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ARCADIS Mr. Timothy A Cazier <br /> November 19, 2014 <br /> and sodium concentrations from the Portland plant and eight other Holcim plants in <br /> the United States from 2005 and 2006. Potassium concentrations on average <br /> ' exceed sodium concentrations by a factor of approximately 11. Sodium, potassium, <br /> and chloride are all highly leachable constituents and behave conservatively in the <br /> environment; that is, they are minimally affected by geochemical conditions in the <br /> ' receiving groundwater (for example pH, redox, cation exchange capacity). It <br /> therefore follows that concentration of these constituents in the groundwater, if <br /> leakage from the landfill was occurring, should mimic the concentrations in the CKD <br /> (thus, potassium concentrations should greatly exceed sodium concentrations). <br /> Based on several years of groundwater monitoring data from the site this is not the <br /> case While chloride is not part of the GMP, previous analyses of chloride suggest <br /> ' the same conclusion Table 3 presents some historical chloride, potassium , and <br /> sodium concentrations in MW-7 between 1998 and 2009. Chloride concentrations <br /> ranged from approximately 25 to 42 mg/L during that time period, compared to 7 to <br /> 17 mg/L for potassium in that well over the same time frame, and 112 to 236 mg/L for <br /> sodium. If these concentrations were a result of leaching from the CKD, potassium <br /> and chloride concentrations should be much higher than sodium concentrations <br /> rather than the opposite. These conclusions are illustrated with graphs of <br /> groundwater sodium concentrations versus K:Na and CI:Na values for groundwater <br /> samples (Figure 3). As shown in Figure 3, groundwater K:Na values are below 0.25 <br /> ' and Cl/Na values are below 0.3, both of which are more than an order of magnitude <br /> below the K:Na >10 and CI:Na >20 values expected for CKD and CKD leachate. <br /> ' CKD leachate testing data also suggests that the landfill is not the source of sodium <br /> in groundwater at MW-7. Table 4 is a summary of Synthetic Precipitation Leaching <br /> Procedure (SPLP) test data for CKD and alkali bypass dust generated from the <br /> ' Portland plant, from 2002 and 1999. While the data set is limited, the results of both <br /> tests show that the concentrations of sodium (158 and 159 mg/L) are less than the <br /> recent and historical concentrations of sodium in groundwater at MW-7. Based on <br /> ' these results it is not feasible that releases from the landfill could be the cause of the <br /> increasing sodium concentrations in groundwater at MW-7. Furthermore, the <br /> elevated chloride concentration in the alkali bypass dust from the SPLP test (4,600 <br /> mg/L) relative to the sodium concentration (158 mg/L) results in a CI:Na value of 29, <br /> generally consistent with the chloride to sodium ratio values greater than 20 in the <br /> CKD composition analysis results (Table 1). <br /> ' Groundwater data were evaluated further to better understand the potential cause of <br /> increasing sodium concentrations at MW-7. Figure 4 demonstrates little relation <br /> ' between sodium and sulfate concentrations for groundwater monitoring locations <br /> with the exception of MW-7, which shows a strong inverse relation between sodium <br /> and sulfate concentrations. These results suggest that water with different <br /> Page <br /> G ICOMMONIHolcuo12 5 5 1 010 5 Correspondeocelrespanse to ORMS TR 10 review of Na letter\sueker revision 20141118\2014 1119 Response to TR 10 review letter docx 3/6 <br />