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Fourth Quarter 2002 Monitoring and Sampling Report 3 7-Eleven, Inc Store No 20632,4627 DaVinci Drive, Stockton, CA December 17, 2002 Monitoring Well Sampling and Analytical Results Quarterly groundwater samples were collected after purging at least four well-casing volumes of groundwater from each monitoring well, unless the well was purged dry Prior to purging, dissolved oxygen (DO) levels were recorded in each well Groundwater samples were collected using disposable bailers Samples were placed In analysis-specific containers with analysis-specific preservative 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 stored on Ice and transported with a chain-of-custody record to a state-certified laboratory for analysis Groundwater samples were analyzed for BTEX and TPH-G using Environmental Protection Agency (EPA) methods 8021BImodified 8015, and for oxygenates MTBE, TBA, DI PE, ETBE, and TAME using EPA method 82608 Dissolved benzene was detected In MW-4R at 49 ug/L and MW-5 at 11 ug/L Dissolved MTBE was detected in all wells at concentrations ranging from 1 4 ug1L In well MW-6 to 31,000 ug/L In well MW-7 Ratios of MTBE to TBA in wells MW-2 and MW-4R possibly indicate ongoing (anaerobic) intrinsic biodegradation MTBE hydrolysis or other analytical biases which might result in TBA detections (not related to biodegradation) are not indicated, as only wells MW-2 and MW-4R have high TBA relative to MTBE, well MW-7 has high MTBE and no detectable TBA Quarterly and historical analytical results for groundwater samples are summarized in Tables 1 and 1A, respectively (Attachment 2) Laboratory analytical reports are Included in Attachment 4 DO levels ranged from 0 9 milligrams per liter(mg/L) In well MW-3 to 1 4 mg/L In the MW-4R, Indicating anaerobic (less than 2 0 mg/L) conditions Additional lateral plume delineation planned for 2003 is pending access to the property (2628 W March Lane, parcel number 110-020-08)to the west of 7-Eleven#20632 The property is owned by Ms Jean Good Lietzau, who has approved access to Shaw for drilling purposes A workplan to Install one additional groundwater monitoring well on said property and downgradient of the impacted MW-7 will be submitted during 2003 Purgewater Transportation and Disposal All purgewater generated during this quarterly monitoring and sampling event was stored onsite in 55-gallon Department of Transportation (DOT)-approved drums, pending characterization and proper disposal at a licensed recycling facility Waste disposal documentation will be forwarded if requested Conclusion and Recommendations In addition to continued quarterly monitoring and sampling, further delineation of the dissolved MTBE plume Is recommended to proceed pending workplan and permit approval during 2003 Submittal of recommendations for remedial action will follow this anticipated additional site assessment 20632Q24 QMR DOC