Regulations & Permits > Guidance & technical assistance > Vapor intrusion overview

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. The links include guidance from the Environmental Protection Agency (EPA). 

We also have an important update, the 2019 changes to cleanup levels and screening levels in CLARC.

The state's vapor intrusion guidance was developed under Washington's cleanup law, the Model Toxics Control Act (MTCA).


Graphic of two houses on top of soil and a groundwater plume of contamination.  Vapors from contaminated soil and groundwater are migrating through cracks into the homes.

This figure shows volatile chemicals migrating from contaminated soil and groundwater plumes into buildings. Chemicals are entering through cracks in the foundation and openings for utility lines. Atmospheric conditions and building ventilation are influencing vapor intrusion. Source: Environmental Protection Agency's vapor intrusion webpage, accessed October 2017.