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V2 ARCADIS Mr. Timothy A. Cazier <br /> November 19, 2014 <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 /> ' Page <br /> G\COMMOMHol-125510M Correspondencelrssponse to DRMS TR 10 rev—of Na letter\sueker revision 20141118\2014 1119 Response to TR 10 review letter docx 5/6 <br />