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Mr Chuck Carmel 41 1 February 24, 1992 Page 2 Figure 1 also shows the water-level elevations for each well and the contours of equal water- level elevation calculated from the October 8, 1991 data Figures 2, 3, 4, and 5 are hydrographs of groundwater elevations from August 1988 to October 1991, for all monitoring wells at this site Analytical results of current groundwater samples along with previous results are summarized in Table 3 (Exhibit E) The complete laboratory report for the July 1991 sampling is presented in Exhibit F Figure 6 shows BETX and TPH-G concentrations for each well sampled In addition, Figure 6 presents an approximation (dashed lune) of the lateral extent of benzene in the groundwater As requested by the County, a compilation of previous records of purge water disposal was conducted Exhibit G contains copies of the available documentation of purge water disposal Discussion The general groundwater flow direction has not changed at this site since the last groundwater monitoring (July 1}91) Water-level elevations have decreased significantly with the most notable decreases occurring in wells near the groundwater extraction well In monitoring wells E-8, E-12, and BHD-1, BETX and TPH-G concentrations decreased PR-1 continues to record nondetectable BETX and TPH-G constituents Groundwater samples taken from wells E-10 and E-11 recorded higher ethylbenzene, xylenes, and TPH-G concentrations than the last quarterly groundwater sampling (July 1991) The TPH-G constituents detected in samples collected October 1991 from E-2, E-12, and BHD-1 were reported as weathered gasoline, by the laboratory The BETX and TPH-G concentrations have remained relatively stable since the groundwater extraction system was started in June 1991 Based on this information, two reasonable assumptions can be made--(1) the hydrocarbon-affected groundwater plume is not migrating off site, and (2) the operation of the groundwater extraction system is having a beneficial` effect on the groundwater quality at this site The slight fluctuations in the TPH-G and BETX levels may be caused by the groundwater extraction system Samples from wells E-10, E-8, and BHD-1 were analyzed for nitrate Only the sample from E-8 contained detectable concentrations The concentration of nitrate (8 2) detected in E-8 is below the Federal Maximum Contaminant Level (MCL) Groundwater samples will not be analyzed for nitrates in subsequent quarters Groundwater from these wells will be analyzed for fecal coliforrn in the first quarter of 1992 The effects of the groundwater extraction system are illustrated on the hydrographs (Figures 2, 3, 4, and 5) The groundwater elevation has dropped an average of 1 29 feet from June to October 1991 The drawdown effect of the groundwater extraction system can also be seen in the groundwater contour map (Figure 1) 569CNR RT%0Cr9[Q M R" Brown and Caldwell ConsUtwts