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1 First Quarter 2002 Monitoring and Sampling Report 3 7-Eleven Inc, Store#14117,_2725 Country Club Boulevard, Stockton, CA April 25, 2002 Monitoring Well Sampling and Analytical Results ' Before sampling, at least four well-casing volumes of water were removed from each well The ' groundwater samples were collected using disposable bailers Groundwater samples were placed in 40- milliliter glass vials, which were acidified with hydrochloric acid to preserve the samples 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 stared on Ice and transported with a chain-of-custody record to a state-certified laboratory for analysis The groundwater samples were analyzed for TPH-G using Environmental Protection Agency (EPA) methods 80218/modified 8015, and for BTEX and oxygenates MTBE, TBA, DIPE, ETBE, and TAME using EPA method 8260E ' The analytical results for groundwater samples are summarized in Table 1 Dissolved benzene, TPH-G, and MTBE concentrations ranged up to 830 micrograms per liter(pg/L), 21,000 µg/l_ and 1,890 �uglL, respectively Highest MTBE levels were reported in well MW-4, located crossgradient next to the UST area, whereas highest benzene concentrations were detected in well MW-3, located crossgradient to the tank area and pump dispenser Island The laboratory analytical reports for the groundwater samples are Included in Attachment 4 The plume Is currently delineated to the south (downgradient) and the west (crossgradient) ' Dissolved oxygen data taken from the monitoring wells indicate generally anaerobic conditions, with dissolved oxygen levels at or near 1 milligrams per liter(mg/L) (Table 1) ' 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 Waste disposal documentation will be forwarded once received ' Conclusion and Recommendations ' Results of the current quarterly sampling event conform to plume delineations presented in the December 12, 2001 additional assessment report Benzene and TPH-G concentrations have declined in ' well MW-2 (located In the UST pit area), and in crossgradient wells MW-1 and MW-3 A 2000-foot door- to-door sensitive receptor survey, a concurrent feasibility study for a dual-vacuum extraction system, and a review of gradient information in SJCPHS files for nearby service stations are recommended for the site per the additional assessment report, and are scheduled to be conducted In the second quarter 2002 t0 14117Q21 doc