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2014 Groundwater <br /> Monitoring Report <br /> ARCADIS <br /> Florence,Colorado <br /> In addition to MW-7, groundwater monitoring wells MW-12 (upgradient well) and MW- <br /> 13 (compliance well) were sampled as part of the annual groundwater monitoring <br /> program. Analytical results are presented in Table 2. <br /> As discussed in section 1.3.4 of this report, the DRMS set NPLs for MW-13 in a letter <br /> dated November 27, 2012. All analytes measured at MW-13 were below their <br /> respective NPLs. <br /> Time series graphs of the potassium to sodium ratio, TDS, sulfate, and manganese for <br /> MW-7, MW-12, and MW-13 were prepared (Figures 3, 4, 5, and 6, respectively) to <br /> evaluate potential impacts of CKD disposal to the groundwater. <br /> In general, the graphs indicate that manganese concentrations in MW-7, MW-12, and <br /> MW-13 have continued to decrease over time. The graphs also indicate that TDS and <br /> sulfate concentrations in MW-7 are generally decreasing through time. TDS <br /> concentrations in MW-12 and MW-13 appear to be stable to slightly decreasing. The <br /> graphs show that sulfate concentrations in MW-12 and MW-13 are generally stable. <br /> The concentrations of analytes found in monitoring well MW-12, which is considered <br /> the background well,from the March 2014 sampling event(Table 2 and Figures 4, 5, <br /> and 6) remain higher than the wells installed downgradient of the CKD. <br /> Sodium concentrations in downgradient monitoring well MW-7 continue to exceed the <br /> NPL for this parameter and are generally slightly increasing over time (see historical <br /> groundwater data tables in Appendix E). The cause of the slightly increasing sodium <br /> concentration is not known, but this trend is not caused by the CKD landfill. As <br /> previously discussed in a letter to Holcim (US) Inc., MW-7 Redevelopment and Semi- <br /> Annual Groundwater Monitoring Summary for Holcim (US) Inc. Portland Plant Quarry <br /> (ARCADIS, 2012), the potassium to sodium ratio (K:Na) is a more useful diagnostic <br /> tool in determining CKD impact than sodium concentrations. In general, a K:Na value <br /> of greater than 0.5 is indicative of impact from CKD. As shown on Figure 3, the K:Na in <br /> all monitoring wells continues to be generally less than 0.10, indicating that there is no <br /> discernible impact from CKD. <br /> Based on March 2014 sampling results that indicate there is no discernible impact from <br /> CKD, and the fact that the concentrations of only one parameter (sodium) exceeds its <br /> NPL, ARCADIS recommends that annual groundwater monitoring continue unless <br /> future results require an increased monitoring frequency. <br /> 9 <br />