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1 <br /> WA <br /> r March 12, 1993 Working To Restore Nature <br /> ARCO Service Station No 2130, Stockton, California <br /> 1 water-level measurements and collect groundwater samples from monitoring wells MW-1 W i7w-10" <br /> through MW-5 for subjective analyses Our technician also visited the site on December 4, _i <br /> 1992, to take water-level measurements and collect ground-water samples from wells MW-1 <br /> through MW-7 for subjective analyses No floating product or product sheen was noted in <br /> samples from the wells during the site visits, however, product odor was noted in some of <br /> 1 the wells during the site visits (Table 2) <br /> The wellhead elevations of the monitoring wells at the site were previously surveyed by Tom <br /> O Morrow of West Sacramento, California, a licensed land surveyor (California Land <br /> Surveyors No 5161) The surveyed elevations and the depth-to-ground-water measurements, <br /> 1 summarized in Table 1, were used to evaluate the potentiometric surface beneath the site <br /> The ground-water flow direction on October 6, 1992, was northeast to east-southeast with <br /> a hydraulic gradient ranging from 0 001 to 0 002 (Plate 11) The two new wells MW-6 and <br /> MW-7 were also surveyed by Tom O Morrow A map is currently being prepared The <br /> survey and ground water elevation data will be presented in the next status report <br /> 1 Ground-Water Sampling and Anal <br /> Ground-water samples were analyzed for TPHg and BTEX using EPA Methods 5030 and <br /> 8020 and standard methods prescribed by the State of California These samples were <br /> analyzed at Columbia Analytical Services, Inc in San Jose, California (Hazardous Waste <br /> Testing Laboratory Certificate No 1426) The samples were also submitted to Sequoia <br /> Analytical in Sacramento, California, for analysis of fecal coliform bacteria These samples <br /> were also to be analyzed for total coliform bacteria if fecal coliform bacteria were not <br /> detected The samples collected from wells MW-6 and MW-7 were also analyzed at <br /> Sequoia Analytical The results of analyses are summarized in Table 3 Copies of the <br />► laboratory analysis reports are in the Appendix <br /> The results of analyses indicated that TPHg was detected in samples from the seven wells <br /> at concentrations ranging from 88 parts per billion (ppb) (well MW-7) to 11,000 ppb (well <br /> MW-1), concentrations of benzene ranged from <0 5 ppb (well MW-6) to 2,500 ppb Fecal <br /> 1 coliform bacteria were not detected in the samples from the wells, therefore, the samples <br /> were analyzed for total coliform bacteria Total coliform bacteria were not detected <br /> WORK IN PROGRESS <br /> The sparging pilot test _was performed in October 1992 to evaluate ground-water <br /> remediation. The results of this test are currently being evaluated and will be discussed in <br /> a separate report. <br /> 1105kchr <br /> 30003-6 3 <br /> 1 <br />