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2010 Groundwater <br />. <br />ARCADIS Monitoring Report <br />Florence, Colorado <br />annual to semi-annual in this well. Sodium was the only parameter that exceeded its <br />compliance standard. Furthermore, the sodium concentration of 228 mg/L is only 1% <br />greater than the compliance value of 226 mg/L. Therefore, the sampling frequency for <br />this well can remain annual. <br />Holcim anticipates that the DRMS will set compliance parameters and standards for <br />MW-12 (background well) and MW-13 (compliance well). <br />Time series graphs of TDS, sulfate and manganese for MW-7, MW-12 and MW-13 <br />were prepared (Figures 3, 4 and 5) to evaluate potential impacts of CKD disposal to <br />the groundwater. In addition, the potassium sodium ratio (K:Na) was plotted for these <br />same wells (Figure 6). The K:Na is a useful diagnostic tool in determining CKD impact. <br />Generally a K:Na value of greater than 0.5 is indicative of impact from CKD. The <br />graphs indicate that TDS and sulfate concentrations in MW-7 are continuing to <br />decrease through time. TDS and sulfate concentrations in MW-12 have decreased <br />when compared to the previous year's concentrations. The graphs also indicate that <br />TDS and sulfate concentrations at MW-13 appear to be stable or decreasing. In <br />general, manganese concentrations in MW-7 and MW-12 have continued to decrease <br />since 2000; concentrations at MW-13 have been generally decreasing since <br />installation in April 2009. The concentrations found in monitoring well MW-12, which is <br />considered the background well, from the March 2010 sampling event (Table 2 and <br />Figures 3, 4 and 5) are as high as or higher than the wells installed downgradient of the <br />CKD. Furthermore, the K:Na in all monitoring wells was generally less than 0.15, <br />indicating that there is no discernable impact from CKD. <br />• <br />G.NCOMMOM25510110 Final Reports and PresentationsWarch 2010\TeAHolam March 2010 Final GW Montoring.d- 8