The environmental closure of sites requires the establishment of contaminant concentrations that can be left in the soil and groundwater. It must be demonstrated that these concentrations, otherwise known as environmentally acceptable endpoints (EAEs), are protective of both human health and the environment. Due to the complexity associated with the soil-contaminant interactions, the release and movement of contaminants in the subsurface environment, and the different mechanisms of contaminant uptake by living organisms, no single approach for the establishment of EAEs has evolved. For example, to date, alternative measures of EAEs for contaminated sites have focused on several direct, and indirect, measurements of reduced contaminant availability: (1) the lack of availability of soil-bound contaminants to microorganisms, (2) the lack of toxicity of the soil-contaminant matrix to test organisms, and (3) the lack of mobility of soil-bound contaminants to the environment. Intrinsic processes of contaminant biodegradation and sorption in the subsurface environment have also been incorporated into these definition of EAEs. The Gas Research Institute (GRI), in conjunction with the Petroleum Environmental Research Forum (PERF), has compiled and summarized the results of the field applications of several of these approaches to hydrocarbon- impacted sites. This paper presents several case studies that demonstrate the use of the different measurements of reduced contaminant availability for the closure of sites contaminated with hydrocarbons.

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