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Description
Vapor intrusion models were developed to predict indoor air concentrations from subsurface sources and then calculate an associated risk using toxicological data and exposure scenarios for the building occupants. Prior to the issuance of final guidance documents in 2015, the United States Environmental Protection Agency (USEPA) guidance on vapor intrusion was in draft form since November 2002. This delay between the draft version and the final guidelines resulted in the utilization of varying methodologies for assessing vapor intrusion by the regulated community and as well as the regulators at both state and local levels. The purpose of this study was to evaluate the accuracy of screening-level vapor intrusion models, using soil vapor samples collected from three sites with known or suspected contamination, and to compare the predicted indoor air results with measured indoor air results. The models evaluated were the County of San Diego Department of Environmental Health Vapor Risk 2000 Model, the Department of Toxic Substances Control (DTSC) version of the Johnson and Ettinger Model (J&E Model), and the USEPA, Office of Solid Waste and Emergency Response (OSWER), Vapor Intrusion Screening Level Calculator (VISLC). The results of this study found that the Vapor Risk 2000 Model more accurately predicts indoor air concentrations, followed by the J&E Model and VISLC. While the Vapor Risk 2000 Model more closely predicts the indoor air concentration, it does have a tendency to underpredict. Due to the underpredictions, there is more potential for false negatives (i.e., screening out sites that do have a potential for vapor intrusion. Similar to previous studies, this study found the Vapor Risk 2000 and J&E Models both over and under predict the indoor air concentrations. This may not necessarily be a reflection on the model's prediction ability, but rather the complexity of vapor intrusion and the confounders of indoor air. Combined with additional lines of evidence (e.g., indoor air sampling), these screening-level vapor intrusion models can assist decision makers in screening in or out sites that are susceptible to vapor intrusion.
