Site Mitigation & Restoration Program

We protect and maintain California’s land and places
by setting strict standards for land restoration and cleanup

Vapor Intrusion

Vapor Intrusion Attenuation Factor Study

The Department of Toxic Substances Control is pleased to share a preview of the process that has been used to derive a potential California-based attenuation factor for vapor intrusion calculations. The study, when complete, will provide the redevelopment sector with an additional tool to facilitate the land revitalization process. Although the study is under peer review and the report is not ready for release, DTSC is providing an overview of the data and process utilized for the calculations. Please e-mail for a copy of the presentation made at the California Land Recycling Conference 2020 – Communities Rising.

To receive future notices on the DTSC Vapor Intrusion Attenuation Factor Study, please subscribe to the DTSC Vapor Intrusion E-List.

Vapor Intrusion E-List

Subscribers will receive e-mail notifications regarding news on topics relevant to vapor intrusion—the migration of volatile contaminants through soil and into buildings and potentially causing unacceptable chemical exposure for building occupants. Topics include subsurface investigations and evaluation of potential exposure and human health risk from vapor intrusion.

Subscribe to DTSC Vapor Intrusion E-List.

Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion

The Department of Toxic Substances Control (DTSC), State Water Resources Control Board, and San Francisco Bay Regional Water Quality Control Board (CalEPA Vapor Intrusion Workgroup) have developed supplemental vapor intrusion guidance for conducting vapor intrusion evaluations in California. The Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion was released for review and public comment on February 14, 2020. Public meetings that had been scheduled for April 2020 were canceled due to the COVID-19 emergency. As a safe alternative, the California Environmental Protection Agency (CalEPA) Vapor Intrusion Workgroup developed and posted video presentations online and, in May 2020, hosted live webcast Question and Answer Sessions in lieu of State-wide public meetings. The public comment period was extended, ending on June 1, 2020.

The CalEPA Vapor Intrusion Workgroup is in the process of reviewing the 575 comments received during the comment period and revising the Supplemental Guidance. It is anticipated that the revised Supplemental Guidance will be released to the public in Spring 2021. The CalEPA Vapor Intrusion Workgroup has been expanded to include representatives of the Office of Environmental Health Hazard Assessment and the Los Angeles and Santa Ana Regional Water Quality Control Boards. The Draft Supplemental Guidance 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

February 2020 – Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion

Executive Summary Fact Sheet: English / Spanish

February 14, 2020 Public Notice – February 2020 Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion [English / Spanish]

Revised – March 24, 2020 Public Notice – February 2020 Draft Supplemental Guidance: English / Spanish

May 4, 2020 Public Notice – Draft Supplemental Guidance – Video Presentations and Live Question and Answer Sessions [EnglishSpanish]

Video Presentations

A general overview and technical presentations on the Draft Supplemental Guidance are available in seven video presentations. The general overview presentation covers basic vapor intrusion information and provides an overview of the Draft Guidance. The technical presentations, provided in four modules, cover the Draft Guidance, the GeoTracker Database, and a case study. The video presentations, “Vapor Intrusion Workgroup – Presentations” are available at DTSC’s YouTube website:

Video Presentations – Draft Supplemental Guidance

Public Question and Answer (Q&A) Sessions – Webcast

The CalEPA Vapor Intrusion (VI) Workgroup hosted live internet sessions on May 14 and May 19, 2020 for the public to ask questions on the YouTube video presentations, the Draft Guidance, and on vapor intrusion in general. The two Q&A sessions included technical and general overview sessions on each day.

Vapor Intrusion Fact Sheet

Vapor Intrusion and Your Health Fact Sheet (general overview of vapor intrusion): English / Spanish