Vapor intrusion is the movement of chemical vapors from contaminated soil and groundwater, through the cracks and gaps in building foundations into the air inside buildings.  Vapor intrusion can be a concern at sites contaminated with solvents and other vapor-forming chemicals.  If uncontrolled, chemical vapors can enter buildings and potentially pose a risk to the health of building occupants.  Evaluating vapor intrusion and assessing potential current and future health risks is complex.  Sites may be affected by different types and amounts of chemical contamination.  A large number of environmental and human-caused conditions also influence vapor behavior and movement.

Vapor Intrusion Fact Sheet

Vapor Intrusion and Your Health Fact Sheet provides a general overview of vapor intrusion.

• Vapor Intrusion and Your Health Fact Sheet [English / Spanish]

Vapor Intrusion E-List

Subscribers will receive e-mail notifications regarding news on topics relevant to vapor intrusion—the movement of chemical vapors through soil and into buildings and potentially causing unacceptable chemical exposure for building occupants.

Subscribe to DTSC Vapor Intrusion E-List.

Vapor Intrusion Guidance Documents and Tools

Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion, February 2023

The California Environmental Protection Agency (CalEPA) Vapor Intrusion (VI) Workgroup developed the Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion (Supplemental VI Guidance) for use with existing State guidance in conducting vapor intrusion evaluations in California. The CalEPA Vapor Intrusion Workgroup consists of staff from Department of Toxic Substances Control (DTSC), State Water Resources Control Board (State Water Board), San Francisco Bay Regional Water Quality Control Board (RWQCB), Los Angeles RWCB, Santa Ana RWQCB, and Office of Environmental Health Hazard Assessment. 

February 2023 – Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion The Supplemental VI Guidance provides a screening process to determine if buildings near known or suspected subsurface contamination by vapor-forming chemicals are potentially affected by vapor intrusion.  The process focuses the investigation and sampling for early assessment of potential vapor intrusion health risks for building occupants.  The Supplemental VI Guidance is meant to promote Statewide consistency in site investigation and cleanup at sites where contaminants in soil gas and groundwater pose an unacceptable risk to current and future building occupants. 

Executive Summary Fact Sheet – February 2023 Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion [English / Spanish]

February 2024 Public Notice –Supplemental Vapor Intrusion Guidance – Video Presentation Posted, Live Question and Answer Sessions [English / Spanish]

The  CalEPA Vapor Intrusion Workgroup released the Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion on February 23, 2023. To keep interested parties informed and engaged, the CalEPA Vapor Intrusion Workgroup developed and posted a Supplemental Vapor Intrusion Guidance video presentation online and hosted two live online Question and Answer (Q&A) Sessions in March 2024.

Video Presentation – 2023 Supplemental Vapor Intrusion Guidance The video presentation provides a general overview of the guidance document:

• vapor intrusion basics and implementation of the guidance
• revisions from the 2020 Draft Supplemental Vapor Intrusion Guidance
• each of the four steps in the screening and evaluation process
• Attachments 1 through 4, additional considerations for vapor intrusion evaluations, including lines of evidence, petroleum-specific considerations, sewers and other vapor conduits, and groundwater as a line of evidence.

Question and Answer Sessions, March 7 and 12, 2024
The CalEPA VI Workgroup hosted live online sessions for interested parties to ask questions on the video overview of the Final Draft Supplemental Vapor Intrusion Guidance.

Response to Comments on February 2020 Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion
The CalEPA Vapor Intrusion Workgroup received and reviewed public comments on the February 2020 Draft Supplemental Vapor Intrusion Guidance and prepared responses for 24 selected generalized comments in the Response to Comments document. The Workgroup revised the Draft Supplemental VI Guidance based upon the comments received.

August 2022 – Vapor Intrusion Update, DTSC Vapor Intrusion Advisory
The August 2022 Vapor Intrusion Update, DTSC Vapor Intrusion Advisory Vapor Intrusion has been superseded by the February 2023 Final Draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion. The DTSC 2011 Final Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air provides information on evaluating the extent of contamination.  

2015 Flow Diagram of DTSC Vapor Intrusion Documents

Advisory – Active Soil Gas Investigations (July 2015)
This Cal EPA Advisory was jointly revised and updated July 2015 by DTSC, Los Angeles Regional Water Quality Control Board (LARWQCB), and San Francisco Regional Water Quality Control Board.  This updated Advisory provides technically consistent approaches and best practices for collecting and analyzing soil gas samples.  Data obtained from soil gas investigations can be used to identify the type of contamination at a site and the spatial distribution – where and how deep the contamination is and concentrations.  The soil gas data can be used to evaluate vapor intrusion, assess health risks,  evaluate the need to manage risks, and plan cleanup.

