Subsurface Vapor Intrusion into Buildings
Concerns have been raised about the potential for sub-surface contamination in either soil or ground water to adversely impact indoor air quality. This concern prompted EPA to consider using the Johnson and Ettinger Model (1991) to develop generic soil screening levels (SSLs) to address vapor intrusion into buildings. EPA decided against using the model to develop generic SSLs in the 1996 Soil Screening Guidance because a number of the sensitive parameters did not lend themselves to standardization on a national basis (e.g., distance from the source to the building).
As an alternative to calculating a list of generic SSLs to address this pathway, EPA has developed a series of spreadsheets that allow for site-specific application of the Johnson and Ettinger Model (1991).
The model in spreadsheet form consists of four separate workbooks in either Microsoft® Excel or Lotus® 1-2-3. Two workbooks are for soil contamination and two are for contamination occurring below the top of the water table. In each case, one workbook provides screening-level results while the other workbook provides second-tier estimates. The screening-level approach employs conservative default values for many model input parameters but allows the user to define values for key variables. The second-tier approach allows the user to define values for all model variables and allows for up to three different soil strata between the top of contamination and the enclosed structure. The user's guide provides step-by-step model instructions as well as methods for estimating model input parameter values.
As presently constructed, the soil contamination component of the model operates under the assumption that the initial soil concentration is below the soil saturation concentration (i.e., that a residual or pure component phase does not exist). Likewise, the ground water contamination component of the model assumes that the initial ground water concentration is below the water solubility limit. Because the Johnson and Ettinger model is one-dimensional, the building is assumed to be directly above the contamination. In addition, the model does not consider convective water movement within the soil column, nor does it consider transformation processes (e.g., biodegradation, hydrolysis, etc.).
User's Guide for the Johnson and Ettinger (1991) Model for Subsurface Vapor Intrusion into Buildings
[PDF (523K) 84 pages]
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This page last updated on November 30, 1998
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