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1 <br /> distance in the north-south direction The source area is estimated to have a vertical distribution <br /> ' S of 16 feet to 23 feet below grade TPH-G concentrations within this defined area range from <br /> approximately 800 mg/kg to 450 mg/kg <br /> No TPH-G or BTEX compounds have been detected in any of the soil samples collected during <br /> the November 1992 monitor well installation and the October 1993 investigation at depths above <br /> 23-feet below grade in areas outside of the described source area Figure 3 shows the <br /> isoconcentration contours for TPH-G within the soil interval from 16 feet to 23 feet below <br /> grade. <br /> The vadose zone outside of the source area is estimated to be impacted from approximately 23 <br /> feet below grade to the saturated zone at approximately 26 5 feet below grade. The northern <br /> extent of impacted soil in the vadose zone is limited to within approximately forty feet north of <br /> the north end of the former excavation The southern extent of impacted soil in the vadose zone <br /> is limited to an area approximately 15 feet north of the southern property boundary The <br /> impacted soil appears to extend across the eastern and western property boundaries Figure 4 <br /> shows the isoconcentration contours for TPH-G at the soil interval of 23 feet to 26 feet below <br /> grade The TPH-G concentrations within this area range from approximately 12 mg/kg to 160 <br /> mg/kg At this soil depth interval, the maximum concentration of TPH-G detected was 270 <br /> mg/kg in boring SI-1 located within the source area <br /> SA POTENTIAL REMEDIAL TECHNOLOGIES <br /> Soils are often remedlated by either removal (excavation) or in-situ treatment. The following <br /> 1 technologies for remediation of soil were evaluated for the Site <br /> 0 Excavation, Transportation and Disposal <br /> 0 In-Situ Bioremediation <br /> 0 In-Situ Soil Vapor Extraction <br /> No Action <br /> Based on discussions with PHS/EHD staff, a single soil remediation cleanup goal has been used <br /> for evaluation of all potential remedial technologies The PHS/EHD staff indicated that typical <br /> cleanup goals are no contaminant concentrations above laboratory detection limits of 10 mg/kg <br /> for TPH-G and 0 05 mg/kg for BTEX. <br /> 5.1. Excavation, Transportation and Disposal <br /> Excavation and off-site disposal is a common alternative to remediate soils The site specific <br /> conditions make this alternative impractical due to costs, because there is approximately 22 feet <br /> of clean soil above the impacted soil zone In order to excavate the impacted soil between 22 <br /> and 26 feet, the overlaying clean soil would have to be transported off-site for temporary storage <br /> 11141cd3 13 <br />