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i Additional Site Assessment Report and Corrective Action Work Plan 5 The Southland Corppmtion,Store#20632 4627 DaMncl Drive Stockton CA January 8- 6 6 0 SUMMARY Based on the reported concentrations of BTEX,TPH-G, and MTBE In the soil samples collected during the installation of the four groundwater monitoring wells on September 21 and 22, 1997,and the geoprobe soil bonngs drilled on February 21, 1997,the lateral and vertical limits of BTEX and TPH-G have been defined Soil impacted with gasoline appears restricted to a limited area surrounding the tank pit and underlying the fuel dispensers The highest dissolved BTEX,MTBE, and TPH-G concentrations from the groundwater grab samples collected from the geoprobe borings February 21, 1997,and the groundwater samples collected from the monitoring wells on October 17, 1997,were reported In boring GP-1 and monitoring well MW-4, located near the tank prt and dispenser Island areas Well MW-2, located downgradient from the UST pit,contains no detectable benzene,440 pg/l_TPH-G,and 1,800 pgA-MTBE These levels are about 10% of those observed near the source area,documenting adequate plume delineation 7.0 CORRECTIVE ACTION WORK PLAN 7.1 Excavation During removal of the USTs and fuel system upgrade at the site (scheduled for 1998)soil underlying the fuel dispensers and surrounding the UST pit will be excavated to the depth of groundwater(approximately 8 feet BGS)to remove the soil source of the dissolved hydrocarbon plume It Is estimated that a total of 200 cubic yards will be removed and stockpiled on site pending characterization and disposal Figure 5 shows the extent of the proposed excavation 7.2 Groundwater Monitoring Well Destruction Prior to the tank removal and subsequent excavation,groundwater monitoring well MW4 will be destroyed following guidelines set forth in California Department of Water Resources Bulletins 74-81 and 74-90 for well destruction This well Is within the proposed area of excavation,and will need to be removed. Permits for the well destruction will be applied for from the SJCPHS The casing of the well will be drilled out to total depth of the well borehole using a track-mounted drill rig equipped with 8-inch diameter hollow stem augers The resultant borehole will be grouted with neat cement from total depth to surface grade using a tremle pipe All well-related materials will be property disposed of in acoordance with state and local requirements FLUOR DANIEL GTI r rpt