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March 18, 1993 <br /> Page 2 <br /> noted during underground construction in the Southern Pacific right-of-way to the <br /> :. north of the site. <br /> Geology/Hydrogeology: The site lies at an elevation of approximately 47 feet <br /> above mean sea level (MSL) and is located in San Joaquin County, in the northern <br /> portion of the San Joaquin Valley. The San Joaquin Valley is a broad, alluvium- <br /> filled basin bounded to the east by the Sierra Nevada Mountain Range and to the <br /> west by the Coast Ranges. The total thickness of alluvial fill in the valley is esti- <br /> mated to be thousands of feet. The alluvial sediments generally consist of poorly <br /> sorted silt and fine sand with less extensive lenses of medium- to coarse-grained <br /> sand and gravel. Quaternary lacustrine deposits also occur in the central and <br /> western portions of the valley, and consist of clay, silt, and sand. <br /> In the vicinity of the site, surficial deposits are characterized as distal alluvial fan <br /> and flood plain deposits. These deposits generally are less than 10 feet thick and <br /> consist of silts;fine sands, and less extensive coarse sand and gravel lenses. <br /> Underlying deposits are referred to as older alluvium and reach a thickness of up <br /> to 400 feet. These deposits consist of interbedded clay, silt, sand, and gravel. <br /> Geomorphology and regional drainage patterns suggest a northerly direction of <br /> groundwater flow. <br /> Site InvestigationsrtiallS �IQ, l�pwas tnovecl. rt; <br /> so tby u c?f tie bite ., r The tam was.pnni3rily <br /> Wd <br /> t c ssaien id tpragez but t bhad aisw been.used to rcontain JieatWg,oik . <br /> Asaiomfiuidl.tankwas nnde a n by.an un4,ggroq _vow etc <br /> ;, ... ' B I f i fovejd c uniig`ez Analytical results indicated that <br /> low levels of petroleum hydrocarbons remained in the soils adjacent to the <br /> excavation. Details of the excavation of this tank are described in a PACIFIC <br /> letter to Unocal dated March 20, 1990. <br /> 9AOW . �roundwater monitoring ,It714hr , <br /> Detailsothisphaseof <br /> investigation are described in PACIFIC's <br /> Soil and Groundwater Investigation Report dated February 13, 1991. <br /> 1rgh U- � Details of this inves- <br /> tigation are described in PACIFIC's Soil and Groundwater Investigation Report <br /> dated September 30, 1991. <br /> RA'C tHC-°filedgrvdnd ,"jponitoring <br /> of this investigation are described in PACIFIC's <br /> Soil and Groundwater Investigation Report dated June 11, 1992. <br /> y 3100104/1 RAP <br />