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1 <br /> Third Quarter 1999 Monitoring and Sampling Report 2 <br /> 7-Eleven Inc Store#20632 4627 Davina Drive Stockton CA October 4,19M <br /> Momtonng Well Sampling and Analytical Results <br /> 1 On August 28, 1999,groundwater samples were collected from four wells(MW-1, MW-2,MW-3 and <br /> MW-5 (well MW-4 was abandoned during UST upgrades in 1998)) Before sampling,at least 4 well <br /> casing volumes of groundwater was removed from each monitoring well unless the well was purged dry <br /> The groundwater samples were collected using disposable bailers Groundwater samples were placed in <br /> analysis-specific containers with analysis-specific preservative The samples were then sealed using <br /> Teflon septum caps, labeled with the job Identification number,the sample number, date,time, and type <br /> of laboratory analysis required The samples were stored on tee and transported under a chain-of- <br /> custody record to a state-certified laboratory Groundwater samples were analyzed for BTEX and TPH-G <br />' using Environmental Protection Agency(EPA) methods 8020/modified 8015, and for oxygenates MTBE, <br /> TBA, DIPS, ETBE, and TAME using EPA method 8260 <br />' Laboratory analytical results for groundwater samples collected on August 28, 1999 are presented in <br /> Table 1 The laboratory analytical reports for the groundwater samples are Included in Attachment 4 <br /> Historical data are included in Table 2 Dissolved benzene levels ranged up to 36 6 micrograms per Ider <br /> (pg/L), and dissolved TPH-G levels ranged up to 2,100 Ng/L Dissolved MTBE concentrations ranged up <br /> to 5,130 lig/L Highest dissolved benzene concentrations were found directly downgradient from the <br /> underground storage tank area, highest TH-G and MTBE levels were found in <br /> downgradient/crossgradient well MW-2 <br />' Observed concentrations and hydrocarbon distribution are similar to previous quarters There are no <br /> private or public municipal or domestic wells within 2,000 feet of the site <br /> Dissolved oxygen levels in the affected areas Indicate localized deplebon,through intrinsic biodegradation <br />' Purge Water Transportation and Disposal <br /> All purge water generated during this quarterly monitoring and sampling event was stored in 55-gallon <br /> Department of Transportation (DOT)-approved drums pending charactenzation and proper disposal <br /> Waste disposal documentation will be forwarded once received <br /> ' 20632g1 rpt IT CORPORATION <br /> M <br />