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1 <br /> l <br /> Control Board regarding monitor well sampling, neither well was purged According to Mr Patton, <br /> a recent study has shown no significant difference in hydrocarbon concentrations in samples - <br />' collected before and after purging, suggesting that purgining may be unnecessary in some instances <br /> The laboratory report and chain-of-custody form are included in Appendix B <br /> 1 <br />' 5.2 Depth to Groundwater <br /> The normal seasonal rise in the water table continued during the quarter (Table 1) The elevation of <br /> the water table was one foot higher than on the previous monitoring date in March <br /> 5.3 Groundwater Gradient and Flow Direction <br /> As in most previous quarters,,groundwater flow is generally to the east, but somewhat more to the' <br /> north than normal The prominent trough remains beneath the Apache building(Figure 6) <br /> 5.4 Groundwater Contamination <br /> As in the previous quarter, BTEX compounds remained below detection limits in MW-5 However, <br /> TPH-g reached its highest concentration since May of 1996, when it reached its maximum of 340 <br /> ppb (Table 2) It is not known whether the increase is real or whether it is due to not purging before <br />' sampling <br /> As expected, gasoline and BTEX were detected in VE-1 "deep", but concentrations were less than <br /> half their values in March No clear pattern in contaminant concentrations is evident in the four <br /> samples that have been collected from this well since February'1996 <br /> 6.0 CONCLUSIONS <br />' As discussed in the First Quarter 1997 report, long-term trends in the concentration of hydrocarbon <br /> vapors being withdrawn from the extraction wells indicate that the vapor extraction system has <br />' been successful in lowering the concentration of gasoline liquids in the soil,'although part of the <br /> decline is probably due to a rise in the water table, reducing the air flow through the deep zone <br /> Data collected since March indicate that the decline has continued <br />' Trends in the concentrations of hydrocarbons in groundwater are less clear Fortunately, <br /> concentrations are generally low, and do not pose a significant health threat <br /> 5 <br /> r <br />