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March 18, 1993 Page 6 REMEDIAL OBJECTIVES To direct the design of remedial action, remedial objectives were identified. These objectives were formulated with attention to site characteristics, public health and safety, and protection of beneficial water uses. Objectives are distinguished as soil- and groundwater-based. o Soil: To the extent economically feasible, and using established technology,prevent the migration of petroleum hydrocarbons from soil beneath the referenced site. o Groundwater: Within physical and economic constraints: (1) eliminate the potential for exposure to groundwater with petroleum hydrocarbon concentrations in excess of acceptable compound levels, (2) eliminate hazardous conditions associated with the presence of petroleum hydrocarbon compounds in the subsurface environment, (3) protect the potential use of ground- water from the shallow water-bearing zone as domestic and municipal supply, and (4) initiate attenuation of petroleum hydro- carbon concentrations. For the most part, the soil objective applies to soils in the vadose zone immediately above the piezometric.surface. The vadose zone beneath the site appears to be of the heaviest impact of hydrocarbons in the vicinity of Wells U-1, U-2, and Boring U-C;between 5 and 6-1/2 feet below grade. Petroleum hydrocarbon concentrations in soil that do not pose a threat to groundwater will constitute the numerical cleanup goal for soil. Acceptable petroleum hydrocarbon concentrations in soil will be determined by using the environmental attenuation factor method proposed by Marshack (Marshack, 1989). The groundwater-based remedial objective applies to groundwater within a boundary delineation defined by acceptable compound levels. In this way, benefi- cial uses of groundwater outside the boundary will be protected, along with public health and%afety. The potential for hydrocarbon migration along groundwater flow lines to water-supply wells defines the primary exposure pathway. The associ- ated potential exposure route is the ingestion of impacted groundwater. Beneficial water use and public health protection require eliminating (reducing) the potential for exposure to groundwater with concentrations in excess of 1 ppb benzene, 680 ppb ethylbenzene, 100 ppb toluene, and 1,750 ppb xylenes. The aforemen- tioned concentrations constitute acceptable compound levels. 3100104/IRAP