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1 not detected in soil samples collected at a depth of 30 feet or 35 feet bsg TPH-d was • detected m soil samples collected from a depths of 15, 20 and 25 feet bsg at concentrations of 5,100 mg/kg, 13,000 mg/kg and 490 mg/kg, respectively TPH-d was not detected in soil collected at a depth of 30 feet bsg or below (Tables 1 and 2) • On 26 October 2001,a total of four soil probe borings (P 12AB and P 13AB)were advanced at the site south of the and near the former UST location Probe borings were advanced m the area of the former USTs to collected depth discrete water samples TPR-d was detected in ' all four of the grab ground water samples analyzed at concentrations from 130 micrograms per liter(µg/1)to 550 µg/l (Table 2) Between June 1996 and January 2002, 16 ground water monitoring and sarnplmg events were performed at the site to monitor dissolved petroleum hydrocarbon concentrations in ground water ' and to characterize ground water flow direction and gradient on the site(Table 3) • During the most recent sampling event TPH-d was detected in ground water samples collected fromeach monitoringwell(MW-1 through MW-4)at concentrations of 3,600 µg/1, 1,100 µg/l, 430 µg/l, and 840,000 µg/1, respectively TPH-g was detected in ground water sample MWA and MW-4 at concentrations of 120 µg/1 and 640 µg/l, respectively ' Ethylbenzene and total xylenes were detected in theground water sample from well MW-4 at concentrations of 1 1µg/l and 0 83 µg/1, respectively(Tables 4 and 5) • Ground elevations have decreased approximately four to five feet of the monitoring period, at some points increasing dissolved hydrocarbon concentrations near the groundwater wells • The lateral extent of the dissolved petroleum hydrocarbon plume is delineated by the current ' area bound by wells MW 1 through MW-5 and soil borings On 28 and 29 October 2002, monitoring well MW-5 and six ozone sparge wells (OPS lA through OPS3B)were installed MoratoringwellMW-5wascornpletedutilizinga2-inch diameter casing with ' 0 020-inch slotted screen from 10 to 30 feet bsg and blank, 2-inch diameter PVC well casing extending to the surface The ozone sparge wells were completed with a pre-fabricated 2-inch diameter, polyvinylchloride (PVC) mess diffuser and blank, 3/4-inch diameter PVC well casing ' extending to the surface The depth of the mass diffusers were from 48 to 50 feet bsg for wells OPS IB through OSP313, from 28 to 30 feet bsg for well OSPIA, from 33 to 35 feet bsg for well OSP2A, and from 38 to 40 feet bsg for well OSP3A ' On 22 November 2002, a California state-licensed survey engineer from Baumbach& Piazza, Inc surveyed a reference point on the casing tops ofthe monitoring wells to the nearest 0 01-foot relative ' to San Joaquin County Bench Mark Datum BM # LM-38 6 1