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Fust Quarter 2002 Mondonng and Samphng Report 4 <br /> 7-Eleven Inc Store#17647, 1048 West Yosemite Avenue Manteca CA Aril 29 2002 <br /> Quarterly analytical results are presented in Table 1 Dissolved benzene was detected In wells MW-1 and <br /> ' MW-3 at low levels of 0 96 micrograms per liter (ug/L) and 0 83 ug/L, respectively Dissolved TPH-G and <br /> MTBE were not detected in any of the wells Dissolved xylene concentrations were detected at low levels <br /> In wells MW-1 (5 4 ug/L) and MW-3 (1 2 ug/L) Dissolved toluene was also detected at a low level in well <br /> ' MW-3(0 62 ug/L) The other oxygenates were not detected, consistent with a trend established during <br /> seven previous quarterly sampling events (Table 1A) Laboratory analytical reports for the groundwater <br /> ' samples are Included in Attachment 4 <br /> Dissolved oxygen (DO) levels ranged from 1 4 milligrams per liter(mg/L) in well MW-3 to 2 0 mg/L in well <br /> ' MWA, Indicating relatively uniform and generally aerobic conditions <br /> Purge Water Transportation and Disposal <br /> ' All purge water collected during this quarterly monitoring and sampling event was stored onsite In <br /> 55-gallon Department of Transportation (DOT)-approved drums pending characterization and proper <br /> ' disposal at a licensed recycling facility Waste documentation will be forwarded as requested <br /> ' conclusion and Recommendations <br /> Groundwater monitoring data continue to Indicate that this site is low risk, based on 1) sustained levels <br /> of low-level to non-detectable dissolved hydrocarbon concentrations in all of the monitoring wells during <br /> seven consecutive quarterly monitoring events, 2) low-level to non-detectable soil and groundwater <br /> hydrocarbon concentrations in the latest downgradient soil borings, and 3) no nearby sensitive receptors <br /> ' within 4,000 feet downgradient of the site Groundwater flow at the site occurs most consistently to the <br /> northwest, with MW-3 lying furthest downgradient from the former tank/pump Island locations Dissolved <br /> MTBE concentrations in well MW-3 have declined since the first quarter 2000, from 108 ug/L to current <br /> ' non-detectable levels Declining dissolved oxygen levels in MW-3 continue to indicate that natural <br /> attenuation/biodegradation is occurring <br /> ' Additional substantiation for no further action will be submitted in the second quarter 2002 report Data <br /> trends appear favorable for site closure <br /> ' 21756q4 rpt <br />