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Identification Of Critical Parameters For The Johnson And Ettinger (1991) Vapor Intrusion Model

API Soil and Groundwater Research Bulletin Number 17

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At sites where soils or groundwater contain chemicals of concern, there is the potential for chemical vapors to migrate from the subsurface to nearby basements, buildings, and other enclosed spaces. The Johnson and Ettinger (1991) model and its extensions (e.g., API Publication 4674) are at this time the most widely used algorithms for assessing the intrusion of chemical vapors to enclosed spaces.

The objective of this work is to help users develop a better understanding of the relationships between model inputs and outputs so that they can identify critical inputs when applying the model. This is accomplished by first providing a brief overview of the Johnson and Ettinger (1991) model, including discussions distinguishing primary and secondary model inputs and the differences between the Johnson and Ettinger (1991) model and its implementation in the USEPA spreadsheets. Then, a flowchart-based approach for identifying critical model inputs is presented and reasonable ranges of model inputs are discussed. Finally, use of the flowchart approach is illustrated and compared with a more traditional sensitivity analysis. Appendix A presents the parametric analysis that is the basis for the flowchart-based approach.