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} l Mr Chuck Carmel November 10. 1992 Page 2 because too large of an area was being influenced at a pumping rate of 14 1 gpm (rate prior to September 1991) Table 1 (Exhibit B) presents the water-level data for this site in tabular torn, and Table 2 (Exhibit C) presents historical flow direction and gradient data for this site Figure 1 also shows the water-level elevations for each well and the contours of equal water- level elevation calculated from the July 29 1992, data Analytical results of current groundwater samples along with previous results are summarized in Table 3 (Exhibit D) The complete laboratory report for the July 1992 sampling is presented in Exlubit E Figure 2 shows BETX and TPH-G concentrations for each well sampled In addntnon, Figure 2 presents an approximation (dashed lune) of the lateral extent of benzene in the groundwater Discussion The general groundwater flow direction has not changed at this site since the last groundwater monitoring (April 1992) Water-level elevations have decreased an average of 1 50 feet This decrease is most likely the result of a combination of the groundwater extraction system operation and lack of precipitation . Changes in concentration of constituents in groundwater since the last quarterly monitoring in April 1992 are summarized as follows The BETX and TPH-G concentrations decreased m monitoring wells and PR-1, PR-2, and BHD-2 continue to record nondetectable BETX and TPH-G concentrations 'Groundwater samples taken from well E-10 recorded increased benzene,ethylbenzene,xylenes :g.lj\ and TPH-G but stable toluene concentrations. The benzene concentration in the sample from :4TgE? well E-4 has increased while the other constituents have remained stable since this; well was . AA;;;Vfw last sampled (April 1992) In wells E-2, E-11, and BHD-1, the TPH-G concentration has increased. The TPH-G concentration has decreased in well E-8. The BETX and TPH-G 0; .M constituents detected in samples collected from the other wells remained relatively stable. A product recovery system was installed at this site around 1984 The system has been ® � modified a number of times since then and operated periodically from 1984 to 1990. bTjli Additional modifications were made in 1991, and the system has been operating nearly r continuously since June 1991. The BETX and TPH-G concentrations have remained relatively stable in nearly all of the wells since the groundwater extraction system was started m June 1991 Based on this information, two reasonable assumptions can be made--(1) the hydrocarbon-affected groundwater plume is not migratmg 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 m the BETX and TPH-G levels may be caused by the changes m the flow rate of the groundwater extraction system or fluctuations in water levels Brawn and Caldwell 674&REFMTSVUL82QiR.RPr Consultants