A Comparison of Soil Gas Data to Vapor Migration Modeling Results. S. L. Sager and A. H. Bass, ARCADIS Geraghty & Miller, Inc., Raleigh, NC
The vapor migration pathway has become a standard exposure pathway in risk assessments. The presence of volatile constituents in soil or groundwater in developed areas almost requires evaluation of this pathway. Several vapor transport models are available, including the Johnson and Ettinger model, the Daugherty model (developed by the Orange County CA Health Care Agency), and the modification of the Johnson and Ettinger model presented in the appendices to the ASTM Risk-Based Corrective Action Standard (E 1739). The first model relies on advection and diffusion to predict transport into building air, while the other two models rely only on diffusion. Site-specific soil data will be used in each model together with standard (for the site) assumptions for building size and air exchange rates. The results will be compared to measured soil gas data. This will help to illustrate how well the models predict indoor air exposure point concentrations. Finally, risk estimates will be calculated to illustrate the difficulty in making risk management decisions based on this exposure pathway.
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