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COLORADO LEGACY LAND <br /> $CHWARTZWALDER MINE <br /> • The mine pool is pumped to a water treatment plant (WTP), treated, clean water is discharged to <br /> Ralston Creek,and reject brine is sent back to the mine.The WTP includes a reverse osmosis (110)and <br /> ion exchange (IX) system that remove uranium and metals from the mine pool water. <br /> • Pumping of the mine pool has consistently maintained the mine pool elevation below the regulatory <br /> limit of 150 feet (ft) below the Steve Level (regulatory limit) even during consecutive months of no <br /> pumping. <br /> o Maintaining the mine pool below the regulatory limit has led to (i) establishing a hydraulic <br /> gradient away from Ralston Creek in the permit area, and (ii) reducing the exposure of wall <br /> rock to oxygen, which minimizes uranium oxidation in the workings and translates to less <br /> mobile uranium to treat. <br /> o The regulatory limit was established as the permit level in 2012 by the Mine Land Reclamation <br /> Board.This elevation is agreed to establish a hydraulic gradient away from Ralston Creek in <br /> the permit area. <br /> • In-situ treatment of the mine pool with molasses and alcohol (carbon and nutrient sources for the <br /> indigenous population of sulfate reducing bacteria [SRB]), has shown promising results in reducing <br /> uranium concentrations to below 10 milligrams per liter (mg/L). These results indicate that in-situ <br /> treatment of the mine pool may be a viable long-term strategy in managing the mine pool. <br /> E.2. INTERCEPTION AND TREATMENT OF ALLUVIAL GROUNDWATER <br /> This section has not changed from the 2012 Mine Plan Amendment 4. <br /> E.3. ISOLATION OF RALSTON CREEK FROM SOURCES OF IMPACTS <br /> This section has not changed from the 2012 Mine Plan Amendment 4. <br /> E.4. MITIGATION PLAN FOR SOLID SOURCE TERM MATERIALS <br /> This section has not changed from the 2021 Mine Plan Amendment 5. <br /> E.5. MINE POOL MITIGATION <br /> The WTP operating strategy is considered in conjunction with in-situ treatment of the mine pool to provide <br /> physical and chemical stabilization of the mine pool. During the period in which the WTP is shut down, in-situ <br /> treatment of the mine pool shall be conducted, as necessary, to maintain chemical stabilization. A <br /> demonstration of the physical and chemical stabilization of the mine pool, including previous in-situ <br /> treatments,is discussed below. <br /> E.5.1. Physical Stabilization of the Mine Pool Demonstration <br /> Physical stabilization of the mine pool began when a 10-horsepower (hp) pump was installed in the #2 Shaft <br /> behind the Steve bulkhead. The pump was capable of dewatering the mine pool at 100 gallons per minute <br /> JUNE 2021 14 AMENDMENT 6 <br />