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r-- <br /> �' 2.0 Site Description <br /> J <br /> 1, 1 <br /> F�F The site is located in the southern part of the City of Stockton, California at 370 55' 7 67" <br /> latitude and 1210 16' 43 45" longitude (Figures 1 and 2) The site is an essentially level <br /> ' commercial trucking facility,which contains an office building,two truck maintenance shops,a <br /> truck-washing facility, a small above-ground storage tank compound, a vehicle fueling facility <br /> ' and a large parking area for tank trailers i <br /> i <br /> _ 3.0 Geology <br /> The site is situated in the northern part of the San Joaquin Valley, in an area underlain by � <br /> several thousand feet of terrestrial and marine sedimentary rocks The northern San Joaquin <br /> Valley has been a lowland area subject to marine intrusion, flooding and incremental i <br /> sedimentation for millions of years The uppermost 1000 feet of sedimentary strata consist of <br /> Holocene, Pleistocene and Pliocene sediments, including the Laguna Formation, the Mehrten <br /> ' Formation and the Valley Spring Formation The sediments are interbedded mixed-fluvial and <br /> ti deltaic sediments, dominated by medium-grained sand and silts Generally, thin beds of <br /> unconsolidated clayey silt, silty clay and sandy clay are abundant in this upper zone, which are <br /> laterally discontinuous over distances of several tens of feet <br /> s 4.0 Hydrogeoiogy <br /> p <br /> Depth to water during this quarter's sampling event varied from 35 18 feet below ground � <br /> surface (bgs) in well MW4 to 3716 feet bgs in well MW-2 The elevation of groundwater in j <br /> j . LL MW-1, MW-2, MW-3, and MW-4 was calculated by EI to be at 22 66, 23 74, 22 66 and 22 83 <br /> feet below mean sea level (MSL) respectively, based upon casing elevation data from Kier & <br /> Wright Civil Engineers and Surveyors All groundwater elevation data including the historical <br /> data is summarized in Table 1 <br /> s <br /> 5.0 Results <br /> 5.1 Groundwater Level Measurements <br /> I <br /> Figure 5 shows groundwater elevations at various dates The <br /> 1 � gr groundwater elevations have { <br /> increased approximately one foot since last quarter and decreased over six feet since the <br /> corresponding season in 2000 The elevations fluctuate over very significant ranges (up to 5 ' <br /> feet in 9 months),which will affect contamination levels,flow direction,gradient,etc <br /> The elevations in wells MW-1, MW-3 and MW-4 move in tandem with MW-2enerall <br /> g y <br /> following the same trend, but, moving higher or lower somewhat randomly This is due to the <br /> Ldifficulty of measuring groundwater elevations in MW-2 because of free product in this well ! <br /> � 3 <br /> I <br /> 2 <br /> 1 <br />