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r z3 - r� In addition to the soil samples p gathered from beneath the tank, a sample of the waste oil sludge from the waste oil tank was gathered and a composite sample of the tank overburden stock pile was obtained. The c:1 sludge sample was analyzed to determine if either PCB's or solvents were present. Neither were detected in the sludge. 1.0 SE'T'TING 3.1 Topography The study area is in the central valley of California within the k.y low-lying Delta Region where the San Joaquin nto [A Rivers join in a maze of channels before discharging rging dintoctheeSan Francisco Bay. The land is almost level with a slope of 5 feet e per mile rising from west; to east. The most notable topographic features are artificial levels and highway embankments. i4 3.2 Geoloqy The Central Valley of California is a lowland between two mcun- tain ranges, the Sierra Nevada on the east, and the Coast Range ,.., or, the west. This Valley has existed as a structural trough, receiving sediments from the adjacent mountains, since pre- Cretaceous times. Through much of its history, the Central Valley has been an arm of the sea, and the materials transported into it were deposited under marine conditions. In late Tertiary times, general uplift of the region resulted in the retreat of the sea, and the onset of continental deposition. f This uplift was accompanied by volcanism to the east which produced volcanic materials subsequently eroded and deposited in pa the Valley as the ]Mehrten and Valley Springs Formations. Contin- ual uplift during the late Cenozoic period resulted in the formation of the Sierra Nevada mountains as they are known today. This uplift accelerated erosion, providing more material for i°r� deposition in the Valley. later, large lakes formed on the west side of the Valley, resulting in excessive deposits of clay, now termed the Corcorran Clay. Pleistocene and recent times have been characterized by glacia- tion in the Sierra Nevada and by the associated deposition of relatively coarse sedimentary materials (silt, sand, and gravel) in alluvial fans along the Valley margins. Recent deposition in IM: the low-lying Delta region includes the accumulation of organic materials. � s :.: The depth to first groundwater at the site varies with seasonal conditions. Typically the groundwater fluctuates between 20' and ' i 25' depths, depending upon the recharge conditions. °4 No local streams or rivers exist at the site or within the immediate proximity. 1 - 5 - I