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Third Quarter 2000 Monitoring and Sampling Report 2 7-Eleven Inc Stare#17647 1048 West Yosemite Avenue Manteca CA August 15 2000 Monitoring Well Sampling and Analytical Results On July 20, 2000, groundwater samples were collected from the three monitoring wells Dissolved oxygen ' (DO)concentrations were measured In the three wells prior to sampling The groundwater samples were collected using disposable bailers Groundwater samples were placed in analysts-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 analysts 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 and TPH-G using EPA methods 8021/modified 8015 , for the oxygenates MTBE, TBA, DIPS, ETBE, and TAME using EPA method 8260 Dissolved oxygen data Indicate continuing depletion of oxygen levels for the two upgradient wells (MW-1 and MW-2), DO level was not recorded for downgradlent well, MW-3 Dissolved oxygen readings taken ranged from 0 6 mg/L to 1 0 mg/L(Table 1) Laboratory analytical results for groundwater samples collected on July 20, 2000 and historical results are summarized In Table 1 Dissolved benzene and TPH-G concentrations were not detected above reporting Iimits in any of the wells sampled Dissolved MTBE concentrations were only detected to downgradlent well ' MW-3 at 54 pg/L The other oxygenates were not reported above detection limits in any of the wells sampled during the last two quarters All gasoline constituents analyzed remained below detection limits In groundwater samples from the two upgradlent wells (MW-1 and MW-2) MTBE concentrations in f� downgradlent well MW-3 declined since the first quarter 2000 The dissolved hydrocarbon plume appears restricted to a limited area between the former underground storage tanks and MW-3 Low and non- detectable dissolved gasoline-constituent concentrations with declining dissolved oxygen levels (MW-3) Indicate that natural attenuation/biodegradation is occurring The laboratory analytical reports for the groundwater samples are Included In Attachment 4 ' Well Search ' As mentioned to the previous quarterly report, IT Corporation performed a well search using multiple sources of Information to assemble a database for wells located within one mile of the site The database for this site Indicates the nearest wells are approximately 993 feet to the north (crossgradient) of the site, ' there are two downgradient wells located approximately 4,956 feet southwest of the site ' Purge Water Transportation and Disposal All purge water generated during this quarterly monitoring and sampling event was stored to 55-gallon ' Department of Transportation (DOT)-approved drums pending characterization and proper disposal Approximately 22 gallons of purged water generated during this sampling event will be removed from the site and transported to a licensed treatment and disposal facility 2175682 rpt