California Regulators Set to Upend Vapor Intrusion Assessment and Mitigation
January 22, 2019 / Morgan Gilhuly and Dave Metres
Real estate development and environmental cleanups will take longer and be more expensive under new vapor intrusion guidance expected from California environmental agencies.
“Vapor intrusion” is the movement of chemical contaminants from groundwater or soil into indoor air. The radon gas found in many homes in the United States is an example of one type of vapor intrusion, but there are many other contaminants that are capable of getting into indoor air.
In 2013, US EPA began to focus on the risk of trichloroethylene (TCE) vapor intrusion as a result of a new—and controversial—assessment of the risks that TCE poses. Some EPA regions, including Region 9, which includes California, began requiring more extensive investigations of TCE vapor intrusion, and more cleanup and mitigation to prevent TCE from getting into indoor air. Many states, including California, have followed EPA’s lead, to a greater or lesser extent. TCE is present at hundreds of California sites.
Now, the California Department of Toxic Substances Control (DTSC), the State Water Resources Control Board (State Water Board), and the San Francisco Bay Regional Water Quality Control Board (San Francisco Regional Water Board) are poised to release new guidance governing the investigation and remediation of vapor intrusion (VI) issues. The guidance is likely to follow EPA’s lead and change substantially the manner in which contaminated sites are investigated, managed, and cleaned up. The agencies have not yet released the guidance, and the details will undoubtedly be important, but even now there are enough bread crumbs to suggest the path that the agencies will likely take.
In May 2018, the staff of the San Francisco Regional Water Board sent a recommendation for the new VI guidance to DTSC and the State Water Board. We expect that the Regional Water Board staff’s recommendations will be the foundation on which the DTSC/State Water Board guidance will be built. The Regional Water Board’s staff comments suggest the scope of the changes to come:
- “More cleanup sites need VI assessments, due to the more stringent VI screening levels for soil gas and groundwater. Additionally, more sites need indoor air sampling.”
- “We are significantly expanding our public outreach efforts at sites that are doing VI assessments, particularly when indoor air sampling is needed.”
- “At some sites, we are requiring more active cleanup to meet more stringent VI screening levels, to avoid reliance on mitigation systems, and to minimize the duration of any VI mitigation.”
- “Where it’s infeasible to meet VI screening levels with cleanup actions, we may need to oversee cleanup cases longer to assure that necessary VI mitigation is carried out for as long as the VI threat remains. As such, fewer cases may qualify for low-threat closure following active cleanup.”
Staff Summary Report, Vapor Intrusion Assessment and Mitigation – Status Report, San Francisco Bay Region, Regional Water Quality Control Board (Meeting Date, May 9, 2018) at 3. The staff recommendation would also:
- Update the approach that agencies use to screen for VI risk at both existing and potential future buildings.
- Increase the required number of sampling events from two to three “to understand temporal variability.”
- Require soil gas sampling from at least two depths.
- Focus on soil gas data in assessing future risks.
- Create a much stronger preference for cleanup instead of measures that simply “mitigate” vapor intrusion (such as vapor barriers). VI mitigation would be viewed as a “short-term solution to provide protectiveness while active cleanup is ongoing. Typically, [RWQCB] should approve mitigation systems after, or in conjunction with active cleanup, and rarely as a stand-alone option.”
Even before the DTSC/State Water Board guidance is issued, it is clear that many sites thought to be closed may be reopened and others will take longer to reach closure. Mitigation measures are also much less likely to be accepted by the agencies as a permanent solution. Cleanup of contaminated soil and groundwater is likely to be required in many more circumstances. Such an approach will likely be controversial because of the enormous costs of cleanup.
We will continue to monitor the State’s development of its VI guidance and report on new developments as they arise.