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C <br /> July 2, 1993 <br /> ARCO Station No 6020, Manteca, California Working To Restore Nature <br /> C <br /> GROUND-WATER MONITORING <br /> On April 20, 1993, a technician from EMCON measured the depth to water and collected <br /> ground-water samples from monitoring wells MW-1 through MW-4 for subjective and <br />'' laboratory analyses On April 2, May 24 and June 15, 1993, a technician from RESNA <br /> measured depths to water and collected ground-water samples for subjective analyses The <br /> technician did not observe floating product or product sheen on samples collected from the <br /> wells (Table 1) <br /> Tom O Morrow Inc (licensed land surveyors) of West Sacramento, California, surveyed the <br /> monitoring wells to provide the elevation of each wellhead relative to mean sea level Data <br /> were combined with the measured depths to ground water to calculate the elevation of the <br /> groundwater surface in each well These data were used to construct the Potentiometric <br /> Surface Map (Plate 3) The evaluated groundwater flow direction on April 20, 1993, was <br /> C north with a hydraulic gradient of 0.002, which is consistent with the data collected during <br /> the May and June monitoring events Groundwater elevations rose approximately 1.3 feet <br /> from first quarter 1993 <br /> Ground-water samples from each well were analyzed for total petroleum hydrocarbons as <br /> gasoline (TPHg) and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) <br /> using Environmental Protection Agency Method 5030/8020 The samples were analyzed at <br /> Columbia Analytical Services, Inc in San Jose, California (Hazardous Waste Testing <br /> Laboratory Certificate No 1426). The results of these analyses are summarized in Table <br /> 1 Copies of the laboratory analysis reports are attached Results of analyses indicated <br /> { TPHg and BTEX concentrations were below laboratory detection limits in groundwater <br /> samples collected from wells MW-1 through MW-4 <br /> We recommend that copies of this report be forwarded to Mr Mike Infurna of the San <br /> Joaquin County Public Health Services, 445 N San Joaquin Street, Stockton, California, <br /> 95210, and Ms Elizabeth Thayer,California Regional Water Quality Control Board, Central <br /> Valley Regional. 3443 Routier Road, Sacramento, California 95827-3098 <br /> 0513kchr <br /> 30055-6 2 <br />