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Third Quarter 1999 Monitoring and Sampling Report 2 7-Eleven, Inc., Store#14117, 2725 Country Club Boulevard, Stockton, CA _ August 30, 1999 Monitoring Well Sampling and Analytical Results ' On August 25, 1999, groundwater samples were collected from groundwater monitoring wells: MW-1, MW-2, MW-3, and MW-4. Before sampling, at least four well-casing volumes of water was 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 job 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 BTEX, MTBE and TPH-G using Environmental Protection Agency (EPA) methods 8020/modified 8015, and for oxygenates MTBE, TBA, DIPS, ETBE, and TAME using EPA ' method 8260. ' The analytical results for groundwater samples collected on August 25, 1999, are summarized in Table 1. Dissolved benzene, MTBE and TPH-G concentrations ranged up to 9.40 micrograms per liter(pg1L), 800 pg/L and 8,400 pg/L, respectively. Highest MTBE levels were in well MW-2. Low concentrations of ' 6.4 lag/L MTBE were found in downgradient well MW-1. The laboratory analytical reports for the groundwater samples are included in Attachment 4. Dissolved oxygen data taken from the monitoring wells on August 25, 1999 indicate generally anaerobic conditions. Dissolved oxygen levels ranged from 0.4 milligrams per liter (mg/L) to 0.7 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. 1 1 '11 1 7q'i`3 rpI