The Current Status of California’s Vapor Intrusion Guidance

By Laurie Berger (May 28, 2020)


In February of this year, three California regulatory agencies[1] released the much-anticipated draft guidance for the investigation of vapor intrusion, “Supplemental Guidance: Screening and Evaluating Vapor Intrusion” (Draft Guidance). The purpose of the Draft Guidance is to promote a state-wide standard practice and a consistent approach for screening buildings for vapor intrusion. The public comment period ends June 1, 2020. The agencies are hoping to finalize the Draft Guidance by the end of 2020.


The Draft Guidance differs from the existing vapor intrusion guidances in several ways in that it:

  • Promotes conducting vapor intrusion sampling early in the investigation process.

  • Encourages decisions based on sampling rather than modeling.

  • Recommends using U.S. EPA’s attenuation factors and screening numbers to decide when to do indoor air sampling.

  • Includes collection of vapor intrusion samples from sewer laterals to determine impact to indoor air.

  • Introduces the concept that both current and future conditions should be evaluated.

DTSC has stated that the Draft Guidance is intended to be used as follows:

  • New Cases: The Draft Guidance should be used now for newly opened cases.

  • Existing Cases: The oversight agency should review each site on a case-by-case basis to evaluate whether adequate sampling has been performed.

  • Closed Cases: Closed cases should also be evaluated on a case-by-case basis, and TCE sites should be given priority. Some agencies may decide to systematically reevaluate their closed sites. In addition, a review of closed sites may be triggered by a change in land use, a property transaction or a referral.

If the Draft Guidance is implemented, the increased requirements will have a number of implications including:

  • The due diligence process may become longer, more complicated and more costly. If a property is found to have a potential vapor intrusion risk, multiple sampling events may be required which could result in delays and increased costs.

  • In more instances vapor intrusion risk may need to be disclosed to potential purchasers and may impact property values.

  • Indoor air sampling may be required sooner in the investigation process and more buildings may require screening.

  • Because more neighboring properties may be impacted, property owners will need to coordinate site access to sample neighboring sites.

  • As described above, each agency will approach closed sites differently, but it is likely that some closed TCE sites will receive higher scrutiny and may be reopened.


The final guidance will potentially have a significant impact on the way vapor intrusion sites are investigated and remediated in California. However, the final guidance is simply guidance – it is not binding on the California regulatory agencies or the public. At this time is difficult to predict how the various agencies within California will apply it. CalEPA is now evaluating whether to promulgate an enforceable vapor intrusion regulation or policy. So although the Draft Guidance is a long-awaited development, a new regulation may soon provide a legally enforceable framework for the evaluation of vapor intrusion sites.

[i] Department of Toxic Substances Control (DTSC), the San Francisco Bay Regional Water Quality Control Board (SF Bay RWQCB) and the State Water Resources Control Board (SWRCB)

Laurie Berger is a Partner at Environmental General Counsel. She handles a wide range of environmental matters.

T: 510-495-1407 E: lberger@egcounsel.com

ENVIRONMENTAL GENERAL COUNSEL LLP

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The opinions expressed are those of the author and do not necessarily reflect the views of the firm, its clients, or any of its or their respective affiliates. This article is for general information purposes and is not intended to be and should not be taken as legal advice.