Vapor Intrusion Guidelines Becoming More Conservative?

In a recent letter (dated December 3, 2013) to the San Francisco Bay Regional Water Quality Control Board (Regional Water Board), the US Environmental Protection Agency (EPA) Region 9 offered guidelines and supplemental information for vapor intrusion (VI) evaluations.  The Regional Water Board was evaluating Superfund sites in the South San Francisco Bay Area (South Bay Sites) where trichloroethene (TCE) or tetrachloroethene (PCE) are contaminants of potential concern.

As history has shown us, when the environmental community in California catches a cold, the rest of the environmental communities in the US and Canada sneeze!  In this letter, the EPA recommends incorporating into existing and future VI evaluation work plans a number of activities that would make VI investigations more labor intensive and consequently more costly.  While the concern about “reopeners” for closed sites is intriguing, we’ll leave that for a future blog entry.

As to the guidelines/recommendations, they include:

  • Identifying women of reproductive age as the sensitive population of concern.
  • Using a “Short-Term Prompt Response Action Level” of 2 µg/m3 in residential settings.
  • Implementing interim measures to mitigate TCE short-term exposure by:
    • Increasing building pressurization and/or ventilation.
    • Installing and operating engineered, sub-floor exposure controls (sub-slab and/or crawlspace depressurization; or in some cases a soil vapor extraction system).
    • Eliminating exposure by temporary relocation.
    • Collecting an additional round of sampling in the colder weather months since the highest indoor air concentrations usually occur when outdoor air temperatures are significantly lower than indoor air temperatures.
    • Sampling in commercial buildings with HVAC-off.  Sampling duration should begin a minimum of 36 hours following shut-down of the building ventilation systems.
    • Buildings that were thought to have a low potential for VI (presence of a sub-floor vapor barrier for example) need to be evaluated and sampled for VI.
    • Any proposal to exclude particular off-property buildings from indoor air sampling must be supported by a robust, site- and building-specific multiple-lines-of-evidence analysis.

Some Questions

  • Will these conservative criteria in EPA Region 9 be adopted elsewhere?
  • Although “guidance” is not enforceable, will regulators consider these guidelines as “law”?
  • Does this suggest that we might see more “reopeners” of closed sites based on these VI recommendations?

We don’t necessarily have the answer to these questions.  But whether you are in EPA Region 9 or elsewhere, when it comes to VI, a measured, thoughtful and scientific approach should help you avoid chasing protracted and costly vapor investigations.

Thanks to Dr. Khaled Chekiri ( and Jeffrey Bolin, M.S., CHMM ( who authored this blog entry.  You can reach both Khaled and Jeff at 248-932-0228.


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