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30 April 2007 <br /> AGE-NC Project No. 97-0312 <br /> Page 4 of 4 <br /> at hydraulic gradients of approximately 0.007 ft/ft to 0.010 ft/ft, respectively; in the area of <br /> site wells SI-1 through Sl-3, the inferred ground water.flow direction was northeast at a <br /> hydraulic gradient of 0..017 ft/ft. Graphs illustrating trends in depth to ground water <br /> measurements and ground water elevation are included in Appendix E. <br /> • TPH-g,benzene,and 1,2-DCA were detected in the ground water sample from well MW-5 <br /> at concentrations of 190 µg/1, 17 µg/l and 1-50 µg/1,respectively. 1,2-DCA was detected in <br /> well MW-6 at a concentration of 6.2 gg/.l.Graphs illustrating concentration trends of TPH-g <br /> and T.PH-d in the wells are included in Appendix E. <br /> • The detected concentrations of benzene and '1,2-DCA in ground water samples collected <br /> during the March 2007 ground water monitoring event exceed the State of California's <br /> maximum contaminant level (MCLS) of 1.0 µg/1 and 0.5 µg/1;respectively. <br /> The reported concentrations and lateral extent of analytes of concern have remained, <br /> relatively stable during the past three years of monitoring.Based on the analytical results of <br /> the ground water samples collected $-orn wells MW-7 and MW-9, the vertical extent of <br /> petroleum hydrocarbon-impacted ground water at the site is defined. <br /> i <br /> 5.0. RECOMMENDATIONS <br /> I <br /> Based on present site conditions,AGE recommends continued monitoring of the on-site monitoring <br /> and domestic wells,but reduce the frequency of sampling in historically non-detect wells MW-2, <br /> MW-4, MW-5 and MW-8 from quarterly to semi-annually, and wells MW-3, MW-6, MW-7, <br /> MW-9,and SI-1 through SI-3 to annually.The second quarter 2007 groundwater monitoring event <br /> is scheduled to take place in June 2007. <br /> 6.0. LIMITATIONS <br /> Our professional services were performed using that degree of care and skill ordinarily exercised by <br /> environmental consultants practicing in this or similar localities. The fmdings were based mainly <br /> upon analytical results provided,by an independent laboratory. Evaluations of the hydrogeologic <br /> conditions at the site for the purpose of this investigation are made from a limited number of <br /> available data points (i.e., ground water samples), and subsurface conditions may vary away from <br /> these data points. No other warranty, expressed or implied, is made as to the professional <br /> interpretations, opinions, and recommendations contained in this report. <br /> Advanced GedEnvironmental,Inc. <br /> k <br />