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oxidation to move from Se(4+) to Se(6+) is unlikely. The SPLP and whole rock analysis <br /> confirm the results of the geochemical analysis. The MW samples were well oxidized by <br /> being exposed to the atmosphere for nearly a year. Most samples had no detectable <br /> selenium present in the whole rock (Table 4). Table 4 shows that MW-04, -09, -11 and - <br /> 12 had selenium present in the rock,yet Table 5 shows that even after a year of weathering <br /> (in crumbled state with increased surface area over natural conditions)no selenium leached. <br /> Local alluvial fines are not a source of selenium as evidenced by the almost identical <br /> dissolved and total selenium concentrations as shown in Tables 2 and 3, respectively, for <br /> early samples when we know total samples contained sediments. Additionally,mining and <br /> water handling methods(as discussed in Section 1.0) further reduce the chance to increase <br /> waters' oxidation state. <br /> COC concentrations for the Site (i.e. uranium, sulfate, and TDS) have decreased slightly <br /> over the eight quarters of sampling. Uranium concentrations in MW-06 and MW-10 are <br /> within the range of analytical error (±25%) of the CDPHE standard and have decreased <br /> over time. Other monitoring wells have concentrations well below the standard for <br /> uranium (Table 2). Like selenium, uranium concentrations are not likely to change <br /> significantly without a major change in redox state (Table 8 and Appendix E). Unlike <br /> selenium, uranium was detected in all the rock samples from the Pierre Shale sampled at <br /> the base of the wells(Table 4). Weathering and subsequent leach tests of the solids yielded <br /> mainly non-detect leachate with the exception of MWs -02, -04, -06 and -07, all which <br /> were an order of magnitude lower than groundwater measurements. The lack of difference <br /> between dissolved and total concentrations in early samples indicates that the fine portion <br /> of the alluvium is not a source of uranium. <br /> 3.2 Sources of Uranium <br /> The source of uranium detected on site is likely from upgradient, weathered Pierre Shale. <br /> In groundwater systems, water chemistry reflects water/rock interactions, whereby solutes <br /> mostly derive from local geologic sources. As shale weathers, authigenic pyrite oxidizes, <br /> releasing ferrous iron, which quickly oxidizes to form iron oxyhydroxides, oxidizes <br /> reduced sulfur to sulfate,and organic carbon oxidizes to form bicarbonate. In addition,pH <br /> Loveland Ready-Mix Concrete 12 December 2019 <br /> 20207_kn.,v„_ba,el,ne„a,rryual,h, n do. T E L E S T O <br />