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June 3, 1993 Working To Restore Nature <br /> ARCO Service Station No 2130, Stockton, California <br /> i <br /> GROUND-WATER MONITORING: SECOND QUARTER 1993 <br /> Subjective Analysis and Water-Level Measurements <br /> i On April 6, 1993, a technician from Emcon measured depths to water and collected ground- <br /> water samples from wells MW-1 through MW-7 for subjective and laboratory analyses <br /> Floating product or product sheen was not noted in samples from the wells (Table 1) <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 /> summarized in Table 1, were used to evaluate the potentiometric surface beneath the site <br /> The ground-water flow direction on April 6, 1993, was to the east-southeast with a hydraulic <br /> gradient of 0 002 (Plate 3) The groundwater flow direction in the past has generally been <br /> towards the southeast The ground-water elevation beneath the site generally increased <br /> approximately 0 50 feet since the last sampling event Ground-water elevation data are <br /> presented on Plate 3 and in Table 1 <br /> Ground-Water SamRling and Analyses <br /> Ground-water samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) <br /> and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using Environmental <br /> Protection Agency Methods 5030 and 8020 and standard methods prescribed by the State <br /> of California These samples were analyzed at Columbia Analytical Services, Inc in San <br /> Jose, California (Hazardous Waste Testing Laboratory Certificate No 1426) The results <br /> of analyses are summarized in Table 2 Copies of the laboratory analysis reports are in the <br /> Appendix <br /> The results of analyses indicated that TPHg was detected in samples from wells MW-1 <br /> through MW-6 at concentrations ranging from 160 parts per billion (ppb) (well MW-6) to <br /> 1 1,600 ppb (well MW-5), concentrations of benzene ranged from 0 6 ppb (well MW-6) to 260 <br /> ppb (well MW-5) TPHg and BTEX were not detected in the samples collected from well <br /> MW-7 TPHg and benzene concentrations are shown on Plate 2 <br /> WORK IN PROGRESS <br /> 1 RESNA is currently evaluating remedial options for soil and ground water using the results <br /> of air sparging and vapor-extraction testing performed at the site RESNA is also currently <br /> evaluating additional offsite drilling and monitoring well installation options <br /> 1� 0429kchr <br /> M3-9 2 <br />