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Workplan for Underground Storage Tank Upgrade 2 Southland Store No 20632,4627 DaVinci Drive,Stockton California _ August 10 1998 was confirmed in the same sample at a concentration of 870 pg/L using EPA method 8260 Attachment 2, Table 1 includes historical analytical results for soil samples collected at the site On September 21 and 22, 1997, Fluor Daniel GTI, supervised drilling and installation of four on-site i groundwater monitoring wells to depth of 15 feet to 20 feet BGS (Attachment 1, Figure 2) The wells were installed to define the vertical and lateral extent of dissolved hydrocarbons beneath the site Selected soil samples collected during the installation of the monitoring wells were analyzed for benzene, toulene, ethylbenzene, and total xylenes (BTEX), and TPH-G, following EPA methods 8015/8020 modified, and the oxygenates tertiary butanol (TBA), MTBE, di-isopropyl ether (DIPS), ethyl- tertiary-butyl ether (ETBE), and tertiary-amyl-methyl ether (TAME) Maxium benzene and TPH-G concentrations were reported in sample MW-4-5' at 0 12 mg/kg and 71 mg/kg, respectively Maximum MTBE and TBA concentrations were detected in sample MW-4-5' by EPA method 8260 at 7 3 mg/kg and 10 mg/kg, respectively DIPS was detected in sample MW-4-10'at 0 0059 mg/kg Since the installation of the monitoring wells, three sampling and monitoring events have been conducted at the site with the latest occuring on June 15, 1998 The highest benzene, MTBE, and TPH-G concentrations have been detected in monitoring well MW-4 at 700 pg/L, 22,000 pg/L, and 26,000 pg/L, respectively Depth to water at the site has ranged from 5 35 feet to 8 37 feet BGS Groundwater gradient is toward the south/southwest Underground Storage Tank Removal/installation During August or early September 1998, the Southland Corporation plans to remove the three 10,000- gallon single-walled steel USTs at the site and associated fuel dispensers and replace them with two 10,000-gallon double walled tanks and new fuel dispensers Prior to removal of the USTs, well MW-4 will be properly destroyed to avoid possible damage during the tank excavation During removal of the existing USTs an estimated 150 cubic yards of tank overburden material will be removed and stockpiled on site The overburden material will be sampled for proper characterization and transported from the site by a licensed waste hauler to an approved disposal facility Some overexcavation (less than 20 cubic yards)will be conducted to remove hydrocarbon-impacted soil near the tank pit area Based on the low to moderated hydrocarbon concentrations in soil samples collected near the existing USTs, strong hydrocarbon vapors are not likely to be enountered during the removal of the USTs During the UST removal, soil samples will be collected beneath each end of the three USTs at the direction and a20632EXE LTR FLUOR DANIEL GTI Q5 r.«1