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I . INTRODUCTION At the request of Chevron U.S.A. Inc. , EA has prepared a work plan to install additional monitoring wells at former Chevron Service Station (SS) 9-7780, located at 3246 East Fremont Street ' in Stockton, California. Seven groundwater monitoring wells have been installed at the site during previous investigations. o � levels of petroleum hydrocarbons have been detected in samples -3f groundwater from wells near the former tank field, but because of extended drought conditions and use of groundwater in the imme- diate area, the depths to static water have increased, leaving all seven monitoring wells dry. Three water supply wells are located within 250 feet east and west of the site. EA proposes to install deeper monitoring wells at the eastern and western boundaries of the site to monitor potential migration of the dissolved constituent plume off the site toward the water supply wells. 1 . 1 SITE SETTING The investigated site is located in the eastern part of Stockton, California, at the intersection of E. f'remont Street and Windsor . Avenue, about 1 ,000 feet west of Highway 99 (Figure 1 ) , in an area of mixed residential/commercial, and industrial character. The facility has been closed, and the buildings and all installa- tions have been removed. The site surface is covered by unim- prov d fill and is slightly ( 1-2 feet ) elevated above the sur- rounding area. The site is on flat terrain approximately 25 feet above mean sea level , near the northern end of the San Joaquin Valley. The topography, typical of the flood plain of the San Joaquin Valley, is flat, sloping gently to the west toward the San Joaquin River . Th: .nearest . surface. waters are .the Stockton Diversion Canal, about three-quarters of a mile northeast, and the intermittent Mormon Slough, about 1 .5 miles south of the site. c51 /97780/6-90/tx 1 I