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• Working to Restore Nature <br /> GROUNDWATER MONITORING: FIRST QUARTER 1994 <br /> Groundwater Technology, Inc (GTI) of Concord, California, was contracted by ARCO to <br /> conduct the field work at the site, GTI subsequently forwarded their field notes and the <br /> laboratory reports to RESNA. Field work included measuring depths to water and <br /> collecting groundwater samples for subjective and laboratory analyses RESNA used these <br /> data to evaluate the direction and gradient of groundwater flow beneath the site <br /> On March 23 and 24, 1994, a technician from GTI measured depths to water and collected <br /> groundwater samples from wells MW-1, MW-2, MW-3, MW-4, and MW-6 through MW-8, <br /> and MW-10 for subjective and laboratory analyses, well MW-5 was inaccessible Floating <br /> 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 The surveyed elevations and the depth-to-groundwater measurements, <br /> summarized in Table 2, were used to evaluate the potentiometric surface beneath the site <br /> The groundwater flow direction on March 23, 1994, was to the 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 groundwater elevation beneath the site increased approximately <br /> 4 95 feet since the last sampling event. Groundwater elevation data are presented on Plate <br /> 3 and in Table 1 <br /> Groundwater samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) <br /> and benzene, toluene, ethylbenzene, and total xylene isomers using EPA Method <br /> 5030/LUFT and EPA Methods 5030/8020 These samples were analyzed at GTEL <br /> Environmental Laboratories, Inc in Concord, California The results of analyses are <br /> summarized in Table 2 Copies of the laboratory analysis reports are presented in Appendix <br /> A <br /> The results of analyses indicated that dissolved gasoline hydrocarbons were detected in all <br /> the wells sampled TPHg concentrations ranged from 130 parts per billion (ppb) (well MW- <br /> 7) to 1,900 ppb (well MW-1), and concentrations of benzene ranged from 6 6 ppb (well <br /> MW-10) to 120 ppb (well MW-1) TPHg and benzene concentrations are shown on Plate <br /> 2 <br /> 0415ccar/30003-15 2 <br />