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April 2014 12 10381640A <br />alkalinity and lowest dissolved calcium, magnesium and sulfate concentrations of the Site wells (Appendix <br />D). The MW -3 samples have pH values ranging from 8.2 to 8.9, and remain consistent with values observed <br />prior to CKD material placement in disposal area A2. <br />The majority of dissolved trace metal concentrations in samples collected from MW -3 are in the range of the <br />other Site wells. From September 2010 to present only four of the 16 constituents have exceeded <br />established benchmark concentrations, including: <br />• Barium — The concentration of barium exceeded the established benchmark <br />concentration of 2.0 mg /L during all 13 the monitoring events since 2010 with a maximum <br />concentration of 2.95 mg /L. <br />• Boron — The concentration of boron exceeded the established benchmark concentration <br />of 0.75 mg /L in 11 of the 13 the samples collected from September 2010 to present with <br />a maximum concentration of 0.85 mg /L. <br />• Iron — The concentration of iron exceeded the established benchmark concentration of <br />0.30 mg /L during the June 2012 sampling event with a concentration of 0.32 mg /L. The <br />remaining 12 samples collected from MW -3 have not demonstrated concentrations of iron <br />in exceedance of the established benchmark concentration. <br />• Chloride — The concentration of chloride exceeded the established benchmark <br />concentration of 1,620 mg /L for three monitoring events, with a maximum concentration <br />of 1,721 mg /L. The remaining 10 samples collected from MW -3 have not demonstrated <br />concentrations of chloride in exceedance of the established benchmark concentration. <br />4.1.4 Monitoring Well MW -4 <br />Monitoring well MW -4 is located hydraulically side - gradient of CKD disposal area A2 (Figure 1). <br />Groundwater samples collected from MW -4 are predominantly sodium - chloride type waters (Figure 4). The <br />samples exhibit similar major ion concentrations to well MW -6 and MW -7, and have the highest chloride and <br />sodium concentrations of the Site wells. The TDS concentrations for well MW-4 are greater than those of <br />the other Site wells (Appendix D). The MW -4 samples have pH values ranging from 7.6 to 8.2 remaining <br />consistent with values observed prior to CKD material placement in disposal area A2. <br />During the April 1999 and July 2000 monitoring period used to determine the benchmark concentrations <br />for MW -4, a number of constituent concentrations were not stable. The concentrations of barium, chloride <br />and TDS increased over this period and the concentrations of manganese and sulfate decreased over <br />this period. These trending concentrations indicate that the well was likely not in equilibrium with the <br />surrounding formation and that its benchmark chemistry may not reflect groundwater conditions prior to <br />drilling. These trends may be the result of disturbance to the system created by drilling and well <br />installation. Therefore, the benchmark concentrations for barium, chloride and TDS may be artificially low <br />and the benchmark concentrations for manganese and sulfate may be artificially high. <br />Golder <br />is \10 \81t340a\ 0400\ gwcharwellinstallfieltlrep _fnl- 30apr14 \10381640a gwchampt _holcim- bcet[cher_fnl- 28apr14- with holcim edits.docx <br />Associates <br />