On February 14, 2020, the State Water Resources Control Board (SWRCB) and the California Department of Toxic Substances Control (DTSC) issued a public notice regarding the release of Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion (Draft Guidance) that  supplements existing vapor intrusion guidance issued in 2011.  The Draft Guidance is now available for public review and comment.  Comments are due by 12:00pm on April 30, 2020.

The Draft Guidance provides information on how to improve vapor intrusion investigations and promotes consistency in such investigations throughout California.  The Draft Guidance establishes a four-step evaluation process to assess vapor intrusion:

Step 1: Decide which buildings should be tested first and how. When there are several buildings, the Draft Guidance recommends starting with those that are occupied and closest to the contamination.  If a building is directly above or very close to the spill, or if it is likely that the sewer could bring toxic vapors inside, go directly to Step 3.

Step 2: Screen buildings from outside.

Step 3: Test indoor air.

Step 4: Take actions to protect public health.

Additional topics covered by the Draft Guidance include:

  • Using United States Environmental Protection Agency (EPA) 2015 attenuation factors.
  • Considering sewers as a potential vapor intrusion migration route and pathway of exposure.
  • Building a California-specific vapor intrusion database, which begins with the SWRCB including additional capabilities to the existing GeoTracker statewide data management system to accept building-specific data and differentiate types of vapor samples.

The SWRCB and DTSC will hold informational public meetings and webinars throughout California to answer questions and receive comments on the Draft Guidance, the first two of which are scheduled for April 1, 2020 at 1:00pm and 6:00pm at CalEPA Headquarters in Sacramento:

CalEPA Headquarters – Sierra Hearing Room

1001 I Street, Sacramento, CA 95814

This meeting will also be webcast from CalEPA’s Live Webcasts page  For additional public meeting dates and locations, as well as more information regarding how to submit comments, please visit DTSC’s Vapor Intrusion website at https://dtsc.ca.gov/vapor-intrusion/.