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-r LU Static groundwater occurred at a depth of approximately 9 feet below grade on February 19, 1992. Groundwater samples were analyzed for TPH-gasoline, TPH-diesel, 4. and'BTEX compounds. Samples obtained from Wells U-1 throughU-b contained concentrations of TPH-gasoline from none detected to 4,700 parts ppb, none detected to ..340 ppb benzene, and none detected to 3,700 ppb TPH-diesel. The highest concentrations of TPH-gasoline and benzene were detected in Well U-5, while the highest concentration of TPH-diesel was detected in Well U-3. a 1. 1.2 Regional Hydrogeology The site lies at an elevation of approximately 47 feet above mean sea level (MSL) and is located in San Joaquin County, in the northern portion of the il San Joaquin Valley. The San Joaquin Valley is a broad, alluvium-filled basin bounded to the east by the Sierra Nevada Mountain Range and to the west by the Coast Ranges. The total thicknes&,of alluvial fill in the valley is estimated to be thousands of feet. The alluvial sediments�: generally consist of poorly sorted silt and fine sand with less extensive lenses L of medium to coarse-grained sand and gravel. Quaternary lacustrine deposits also occur in the central and western portions of the valley, and consist of clay, silt, and sand. Iii the vicinity of the site, surficial deposits are characterized as distal alluvial fan and r I� flood plain deposits. These deposits generally are less than 10 feet4hick and consist of silts, fine sands, and less extensive coarse sand and gravel lenses. Underlying deposits are referred to as older alluvium and reach a thickness of upto 400 feet. These deposits consist of 'interbedded clay, silt, sand, and gravel. Geomorphology and regional drainage patterns suggest a northerly direction of groundwater flow. p y I '9 . 4 3100103/REPORT'S 3. r June 11, 1992