Vapor intrusion

When soil or groundwater is contaminated, potentially hazardous vapors can migrate into buildings. These volatile organic or inorganic compounds (or both) can impact indoor air quality. This “vapor intrusion” can cause unhealthy levels of hazardous substances in indoor air. We provide guidance to help you investigate vapor intrusion concerns at your cleanup site and determine what to do about it.

Contaminants move in the direction of groundwater flow and can enter crawlspaces, basements, and homes. — Volatile chemicals can migrate from contaminated soil and groundwater into buildings through foundation cracks and utility line openings.

Vapor Intrusion guidance and screening levels

The state's vapor intrusion guidance was developed under Washington's cleanup law, the Model Toxics Control Act (MTCA). It explains how to investigate and manage potential vapor intrusion concerns.

Guidance for evaluating vapor intrusion in Washington state: Investigation and remedial action (updated March 2022).
- Evaluate whether vapor intrusion could contaminate indoor air at your site.
- Find recommendations for protecting people who live or work in impacted buildings.
Focus on trichloroethylene (TCE) in residential indoor air (September 2019)

Technical guide for assessing and mitigating the vapor intrusion pathway from subsurface vapor sources to indoor air (OSWER publication 9200.2-154, June 2015).
Technical guide for addressing petroleum vapor intrusion at leaking underground storage tank sites (EPA 510-R-15-001, June 2015).
EPA Region 9 Response Action Levels and Recommendations to Address Near-Term Inhalation Exposures to TCE in Air from Subsurface Vapor Intrusion (2014).
EPA Region 10 Recommendations Regarding Trichloroethylene Toxicity in Human Health Risk Assessments (December 13, 2012).

Contact information

Mark Gordon, P.E.
Mark.Gordon@ecy.wa.gov
360-407-6357

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Vapor intrusion

Vapor Intrusion guidance and screening levels

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