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February 14, 1992 ����� <br /> . ARCO Service Station No 2130, Stockton, California <br /> 1 <br /> Residual hydrocarbons as TPHg ranged from 8 4 to 2,400 parts per million (ppm) in soil <br /> samples collected from 15 to 60 feet bsg from boring B1 (Table 4) TPHg ranged from 10 <br /> ppm (61 feet bsg) to 3,000 ppm (31 feet bsg) in soil samples collected from B3 Other <br /> borings that yielded detectable levels of residual hydrocarbons were B5 (58 Qpm at 51 feet <br /> bsg), B7 (530 ppm at 56 feet bsg), B2 (5 5 ppm at 61 feet bsg) and B4 (7 4 ppm at 41 feet <br /> bsg) TPHg and BTEX was not detected in samples collected from borings 136 and B8 <br /> located to the east of the existing tank cavity Residual hydrocarbons in soil (detected in <br /> borings B1, B2, B3, B5 and B7) are located north, south and west of the existing tanks, B4 <br /> is located north the existing dispenser islands <br /> Results of laboratory analyses of water samples indicated concentrations of TPHg ranged <br /> from 2,100 parts per billion (ppb) in the sample collected from well MW-3 to 18,000 ppb <br /> in the sample collected from well MW-1 Concentrations of benzene ranged from 41 ppb <br /> in the sample collected from well MW-3 to 1,600 ppb in the sample collected from well <br /> MW-1 Concentrations of fecal coliform bacteria ranged from 3 8 colony forming units per <br /> 100 milliliters (CFU/ml) in the samples collected from wells MW-1 and MW-2 to 7 7 <br /> CFU/ml in the sample collected from well MW-3 Results of analyses of water samples are <br /> presented in Table 5 <br /> Evaluation of Ground-Water Gradient <br /> Tom O Morrow, Inc (Morrow) of West Sacramento, California (Licensed Land Surveyor <br /> No 5161), surveyed the elevations and positions ("x" and "y" lateral coordinates) of <br /> monitoring wells MW-1 through MW-3 on January 15, 1991 Morrow measured the <br /> monitoring wells with respect to the City of Stockton Bench Mark 2N-2 located in a brass <br /> disk in a monument well at the northeast corner of Hammer Lane and El Dorado Street <br /> According to Morrow personnel, Bench Mark 2N-2 is referenced to the United States <br /> Geodetic Survey and is at an elevation of 13 82 feet above mean sea level The elevation <br /> 30003-4W 6 <br />