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June 26, 1992 <br /> . ARCO Service Station No. 549, Stockton, California <br /> with sand and sandy silt lenses. From approximately 15 to 28 feet below grade, sediments <br /> consists of silt with some sand in the northern west portion of the site and laterally grading <br /> i <br /> southeast to a sandy silt. Sediments from 28 to the total depth explored (65 feet below <br /> grade) consist of silt with some clay in the western portion of the site and laterally grade <br /> east to a sandy silt. This unit also contains sand and silt lenses. First ground water beneath <br /> the site was encountered during drilling at 50 feet below grade. The interpreted subsurface <br /> conditions are shown on geologic cross-section A-A' and section B-B' (Plates 26 and 27). <br /> The trace of the geologic cross-sections is included on Plate 2. <br /> Evaluation of Soil Conditions <br /> �TPHg was-..identified in.all .soil .samples collected from the borings? The soil samples <br /> collected from 30 feet or less contained TPHg concentrations ranging from 1 ppm (borings <br /> S B-7, B-8, and B-9) to 340 ppm (boring B-10). The soil samples collected from 40 feet or <br /> deeper contained TPHg concentrations ranging from 1 ppm (borings B-6 through B-11 and <br /> B-14) to 11 ppm (boring B-13). Benzene concentrations were below laboratory detection <br /> e limits in all samples, except those collected from borings B-11 and B-14. Benzene <br /> concentrations in samples collected from these two borings were 0.031 ppm and 0.025 ppm, <br /> respectively. Generally, higher hydrocarbon concentrations were detected near the gasoline <br /> tanks. <br /> Soil samples collected adjacent to the waste-oil tank (boring B-12) did not contain <br /> detectable concentrations of TEHg,TPHd, BTEX compounds, VOCs, and PCB's. LWith the <br /> _ p <br /> i eXception..of_nickel,.and zi the concentration of all metallic analytes from boring B-12 <br /> �_._.._ <br /> were below, their respective So ble Threshold.Umit-Concentrations outlined in Title 22_of] <br /> \the_California-Code of...Regul ions? Total lead was detected at concentrations of 6.4 and <br /> a epi = IWt✓G <br /> 3OW4-a 8 <br />