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<br /> <br />G:\COMMON\Holcim\25510\05 Correspondence\response to DRMS TR 10 review of Na letter\sueker revision 20141118\2014 1119 Response to TR 10 review letter .docx <br /> <br />Mr. Timothy A. Cazier <br />November 19, 2014 <br />Page: <br />5/6 <br />3) The use of the K/Na ratio: <br />The DRMS has stated: “The 2009-2010 K:Na ratio for reported values are roughly <br />0.05, an order of magnitude less. Furthermore, if Na concentrations continue to <br />increase, while K concentrations remain essentially the same, the proposed ratio of <br />0.5 will be quite easy to achieve. Of greater concern is that both Na and K <br />concentrations could increase over time, but as long as the concentration of Na is at <br />least twice that the K, the proposed standard would be met. Significant increases in <br />either Na or K and Na should be viewed as a concern from the Division’s viewpoint. <br />A greater discussion on the K:Na chemistry as it relates to CKD and a more <br />compelling argument for the K:Na ratio needs to be provided to the Division before <br />this approach can be considered.” <br />Response: <br />While we concur that significant increases in sodium or potassium should be closely <br />monitored, the discussion provided in this letter has demonstrated that increases in <br />sodium are not related to releases from CKD. If they were, a correspondingly greater <br />increase in potassium concentration should be observed. This is clearly not the <br />case. As shown in Figure 3, K:Na values for all site groundwater samples were less <br />than 0.25 and most were less than 0.15; well below the K:Na value of greater than 10 <br />for CKD. When sodium concentrations increased in groundwater at MW -7, the K:Na <br />value decreased substantially, demonstrating a behavior that is the opposite of what <br />would be expected from contributions of CKD leachate. <br />We believe that we have provided a convincing argument that the ratio of potassium <br />and sodium is a useful indicator of CKD impacts. ARCADIS has successfully used <br />K:Na ratios in other states, particularly Michigan to assess impacts to groundwater <br />from CKD waste areas. A K:Na ratio threshold of 0.5 is a reasonable, and we <br />believe conservative indicator of groundwater impact from CKD leaching. <br />If the Division has additional questions or concerns about the suggested monitoring <br />approach, we would suggest that a meeting be convened to further discuss this <br />issue. Please let us know a convenient meeting time. <br />Furthermore , we propose to complete an additional round of groundwater <br />monitoring at the site in December In addition to the current list of parameters <br />included in the GMP, we will analyze groundwater samples for chloride. <br />