Vapor intrusion: 2015 changes to toxicity values and screening levels

If you’re evaluating vapor intrusion at your contaminated cleanup site, use our updated screening levels and a sub-slab attenuation factor.

In 2015, we updated Table B-1 in our 2009 draft vapor intrusion guidance. We also reduced the sub-slab attenuation factor from 0.1 to 0.03, which raised the sub-slab soil gas screening levels by about a factor of three. This changed all sub-slab screening levels.

You should still use the 2009 guidance but not Table B-1 in Appendix B. Download the 2015 Excel file instead.

In 2015, we updated our 2009 table of toxicity values and screening levels to reflect recent toxicological information. We also reduced the sub-slab attenuation factor from 0.1 to 0.03. This raised the sub-slab soil gas screening levels by about a factor of three.

Read the summary of changes below then access our 2015 Excel table [EXCEL FILE 1]. The 2015 Excel file replaces Table B-1 in Appendix B in October 2009 draft, Guidance for evaluating soil vapor intrusion in Washington State: Investigation and remedial action.

Can I still use the 2009 draft vapor intrusion guidance?

Yes, but you shouldn’t use Table B-1 in Appendix B of the 2009 draft vapor intrusion guidance. Use the 2015 Excel file instead.

What’s the biggest change I should know about?

The sub-slab attenuation factor changed from 0.1 to 0.03, which changed all of the sub-slab screening levels.

Summary of changes, in general

Table B-1 contained 70 chemicals (not including six petroleum fraction entries). Seven of these chemicals have been removed from the list due to lack of toxicity values in Cleanup Levels and Risk Calculation (CLARC). Of the remaining 63 chemicals, toxicity values for 32 have changed. Groundwater and deep soil gas screening levels changed for 29 chemicals in 2015.

Summary of changes in detail

Seven chemicals do not have toxicity values in CLARC and have been removed from the old vapor intrusion 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 (32) 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 three 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.