indoor source, can we identify this and resolve the issue?
  4. If due to VI, where is it coming into the structure?

We answer each of these questions within a few days of monitoring combined with a few discrete samples. As such, once you have this data in hand, you can proceed to the next step of either mitigation or site closure.

Q. In a specific example given during the presentation, a furniture facility had daytime TCE increases. Were you able to determine why TCE was not listed on the adhesive spray cans? Was it simply because TCE was present at less than 1% of formulation, and thus not required to be listed? Is it common for products to contain TCE and not report this?

A. We were not able to determine why TCE was not listed. TCE was not listed on the MSDS either. We’ve encountered similar situations with other materials. For instance, we recently encountered a disinfectant in the restroom at a facility where indoor TCE was detected. The container did not mention TCE, and the MSDS stated that it included “40% additional ingredients.” After an analysis in
the field, we determined that it did contain TCE.

This is something that OSHA has not yet caught up with. Given all the products on the market that include TCE, we will continue to be vigilant about this. Having the analyzer on-site has helped, as we were able to resolve the issues while in the field without having to wait for a fixed laboratory result.

Q. Have you found that in climates with large seasonal variations it is necessary to return to the site during different seasons to account for vapor intrusion variations? (i.e. A/C vs. heating season)

A. Since we can track conditions continuously, the consultants we have worked with have observed the initial data generated including spatial and temporal patterns, and then intentionally induced building manipulations to evaluate cause-and­effect. This includes turning the HVAC on and off, covering drains, sealing cracks, and tracking differential pressure, which is the main driver for concentration
“spikes”. With these observations, consultants have been able to convince their regulators to move the project to the next phase in the life cycle of VI manage­ment. As such, they’ve been able to proceed based on a single mobilization.

Q. How often do regulators recommend continuous monitoring vs. summa canisters to environmental consultants for sites enrolled in regulatory programs? Is continuous monitoring becoming more prevalent?

A. Yes, continuous monitoring is becoming more prevalent as practitioners see the large benefits it offers. EPA has required it on 2 thermal remediation sites to monitor for off-gassing. MA-DEP has required it on construction sites to monitor fugitive emissions. In many cases, regulators cannot require it, but they recommend it. Every agency appreciates the data because you get hundreds to thousands of data points and can see the picture much better than from a few canister or passive data points.

Q. Is calculating an average attenuation factor by using the ratio of average indoor air divided by average subslab a more representative or realistic average than calculating the average of the paired indoor and subslab measurements, especially considering that vapor migration is often deflected laterally under a slab?

A. Both methods are flawed. At sites we have monitored both sub-slab and indoor air and we see large variations in the indoor air but little variation in the sub-slab. This does not provide actionable data to find a remedy. When using our system, the data shows what is really going on which allows you to take immediate actions to find remedies.

Q. Blayne mentioned the use of radon as the indicator of VI or as the tool for attenuation factor estimation. Could you say a little more about your experience of using radon as an indicator, please?

A. Radon gives a much more realistic value for the attenuation factor than the ultra-conservative default value of 0.03. I collect radon data whenever I do sub-slab sampling.

Q. Does the enhanced monitoring show any helpful data for site specific attenuation factors? Regulators tend to suggest that attenuation factors can change over time.

A. Yes, it would show repeated measurements of both indoor air & sub-slab soil gas so that one can see if they change together. We have not done many sites with both indoor air & sub-slab data, but the limited data to date clearly shows that indoor air fluctuates much more than sub-slab soil gas, hence the attenuation factor is not constant.

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