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First Quarter 2002 Monitoring and Sampling Report 2 7-Eleven, Inc,Store#21756 853 E Yosemite Avenue,Manteca CA May 20,2002 A potentiometric surface map was prepared using the quarterly groundwater elevation data (Figure 2) Results Indicate that the groundwater flow is toward the northwest at a gradient of about 0 001 ft/ft The groundwater monitoring results from the current monitoring and sampling event are presented in Table 1 (Attachment 2) Historical data are included in Table 2 Field data sheets are Included in Attachment 3 1 MonitoringWell Sampling and Analytical Results p 9 Y The groundwater samples were collected using disposable bailers Groundwater samples were placed in analysis-specific containers with ana[ysis-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, MTBE, and TPH-G ' using EPA methods 8021/modified 8015 and for oxygenates MTBE, TBA, DIPE, ETRE, and TAME using EPA method 8260 iDissolved oxygen (DO) concentrations were measured In the three wells prior to sampling Dissolved oxygen readings ranged from 1 3 milligram per liter (mg/L) to 2 9 mg/L, indicating aerobic conditions (Table 1) Quarterly analytical results are summarized in Table 1 and historical results are summarized in Table 2 Dissolved benzene was detected only in well MW-1 at a concentration of 2 1 micrograms per liter(ug/L) Dissolved TPH-G levels ranged between non-detectable (well MW-3) and 400 ug/L (well MW-1) Dissolved MTBE concentrations ranged between non-detectable (well MW-3) and 1,500 ug/L (well MW-1) The other oxygenates were not reported above detection limits in any of the wells sampled The laboratory analytical reports for the groundwater samples are included in Attachment 4 Sensitive Receptors ' As mentioned in previous quarterly reports, a well search database for public water supply wells located within one mile of the site Indicates that the nearest well is an active municipal well located 1,987 feet downgradient of the site, it is 155 feet deep, with top of screen at approximately 65 feet below grade Purge Water Transportation and Disposal 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 by a licensed waste hauling company 1