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COLORADO LEGACY LAND <br /> SCHWARTZWALDER MINE <br /> 2013 to a minimum of approximately 2 mg/L,an approximate 90% reduction in concentration. There was a <br /> rebound in dissolved uranium concentrations in 2014,which subsequently decreased again after the injections <br /> of MicroC®and molasses in 2015.The dissolved uranium concentrations again rebounded to a maximum of <br /> approximately 40 mg/L before the second in-situ treatment in 2017 followed by a decrease to a minimum of <br /> approximately 4 mg/L, an approximate 90% reduction in concentration. The decreasing uranium <br /> concentrations indicate that a biochemically reducing environment is being achieved to form some insoluble <br /> uranium species that precipitate out of the mine pool. <br /> Also shown on Figure E-6 are the TDS concentrations. Except for the noted period of suspect data, the TDS <br /> concentrations have been generally stable.This stability supports the viability of the RO technology treatment <br /> system,which is discussed in Section E.5.2.4. <br /> As shown on Figure E-7, dissolved molybdenum concentrations indicate a consistent pattern of several <br /> quarters of decreasing concentrations with the in-situ treatments followed by an increase in concentrations. <br /> The dissolved molybdenum concentrations decreased from approximately 1.5 mg/L before the first in-situ <br /> treatment in 2013 to a minimum of approximately 0.04 mg/L,an approximate 97%reduction in concentration. <br /> There was a rebound in dissolved molybdenum concentrations in 2014, which decreased again after the <br /> injections of MicroC®and molasses in 2015.The dissolved molybdenum concentrations again rebounded to a <br /> maximum of approximately 6 mg/L before the second in-situ treatment in 2017 followed by a decrease to a <br /> minimum of approximately 0.05 mg/L,an approximate 99%reduction in concentration,after which dissolved <br /> molybdenum concentrations started increasing. The decreasing dissolved molybdenum concentrations is <br /> another indication of a reducing environment. <br /> As shown on Figure E-7,the molybdenum concentrations increased in 2018 following the in-situ treatment in <br /> 2017, decreased after the in-situ treatment in 2020, and started to increase until the last sampling event in <br /> September 2020. The pattern of increasing and decreasing molybdenum concentrations with in-situ <br /> treatments is consistent. As shown on Figure E-6, there was not a significant decrease in uranium <br /> concentrations after the 2020 in-situ treatment as was seen in the previous in-situ treatments.There may be <br /> several factors for the absence of the significant decrease,but whatever the cause was for this limited uranium <br /> reduction is speculative at this time.What is known is that the removal of alluvial waste rock was occurring in <br /> this time period,with the open hole being filled by this rock material.It is possible that this caused a temporary <br /> increase in mine uranium concentrations as uranium containing waste rock materials that had been oxidizing <br /> on surface were placed back into the mine workings,and some of them may have fallen into the mine pool and <br /> contributed to temporary leaching of uranium. In any case, the mine pool was maintained in a reducing <br /> condition as a result of this treatment and while uranium concentrations were not reduced as a result of the <br /> in-situ treatment in 2020,the molybdenum concentrations were reduced. <br /> A red circle is shown on Figures E-6 and E-7 for data points that had a high degree of variability in the months <br /> preceding the 2017 in-situ treatment. These data are suspect because in the nearly 10 years of other data <br /> shown on these figures,uranium concentrations have not exceeded 25 mg/L and molybdenum concentrations <br /> have not exceeded 2 mg/L,with the possible exception of one sampling event in November 2017.This is also <br /> during the period that Cotter had new staff on site,and CLL believes that a consistent labeling of samples from <br /> the mine may not have been performed. The nomenclature used for the Site included the term "mine refill' <br /> which was originally used by Cotter to refer to mine pool samples removed by operating the pump in the mine <br /> to sample the mine pool as it filled. When the permanent WTP plant RO operations started in 2017, it is <br /> plausible to think that"mine refill'was taken from the RO concentrate that was being reinjected into the mine <br /> by the new plant.The sudden increase and decrease in uranium and molybdenum concentrations during this <br /> AUGUST2022 25 AMENDMENT <br />