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1 <br /> First Quarter 2000 Monitoring and Sampling Report 2 <br /> 7-Eleven Inc Store No 17334 4501 North Pershing Avenue Stockton,CA March 6 2000 <br />' Monitoring Well Sampling and Analytical Results <br />' Quarterly groundwater samples were collected after purging at least 4 well-casing volumes of groundwater <br /> from each monitoring well, unless the well was purged dry The groundwater samples were collected using <br /> disposable bailers Groundwater samples were placed in analysis-specific containers with analysis-specific <br />' preservative The samples were then sealed using Teflon septum caps, labeled with the lob identification <br /> number, the sample number, date, time, and type of laboratory analysis required The samples were <br /> stored on ice and transported with a chain-of-custody record to a state-certified laboratory for analysis <br /> Groundwater samples were analyzed for BTEX and TPH-G using Environmental Protection Agency (EPA) <br /> methods 8021 Blmodified 8015, and for oxygenates MTBE, TBA, DIPE, ETRE, and TAME using EPA <br /> method 8260B <br />' Analytical results for the quarterly sampling event are presented in Table 1 and Figure 1, and historical <br /> laboratory analytical results are summarized in Table 2 Highest dissolved benzene and TPH-G <br /> concentrations were reported in well MW-5A at 3,980 micrograms per liter(pg/L) and 53,000 pg/L, <br /> respectively MTBE was detected in groundwater from wells MW-4 and MW-5A at concentrations of <br />' 7,770 pg/L and 1,460 pg/L, respectively Dissolved benzene, TPH-G, and MTBE concentrations are plotted <br /> on Figure 2 The laboratory analytical reports are included in Attachment 4 <br /> Quarterly data obtained during this sampling event are consistent with previous findings, indicating the <br /> hydrocarbon plume is primarily centralized in the vicinity of the underground storage tanks Concentrations <br /> of benzene and TPH-G in the deeper nested well MW-56, are more than 99% lower than those observed in <br />' the shallow well MW-5A <br /> Prior to purging, dissolved oxygen (DO) levels were recorded in each well Dissolved oxygen levels ranged <br />' from 1 2 milligrams per liter (mg/L) to 1 7 mg/L (Table 1) <br /> Purgewater Disposal <br />' All ur ewater generated during this quarterly monitoring and sampling event was stored in 55-gallon <br /> p g g 9 <br />' Department of Transportation (DOT)-approved drums, pending proper transport and disposal Waste <br /> disposal documentation will be forwarded once received <br /> 17334849 qmr <br />