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Between July 26 and 28, 1988, WA remov ' 15 ubic yards of soil half way along the southern and western walls of the excavation to a „ depth of 24 feet In a proposal to the County dated November 22, 1988, Precision t Instruments of Stockton requested to backfill a portion of the excavation Upon approval in December 1988, the entire excavation Q was backfilled. � 3 ' Western Geologic ResQurgQ�s, Inr,,, In September and October 1989, another investigation was performed by Western Geologic Resources, Inc (WGR) near the former tank locations Six boreholes were drilled (B-10 through B-15), from which soil samples were collected for chemical analyses (Figure 2-2) Groundwater was observed at 26 8 feet below grade One of the boreholes (B-10) was completed as a ' 4-inch monitoring well (MW-4) Groundwater samples from wells MW-1 through MW-4, collected on October 3, 1989, showed no detectable concentrations of TPH and BTEX ' ERM-West. In March 1991, ERM-West drilled soil boring B-16 approximately 1 5 feet west of boring B-15 One soil sample was ' collected at the 25 5- to 26 0-foot interval to confirm the presence of diesel as reported by WGR "Laboratory analyses showed a TPH-diesel concentration of 1,300 mg/kg Groundwater samples were also collected from the four monitoring wells Analytical results for groundwater samples are presented to Table 2-1 In November 1991, five additional borings were drilled and water samples were collected using the HydroPunch, as presented in Figure 2-3 Two of the borings (B-17 and B-20) were drilled on Safeway property, and three borings (B-18, B-19, and B-21) were drilled on Navy Drive Two of the borings (B-17 and B-21) were converted into monitoring wells (MW-5 and MW-6, respectively) Three of the four existing monitoring wells (MVI-1, MW-2, and MW-3) were abandoned because of declining water levels Analytical results from November 1991 soil samples are presented in ' Table 2-2 Elevated TPH-diesel concentrations were detected in boring B-17 at 25 5 to 26 0 feet below grade, and in B-19 and B-21 at 30 0 to 30 5 feet below grade A contour map illustrating the ' analytical results for the 30 0- to 30 5-foot interval is presented in Figure 2-4 ' As shown in Table 2-3, groundwater analytical results from HydroPunch samples showed elevated concentrations of TPH-diesel in borings B-16, B-19, and B-21 A contour map of the HydroPunch analytical data, which also includes analytical data for groundwater samples collected from monitoring wells, is presented in Figure 2-5 ' 2-2