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_ "AMuAM <br /> tin"/wA <br /> Working to Restore Nature <br /> groundwater, on March 22, 1994, was east-southeast to southeast however, the <br /> potentxometric surface exhibits a mound in the southwest corner of the site the hydraulic <br /> gradient ranged from 0 002 to 0 007 as shown on Plate 3 The groundwater elevation <br /> increased by approximately 0 5 foot in wells MW-1 through MW-6 and 148 feet in well <br /> MW-7 since the previous monitoring event. <br /> Groundwater 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 (EPA) Methods 5030/8020 and Modified 8015 The sample from well <br /> MW-2 was analyzed for total oil and grease (TOG) using EPA Method 413.1 also. These <br /> samples were analyzed at GTEL Environmental Laboratories, Inc in Concord, California <br /> (Hazardous Waste Testing Laboratory Certificate E1075) The results of analyses are <br /> summarized in Tables 1 and 2 Copies of the laboratory analysis reports are in the <br /> Appendix <br /> Results of analyses indicated dissolved gasoline hydrocarbons were detected in samples from <br /> the seven wells Concentrations of TPHg ranged from 29,000 (well MW-2) parts per billion <br /> (ppb) to 79,000 ppb (well MW-6), and benzene concentrations ranged from 3,000 ppb (well <br /> MW-7) to 12,000 ppb (well MW-3) TOG was not detected in well MW-2 (Table 2) <br /> Concentrations of TPHg and benzene are shown on Plate 2 <br /> 1 <br /> WORD IN PROGRESS <br /> RESNA is currently preparing a Problem Assessment Report ARCO will continue <br /> quarterly groundwater sampling. <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> The direction of groundwater flow has ranged from the northeast to the southeast <br /> Dissolved gasoline hydrocarbons were detected in samples from the seven wells TOG was <br /> not detected in the sample collected from well MW-2 Based on relatively high <br /> concentrations of dissolved hydrocarbons in wells MW-6 and MW-7 (hydraulically <br /> upgradient from the ARCO service station), it appears a hydrocarbon source exists offsite <br /> and upgradient We recommend continued quarterly evaluation of groundwater beneath the <br /> site, including analyzing water samples for halogenated volatile organic compounds <br /> (HVOCs), TPHg, and BTEX We also recommend water sample from wells MW-2 and <br /> MW-6 be analyzed for TOG and HVOCs to evaluate whether these previously detected <br /> hydrocarbons are from an offsite source <br /> 0419ccaF/31009-1 1 3 <br />