ARCHIVED REPORTS XR0001331 - Laserfiche WebLink

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June 9, 1993 �5�, ARCO Service Station 2168, Stockton, California Working To Restore Nature water, performed subjective analyses of ground water, and collected ground-water samples from the wells for laboratory analyses The technician noted no floating product or sheen in the five wells (Table 1) The wellhead elevations of the monitoring wells at the site were previously surveyed by Tom O Morrow, Inc of West Sacramento California, a licensed land surveyor (California Land Surveyors No 3275) The surveyed elevations and the depth-to-groundwater measurements, summarized in Table 1, were used to evaluate the potentiometric surface beneath the site The ground-water flow direction on February 23, 1992, was to the northeast with a hydraulic gradient of 0 0009 to 0 0013, and the groundwater flow direction on March 10, 1993, was to the northeast with a hydraulic gradient of 0 001 (Plate 21) The average depth to ground water increased by 0 77 feet since the previous monitoring event The average depth to water in March was 40 feet bsg Analylical Methods Water samples collected from wells MW-4 and MW-5 on January 26, 1993, were analyzed for TPHg using modified EPA Method 8015, BTEX using EPA Method 602,volatile organic • compounds (VOCs) using EPA Method 601, and total coliform bacteria using membrane filtration These analyses were performed by Sequoia Analytical Ground-water samples collected March 10, 1993, were analyzed for TPHg and BTEX using EPA Methods 5030/8015 and 8020 and standard methods prescribed by the State of California Samples were also analyzed for VOC's using EPA Methods 5030/601, and the sample from well MW-2 was analyzed for total oil and grease (TOG) using EPA Method 5520B These samples were analyzed at Columbia Analytical Services, Inc in San Jose, California (Hazardous Waste Testing Laboratory Certificate No 1426) The sample from well MW-3 was also submitted to Sequoia Analytical in Sacramento, California, for analysis of total and fecal coliform bacteria. Copies of the laboratory analysis reports are in the Appendix The results of analyses are summarized in Tables 1 and 3 Results of Water Sample Analyses Results of laboratory analyses of water samples collected from wells MW-4 and MW-5 in January 1993 indicated TPHg was detected at 81,000 and 43,000 parts per billion (ppb) in wells MW-4 and MW-5, benzene concentrations in these wells were 5,600 and 7,700 ppb, respectively Concentrations of TPHg in samples collected from wells MW-1 through MW-5 in March 1993 ranged from 16,000 to 110,000 ppb (well MW-4), benzene concentrations ranged from 3,300 to 16,000 ppb TOG was not detected in the sample collected from well MW-2 0209ccar 31009-7 4