• Summary of Changes – Advisory – Active Soil Gas Investigations (2015)
• Frequently Asked Questions (FAQ’s)(August 2015)

Final Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (October 2011; also known as the Vapor Intrusion Guidance) DTSC’s Vapor Intrusion Guidance provides a stepwise and sometimes iterative process for the investigation of vapor intrusion and describes procedures for screening and site-specific evaluation of potential risks associated with this exposure pathway.  The DTSC Screening-Level Model spreadsheets that used the Johnson and Ettinger vapor intrusion model to predict theoretical indoor air concentrations of contaminants from soil gas and groundwater data and referenced in the 2011 guidance were outdated and removed from use in 2017.  DTSC is modifying the USEPA’s September 2017 Version 6.0 of the Johnson and Ettinger Model for use on California sites.  

• Summary of Changes Between Interim Final and Final Vapor Intrusion Guidance

Human Health Risk Assessment DTSC recommends consulting Human Health Risk Assessment (HHRA) Note 3 for the DTSC-recommended indoor air screening levels when assessing vapor intrusion health risks.  DTSC also recommends consulting HHRA Note 4 when conducting a human health risk assessment.  See the DTSC Human and Ecological Risk Office webpage for information on risk assessment and HHRA Notes 3 and 4.

Johnson and Ettinger Vapor Intrusion Model

DTSC is releasing a modified version of the USEPA Johnson and Ettinger Model (JE Model) Excel spreadsheet for practitioners working on vapor forming chemical release sites in California. The DTSC version of the JE Model is based on the 2017 USEPA spreadsheet tool (Version 6.0) and provides modifications to correct errors identified in the USEPA spreadsheet and to allow for the use of DTSC-recommended model input values for toxicity factors and building parameters. The DTSC-modified JE Model spreadsheet also includes a refinement of the algorithm to calculate vapor transport across the capillary fringe.

Mathematical modeling such as the appropriate application of the JE Model may be used as a supporting line of evidence, when used with other lines of evidence in the conceptual site model, to evaluate the vapor intrusion exposure pathway. It is recommended that model users review the USEPA Documentation on Implementation of JE Model (USEPA, 2017) which provides information regarding the use of the JE Model to evaluate vapor intrusion into buildings. A User’s Guide on DTSC-modified JE Model has also been prepared to provide additional information on the DTSC modifications to the 2017 USEPA spreadsheet.

Instructions to Download the DTSC-Modified JE Model

1. Click the following link DTSC JE Model 2024.xlsm.
2. You will be required to save the file.
3. Open Windows File Explorer and find the file you saved.
4. Right-click on the file and select “Properties.”

5. On the “General” tab, select the “Unblock” option near the bottom. Select “OK.”
6. Open the spreadsheet and select the “Enable Content” option that appears in a highlighted yellow row.

User Guides:

• Download DTSC JE Model User’s Guide 2024
• Download USEPA JE Model User’s Guide 2017

If you have questions or comments regarding use of the DTSC-modified JE Model, please email DTSC_JEModel@dtsc.ca.gov.

Vapor Intrusion Public Participation Advisory (March 2012) DTSC developed an Advisory to determine and implement appropriate public participation coordination and activities at sites where a potential vapor intrusion risk was identified.  The Advisory is a companion document to DTSC’s Vapor Intrusion Guidance and Vapor Intrusion Mitigation Advisory.  In addition, the Advisory supplements DTSC’s Public Participation and Procedures Manual.  The Advisory is currently under review.

Vapor Intrusion Mitigation Advisory, Revision 1 (October 2011) The VI Mitigation Advisory provides a framework that guides the reader through the decision process for:

• determining if mitigation is appropriate for the project site,
• selecting a mitigation system that is protective of human health, and
• ensuring that implementation is sustainable for the duration of mitigation.

The VI Mitigation Advisory emphasizes public participation and implementation considerations.  The Advisory also identifies likely technologies for vapor intrusion mitigation, but does not identify proven technologies.

Other Vapor Intrusion Resources

U.S. EPA – Vapor Intrusion
ITRC