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I <br /> . April 15, 1993 Working To Restore Nature <br /> i ARCO Service Station No 2076, Lodi, California <br /> feet to the total depth explored, sediments consist of interbedded layers of sand, silt, and <br /> clay ranging in thickness from 2- to 12-feet Overlaying this unit, from approximately 20 to <br /> 30 feet, a laterally continuous silt layer is present, as depicted on Plate 4 This unit is <br /> i <br /> subsequently overlayed, from approximately below suface grade to 20 feet below grade, by <br /> sediments consisting of sandy silt and sand <br /> Site Hydroaeology <br /> During the initial assessment conducted in October 1990 ground-water was encountered at <br /> 31 feet below grade in borings B-1 and B-2 In October 1992, the static ground-water <br /> measured in the monitoring wells level was approximately 52 feet below grade The <br /> measured depths to ground water were combined with the wellhead elevations (surveyed by <br /> Tom O Morrow, Inc , licensed land surveyors of West Sacramento, California) to calculate <br /> • the elevation of the ground-water surface in each well Surveying data is presented in Table <br /> 6 These data were used to construct the Potentiometric Map presented on Plate 5 Based <br /> on the potentsometric data, the groundwater flow direction on October 23, 1992, was <br /> northwest with an approximate hydraulic gradient of 0 02 The flow direction and gradient <br /> may be subject to seasonal fluctuations <br /> Residual Hydrocarbons in Soil <br /> The results of laboratory analyses of soil samples collected from the borings and from the <br /> tank and product-line excavations were used to evaluate the lateral and vertical extent of <br /> residual hydrocarbons in soil The sample locations and the concentrations of total <br /> petroleum hydrocarbons as gasoline (TPHg) are presented on Plate 6 Tables 1 show the <br /> analytical results for soil samples collected at the site <br /> 3ooas-s 9 <br />