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2018 GROUNDWATER MONITORING REPORT <br />arcadis.com 7 <br />discernible impact from the CKD disposal area. The K:Na ratios have stabilized or are declining <br />in the last few years. <br /> Total Dissolved Solids: TDS concentrations in MW-7 are generally decreasing through time <br />(Figure 4). The concentrations of TDS and sulfate are generally stable in MW-12 and MW-13. All <br />TDS concentrations remain below their respective NPLs. <br /> Sulfate: Sulfate concentrations show a similar trend as TDS (Figure 5). MW-7 concentrations are <br />generally decreasing through time and are generally stable in MW-12 and MW-13. All <br />concentrations remain below their respective NPLs. <br /> Manganese: Manganese concentrations in MW-7, MW-12, and MW-13 have decreased over <br />time and have stabilized in the last 3 to 5 years (Figure 6). Manganese concentrations remain <br />well below the respective NPLs at MW-7 and MW-13. <br /> Total Iron: Total iron concentrations have exhibited considerable fluctuations at all three wells <br />since monitoring for this parameter began in 2003 (Figure 7). Concentrations in MW-7 have <br />decreased in the last two years and was less than 10% above the DRMS issued NPL in 2018. <br />Because total iron concentrations are strongly correlated to the amount of suspended solids <br />contained in a groundwater sample, it is not surprising to observe these fluctuations in <br />concentrations as small differences in how a sample was collected could impact the suspended <br />solids concentration in that sample. <br /> Dissolved Iron: Dissolved iron has stabilized at all three wells (Figure 8) and concentrations in <br />MW-13 have remained below the DRMS issued NPL since 2009. <br /> The concentrations of analytes found in monitoring well MW-12, which is considered the <br />background well, from the March 2018 sampling event (Table 2 and Figures 3, 4, 5, 6, and 8) <br />remain generally higher than the wells installed downgradient of the CKD. As previously <br />mentioned, the total iron concentrations (Figure 7) have been relatively unstable in all three wells <br />over the years, though the average concentration is highest at MW-12. <br /> <br />