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.
Ecology released Implementation Memo No. 14 which provides an updated process for assessing whether existing site conditions are such that petroleum vapor intrusion may be a concern. The document is available at: https://fortress.wa.gov/ecy/publications/SummaryPages/1609046.html.
Ecology has revised the table of vapor intrusion screening levels to reflect updated 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 at: http://www.ecy.wa.gov/programs/tcp/policies/VaporIntrusion/Vapor%20Intrusion%20Table%20update%20April%206%202015.xlsx
These changes to the toxicity values and screening levels are summarized here.
Table B-1 in the draft Guidance for Evaluating Soil Vapor Intrusion in Washington State: Investigation and Remedial Action (October 2009) is outdated and should not be used. The draft Guidance was revised February 2016 to reflect this change. Publication No. 09-09-047 can be found on Ecology’s Publications page at: https://fortress.wa.gov/ecy/publications/SummaryPages/0909047.html
On June 11, 2015, EPA released two guidance documents related to vapor intrusion:
Find both documents on EPA’s Vapor Intrusion site at: http://www.epa.gov/vaporintrusion
This page last revised: May 19, 2016
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