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decreases due to the hydrolysis of water during the pyrite oxidation,which dissolves calcite, <br /> releasing calcium to solution. The presence of gypsum(as calcium and sulfate),alkalinity, <br /> and iron oxyhydroxides identifies shale weathering. Oxyanions, such as uranium mobilize <br /> under oxidizing conditions,which will sorb to positive surfaces such as organic carbon and <br /> iron oxides. Further oxidation of organic carbon releases uranium to solution, whose <br /> concentrations in groundwater is then controlled by sorption/desorption dynamics <br /> associated with iron oxides, ternary uranyl-calcium-carbonato complex formation, and <br /> precipitation of uranium minerals(thermodynamically favored under reducing conditions). <br /> Using gypsum as a marker for weathered shale, bi-plots of water chemistry show that <br /> calcium and sulfate strongly correlate in all monitoring wells at the Site (Figure 13). <br /> Conversely, calcium and alkalinity, composed mostly of bicarbonate, are not as well <br /> correlated in groundwater (Figure 13), showing that groundwater chemistry is generally <br /> controlled by gypsum and,to a lesser extent, calcite solubility. We can infer,based on the <br /> strong correlation between sulfate and uranium concentrations (Figure 13),that weathered <br /> shale is the primary source of concentrated uranium in groundwater at the Site. Monitoring <br /> wells in the northern portion of the Site(e.g.MW-06, MW-08, MW-09,and MW-10)have <br /> elevated uranium,calcium,and sulfate that can be attributed to gypsum dissolution,which, <br /> in turn, is related to shale weathering. Geologic logs collected during drilling show that <br /> these monitoring wells had a weathered shale cap below the alluvium and above the Pierre <br /> Shale, with significant amount of iron oxyhydroxides and clay. Leach tests of cuttings <br /> show quantifiable uranium concentrations in MW-06 and MW-07, but were lower than the <br /> detection limit for all other monitoring wells, indicating minute uranium mineral <br /> dissolution and insignificant uranyl desorption from iron (oxy)hydroxides. Naturally <br /> elevated uranium concentrations in monitoring wells are likely due to elevated nitrate <br /> concentrations associated with local agricultural activities, resulting in both uranium and <br /> organic matter oxidation(i.e. from microbially mediated dissimilatory nitrate reduction)as <br /> well as the formation of uranyl—calcium—carbonato complexes,thereby stabilizing aqueous <br /> uranium concentrations. <br /> Loveland Ready-Mix Concrete 13 December 2019 <br /> 20200407_1nucpitbasthne,atcryuzllmsummary doc., T E L E S T O <br />