Draft Vapor Intrusion Guidance
Graphic adapted from figure by Thomas McHugh, GSI Environmental.
Used by permission.
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Due to these changes, Table B-1 in Appendix B of the October 2009 draft Guidance for Evaluating Soil Vapor Intrusion in Washington State should no longer be used.
December 8, 2010
Ecology has suspended for one year work on updating the MTCA cleanup regulation. We will continue work on finalizing the VI guidance.
April 30, 2010The Washington Department of Ecology is in the process of revising and updating the Models Toxics Control Act (MTCA) cleanup regulation. As part of this effort, Ecology is updating clarifying provisions on addressing threats posed by subsurface vapor phase contaminants.
Ecology has formed an advisory group to provide input on vapor intrusion issues. In forming this Vapor Workgroup, Ecology has two main goals:
The first meeting will review the purpose and objectives of the workgroup, discuss the guidance (including public comments received) screening levels, rule revisions, and a strategy for working through remaining issues.
Here is a link to information about the MTCA Cleanup Regulation Update:
Earlier Activity:The Washington State Department of Ecology’s Toxics Cleanup Program asked for comments on a Draft Guidance for Evaluating Soil Vapor Intrusion in Washington State: Investigation and Remedial Action.
All comments on the document provided to Ecology by November 30, 2009, will be considered when the guidance is finalized.
This technical guidance is intended to help responsible
parties, environmental professionals, and Ecology site managers
assess vapor intrusion at cleanup sites in Washington.
The draft guidance addresses a wide range of vapor intrusion
issues. With a number of these issues, Ecology recognizes
that a national consensus has yet to emerge. Ecology asked
for feedback on:
What is the relationship between this draft guidance and the ongoing MTCA Cleanup Regulation Update?
This draft guidance supports implementation of the Model Toxics Cleanup Act (MTCA) cleanup regulation. Ecology is currently in the process of reviewing and updating this regulation. As part of this process, Ecology is examining the investigation and cleanup requirements applicable to vapor intrusion to determine if changes should be made.
Feedback on this guidance document is helping Ecology determine what rule changes (if any) might be needed to effectively deal with vapor intrusion problems at cleanup sites.
Ecology plans to complete work on the vapor intrusion guidance document in 2010. The rulemaking process is currently scheduled to be completed in 2011. If necessary, Ecology will update the vapor intrusion document to reflect regulatory changes following rule adoption.
All comments received by 5 p.m. on November 30, 2009, are being considered. Although we are unable to respond to each comment individually, Ecology will issue a general responsiveness summary that describes the issues identified by reviewers and explains the changes we made to the draft document in response.
If you have questions, please contact:
This page last revised: April 20, 2015
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