Draft Vapor Intrusion Guidance

Vapor Intrusion:  Changes to the 2009 Toxicity Values and Screening Levels

The 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  This new Excel table, replaces Table B-1 in Appendix B of the October  2009 draft Guidance for Evaluating Soil Vapor Intrusion in Washington State.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:
  • Acetophenone
  • 2-chloropropane
  • 1,2-dichloroethylene (cis)
  • 1,2-dichloroethylene (trans)
  • Diisopropyl ether
  • Methylcyclohexane
  • 1,3,5-trimethylbenzene
2.  Toxicity values (and therefore screening levels) are unchanged for 31 chemicals.

3.  Thirty-two chemicals had additions/deletions/changes to their toxicity values since 2009 (some chemicals had more than one):
  • Noncancer values added = 6
  • Noncancer values removed = 1
  • Noncancer values changed = 17
  • Cancer values added = 6
  • Cancer values removed = 2
  • Cancer values changed = 9

4.  Due to these changes in toxicity values, groundwater and deep soil gas screening levels:

  • Increased (became less stringent) for 16 chemicals.
  • Decreased (became more stringent) for 13 chemicals.
  • Were unchanged for 3 chemicals (because the complementary cancer or noncancer value was unchanged and was more stringent than the changed parameter).

5.  Magnitude of the changes for groundwater and deep soil gas:

  • The 2015 screening levels are 0.0001 to 0.001 times the 2009 value for 1 chemical.
  • The 2015 screening levels are 0.001 to 0.01 times the 2009 value for 2 chemicals.
  • The 2015 screening levels are 0.01 to 0.1 times the 2009 value for 2 chemicals.
  • The 2015 screening levels are 0.1 to 1.0 times the 2009 value for 8 chemicals.
  • The 2015 screening levels are 1.0 to 10 times the 2009 value for 7 chemicals.
  • The 2015 screening levels are 10 to 100 times the 2009 value for 7 chemicals.
  • The 2015 screening levels are 100 to 1000 times the 2009 value for 1 chemical.
  • The 2015 screening levels are 1000 to 10000 times the 2009 value for 1 chemical.

 



This page last revised: April 20, 2015