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SWRCB & DTSC Issue Draft Guidance for Vapor Intrusion

The State Water Resources Control Board (SWRCB) and Department of Toxics Substances Control (DTSC) recently released draft joint supplemental guidance for screening and evaluating vapor intrusion. The draft guidance contains recommended improvements for vapor intrusion investigations and is intended to help promote consistency across the state, using attenuation factors recommended by USEPA. More specifically, the draft guidance provides four detailed steps to help decide whether there is a vapor intrusion that could pose a risk to the health of individuals inside buildings. Those steps include:

  • Step 1 - Decide which buildings should be tested first and how.
  • Step 2 - Screen buildings from outside.
  • Step 3 - Test indoor air.
  • Step 4 - Act to protect public health.

Also notable, among the vapor-forming chemicals highlighted within the draft guidance and related materials are references to Tetrachloroethylene (PCE), Trichloroethylene (TCE) and Napathalene. The draft guidance is clear, however, that petroleum releases from underground storage tanks (UST) must be evaluated for vapor intrusion under the State Water Resources Control Board's (SWRCB) Resolution 2012-0062, Low Threat UST Case Closure Policy adopted in 2012 rather than under this draft guidance.

While the SWRCB and DTSC had originally scheduled a host of public meetings for April, amid the COVID-19 crisis they have postponed those meetings and have extended the written comment period through June 1st at 12 noon.

For more information, please see