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Fourth Quarter 2001 Monitoring and Sampling Report 2 7-Eleven, Inc Store No 20632,4627 Qaymci QrFve Stockton,CA December 17,2001 ' gradient of less than 0 002 foot per foot 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 m Attachment 3 1 Monitoring Well Sampling and Analytical Results ' Quarterly groundwater samples were collected after purging at least 4 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 8021 B/modified 8015, and for oxygenates MTBE, TBA, DIPE, ETRE, and TAME using EPA method 8260B ' Analytical results for the quarterly sampling event are presented in Table 1, and historical laboratory analytical results are summarized in Table 2 Highest dissolved benzene concentrations were reported in well MW-3 at 17 micrograms per liter(ug/L) Dissolved MTBE was found in wells MW-2 (6,600 ug/L) and MW-5 (76 ug/L), no detectable MTBE was found in well MW-3 Selected dissolved constituents are plotted on Figure 2 The laboratory analytical reports are included In Attachment 4 ' Prior to purging, dissolved oxygen (DO) levels were recorded in each well Dissolved oxygen levels indicate anearobic conditions (less than 1 1 milligram per liter(mg/L)) (Table 1) ' As mentioned in previous quarterly reports, a well search database for public water supply wells located within one mile of the site indicates that there are no public water supply wells located within 1 mile ' downgradient from the site ' Purgewater Disposal ' All purgewater generated during this quarterly monitoring and sampling event was stored in 55-gallon Department of Transportation (DOT)-approved drums, pending proper transport and disposal Waste disposal documentation will be forwarded once received 20632Q14 QMR DOC 1 1