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� 16 1444 MARIPOSA <br /> WKA No 2307 02 <br /> May 24, 1993 <br /> Page 3 <br /> ' Sample tubes were sealed with polytetrafluoroethylene (PTFE)-coated sheets, plastic end caps and <br /> duct tape to reduce volatile hydrocarbon loss Selected samples were placed in an ice chest <br /> containing ice, and submitted under chain-of-custody to a California-certified laboratory for the <br /> analyses described above <br /> FINDINGS <br /> Two soil borings (B2 and B3) were drilled at approximate 30° angles from vertical beneath the <br /> ' former underground storage tanks to depths of 71 and 81 feet below site grade (Plate 2) The <br /> soils in these borings consisted primarily of silty clays and clayey silts, two thin sand layers were <br /> ' observed at depths of approximately 49 to 53 feet and 63 to 68 feet A slight petroleum odor <br /> was encountered during the drilling of the two angle borings Laboratory analysis of samples <br /> B2-11I through B2-171 revealed TPH gasoline concentrations ranging from 2 1 mg/kg to 17 <br /> mg/kg at depths of 46 to 73 feet <br /> ■ Analysis of samples obtained from boring B3 revealed trace concentrations of TPH gasoline and <br /> BTEX at 43 5 feet, and no detectable concentrations of TPH or BTEX at 47 and 515 feet Soil <br /> ' samples obtained from depths of 56 and 69 feet contained TPH gasoline concentrations ranging <br /> from 0 8 mg/kg to 49 mg/kg <br /> 1 <br /> Boring Bl was constructed approximately five feet easterly of the excavation and extended to a <br /> ' depth of 86 5 feet Drilling was discontinued when ground water was encountered in the boring <br /> at a depth of approximately 85 feet Boring B4 was constructed approximately ten feet westerly <br /> of the excavation to a depth of 49 5 feet A slight petroleum odor was reported in each of the <br /> borings <br /> Analysis of samples 81-81 and B1411, obtained from depths of 415 and 56 5 feet, respectively, <br /> revealed TPH gasoline concentrations of 6 6 mg/kg to 8 8 mglkg Samples B1-141 and, B1-15I <br /> obtained from depths of 715 and 76 5, respectively, revealed no detectable concentrations of <br /> ti TPH gasoline and only trace BTEX concentrations at 715 feet <br /> o <br /> WALLACE KUHL <br /> Rct.cled[nxpzr &ASSOCIATES INC <br />