California Agencies Proceed With Revisions to Vapor Intrusion Guidance

California agencies issued a public notice that they will hold a workgroup to answer questions and engage with stakeholders on the agencies’ latest vapor intrusion guidance. The workgroup comes following years of confusion among stakeholders regarding the agencies’ application of draft guidance for addressing vapor intrusion, including during site cleanup and redevelopment.

In February 2023, the California Department of Toxic Substances Control (DTSC) and the State Water Resources Control Board (SWRCB), along with other agencies, published their “Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion.” That guidance provided a revised approach for practitioners and regulators to use when screening buildings for risks from subsurface vapor contamination, supplementing guidance issued in 2011 and 2020. Although the guidance does not set requirements per se, developers and others can expect the agencies to apply the criteria when overseeing site redevelopment. The guidance has been subject to criticism for, among other things, rigidity in its formula for calculating the attenuation of vapor.

The California agencies issuing the recent public notice include the California Environmental Protection Agency, DTSC, and SWRCB. Each of these agencies can play a role in site cleanup and redevelopment and the governing standards and policies. In exercising jurisdiction over a site, the agencies may require vapor intrusion assessment and remedial measures. Therefore, the guidance they publish to instruct regulators in the field is impactful for how vapor is assessed and the resulting remedial measures that may be required for a particular site, which are also a key driver of costs incurred for redevelopment.

The sessions will be held online on March 7 and 12, 2024. Participants may submit questions in advance.

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