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COLORADO LEGACY LAND <br /> SCHWARTZWALDER MINE <br /> The main takeaway from Table E-3 is the significant decrease in the concentrations of total and dissolved <br /> uranium and molybdenum, approximately 60% to 70%. For example, the mean concentrations of total and <br /> dissolved uranium decreased from 34.37 mg/L and 41.14 mg/L, respectively, to 13 mg/L and 12 mg/L, <br /> respectively. The mean concentrations of total and dissolved molybdenum decreased from 1.39 mg/L and <br /> 1.85 mg/L, respectively, to 0.60 mg/L and 0.58 mg/L, respectively. Therefore, the overall decrease in <br /> constituent concentrations further demonstrate that chemical stabilization of the mine pool has been achieved <br /> for the last three plus consecutive years. <br /> E.5.2.4. Chemical Stabilization Functional Definition <br /> Since physical stabilization of the mine was achieved and is being maintained by RO technology, it is relevant <br /> to define what is meant functionally by "chemical stabilization", not just on a constituent-by-constituent <br /> evaluation,as performed in the prior section,but also from a bulk chemistry perspective.As shown in the prior <br /> table,the mean total dissolved solids (TDS) concentrations have remained unchanged or slightly decreased in <br /> the last 4 years compared to the mine refill period (2,850 mg/L vs. 2,917 mg/L) and remains in a "brackish" <br /> water TDS range.This is important because RO technology effectiveness relies on bulk rejection of dissolved <br /> constituents,and the mine pool water chemistry as measured by this bulk parameter has not changed at all as <br /> a result of this combined seasonal RO treatment and occasional in-situ treatment. If the TDS concentrations <br /> had appreciably changed, some concern might be validated that a loss of treatment capacity of this core <br /> treatment technology, which forms the basis of the financial assurance, could be projected. However, as no <br /> increase of TDS concentrations has resulted,the RO technology appears to remain viable as long as it can be <br /> projected by this data set,and no trend of loss of use or efficiency of RO can be projected from this data. <br /> What this indicates is that for the foreseeable future, RO technology can continue to create high quality, low <br /> dissolved solids discharge water that will continue to keep the mine pool dewatered and the Site in compliance <br /> with its discharge permit. (In fact, RO is commonly used in desalination plants to treat water with more than <br /> 10 times the concentration of TDS shown above without the loss of the treatment capacity.)When considered <br /> on this basis,the mine pool is chemically stable such that RO can be used to efficiently dewater the mine on a <br /> seasonal basis,and thus is definitionally demonstrated to be chemically stable. <br /> E5.2.5. Physical and Chemical Stabilization Conclusion <br /> It is important to note that the regulatory limit of dewatering the mine pool to 150 ft below the Steve level was <br /> specifically chosen by the DRMS to(i) re-establish a hydraulic gradient away from Ralston Creek in the permit <br /> area, and (ii) reduce the exposure of wall rock to oxygen in order to minimize uranium oxidation in the <br /> workings (MLRB, 2012). The hydraulic gradient away from Ralston Creek means there is no connection <br /> between the mine workings and Ralston Creek,i.e.,uranium concentrations and other analytes in the mine pool <br /> are not adversely affecting Ralston Creek.As discussed above,physical stability of the mine pool over the last <br /> three consecutive years has been demonstrated and physical stability will continue for the following reasons: <br /> • The mine pool elevations over the past nearly 4 consecutive years shown on Figure E-3 are below the <br /> regulatory limit.The noted'exception'on the chart during the winter of 2019 had been verified to be <br /> AUGUST 2022 32 AMENDMENT 6 <br />