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Second Quarter 2002 Monitoring and Sampling Report 4 7-Eleven, Inc Store No 97334 4501 North Pershing Avenue Stockton CA July 29, 2002 ' A potentiometric surface map prepared using the quarterly groundwater elevation data is shown on Attachment 1, Figure 2 Based on the groundwater elevation data, groundwater flow is toward the 1 northeast at an approximate gradient of about 0 004 foot per foot, consistent with historic measurements Groundwater monitoring results for the quarter and historical monitoring results are presented in Tables 1 and 2, respectively (Attachment 2) Field data sheets are included in Attachment 3 Monitoring Well Sampling and Analytical Results Prior to purging, dissolved oxygen (DO) levels were recorded in each well 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 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 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, DIPE, ETBE, and TAME using EPA method 82808 Dissolved benzene concentrations were detected at 2,200 pg/L in well MW-5A Dissolved MTBE concentrations were highest in well MW-4 (1,900 pg/L) Well MW-5A contained 1,500 pg/L MTBE, while in well MW-5B, MTBE was not detected Quarterly and historical analytical results for the groundwater samples are presented in Table 1 and 1A, respectively (Attachment 2) The laboratory analytical reports ' are included in Attachment 4 Dissolved oxygen levels ranged from 0 8 milligrams per liter(mg/L) in wells MW-2, MW-3, MW-5A, and MW-5B, to 1 0 mg/L in well MW-4, indicating generally anaerobic conditions Purgewater Disposal Allur ewater generated during this quarterly monitoring and sampling event was stored in 55-gallon p 9 Department of Transportation (DOT)-approved drums, pending proper transport and disposal at a licensed ' recycling facility Waste disposal documentation will be forwarded If requested 1 17334Q22 QMR DOC