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November 12, 1996 Page 3 1 4 Stockton community water supplies were also surveyed as part of defining the physical - �� characteristics of the site Stockton receives its drinking water supply from the surface water of New Hogan Reservoir and groundwater at various locations throughout the City and San Joaquin County Based on a list of active water-supply weIIs provided by California Water Services, there are two additional groundwater-supply wells,located between a 1/2- to 1-mile radius of the site These wells are located on Ellis Street east of Bonnie Lane, and at Commerce Street and Wyandotte Street A list of private and municipal wells, and,available well construction detail information is presented in Table I Well locations are shown on Figure 1 PREVIOUS SITE INVESTIGATIONS November 18, 1987. A soil vapor contaminant assessment (SVCA) was performed on site by EA Ten sample points were driven to depths ranging from 3 to S feet bgs at locations in the area of the waste-oil tank, dispenser islands, and the gasoline UST complex Petroleum hydrocarbons were not detected above I part per million (ppm) in the 21 soil vapors samples collected Februaiy 24, 1988 One 1,000-gallon fiberglass waste-oil UST and three 10,000-gallon fiberglass gasoline USTs were excavated and removed during the site demolition activi- ties No holes were observed in any of the tanks Laboratory results indicated that the soil sample collected beneath the waste oil tank (Sample WOF#1) reported 26 ppm'of high-boiling point hydrocarbons and 10 ppm of low-boiling point hydrocarbons No chlorinated solvents, benzene, toluene, ethylbenzene, and xylenes (BTEX compounds), 'or polychlorinated biphenyls (PCBs) were detected (Table 2) After removing the three 10,000-gallon gasoline USTs, the northeast portion of the tank pit was overexcavated to a depth of 25 feet bgs' One soil sample (AOP#I) was collected from the bottom of the gasoline'tank excavation and reported high- and low-boiling point hydrocarbons at 55 and 340 ppm, respectively, but no benzene was detected (Table 2) November 1988. 'EA dnlled six bonngs on site to depths between 41 and 50 feet bgs and converted the borings into 4-inch diameter monitoring wells (MW-I through MW-6),' The maximum concentration of petroleum hydrocarbons (3,300 ppm total ' purgeable petroleum hydrocarbons calculated as gasoline [TPPH-g) and 9 6 ppm benzene) detected in soil was reported from the samples collected from Well MW-4, located proximal to the northeast corner of the former�UST complex (Table Z) While installing,Well MW-5, an abandoned 550-gallon steel UST was encountered and accidentally punctured (Figure 2) The liquid inside the tank was sampled and character- ized as weathered gasoline Soil around the UST was later excavated to expose the 3201337MCLOSUKE2