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i I F ' E 2.0 Site Description . I The site is located in the southern part of the City of Stockton, California at 370 55' 7 67" ' latitude and 1210 16' 43 45" longitude (Figures 1 and 2) The site is an essentially level E commercial truckmg facility,which contains an office building,two truck maintenance shops,a truck-washing facility,, a small above-ground storage tank compound, a vehicle fueling facility ; and a large parking area for tank trailers 3.0 Geology � The site is situated in the northern part of the San Joaquin Valley, in an area underlain by � several thousand feet of terrestrial and marine sedimentary rocks The northern San Joaquin � ' Valley has been a lowland area subject to marine intrusion, flooding and incremental sedimentation for millions of years The uppermost 1000 feet of sedimentary strata consist of Holocene, Pleistocene and Pliocene sediments, including the Laguna Formation, the Mehrten Formation and the Valley Spring Formation The sediments are interbedded mixed-fluvial and deltaic sediments, dominated by medium-gramed sand and silts Generally, thin beds of unconsolidated clayey silt, silty clay and sandy clay are abundant in this upper zone, which are 1 laterally discontinuous over distances of several tens of feet 4 4.0 Hydrogeology Depth to water during the quarter's sampling event vaned from 36 3feet below ground surface(bgs) in well MW- to 37 30 feet bgs in well MW-2 The elevation of groundwater in ' f • MW-1, MW-2,MW 3, and MW4 was calculated by EI to be at 23 84, 23 88, 23 98 and 24 08 feet below mean sea level (MSL) respectively, based upon casmg elevation data from Kier & Wright Civil Engineers and Surveyors All groundwater elevation data including the historical ' data is summarized in Table 1 r 5 0 Results ' 5.1 Groundwater Level Measurements Figure 5 shows groundwater elevations at various dates The groundwater elevations have i decreased approximately three feet since last quarter and decreased over eight feet since the i corresponding season in 2000 The elevations fluctuate over very significant ranges (up to 5 feet in 9 months),which will affect contamination levels,flow direction, gradient,etc The elevations in wells MW-1, MW-3 and MWS move in tandem, with MW-2 generally following the same trend, but, moving higher or lower somewhat randomly This is due to the difficulty of measuring groundwater elevations in MW-2 because of free product in this well This quarter EI has calculated the corrected depth to water(CDTW)using the calculation found on page 4 of Appendix B This CDTW has allowed MW-2 to now move in tandem with the other wells • I I