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AZ MA <br /> June 9, 1993 Working To Restore Nature <br /> ARCO Station No. 6020, Manteca, California <br /> GROUND-WATER MONITORING <br /> On February 26, 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 March 1, 1993, a technician from RESNA measured depths to <br /> water and collected ground-water samples for subjective analyses. The technician did not <br /> observe floating product or product sheen on samples collected from the 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 /> ground-water surface in each well These data were used to construct the Potentiometric <br /> Map presented on Plate 3 The evaluated ground-water flow direction on February 26, <br /> 1993, was slightly west of north with a hydraulic gradient of 0 002. <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 ground-water <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 /> 0329kchr <br /> 30055-6 2 <br />