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1 <br /> I ' 2.0 Site Description { <br /> The site is located in the southern part of the City of Stockton, California at 370 55' 7 bT' <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 <br /> 3.0 Geology <br /> rThe 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 <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 /> deltaic sediments, dominated by medium-gramed 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 /> 4.0 Hydrogeology <br /> Depth to water during this quarter's sampling event vaned from 3176 feet below ground j <br /> surface (bgs) in well MW4 to 33 72 feet bgs in well MW-2 The elevation of groundwater in <br /> MW-1,MW-2,MW-3, and MW4 was calculated by EI to be at 18 95, 20 30, 19 05, and 19 41 <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 /> 5.0 Results <br /> 5.9 Groundwater Level Measurements <br /> Figure 5 shows groundwater elevations at various dates The groundwater elevations have <br /> increased approximately two feet 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 /> 1 The elevations in wells MW-1, MW-3 and MW-4 move in tandem, with MW-2 generally <br /> following the same trend, but, moving higher or lower somewhat randomly This is due to the <br /> difficulty of measuring groundwater elevations in MW-2 because of free product in this well <br /> t <br /> f <br /> I <br /> I <br />