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r <br /> 1961 <br /> i, <br /> Mr. Chuck Carmel <br /> February 24, 1992 <br /> Page 2 <br /> r 'I <br /> Figure l also shows the water-level elevations for each well and the contours of equal water- <br /> level elevation calculated from the October 8, 1991 data. Figures 2, 3, 4, and 5 are <br /> hydrographs of groundwater elevations from August 1938;o October 1991,for all monitoring i <br /> wells at this site. <br /> •fF! <br /> Analytical results of current groundwater samples along with previous results are summarized <br /> in 'fable 3 (Exhibit E). The complete laboratory report for the July I991 sampling is I <br /> presented in Exhibit F. Figure 6 shows BETX and Tl'H-G concentrations for each well <br /> sampled. In addition, Figure 6 presents an approximation(dashed line) of the lateral extent { <br /> f <br /> of benzene in the groundwater. <br /> s � <br /> As requested by the County, a compilation of previous records of purge water disposal was { <br /> conducted. Exhibit G contains copies of the available documentation of purge water disposal. , <br /> Discussion <br /> The general groundwater flow direction has not changed at this site since the Jast groundwater <br /> monitoring (July. 1991). Water-level elevatiers have decreased significantly with the most <br /> =lotable decreases occurring in wells near the groundwater extraction well. } <br /> In monitoring wells E-8, E-12, azd BHD-1, BETX and TPH-G concentrations decreased, f <br /> PR-I continues to record nondetectable BETX and TPH-G constituents. Groundwater samples ' E. <br /> taken from wells E-10 and E-11 recorded higher ethylbenzene, xylenes, and TPH-G } <br /> concentrations than the Iast quarterly groundwater sampling (July';1991). The TPH-G <br /> constituents detected in samples collected October 199I from E-2, E-12, and BHD-1 were <br /> reported as weathered gasoline; by the Iaboratory. <br /> The BETX and TPH-G concentrations have remained relatively stable since the groundwater s } <br /> extraction system was started in June 1991. Based on this information, two reasonable , <br /> assumptions can be made--(I)the hydrocarbon-affected <br /> groundwater plume is not migrating. <br /> off site, and (2) the operation of the groundwater extraction system.is having a ben=eficial <br /> effect on the groundwater quality at this site. The slight fluctuations in the TPH-G and BETX <br /> levels may be caused by the groundwater extraction system. <br /> J <br /> Samples from wells E-10, E-8, and BHD-I were analyzed for nitrate. Only the sample from <br /> E-8 contained detectable concentrations. The concentration of nitrate (8.2) detected in E-8 <br /> is below the Federal Maximum Contaminant Level (MCL). Groundwater samples will not <br /> be analyzed for nitrates in subsequent quarters. Groundwater from these wells will be <br /> catalyzed for fecal coliform in the first quarter of 1992. <br /> 'i <br /> The effects of the groundwater extraction system .are illustrated on the hydrographs (Figures <br /> 2, 3,4,and 5). The groundwater elevation has dropped an average of 1.29 feet from June to <br /> October 1991. The drawdown effect of the groundwater extraction system can also be seen ! <br /> in the groundwater contour map (Figure 1), <br /> 1 . <br /> ;I <br /> Brawn anti Caldwell 569MMRT.T%( T91Q1R.RPr I�' <br /> (.ansUrtints <br /> �s <br /> � tt. <br /> 3 <br /> f <br /> r <br />