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distance in the north-south direction The source area is estimated to have a vertical distribution of 16 feet to 23 feet below grade TPH-G concentrations within this defined area range from ' approximately 800 mg/kg to 450 mg/kg No TPH-G or BTEX compounds have been detected in any of the soil samples collected during the November 1992 monitor well installation and the October 1993 investigation at depths above ' 23-feet below grade an areas outside of the described source area. Figure 3 shows the isoconcentration contours for TPH-G within the soil interval from 16 feet to 23 feet below grade The vadose zone outside of the source area is estimated to be impacted from approximately 23 feet below grade to the saturated zone at approximately 26 5 feet below grade The northern extent of impacted soil in the vadose zone is limited to within approximately forty feet north of the north end of the former excavation. The southern extent of impacted soil in the vadose zone is limited to an area approximately 15 feet north of the southern property boundary. The impacted soil appears to extend across the eastern and western property boundaries. Figure 4 shows the isoconcentration contours for TPH-G at the soil interval of 23 feet to 26 feet below grade The TPH-G concentrations within this area range from approximately 12 mg/kg to 160 mg/kg At this soil depth interval, the maximum concentration of TPH-G detected was 270 mg/kg in boring SI-1 located within the source area. 5.0 POTENTIAL REMEDIAL TECHNOLOGIES Soils are often remediated by either removal (excavation) or in-situ treatment The following technologies for remediation of soil were evaluated for the Site. • Excavation, Transportation and Disposal In-Situ Bioremediation ' 0 In-Situ Soil Vapor Extraction No Action Based on discussions with PHS/EHD staff, a single soil remediation cleanup goal has been used for evaluation of all potential remedial technologies. The PHS/EHD staff indicated that typical cleanup goals am-no-contaminant concentrations above laboratory detection limits of 10 mg/kg for TPH-G �05mg for BTEX. oor� ' 5.1 Excavation, Transportation and Disposal Excavation and off-site disposal is a common alternative to remediate soils The site specific conditions make this alternative impractical due to costs, because there is approximately 22 feet of clean soil above the impacted soil zone. In order to excavate the impacted soil between 22 and 26 feet, the overlaying clean soil would have to be transported off-site for temporary storage t111OW3 13 1