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i <br /> f. Table 1-1 <br /> Plant 33 Groundwater Wells <br /> 1 . <br /> ` Well Number Well Diameter Well Depth Pumping Rate <br /> i (Figure 2-2) Well Purpose (inches) (ft) (gpm) <br /> W-1 Process Water 18 450 1,000 <br /> W-2 Process Water 10 253 375 <br /> W-3 Process Water 14 553 800 <br /> Site History <br /> r Little is known about the Disco location before 1966, when the Disco gasoline station <br /> opened for business. The gas station had four dispensing islands. Three 10,000-gallon <br /> underground tanks supplied the dispensing islands with gasoline. <br /> i' <br /> Del Monte purchased the Disco property in 1972. Del Monte did not use or operate <br /> the underground tanks. The three underground tanks were excavated and removed in <br /> 1985. <br /> The site is presently vacant. The tank excavation site is paved, and some of the <br /> surrounding area is also covered with asphalt; the rest of the area is unpaved soil. The <br /> + Disco station dispensing islands' concrete pads were removed in November 1991. <br /> Previous Investigations <br /> In October 1985, Dei Monte. removed the three 10,000-gallon underground tanks <br /> (Exceltech Inc., 1985). Upon excavation, it was discovered that the tanks were filled <br /> with water. A water sample was taken from each tank and analyzed. Volatile hydro- <br /> carbon concentrations were less than 5.6 mg/l, and total lead was nondetectable for <br /> each sample. The water from the tanks was discharged to the sanitary sewer by <br /> permission of the City of Stockton Municipal Utilities Department. . <br /> r <br /> iUpon removal of the tanks, the soil beneath the tanks had a gasoline odor. No obvious <br /> fuel leakage source (i.e., pipe breaks or tank holes) was located. Soil samples below <br /> the tank excavation were sampled and analyzed. Table 1-2 presents the results of the <br /> analyzed soil samples. <br /> Based on the results presented in Table 1-2, it was assumed.that the soil contamination <br /> was limited to a depth of approximately seven feet below the tanks (Exceltech, 1985). <br /> The contaminated soil was excavated and aerated for a 2-day period to reduce volatile <br /> ' .organic levels below 1,000 mg/kg. After aeration, two random soil .samples revealed <br /> volatile hydrocarbon concentrations of 183 and 20 mg/kg. The excavated soil was <br /> backfilled into the tank pit. <br /> SF0316041RP\004.51 1-4 <br /> i - <br />