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JOHNSON AND ETTINGER (1991) VAPOR INTRUSION MODEL WITH SUB-SLAB CONCENTRATION
Citation:
TILLMAN, F. AND J. W. WEAVER. JOHNSON AND ETTINGER (1991) VAPOR INTRUSION MODEL WITH SUB-SLAB CONCENTRATION. U.S. Environmental Protection Agency, Washington, DC, EPA/600/C-06/002, 2005.
Impact/Purpose:
To assess quantitative and qualitative methodologies evaluation of vapor intrusion, including quantification of uncertainties, to be used in the decision making process.
Description:
Migration of volatile chemicals from the subsurface into overlying buildings is known as vapor intrusion (VI). Under certain circumstances, people living in homes above contaminated soil or ground water may be exposed to harmful levels of these vapors. Vapor intrusion is a particularly difficult pathway to assess, as challenges exist in delineating subsurface contributions to measured indoor air concentrations as well as in adequate characterization of subsurface parameters necessary to calibrate a predictive flow and transport model. Often, a screening-level model is employed to determine if a potential indoor inhalation exposure pathway exists and, if such a pathway is complete, whether long-term exposure increases the occupants risk for cancer or other toxic effects to an unacceptable level. A popular screening-level algorithm currently in wide use in the United States and Canada for making such determinations is the Johnson and Ettinger (J&E) model. The form of the J&E model most widely used has as an output an attenuation factor defined as the ratio of the indoor air contaminant concentration to that of the vapor source concentration. This attenuation coefficient is dimensionless and is often used to back-calculate cleanup goals based on indoor air contaminant measurements and acceptable risk levels, or to predict potential indoor air contaminant exposure and risk based on measured source concentrations. However, use of the attenuation factor does not allow for the direct computation of sub-slab vapor concentration. This Microsoft Excel workbook provides a means to calculate sub-slab vapor concentrations based on user-input values for subsurface and building parameters. Use of this model allows practitioners to compare predicted sub-slab contaminant concentrations with field-measured sub-slab data.