Draft Vapor Intrusion Guidance

Vapor intrusion (VI) refers to the vapor phase migration of volatile organic and/or inorganic compounds into occupied buildings from underlying contaminated groundwater or soil.  Because vapor intrusion can potentially result in unacceptable concentrations of hazardous substances in indoor air, the vapor intrusion pathway should be assessed whenever volatile contaminants are present in the subsurface of a site.  The draft technical guidance provides techniques for evaluating whether vapor intrusion has the potential to contaminate indoor air and also recommends ways to protect building occupants.

Graphic adapted from figure by Thomas McHugh, GSI Environmental.
Used by permission.

August 20, 2015

On June 11, 2015 EPA released 2 guidance documents related to vapor intrusion.  This included:

Ecology issued draft vapor intrusion guidance in October, 2009 for review.  Numerous comments were received and Ecology subsequently established an external workgroup to obtain feedback and direction to help finalize the draft guidance.  An initial meeting was held in May, 2010 and good discussion took place on the content and overall level of detail to include in the guidance.  For a number of reasons, further work on the guidance was suspended shortly after that meeting and the 2009 draft guidance has been relied on since that time.

Now that EPA has finalized their 2 major guidance documents related to vapor intrusion, Ecology believes it is an opportune time to update and ultimately finalize the 2009 draft guidance.  Ecology intends to evaluate the new EPA guidance documents and prepare an updated version of the draft guidance that will be then made available for public review.  Ecology will also evaluate the comments received in 2009 and address as many of them as possible while considering the changes that have occurred in assessing, investigating and mitigating vapor intrusion since the draft guidance was originally released.  Ecology may re-establish an advisory workgroup to provide additional assessment of the guidance.

April 6, 2015

Ecology has updated the table of vapor intrusion screening levels to reflect recent toxicological information.  In addition, the sub-slab attenuation factor was reduced from 0.1 to 0.03 which raises sub-slab screening levels by about a factor of 3.  An Excel spreadsheet with revised groundwater, sub-slab soil gas, and deep soil gas screening levels is now available.

Due to these changes, Table B-1 in Appendix B of the October 2009 draft Guidance for Evaluating Soil Vapor Intrusion in Washington State should no longer be used.  

Who should I contact if I have questions?

If you have questions, please contact:

Jim White
(360) 407-7324

Jodi Gearon
(360) 407-7235

This page last revised: August 20, 2015