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l Fourth Quarter 9999 Monitoring and Sampling Report 2 i 7-Eleven, Inc ,Store#20632,4627 DaVinci Drive Stockton CA December 27, 1999 Monitoring Well Sampling and Analytical Results On November 24, 1999, groundwater samples were collected from four wells (MW-1, MW-2, MW-3 and MW-5), well MW-4 was abandoned during UST upgrades In 1998 Before sampling, at least 4 well casing volumes of groundwater was removed from each monitoring well 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 lob identification number, the sample number, date, time, and type of laboratory analysis required The samples were stored on Ice and transported under a chain-of-custody record to a state-certified laboratory Groundwater samples were analyzed for BTEX and TPH-G using Environmental Protection Agency (EPA) methods 8021 Blmodified 8015, and for oxygenates MTBE, TBA, DIPE, ETRE, and TAME using EPA method 82606 Laboratory analytical results for groundwater samples collected on November 24, 1999 are presented in Table 1 The laboratory analytical reports for the groundwater samples are Included in Attachment 4 Historical data are Included in Table 2 Dissolved benzene levels ranged up to 21 4 micrograms per liter(pg/L), and dissolved TPH-G levels ranged up to 3,490 pg/L Dissolved MTBE concentrations ranged up to 7,450 pg/L Highest TPH-G and MTBE levels were found directly downgradtent from the underground storage tank area in well MW-2 Highest dissolved benzene concentrations were found in I. crossgradient well MW-5 at 21 4 pg/L Dissolved MTBE concentrations versus water table elevations are plotted on Figures 3 and 4 Observed concentrations and hydrocarbon distribution are similar to previous quarters There are no private or public municipal or domestic wells within 2,000 feet of the site Dissolved oxygen levels Indicate generally anaerobic conditions of less than 2 milligrams per liter (mg/L), due to Intrinsic biodegradation 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 20632849 rpt IT CORPORATION