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Implementation Memorandum No. 21: Frequently Asked Questions (FAQs) Regarding Vapor Intrusion (VI) and Ecology's 2009 Draft VI Guidance (Historical)

Publication number Date Published Date Revised
18-09-046June 2018November 2018
VIEW NOW This publication is historical. It is unavailable on our website. To request a copy, please use the contact listed below.
Author(s) Mark Gordon, P.E., Policy & Technical Support Unit, Toxics Cleanup Program
Description This implementation memo applies to any cleanup site where vapor intrusion is a potential concern. In 2009, the Washington State Department of Ecology published draft vapor intrusion guidance, publication no. 09-09-047. This memo answers frequently asked questions about that guidance. Many of the questions are about technical or policy changes that have happened since we published the draft guidance in 2009.

REVISION NOTE: This memo was originally published as a review draft on June 22, 2018. In November 2018, we finalized it based on comments received during the draft memo’s public comment period July 5 through August 10, 2018.
NOTES This publication has been replaced by a new publication. In March 2022, this document was incorporated into “Guidance for Evaluating Vapor Intrusion in Washington State: Investigation and Remedial Action,” which is available at
The mission of the Department of Ecology is to protect, preserve, and enhance Washington’s environment. To help us meet that goal, please consider the environment before you print or request a copy.

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Keywords air contamination, Vapor Intrusion pathways, trichloroethylene (TCE), Vapor Intrusion (VI), volatile organic compounds (VOC), soil contamination, groundwater contamination, indoor air quality, Subsurface vapor, trichloroethene (TCE)
WEB PAGE Vapor Intrusion

Guidance for Evaluating Vapor Intrusion in Washington State: Investigation and Remedial Action

Implementation Memorandum No. 22: Vapor Intrusion (VI) Investigations and Short-Term Trichloroethene (TCE) Toxicity

Implementation Memorandum No. 18: Petroleum Vapor Intrusion (VI): Updated Screening Levels, Cleanup Levels, and Assessing PVI Threats to Future Buildings

Implementation Memorandum No. 14: Updated Process for Initially Assessing the Potential for Petroleum Vapor Intrusion

Model Toxics Control Act Regulation and Statute: MTCA Cleanup Regulation Chapter 173-340 WAC, Model Toxics Control Act Chapter 70.105D RCW, Uniform Environmental Covenants Act Chapter 64.70 RCW