Evaluation of the Johnson and Ettinger Model for Prediction of Indoor Air Quality

Authors

  • Ian Hers,

    1. Ian Hers is completing Ph.D. studies at the University of British Columbia and is a senior consultant with Golder Associates Ltd. (ihers@golder.com) in Vancouver, British Columbia.
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  • Reidar Zapf-Gilje,

    1. Reidar Zapf-Gilje is an adjunct professor at the University of British Columbia (rzapf-gilje@shaw.ca) where he teaches graduate courses in the Department of Civil Engineering.
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  • Paul C. Johnson,

    1. Paul C. Johnson is an associate professor and the assistant chair in the Department of Civil and Environmental Engineering at Arizona State University. His degrees are in chemical engineering, a B.S. from the University of California, Davis, and a Ph.D. from Princeton University.
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  • Loretta Li

    1. Loretta Y. Li is an associate professor in the Department of Civil Engineering at The University of British Columbia, with degrees from McGill University and Queen's University.
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Abstract

Screening level models are now commonly used to estimate vapor intrusion for subsurface volatile organic compounds (VQCs). Significant uncertainty is associated with processes and models and, to date, there has been only limited field-based evaluation of models for this pathway. To address these limitations, a comprehensive evaluation of the Johnson and Ettinger (J&E) model is provided through sensitivity analysis, comparisons of model-predicted to measured vapor intrusion for 11 petroleum hydrocarbon and chlorinated solvent sites, and review of radon and flux chamber studies. Significant intrusion was measured at five of 12 sites with measured vapor attenuation ratios (αm's) (indoor air/source vapor) ranging from ∼1 × 10−6 to 1 × 10−4. Higher attenuation ratios were measured for studies using radon, inert tracers, and flux chambers; however, these ratios are conservative owing to boundary conditions and tracer properties that are different than those at most VOC-contaminated sites. Reasonable predictions were obtained using the J&E model with comparisons indicating that model-predicted vapor attenuation ratios (αp's) were on the same order, or less than the αm's. For several sites, the αm were approximately two orders of magnitude less than the αp's indicating that the J&E model is conservative in these cases. The model comparisons highlight the importance in using appropriate input parameters for the J&E model. The regulatory implications associated with use of the J&E model to derive screening criteria are also discussed.

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