Q&A Brief: Webinar on Federal Vapor Intrusion Guidance

On August 6, 2013, EDR Insight hosted a webinar on vapor intrusion risk, titled Sorting Out the Implications of U.S. EPA VI Guidance. Our panelists were:

  • David Gillay,
    Partner with Barnes & Thornburg and Chair of the Brownfields & Environmental Transactional Practice Group;
  • Blayne Hartman,
    Hartman Environmental GeoSciences, a nationally recognized expert on soil vapor sampling, soil vapor analysis and vapor intrusion; and
  • Brad Willy, president, and Craig Brown, manager of operations at TerraVapor, a leading vapor intrusion mitigation firm.

Recent developments on the regulatory front point to the high priority that the vapor exposure route is now being given by regulatory authorities at contaminated sites. These leading experts presented timely content focused on:  the implications of the U.S. EPA’s vapor intrusion guidance and states’ responses, best practices for conducting effective vapor assessments, and real-world case studies on installations of mitigation systems at properties with vapor issues. More than 1,000 attendees, mostly environmental professionals, tuned in from across the country to hear the latest on vapor intrusion assessment and mitigation. One of the most interesting aspects of hosting an event this large was reviewing the questions submitted as David, Blayne, Craig and Brad presented. The questions from the audience were too numerous to address during the live event, so the panelists were generous enough to provide their answers to be distributed to attendees in this brief. Below is the complete list of questions, categorized by major topic.

Regulations, Reference Documents and Guidance

Q:  How do you determine the correct screening levels?

David Gillay/Blayne Hartman: First, determine the acceptable exposure risk that governs any response action at your site. Many states have look up tables.  If a look up table is not available in your state, then start with indoor air screening levels from the EPA Regional Screening Levels and calculate soil gas screening levels using a default attenuation factor.

Q:  What are EPA standards when a state does not have standards?

Gillay/Hartman: Go to the EPA Regional Screening Levels and then determine the acceptable exposure risk.

Q:  What reference documents for background concentrations of VOCs in homes and buildings are you aware of?

Hartman: Go to the EPA-OSWER vapor intrusion web site for a document about background concentrations.

Q: There are so many guidance documents and technical manuals on vapor intrusion.  What laws protect us and who enforces them?  Meaning, if we feel our occupants are not being protected (i.e., guidance is not being adequately followed), who will help us enforce the applicable guidance?

Gillay:  Given the sheer volume and evolution of VI science, a potentially liable party should develop an overarching policy on potential VI risk and liability and then periodically review and update that policy.  If it is determined that an unacceptable risk potentially exists due to the VI pathway, then the appropriate regulatory agency should be contacted and/or litigation should commence.

Q:  If a state has VI Guidance in use, which guidance documents prevail: U.S. EPA’s or State guidance?

Gillay: Generally speaking, the state’s VI guidance, policy, and rules will apply. However, the U.S. EPA retains the power to “over file” if it is determined that the state’s approach does not adequately protect human health or the environment. Often times, the U.S. EPA will assert that there is an imminent risk.

Q:  Would state Risk Based Correction Actions (RCBA) program guidelines/requirements for petroleum vapors fulfill VI requirements for petroleum?  Also would they apply to other VOCs -there’s no state guidance / requirements / formulas for TCE etc.?

Gillay: I would retain a qualified environmental professional to determine whether a particular state’s RBCA program guidelines/requirements adequately address the potential VI pathway.

Q:  Is a vapor migration assessment only required for CERLCA exposure sites?

Gillay: The potential vapor intrusion pathway should be assessed at any contaminated site where volatile chemicals are present.

Q: Is there any evidence that anyone has been harmed by vapor intrusion?

Gillay: Please refer to the IRIS database for chemical assessments for PCE and TCE.

Vapor Assessment, Sampling and Modeling

Q: Who do the Oscars belong to? And was this person having air sampling done at their house?

Hartman: Angelina Jolie. (Only fooling.  It was a film editor’s house.  The movie was “From Here to Eternity.”).  And yes, we were testing the indoor air.

Q: Can you please confirm Blayne Hartman’s e-mail.

Hartman: Blayne@hartmaneg.com

Q: Here in NC, the state is leaning toward doing indoor air AND soil gas (e.g., per draft OSWER guidance and multiple lines of evidence). Is EPA reconsidering this approach?? I sure hope so. Also, I know radon testing was being downplayed for attenuation factor development for hydrocarbons – any change on this front?

Hartman: EPA-OSWER prefers indoor air and sub-slab data. EPA-OUST is less supportive of indoor air due to the numerous indoor sources of hydrocarbons. Acceptance of radon as a surrogate for slab-specific attenuation is mixed.

