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December 27, 1995 Page 2 1 . includes rationale to support design elements and an implementation schedule for the remedial alternative'selected in the CAP Within the CAP, all pertinent data was reviewed and summarized in a conceptual site model The model served as a basis for generating remedial objectives and associated response actions It was determined that the primary source of petroleum hydrocarbon residuals beneath the site was the former product storage and distribution facilities The secondary source of petroleum hydrocarbon residuals was identified as soil and ground- water impacted with weathered gasoline The compounds of concern that distinguish the residual plume are the constituents of gasoline, including benzene, toluene, ethylbenzene, and xylenes Groundwater and soil-based remedial objectives were established predicated on site- specific environmental, public health, and safety goals Groundwater and soil remedial measures are necessary to achieve remedial objectives Appropriate response actions were identified and associated technologies were combined into remedial alternatives Two alternatives were evaluated that incorporate soil and groundwater remediation (1) soil excavation with air sparging of groundwater (Alternative 1), and (2) soil vapor 1 extraction (SVE)Ibioventing with air sparging of groundwater(Alternative 2) It was determined that Alternative 2 was the most feasible for long-term application and would provide BAT at this site Elements of Alternative 2 are • plume delineation and off-site source search, • SVE/bioventing with air sparging, and remediation system and groundwater momtonng and samphng DESIGN BASIS A combination of SVE, air sparging, and enhanced biodegradation is proposed to address hydrocarbon mass reduction (vadose, capillary fringe, and saturated zones) Presently, total petroleum hydrocarbons calculated as gasohne(TPH-g) concentrations in soils beneath the site are va, nable Wells that characterize the perimeter of the targeted remedial zone are Wells MW-3, MW-2R, V-1, and V-5 Recent borings m the vicinity of the underground storage tanks (USTs) indicate that TPH-g in soils range m concentrations from not detected to 10,000 parts per nulhon (ppm) Soil borings SB-I through SB-3 were drilled in December 1993 after deactivation of the SVE system Maximum TPH-g concentrations at Boring SB-1 was 1 ppm at the 25 foot below ground surface (bgs) interval Maximum TPH-g concentrations in soil at Bonngs SB-2 and SB-3 were both 2,000 ppm at the 25 and 30 foot bgs interval, respectively In June I995, four additional soil borings were drilled m the vicinity of the USTs, SB-10 through SB-13 Al alytical results indicate that maximum TPH-g concentrations at t 1 3241333B11A'RKP1,N3 i