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ED L.4 <br /> v <br /> ��Ir�Si <br /> I Former Canteen Facility April 14,2004 <br /> uarterl Groundwater Momtorm Report _ Pie 4 <br /> I • MTBE was detected in monitor wells MW-3, MW-3A, MW-3D, MW-11, and MW- <br /> 13 at concentrations of 78, 270, S 6, 14, and 1,900 pg/l, respectively The CAMCL <br /> for MTBE is 13 µg/l, exceeded in MW-3, MW-3A,MW-11, and MW-13 <br /> • 1,2-DCA was detected at a concentration of 96 µg/L 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 illustrate <br /> the isoconcentration contours for benzene and TPH(g) concentrations, respectively, in the <br /> shallow aquifer wells Figures 5 and 6 illustrate the concentrations for benzene and TPH(g), <br /> respectively, in the one deep aquifer well (MW-13B) The field notes and laboratory reports for <br /> Ithis quarterly monitoring event are attached as Appendix A <br /> INVESTIGATION SUMMARY and CONCLUSIONS <br /> ISampling and analysis was performed in February 2004 to evaluate the current concentrations of <br /> petroleum hydrocarbons of Site groundwater monitoring wells Based on the results, AES has <br /> Ideveloped the following conclusions <br /> • Monitor wells MW-3, MW-3A, MW-3D, MW-11, MW-13, and MW-13A had <br /> Idetectable concentrations exceeding the CAMCL concentrations of at least one of the <br /> following constituents benzene, toluene, ethylbenzene, xylenes, MTBE, and 1,2- <br /> DCA <br /> • Groundwater impacts appear to be generally confined onsite, although the only <br /> I detectable 1,2-DCA concentrations are centered offsite on monitor well MW-11 The <br /> majority of the groundwater impacts are centered on the MW-3 and MW-13 series <br /> wells <br /> IRECOMMENDATIONS <br /> AES recommends the following for the Former Canteen Facility <br /> • Continue groundwater monitoring and reporting, including measurement of depth to <br /> groundwater in each well, evaluating monitor well status, preparation of a <br /> potentiometric 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 /> • • The schedule for groundwater monitoring is as follows <br /> I <br /> I <br />