For over 50 years, use of trichloroethene (TCE) at a U.S. manufacturing facility for degreasing equipment and products resulted in widespread soil and groundwater contamination. Groundwater flowing underneath off site properties required the evaluation of the vapor intrusion pathway to verify that the building occupants were not being exposed to unacceptable levels of volatile organic compounds entering the structures through vapor intrusion.
Under conventional procedures, performing indoor air sampling at the occupied, non-residential properties at this site could have cost several hundred thousand dollars, without necessarily reducing human exposure to TCE vapor intrusion by any significant degree.
In this “Vapor Intrusion Pathway Modeling” article, TRC’s Graham Crockford and Stacy Metz explain how they used established risk assessment tools in an innovative way to develop and implement a vapor intrusion evaluation strategy to limit the amount of indoor air sampling necessary to determine that TCE concentrations were below acceptable levels in indoor air.
Due to complicated geologic/hydrogeologic conditions and a wide variety of land use within the area of affected groundwater, the potential for unacceptable vapor intrusion was highly variable. Moreover, the area of most concern for vapor intrusion did not necessary correspond the areas with the highest groundwater concentrations. TRC used the Johnson and Ettinger Model (JEM) within GSI’s Risk-Based Corrective Action (RBCA) tool to model building and area-specific vapor intrusion. Building uses, soil types, the proximity of building foundations to groundwater, and other factors were identified for each building/evaluation area in order to calculate potential risk. Allowing TRC to concentrate investigation and monitoring to properties that may have the potential for unacceptable exposures to TCE vapors.
Overall, as the paper explains, TRC’s innovative approach led to an expedited evaluation process while controlling cost of groundwater remediation and long-term vapor intrusion monitoring at this site, all while fully addressing environmental and human health concerns.
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