SITE INFORMATION AND CORRESPONDENCE

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Chronology Former Chevron Service Station 9-1918 n 1- 45 East Harding Stockton CA 95203 Site Code: 1138 The site is located on the northwest corner of the intersection of Harding Way and EI Dorado Street within the City of Stockton in San Joaquin County on APN 127-070-36. The site has operated as a Chevron (Standard Oil) retail gasoline station from 1947 to 1988. The site is located in a residential/commercial area with other nearby gasoline stations. The nearest groundwater production well that is owned by California Water Service, a water purveyor, is located 1,600 feet north of the site. Construction details for this well were unavailable. Nine other groundwater production wells are located within approximately 3,000 feet of the site. The nearest surface water, Yosemite Lake located at the east end of Smith's Canal, is located 3,500 feet west of the site. The depth to first water beneath the site has ranged from 35.36 feet below ground surface (bgs) in February 1989 to 58.01 feet bgs in October 1992. The gradient has generally been towards the north east at .0025 feet per feet. Underground storage tanks were removed in 1988 and followed by a preliminary investigation of the extent of the discharge. The investigation evidenced petroleum hydrocarbon soil and groundwater contamination. During November 1988, six monitoring wells (MW1 - MW6) were installed. Subsequently, three additional underground storage tanks were discovered and removed. The remedial investigation comprised the installation of five vapor extraction wells and further monitoring wells to investigate the groundwater contaminant plume's boundary (VW1 - VW6 and MW7 - MW 13). Vapor extraction operated from November 1990 to February 1992 and from September 1992 to November 1992 for an approximate total of 17 months. An estimated 12,000 pounds or 1,967 gallons of petroleum hydrocarbon products were removed. Due to changes in the static groundwater level beneath the site, during December 1993 additional monitoring wells (MW2R and MW14) were installed to define the groundwater contaminant plume's boundaries and soil borings (SB1 - SB3) sampled to evaluate the remediation system. Remaining soil contamination was evidenced. During the installation of MW2R, one additional underground storage tank was discovered and subsequently removed. The results of ground penetrating radiometry did not indicate any additional tanks on site. During May 1994, soil borings (SB4 - SB9) were drilled so that Chevron could determine the vertical and horizontal extent of the soil contamination. In June 1995, Chevron drilled four additional soil borings (SB10- S131 3) to evaluate concentrations of the remaining petroleum hydrocarbon products. Groundwater contamination has been evidenced since groundwater monitoring was initiated in 1989. Chevron has requested site closure. Based on available information, PHS/EHD does not recommend site closure. PHS/EHD requests that the groundwater quality be monitored with appropriately screened wells and further evaluation of the potential impact that the remaining soil poses to groundwater quality. 1987 11/18/87 A pre-tank removal assessment was performed during which 21 soil vapor samples were collected for analysis. The results report of this assessment is unavailable.