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1 .2 Site Location <br /> cation <br /> The Stockton Service Center is at 1804 West Main Street, at the southwestern <br /> corner of the intersection of West Main Street and Los Angeles Avenue in Stockton, <br /> California The site is approximately 1,000 feet south of the Port of Stockton and the <br /> ' Stockton Deep Water Channel <br /> 1 .3 Site History <br /> The history of the Stockton site has been presented in detail in the ASA/RO <br /> ' Report <br /> The Stockton Service Center is an operations and maintenance yard that <br /> ' formerly had three underground storage tanks (USTs) and a pump dispenser located <br /> adjacent to the shop and garage for refueling vehicles These UST's (two containing <br /> leaded gasoline, and one containing unleaded gasoline) were replaced by two <br /> aboveground tanks, and between 1987 and 1989, the USTS were removed by the <br /> District Based on previous investigations, Waste Science estimates that the <br /> i <br /> ' petroleum hydrocarbon groundwater plume is approximately 50 feet in diameter, <br /> centered around MW-08 (Figure 1) <br /> i <br /> 1 .4 Site Geology j <br /> Based on soil boring logs from the additional assessment and previous <br /> ' <br /> investigations, the geology of the site consists of two <br /> g g gy sedimentary units The upper <br /> unit extends from the surface to approximately 10 to 15 feet below ground surface <br /> ' (bgs) and consists of clay and silty clay The lower unit extends from 10 feet bgs to <br /> approximately 25 feet bgs and consists of fine grained sand, silty sand, and sandy silt <br /> 1 <br /> 1 .5 Site Hydrogeology <br /> The site is basically flat and at an elevation of approximately 5 feet above mean <br /> i <br /> sea level (msl) Surface water drains to the east Groundwater has been measured <br /> at approximately 10 to 12 feet bgs Groundwater elevations measured during the <br /> ' Third Quarter of 1993 indicated that the groundwater gradient was 0 002 feet per <br /> foot(ft/ft)in the southwest direction Groundwater measurements during the Fourth <br /> ' Quarter of 1993 and the First Quarter of 1994 also indicate that the groundwater <br /> gradient is 0 002 ft/ft in a southwesterly direction These gradients correlate to the <br /> 9488 East Bay Municipal Utility District <br /> 40429601 rap 3 Remedial Action Plan <br />