Draft Vapor Intrusion Guidance
Vapor Intrusion: Changes to the 2009 Toxicity Values and Screening LevelsThe Washington State Department of Ecology has updated the table of vapor intrusion (VI) 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 soil gas screening levels by about a factor of 3. This new Excel table, replaces Table B-1 in Appendix B of the October 2009 draft Guidance for Evaluating Soil Vapor Intrusion in Washington State. The guidance document should still be used, but Table B-1 should not.
Table B-1 contained 70 chemicals (not including 6 petroleum fraction entries). Seven of these chemicals have been removed from the list due to lack of toxicity values in CLARC. Of the remaining 63 chemicals, toxicity values for 32 have changed. Groundwater and deep soil gas screening levels have changed for 29 chemicals in 2015.
Important: The sub-slab attenuation factor has been changed from 0.1 to 0.03, resulting in changes to all of the sub-slab screening levels.
The following is a more detailed summary of the updates:
1. Seven chemicals do not have toxicity values in CLARC and have been removed from the old VI list:
3. Thirty-two chemicals had additions/deletions/changes to their toxicity values since 2009 (some chemicals had more than one):
4. Due to these changes in toxicity values, groundwater and deep soil gas screening levels:
5. Magnitude of the changes for groundwater and deep soil gas:
This page last revised: April 20, 2015
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