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ARCADiS Mr. Timothy A. Cazier <br /> November 19, 2014 <br /> ' ARCADIS Response.- <br /> As presented below, multiple lines of evidence support the conclusion that increasing <br /> concentrations of sodium in groundwater samples collected at MW-7 are not <br /> associated with leachate from the CKD landfill. <br /> We have further evaluated the effect of depth to water in monitoring well MW-7 (see <br /> Figure 1 for location) to water quality in that well by preparing concentration versus <br /> depth to groundwater graphs for sulfate and potassium, two of the other constituents <br /> analyzed as part of the Groundwater Monitoring Plan (GMP) for the site. These <br /> graphs are presented in Figure 2 along with a sodium concentration versus depth to <br /> ' groundwater graph. The graphs demonstrate that while sodium concentration <br /> increase with increasing depth to groundwater, sulfate and sodium concentrations <br /> are inversely related to depth to groundwater. The correlation between and sulfate <br /> and potassium concentrations and depth to water is not as strong when compared to <br /> sodium after 2010, as indicated by the two observed "spikes" in concentration <br /> (Figure 2), particularly for sulfate. However, for both potassium and sulfate, when <br /> depth to groundwater decreases, constituent concentrations increase All three <br /> constituents are present in the CKD (see Table 1), and potassium and sulfate are <br /> present in the CKD at much higher concentrations than sodium (see discussion <br /> below) and all three constituents are highly leachable.. It follows that if the observed <br /> increases in sodium concentrations were associated with the CKD landfill, then <br /> corresponding increases in sulfate and potassium should be observed. The <br /> ' historical data for these two constituents do not exhibit this pattern. <br /> In addition to the observed relationship between depth to water and sodium, sulfate, <br /> and potassium concentrations, there are additional lines of evidence that the <br /> increase in sodium concentrations are not related to releases from the CKD landfill. <br /> The basis for this position is that the concentrations of sodium in the groundwater <br /> should reflect its concentration in the CKD as well as its concentration relative to <br /> other constituents in the CKD We present below both compositional and leach test <br /> data from the CKD to demonstrate that sodium concentrations in groundwater at <br /> MW-7 are not attributable to leaching from CKD. <br /> CKD chemistry indicates high concentrations of potassium and chloride relative to <br /> ' sodium. Table 1 is a summary of compositional CKD analyses from the Portland <br /> plant for 2014 for sodium, potassium, and chloride. Sodium and potassium analyses <br /> are presented as oxides of these parameters. The data indicate that the average <br /> potassium concentration is greater than sodium by more than a factor of 10 (K:Na > <br /> 10). Chloride concentrations in the CKD exceed sodium concentrations in the CKD <br /> by nearly factor of 20 (Cl-.Na >20). Table 2 summarizes compositional potassium <br /> Page <br /> G IC0MMONWo1am125510105 Cormspondencelresponse to DRMS TR 10 review of Na letter\sueker revision 2014111 M2014 1119 Response to TRIO review letter docz 2/6 <br /> i <br />