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5.0 GROUNDWATER MONITORING <br /> ' 5.1 Monitoring Procedures <br /> ' Groundwater was monitored and sampled on September 18, 1997 After the wells were opened;the <br /> depth to groundwater was measured with a Solmst water level meter The results are shown on the <br /> Well Monitor Report(Appendix C) and in Table 1 <br /> ' After the depth to groundwater was measured, the wells were purged of 10-15 gallons of water <br /> using a Grundfos submersible pump, and the purged water was stored in 55-gallon drums near the <br /> ' vapor extraction unit The wells were allowed to recharge for approximately 60 minutes, and then <br /> disposable plastic bailers were used to collect samples from each monitoring well and from VE-1 <br /> "deep" Three 40-m1 sample vials were collected from each well and were delivered to Sequoia <br /> ' Analytical in Sacramento The laboratory report and chain-of-custody form are included in <br /> Appendix B <br /> ' 5.2 Depth to Groundwater <br /> The normal seasonal fall in the water table started during the quarter(Table 1) The elevation of the <br /> ' water table was three feet lower than on the previous monitoring date in June <br /> 5.3 Groundwater Gradient and Flow Direction <br /> As in most previous quarters, groundwater flow is generally to the east, but with a prominent cast- <br /> trending trough beneath the Apache building (Figure 6) <br /> 5.4 Groundwater Contamination <br /> At the request of Mr Ron Rowe of PHS/EHD, groundwater samples were analyzed for the <br /> presence of gasoline oxygenates in addition to gasoline and BTEX Although water samples had <br /> ' been analyzed for MTBE on two previous occasions, this is the first time that all seven samples <br /> have been analyzed for other oxygenates The results are shown in Appendix B an j in Tables 2 and <br /> 3 <br /> ' As in all previous quarters, gasoline and BTEX were detected in VE-1 "deep" and in MW-5 <br /> Concentrations were 20-50% below their values in June, except for the BTEX compounds in MW- <br /> 5, which were not detected in June In the Second Quarter Report'we noted that no clear pattern in <br /> contaminant concentrations was evident in the four samples that had been collected from MW-5 <br /> since February 1996, this statement remains true <br /> ' No contaminants were detected in MW-4 confirmingour earlier su estion that the detection of <br /> gg <br /> BTEX in this well in the second quarter was a false positive caused by sampling or laboratory error <br /> 5 <br /> 1 <br /> 1 - <br />