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December 27, 1995 <br /> Page 2 <br /> i <br /> t <br /> _ - <br /> includes rationale to support design elements and an implementation schedule for the <br /> remedial alternative selected in the CAP <br /> Within the CAP, all pertinent data was reviewed and summarized in a conceptual site <br /> model The model served as a basis for generating remedial objectives and associated <br /> response actions It was determined that the primary source of petroleum hydrocarbon <br /> residuals beneath the site was the former product storage and distribution facilities The <br /> secondary source of petroleum hydrocarbon residuals was identified as soil and ground- <br /> water impacted with weathered gasoline The compounds of concern that distinguish the <br /> residual plume are the constituents of gasoline, including benzene, toluene, ethylbenzene, <br /> and xylenes <br /> Groundwater and soli-based remedial objectives were established predicated on site- <br /> specific environmental, public health, and safety goals Groundwater and soil remedial <br /> measures are necessary to achieve remedial objectives Appropriate response actions <br /> were identified and associated technologies were combined into remedial alternatives <br /> Two alternatives were evaluated that incorporate soil and groundwater remediation <br /> (1) soil excavation with air sparging of groundwater(Alternative 1), and (2) soli vapor <br /> extraction (SVE)/bioventing with air sparging of groundwater (Alternative 2) It was <br /> determined that Alternative 2 was the most feasible for long-term application and would <br /> provide BAT at this site Elements of Alternative 2 are <br /> + plume delineation and off-site source search, <br /> • SVE/bioventing with air sparging, and <br /> • remediation system and groundwater monitoring and sampling <br /> DESIGN BASIS <br /> A combination of SVE, air sparging, and enhanced biodegradation is proposed to <br /> address hydrocarbon mass reduction (vadose, capillary fringe, and saturated zones) <br /> Presently, total petroleum hydrocarbons calculated as gasoline (TPH-g) concentrations <br /> m soils beneath the site are variable Wells that characterize the perimeter of the <br /> targeted remedial zone are Wells MW-3, MW-2R, V-1, and V-5 Recent borings in the <br /> viciruty of the underground storage tanks (USTs) indicate that TPH-g in soils range in <br /> concentrations from not detected to 10,000 parts per million(ppm) Soil bonngs SB-1 <br /> through SB-3 were dniled in December 1993 after deactivation of the SVE system <br /> Maximum TPH-g concentrations at Bonng SB-1 was 1 ppm at the 25 foot below ground <br /> surface(bgs) interval Maximum TPH-g concentrations in soil at Borings SB-2 and <br /> SB-3 were both 2,000 ppm at the 25 and 30 foot bgs interval, respectively <br /> In June`1995, four additional soil borings were drilled in the vicinity of the USTs, SB-10 <br /> . through SB-13 Analytical results indicate that maximum TPH-g concentrations at <br /> 3201333B%%Aq .PL1'3 <br />