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2905 West Benjamin Holt Drive, Stockton, California March 16, 1994 <br /> Chevron U.S.A. Products Company Page 7 <br /> 3.3 Proximity and Quality of Nearby Water Supplies <br /> Local surface water bodies located within one mile of the site include Fourteenmile Slough and <br /> associated drainage canals to the south and west, Lincoln Lake approximately 1 mile west of the site, <br /> Fivemile Slough approximately 0.5 mile north of the site and intermittent Fivemile Creek approximately <br /> one mile northwest of the site that drains into Fivemile Slough (Figure 1). The surface water bodies <br /> within one mile of the site serve as ornamental features (Lincoln Lake) or drainage ways for the low-lying <br /> Stockton area. <br /> A total of nine water wells have been located within a one-mile radius of the site in previous <br /> investigations (CRWQCB, 1987), four of which are used for drinking water purposes. The two wells <br /> located downgradient of the Chevron service station are the only potential concerns with regard to the <br /> dissolved hydrocarbon plume. The City municipal well closest to the site (Well 20M2) is located 100 feet <br /> east of the Chevron service station on the grounds of Swenson Park Golf Course near the northwest <br /> corner of West Benjamin Holt Drive and Plymouth Road (Figure 2). This, as other nearby municipal <br /> water wells, extracts fresh groundwater from aquifers greater than 200 fleet deep. The base of the <br /> ... sanitary seal in well 20M2 is at 55 feet BGS in a clay layer that continues to 72 feet BGS (CRWQCB, <br /> 1987). One of the City wells (20F1), located in the northeast portion of Swenson Park Golf Course <br /> approximately 0.5 mile northeast of the site, is perforated discontinuously from 85 feet BGS to 403 feet <br /> BGS (CRWQCB, 1987). <br /> 3.4 Potential Effects of Residual Contaminants on Water Supply <br /> Based on the last round of quarterly monitoring and sampling, and historical analytical data for <br /> groundwater, the immediate threat posed to currently usable water supplies by impacted groundwater at <br /> the site is negligible. Surface water bodies are at no risk of being impacted with dissolved hydrocarbons <br /> based on their position relative to the hydraulic gradient at the site and their distance from the <br /> boundaries of the dissolved hydrocarbon plume. <br /> City well 20M2 extracts groundwater from aquifers greater than 200 feet deep near the boundary of the <br /> dissolved hydrocarbon plume. City well 20F1, which is perforated as shallow as 85 ft. BGS is more than <br /> 2,500 feet cross gradient of the projected boundary of the dissolved hydrocarbon plume. Benzene <br /> concentrations in the vicinity of 20M2 (MW-8 at <0.5 ppb) are below the state action levels (1 ppb <br /> 5673PAR.RST '�_� <br /> —1F, GROUNDWATER <br /> L]' 17 TECHNOLOGY <br />