Analysis of vapor intrusion of volatile organic compounds from the subsurface into buildings: Comparison of measured concentrations and attenuation factors of contaminants versus estimated concentrations and attenuation factors utilizing the Johnson and Ettinger Model
Lesakowski, Michael A., Jr.
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Vapor intrusion of volatile organic compounds (VOCs) from the subsurface into buildings is a topic of concern for sites with known groundwater VOC contamination. Due to the time and cost constraints of completing a comprehensive groundwater, soil gas, sub-slab vapor and indoor air assessment for all sites with a potential vapor intrusion exposure pathway, use of mathematical models, such as the Johnson and Ettinger (J&E) Model, may be used as a screening tool to predict indoor air VOC concentrations, or unacceptable human health risk levels, based on known VOC concentrations in groundwater. The J&E model predicts an indoor air concentration when input parameters, including chemical concentration and site-specific physical properties of the subject building and surrounding soil, are provided. The model-predicted vapor concentration in the indoor space ( C building ) is related to the vapor concentration at the source of the contamination ( C source ) by an attenuation factor (a), such that ( C building ) = ( C source ) * (α). Four sites, three with chlorinated VOC-impacted media and one with petroleum VOC-impacted media were chosen to evaluate whether the J&E Model could reasonably predict concentrations of VOCs in indoor air, or attenuation factors, using observed groundwater concentration data. The model-predicted indoor air VOC concentrations and attenuation factors were compared to the measured indoor air concentrations and attenuation factors. Results indicate that the model predicted indoor air concentrations of chlorinated VOCs are conservative, but typically within the same order of magnitude as the observed concentrations. The model-predicted indoor air concentrations of petroleum VOCs were consistently greater than the observed air concentrations. The J&E Model appears to be a valid screening tool when evaluating chlorinated VOC contamination in the context of predicting actual indoor air concentrations for buildings or future buildings and when evaluating petroleum VOC contamination in the context of whether future sampling efforts would be required.