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4�ED 1 <br /> I � <br /> ICanteen Facility July 10,2001 <br /> uarterly Groundwater Monitonng Report Page 4 <br />' • MTBE was detected in MW-3, MW-3A, MW-313, MW-11 and MW-13 at <br /> concentrations ranging from 4 3 µg/l to 1900 µg11 The CAMCL for MTBE is 13 <br /> I µg11, exceeded in MW-3A and MW-13 <br /> • 1,2-DCA was detected at a concentration of 8 3 µg1L in MW-11, which exceeds the <br /> CAMCL of 0 5 µg/L <br /> Historical groundwater analytical results are summarized on Table 2 Figures 3 and 4 <br /> illustrate the isoconcentration contours for benzene and TPH(g) concentrations, <br /> respectively, in the shallow aquifer wells Figures 5 and 6 illustrate the isoconcentration <br /> contours for benzene and TPH(g) concentrations, respectively, in the one deep aquifer <br /> Iwell (MW-13B) <br /> INVESTIGATION SUMMARY and CONCLUSIONS <br />' Sampling and analysis was performed in May 2001 to evaluate the current concentrations of <br /> petroleum hydrocarbons of on-Site groundwater Based on the results, AES has developed the <br /> following conclusions <br /> • Monitor wells MW-1, MW-2, MW-3A, MW-31), MW-4, MW-5, MW-6, MW-11, <br /> MW-13, MW-13A, and MW-13B had detectable concentrations exceeding the <br /> CAMCL concentrations of at least one of the following constituents benzene, <br /> Itoluene, ethylbenzene, xylenes, MTBE, and 1,2-DCA <br /> Groundwater impacts appear to be generally confined onsite, although the only <br /> detectable 1,2-DCA concentrations are centered offsite on MW-11 The majority of <br /> the groundwater impacts are centered on the MW-3 and MW-13 series wells <br /> IRECOMMENDATIONS <br /> AES recommends the following for the Canteen Facility <br /> • Continue quarterly groundwater monitoring and reporting, including measurement of <br /> depth to groundwater in each well, evaluating monitor well status, preparation of a <br /> I potentiometne surface contour map containing the calculated gradient and <br /> approximate rate of groundwater movement, and preparation of isoconcentration <br /> contour maps for benzene and TPH(g) at the two different screened aquifer depths <br /> Groundwater samples will be analyzed for BTEX by EPA method 8020, TPH(g) by <br /> EPA method 8015 modified, and TBA, MTBE, DIPE, ETBE, TAME, 1,2-DCA, and <br /> EDB by EPA method 8260B Groundwater monitoring will be performed in the <br />