Vapor Intrusion Screening Levels (VISLs)
EPA developed a spreadsheet calculator, the Vapor Intrusion Screening Level (VISL) Calculator (XLSM)(14 pp, 1 MB) that:
- lists chemicals considered to be volatile and sufficiently toxic through the soil gas intrusion pathway; and
- provides generally recommended, media-specific, risk-based screening-level concentrations for ground water, near-source soil gas, sub-slab soil gas, and indoor air (i.e., the VISLs).
The primary objective of risk-based screening is to identify sites or buildings unlikely to pose a health concern through the vapor intrusion pathway. Generally, at properties where subsurface concentrations of vapor-forming chemicals (e.g. groundwater or "near source" soil gas concentrations) fall below screening levels (i.e., VISLs), no further action or study is warranted, so long as the exposure assumptions match those taken into account by the calculations and the site fulfills the conditions and assumptions of the generic conceptual model underlying the screening levels. In a similar fashion, the results of risk-based screening can help the data review team identify areas, buildings, and/or chemicals that can be eliminated from further assessment.
Exceeding a subsurface screening level generally suggests, however, that further evaluation of the vapor intrusion pathway is appropriate.
Additional information about risk-based screening and the VISLs can be found in EPA's vapor intrusion guidance.
Additional information about the structure and operations of the VISL calculator can found in the Vapor Intrusion Screening Level (VISL) Calculator Users' Guide (PDF)(11 pp, 577 K, About PDF).