Q: Do you see the J&E model being replaced with a less conservative model in the near future?

Hartman: No. Also, modeling is being eliminated as an exit ramp by the U.S. EPA.

Q: Are there any concerns with gas well “fracking” as gas seeps upward in and through ground water and into structures? 

Hartman: No,since there is no positive gas pressure as there is with fracking.

Q: What determines if you use cancer vs. non-cancer levels?

Hartman: Both are applicable. In states that regulate cancer risk at 1 in 1 million, the cancer value is typically lower and so it controls the assessment. In states that regulate cancer risk at 1 in 100,000, the non-cancer screening level can be lower than the cancer screening level. So, ultimately, it depends upon the state and the compound.

Q:  If EPA is releasing new J&E Model user guide, how is modeling no longer an exit strategy? Especially considering that the J&E Model is conservative.

Hartman: I’m as confused by this as you are, but some states do allow modeling to be used as an exit, so a new version of the model could be useful in those areas.

Q:  How does the EPA reconcile the default attenuation factors with acceptance of the J&E model? Because running the J&E model with default conservative assumptions results in more attenuation (i.e., if you “fail” at the default attenuation factors, just run the J&E model and you might be OK.).

Hartman: You are correct.  The proposed default attenuation factor of 0.3 in the new guidance would be ~15 times more restrictive than the default J-E model would predict (0.002).  So, OSWER will not let you use the model as an exit.

Vapor Mitigation

Q:  In TerraVapor’s case studies, you showed a couple of sub-slab extraction points. Is there a “rule of thumb” for how many points are needed? Is it based on area covered, distance between points, contaminant concentration, or some combination thereof?

TerraVapor:  There is no real rule of thumb. We rely on our experience with similar sized buildings with similar footprints. Once again, all structures are different and to effectively design/install a quality system for each structure; it all begins with performing an effective pilot study.

Q: Are you willing to share ballpark cost information for the case studies you presented?

TerraVapor:   Of course, but bear in mind that these projects were located in our backyard here in Indiana. That said, this is a breakdown of approximate pricing for case study we presented during the webinar:

Case Study #1

6,500 sqft footprint/SSDS system $35,000

Case Study #2

2,800 sqft footprint/ERV system $30,000

Case Study #3

SSDS EPA Superfund residential site…$2,000 per SSDS/Structure

Q:  How do the sub-slab depressurization systems installed by TerraVapor differ from typical radon mitigation systems?

TerraVapor: The concept of installing a SSDS is very similar to that of a radon system,however, as we described during the webinar, there needs to be a clear technical comprehension of the sub-slab characteristics along with the building’s infrastructure to effectively mitigate. This knowledge is gleaned from an effective pilot study, which will then drive the system design, and finally leading to an effective installation. Lastly, as it relates to installation, Terra Vapor utilizes professionals who MUST BE OSHA-trained and Hazwoper-certified, along with certified electricians and plumbers to install our systems.

Q: How do you address condensate accumulation in the sub-slab depressurization system?

TerraVapor:  Properly designed systems, based upon the pilot study, will address and thus eliminate the concern of condensation within the fan or blower unit chosen to mitigate. These fans/blowers are designed to address and discard “normal’ condensation.

Q:  What has been your experience and recommendation relative to monitoring of a passive vapor mitigation system?

TerraVapor: Repeat sampling events to verify that no component of the system has been compromised is the only method that we are aware of relating to monitoring these systems.To the best of our knowledge, there is no current technology to monitor a passive mitigation system.

Q: When extracting sub slab vapors from a site impacted by chlorinated solvents, are HAPs a concern and is permitting required?

Gillay: The applicable air regulations should be reviewed to determine if any thresholds are triggered, thus requiring a permit.

 Q: How can you convince a client/regulator that an SSDS or ventilated sub-slab with a continuous monitored vacuum of 1 to 1.5 in water column is sufficient documentation of a successful elimination of VI pathway? There seems to be a need/desire to conduct indoor air testing for multiple lines of evidence (but this can/will open so many other non-subsurface contaminant sources into the analyses).  Any suggestions?

Gillay:  As I mentioned during the live presentation,one way to convince a client/regulator that you have adequately addressed the VI pathway is to retain experienced and qualified team members that have a proven track record of success.


EDR Insight wishes to thank all of the attendees who submitted a question during the live event. We hope to have you join us for future webinars!

And EDR Insight’s special thanks are extended to David,Blayne, Craig and Brad for being so generous with their time and expertise.

Have a question about vapor intrusion? Visit EDR Insight’s online archives on vapor intrusion, including past webinars, tip sheets and research briefs.