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ARCADIS <br />(US) Inc., MW -7 Redevelopment and Semi - Annual Groundwater Monitoring Summary <br />for Holcim (US) Inc. Portland Plant Quarry (ARCADIS, 2012b). Sodium and iron <br />concentrations again exceeded their NPLs by more than 10% (10.6 and 120 percent, <br />respectively). <br />However, as discussed in the above — referenced semi - annual sampling letter <br />(ARCADIS, 2012b) although sodium concentrations exceed the NPL, the potassium to <br />sodium ratio (K:Na) is a more useful diagnostic tool in determining CKD impact than <br />sodium concentrations. Generally a K:Na value of greater than 0.5 is indicative of <br />impact from CKD. Including the September 2012 results, the K:Na in MW -7 has been <br />less than 0.16 with an overall decreasing trend (see attached Figure 3), indicating that <br />there is no discernable impact from CKD. <br />3.2.2 2013 Results <br />Concentrations of metals and other constituents measured in groundwater at well MW- <br />7 were compared to the NPLs proposed in the GMP presented to the DRMS in <br />February 2009. The concentration of sodium (297 mg /L) exceeded the DRMS - <br />approved compliance standard of 226 milligrams per liter (mg /L) at well MW -7 by <br />approximately 31%. No other analytes measured at MW -7 exceeded their respective <br />NPLs. <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 previously noted, the DRMS set NPLs for MW -13 in a letter dated November 27, <br />2012. The concentration of sulfate (2300 mg /L) exceeded the DRMS- approved NPL of <br />2200 mg /L at well MW -13 by approximately 4.5 %. No other analytes measured at MW- <br />13 exceeded their respective NPLs. <br />Time series graphs of TDS, sulfate, and manganese for MW -7, MW -12, and MW -13 <br />were prepared (Figures 4, 5, and 6) to evaluate potential impacts of CKD disposal to <br />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 have remained about the same when compared <br />2013 Groundwater <br />Monitoring Report <br />Florence, Colorado <br />W] <br />