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Additional Site Assessment and Soil Vapor Extraction Test,Second Quarter 2002 Groundwater Mon,tonng Data 5 7-Eleven, Inc, Store 21756,853 E Yosemite Avenue, Manteca, California August 5,2002 70 RESULTS OF GRAB GROUNDWATER SAMPLE ANALYSIS Table 2 summarizes the laboratory analytical results for the groundwater samples collected on April 1, 2002 No analytes were detected above laboratory reporting limits in any of the samples collected for analysis Copies of laboratory reports and chain-of-custody documents are Included in Appendix C ' 80 GROUNDWATER MONITORING WELL DATA ' 111 Groundwater Monitoring Data Before monitoring, the well caps were opened to allow the water in each well to stabilize to atmospheric pressure The depth to water was measured to the nearest 0 01 foot from the top of the well casing using an Interface probe A potentiometric surface map prepared using the groundwater elevation data collected from wells MW-1 through MW-4 on April 8, 2002 Is shown on Figure 2 Based on the potentlometrlc surface map, groundwater flow is generally toward the north-northwest at an approximate gradient of 0 001 foot per foot Recent groundwater elevations and historical data are summarized In Tables 1 and 1A, respectively Field data sheets are Included in Appendix B 82 Monitoring Well Sampling and Analytical Results I I ' Dissolved oxygen (DO) levels concentrations were measured, and at least 3 well-casing volumes of groundwater were removed from each monitoring well prior to sampling, 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 Groundwater samples were analyzed for BTEX and TPH-G using EPA method 8020/modified 8015, and for the oxygenates MTBE, DIPE, ETBE and TAME using EPA method 8260 Dissolved benzene and TPH-G were not detected in any of the wells Dissolved MTBE levels ranged from non-detectable (wells MW-3 and MW-4)to 2 4 ug/L (well MW-2)and 2,500 ug/L (well MWA) DO readings ranged between 1 3 milligrams per liter (mg/L) in well MWA to 2 0 mg/L in well MW-2, ' Indicating primarily anaerobic conditions ' Quarterly and historical analytical results for the groundwater samples are presented in Tables 1 and 1A, respectively The laboratory analytical reports for the groundwater samples are Included in Appendix C 1 21756SAR doc 1