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' First Quarter 2001 Monitoring and Sampling Report and Request for No Further Action 2 7-Eleven Inc Store#17647 1048 West Yosemite Avenue Manteca CA March 30 2001 1 Groundwater monitoring results for the quarter are presented in Table 1 (Attachment 2) A potentiometnc surface map was prepared using the quarterly groundwater elevation data (Figure 2), which Indicates that ' as of the date of the sampling event, groundwater flow was toward the northwest at a gradient of approximately 0 002 ft/ft Field data sheets are Included in Attachment 3 Monitoring Well Sampling and Analytical Results 1 Groundwater samples were collected from the three monitoring wells Dissolved oxygen (DO) concentrations were measured In the three wells pnor 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 chatn-of-custody record to a state-certified laboratory Groundwater samples were analyzed for BTEX and TPH-G using EPA methods 8021/modified 8015, and for the oxygenates MTBE, TBA, DIPS, ETRE, and TAME using EPA method 8260 Dissolved oxygen data Indicate relatively uniform,generally anaerobic conditions Dissolved oxygen levels ranged between about 1 1 and 1 3 milligrams per liter(mg/L) 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 ' except as noted due to laboratory contamination of the method blank for ethylbenzene Dissolved MTBE concentrations were only detected in downgradient well MW-3 at 68 pg/L The other oxygenates were not ' reported above detection limits in any of the wells as has been the case for a total of five quarterly sampling events 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 1 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 1 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 t' 2175684 rpt