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Mr Daniel K Barber,P E <br /> ' September 9, 2003 <br /> Page 12 of 17 <br /> (LLNL, 1996), diesel contamination in groundwater likely does not extend offsite more than <br /> 200 feet <br /> ' Inferred Groundwater Migrational Pathway <br /> Groundwater flow direction over the course of the nine groundwater monitoring events are <br /> generally northward, with an approximately 40-degree variation in computed flow direction, <br /> from north-northwest to north-northeast Measured groundwater elevations in the monitoring <br /> wells range from approximately 6 to 9 feet above mean sea level, with seasonal variation of <br /> approximately 2 5 feet over the five quarters of monitoring between June 2002 and June 2003 <br /> The computer hydraulic gradient is relatively flat <br /> Hydrochemical Trends/Plume Stability <br /> For most of the site wells, five quarters of groundwater sampling data was analyzed Well <br /> MW-1 included an additional two quarters of groundwater sampling data because it was <br /> installed earlier Wells MW-2, MW-3, MW-4, MW-5, and MW-6 were installed in June <br /> 2002 <br /> Figure 6 shows the hydrocheanical trend from seven sampling events at the "source" well <br /> MW-1, which has consistently shown the highest residual concentrations--ranging from a <br /> high of 2 38 to 12 mg/L In the last five monitoring events, from June 2002 to June 2003,the <br /> plume has shown relative stability, ranging from 12 to 1 6 mg/L <br /> ' Figure 7 shows the hydrochemical trend from the five sampling events at wells MW-2, <br /> MW-3, MW-4, MW-5, and MW-6 Concentrations in these wells ranged from 0 05 to 0 71 <br /> mg/L Well MW-2 had the least stable trend, while wells MW-4 and MW-4 showed the most <br /> stable tend line Wells MW-3 and MW-5 showed a relatively stable concentration pattern <br /> Water levels measured during the groundwater events suggest some influence on dissolved <br /> phase TPH Generally, when the water levels were higher, the dissolved TPHd was slightly <br /> higher However, there are exceptions to this correlation Appendix contains a plot of the <br /> water levels for all five wells between June 2002 and June 2003 <br /> GROUNDWATER IMPACTS AND BENEFICIAL USES <br /> In general, impacts of contamination on the environment by hydrocarbon contaminants are <br /> evaluated on a case-by-case basis by the regulators, with consideration given to drinking <br /> water standards when appropriate Because no shallow water-bearing zone or aquifer in this <br /> Stellar Environmental Solutions <br /> ' 2 PRolECISV 003,I:W a holed1003-K�KMMladi C]eunReP°N wl�f'^+•REPIRTSeP�mber 91003 dar <br />