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• Fourth Quarter 2000 Monitoring and Sampling Report 2 7-Eleven Inc,Store#17647, 1048 West Yosemite Avenue Manteca CA December 19 2000 Monitoring Well Sampling and Analytical Results Groundwater samples were collected from the three monitoring wells Dissolved oxygen (DO) concentrations were measured in the three wells prior to sampling The groundwater samples were collected using disposable bailers Groundwater samples were placed in analysis-specific containers with analysis-specific preservative The samples were then sealed using Teflon septum caps, labeled with the fob identification number,the sample number,date,time, and type of laboratory analysis required The samples were stored on ice and transported with a chain-of-custody record to a state-certified laboratory Groundwater samples were analyzed for BTEX and TPH-G using EPA methods 8021/modified 8015 , for the oxygenates MTBE, TBA, DIPE, ETBE, and TAME using EPA method 8260 Dissolved oxygen data Indicate greater depletion of oxygen in the downgradient well MW-3 (0 4 milligrams per liter),than in the two upgradient wells, MWA and MW-2 (1 7-1 5 mg/L), (Table 1) Laboratory analytical results for quarterly groundwater samples are summarized in Table 1 Dissolved BTEX and TPH-G concentrations were not detected above reporting limits in any of the wells sampled Dissolved MTBE concentrations were only detected in downgradient well MW-3 at 31 pg/L. The other oxygenates were not reported above detection limits in any of the wells sampled during the last two quarters All gasoline . constituents analyzed remained below detection limits in groundwater samples from the two upgradient wells (MW-1 and MW-2) MTBE concentrations In downgradient well MW-3 have declined since the first quarter 2000 The dissolved MTBE plume appears restricted to a limited area between the former underground storage tanks and MW-3 Low and non-detectable dissolved gasoline-constituent concentrations with declining dissolved oxygen levels (MW-3) indicate that natural attenuation/biodegradation is occurring The laboratory analytical reports for the groundwater samples are included in Attachment 4 Well Search As mentioned previously, a well search database for this site indicates the nearest wells are approximately 993 feet to the north (crossgradient) of the site,there are two downgradient wells located approximately 4,956 feet southwest of the site Purge Water Transportation and Disposal All purge water generated during this quarterly monitoring and sampling event was stored In 55-gallon Department of Transportation (DOT)-approved drums pending characterization and proper disposal Approximately 22 gallons of purged water generated during this sampling event will be removed from the site and transported to a licensed treatment and disposal facility 21756g4 rpt