California’s Department of Toxic Substances Control (DTSC) and the State Water Resources Control Board have issued draft supplemental Vapor Intrusion guidance. The draft “Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion” was released for review and public comment on February 14, 2020. However, because of the Covid-19 public health emergency, the public comment period is extended to June 1, 2020, and the original public information meetings scheduled for April 2020 are postponed until further notice.
The draft guidance supplements existing CalEPA guidance and is intended to promote consistency across the various California regulatory agencies. It provides information on the following topics:
- Soil gas, subslab, indoor air, and outdoor air sampling recommendations that are focused on understanding spatial and temporal variability
- Recommendations for use of USEPA 2015 vapor intrusion attenuation factors
- Risk management framework for vapor intrusion
- California-specific vapor intrusion database in Geotracker
The proposed screening levels are 15 – 30 times lower than values previously used in California. As a result, the new guidance will substantially increase the number of contaminated sites requiring vapor intrusion investigation. The guidance is available at https://dtsc.ca.gov/vapor-intrusion