Laserfiche WebLink
Executive Summary <br /> Geochemical analysis of quarterly samples (since February 2018) taken from 14 <br /> groundwater monitoring wells installed as part of ongoing Project permitting helped <br /> Telesto establish baseline groundwater quality. The 14 monitoring wells are located within <br /> the boundaries of the Project (Figure 3) and intercept groundwater flow in the shallow <br /> alluvial aquifer that extends across the Site. In addition to monitoring well data, Telesto <br /> evaluated the geology from well completion logs (Appendix ), and published data to <br /> develop a conceptual understanding of local and regional groundwater flow, groundwater <br /> quality, and geologic setting. We constructed time-series plots to evaluate geochemical <br /> trends and establish baseline conditions at monitoring points across the Site. <br /> Thermodynamic-equilibrium models summarized the mineralogy necessary to support the <br /> observed data,and subsequently predict potential changes in groundwater quality resulting <br /> from mining. Because baseline data indicate that uranium concentrations are near or <br /> slightly above drinking water standards, it became the primary groundwater constituent of <br /> concern (COC) at the Site for this analysis. We also evaluated other constituents that are <br /> present but at lower concentrations, such as selenium, for their potential change due to <br /> mining and because of public concern. <br /> The primary result of this analysis is that the northern portion of the Site has naturally <br /> elevated uranium concentrations that result from the weathering of underlying Pierre Shale, <br /> enhanced by the presence of septic introduced nitrates in the groundwater. Mining plans <br /> maintain relatively undisturbed,partially-saturated alluvial material above the Pierre Shale <br /> unit to prevent further oxidation of the Pierre Shale, and mitigate any potential release of <br /> uranium at concentrations above WQCC standards. In addition, geochemical modeling <br /> and iron couple measurements showed that the pre-mining oxidation state of the alluvial <br /> aquifer is such that that uranium is fully oxidized,and is either mobile in the aqueous phase <br /> or adsorbed to iron (oxy)hydroxides present in the weathered zone at the alluvium/Pierre <br /> Shale geologic contact. This suggests that uranium concentrations cannot increase beyond <br /> current concentrations with further introduction of oxidizing agents (e.g. exposure to the <br /> atmosphere in dewatering swales)in the alluvial aquifer. Selenium behaves geochemically <br /> Loveland Ready-Mix Concrete v December 2019 <br /> 20200 „_ ,w, besehnexstergwirt,summury do, T E L E S T O <br />