The migration of contaminants from the subsurface into the indoor air environment, in a process described as soil vapor intrusion, is gaining attention as a potential pathway for exposure to contaminated soil and water. Indoor, outdoor and soil air samples were collected from forty homes in North Texas to investigate the attenuation of trichloroethylene (TCE) from contaminated groundwater into residential buildings. The mean and standard deviation of the soil and indoor air attenuation factors (ratio of indoor air concentration to soil vapor concentration) were 0.14 and 0.17, respectively. Five of the 40 values were greater than 0.1 which is the suggested upper-bound by the U.S. EPA (2002). Statistical tools were used to draw correlative relationships between contaminant groundwater, soil air and indoor air concentrations. The VolaSoil model described by Waitz et al. (1996), was modified for use as a screening tool for future investigations of indoor TCE concentration. Using measured soil vapor data, the model under predicted indoor air TCE concentrations likely due to heterogeneities in the unsaturated subsurface. Inputting groundwater TCE concentrations, the model was able to capture the contaminant migration processes and produce results consistent with measured indoor TCE concentrations. Therefore, the model described in this paper maybe appropriate to be use as a screening tool in future investigations in the contamination area.

This book introduces key concepts in modeling and risk assessments of vapor intrusion, a process by which the subsurface volatile contaminants migrate into the building of concern. Soil vapor intrusion is the major exposure pathway for building occupants to chemicals from the subsurface, and its risk assessments determine the criteria of volatile contaminants in soil/groundwater in brownfield redevelopment. The chapters feature the recent advances in vapor intrusion studies and practices, including analytical and numerical modeling of vapor intrusion, statistical findings of United States Environmental Protection Agency’s Vapor Intrusion Database and Petroleum Vapor Intrusion Databases, the challenges of preferential pathways, and the application of building pressure cycling methods, and field practices of vapor intrusion risk assessments at developed contaminated sites and in brownfield redevelopment. This volume also summarizes the advantages and limits of current applications in vapor intrusion risk assessment, laying the groundwork for future research of better understanding in risk characterization of soil vapor intrusion using models. Written by experts in this field, Vapor Intrusion Simulations and Risk Assessments will serve as an invaluable reference for researchers, regulators, and practitioners, who are interested in perceiving the basic knowledge and current advances in risk assessments of soil vapor intrusion.

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This document has been developed by the Health Risk Assessment Branch of the Air Force Institute for Operational Health (AFIOH) as an informational resource for Mr Force environmental managers who are interested in evaluating the vapor intrusion pathway (VIP), This pathway has received substantial scrutiny in recent years by the U.S. Environmental Protection Agency (EPA) and state environmental regulatory agencies; the potential health risks from vapor intrusion are being evaluated at numerous sites across 'the country. Exposures related to this pathway can result from the volatilization and migration of chemicals from contaminated groundwater and subsurface soil that can leak through cracks and holes in buildings located above the contamination. EPA has developed a detailed vapor intrusion guide (EPA, 2002a) that uses a tiered approach to evaluate the potential risks associated with this pathway. This Air Force-specific document generally follows and supports the modeling and risk assessment approaches recommended by EPA. The primary focus of this document is to provide a discussion of various approaches, problems, and solutions related to assessing and managing the VIP. This guidance covers such areas as sampling and analysis, analytical methods, indoor air quality, risk assessment, remediation, and risk management.