Identification of critical parameters for the Johnson and Ettinger (1991) vapor intrusion model

At sites where soils or groundwater contain chemicals of concern, e.g., benzene, and TCE, there is the potential for chemical vapors to migrate from the subsuface to nearby basements, buildings, and other enclosed spaces. The Johnson and Ettinger (1991) model and its extensions are the most widely used algorithms for assessing the intrusion of chemical vapors to enclosed spaces. Users need help in developing a better understanding of the relationships between model inputs and outputs so that they can identify critical inputs when applying the model. A discussion on the Johnson and Ettinger (1991) model covers primary and secondary model inputs; differences between the 1999 model and its implementation in the EPA spreadsheets; flowchart-based approach for identifying critical model inputs; reasonable ranges of model inputs; and comparison of the flowchart approach with a more traditional sensitivity analysis.