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Vapor Intrusion

Vapor Intrusion Screening Level Calculator

The Vapor Intrusion Screening Level (VISL) calculator identifies chemicals that are considered to be sufficiently volatile and toxic to warrant an investigation of the soil gas intrusion pathway when they are present as subsurface contaminants.

What is vapor intrusion?

The calculator provides generally recommended, media-specific, risk-based screening-level concentrations for:

  • Groundwater;
  • Near-source soil gas;
  • Sub-slab soil gas; and
  • Indoor air.

These screening-level concentrations (i.e., the VISLs) are based on:

  • Default residential or nonresidential exposure scenarios;
  • A target cancer risk level of one per million (10-6); and
  • A target hazard quotient of 0.1 for potential non-cancer effects.

The primary objective of risk-based screening is to identify sites or buildings unlikely to pose a health concern through the soil gas intrusion pathway. Generally, at properties where subsurface concentrations of vapor-forming chemicals, such as those in groundwater or “near source” soil gas, fall below the recommended screening levels (i.e., VISLs), no further action or study is warranted. This condition is generally true so long as the exposure assumptions match those accounted for in the calculations, and the site fulfills the conditions and assumptions of the generic conceptual model underlying the screening levels. Similarly, 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.

The VISL calculator output also provides risk estimates for residential and commercial/industrial exposures to soil gas, air and groundwater. The calculator uses the same database of toxicity values, chemical parameters, and inhalation exposure equations as the Regional Screening Levels (RSLs) for Chemical Contaminants at Superfund Sites. The calculator provides default parameters that can be changed to reflect site-specific exposure scenarios.

No consideration is given to ecological effects in the values presented in this calculator. Radionuclides are not addressed on this website.

To ensure proper use of the calculator, please review the What's New, User's Guide, and Frequently Asked Questions links. If the calculator is used with non-default inputs to support a risk management decision regarding a site, the inputs should be clearly identified and justified by the user.

This VISL calculator is based on the Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air (June 2015). Additional information about risk-based screening and the generic conceptual model underlying the VISLs can also be found here.

EPA developed this website with the Department of Energy’s Oak Ridge National Laboratory under an interagency agreement.