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Former Canteen Facility October 15, 2003 <br /> Quarterly Groundwater Monitoring Re ort Pa e 4 <br /> • MTBE was detected in MW-3, MW-3A, MW-3D, and MW-11 at concentrations of <br /> 130, 400, 20, and 36 µg/l, respectively The CAMCL for MTBE is 13 µg/l, <br /> exceeded in MW-3, MW-3A,MW-3D, and MW-11 <br /> • 1,2-DCA was detected at a concentration of 110 ltg/L in MW-11,which exceeds the <br /> CAMCL of 0 5 pg/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 /> this quarterly monitoring event are attached as Appendix A <br /> INVESTIGATION SUMMARY and CONCLUSIONS <br /> Sampling and analysis was performed in August 2003 to evaluate the current concentrations of <br /> petroleum hydrocarbons of Site groundwater monitoring wells Based on the results, AES-RS <br /> has developed the following conclusions <br /> • Monitor wells MW-3, MW-3A, MW-3D, and MW-11 had detectable concentrations <br /> exceeding the CAMCL concentrations of at least one of the following constituents <br /> benzene, toluene, 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 monitor well MW-11 The <br /> majority of the groundwater impacts are centered on the MW-3 and MW-13 series <br /> wells <br /> RECOMMENDATIONS <br /> AES-RS 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 /> • <br /> ,v1001 <br /> U <br />