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ARCADIS <br />Tracer Testing <br />Overview: The Reclamation Plan includes an assessment of the °mine pool end state" through evaluation <br />of the fate and transport of tracer compounds added during the mine pool treatment process. <br />Data Adequacy: Initiating a recirculation circuit is unlikely to result in complete mixing due to the <br />complexity of mine pool hydraulics and potential chemical and density stratification, which would impact <br />the success of in -situ treatment due to inadequate mixing. A recirculation tracer study should be <br />conducted prior to pumping the mine pool or initiating in -situ treatment to provide a better understanding of <br />mixing within the mine pool. This study should be configured to provide a better understanding of the <br />hydraulics, residence time, and mixing of like- and different - density fluids (via a two -stage test). The tracer <br />testing will also provide additional information about the connectivity between the mine pool and the <br />alluvium /creek, and can help identify conduits for flow from the mine pool to the alluvium. <br />Recommendations: Conduct a recirculation tracer study prior to pumping the mine pool or initiating in- <br />situ treatment. <br />Bench -Scale and Pilot -Scale Testing <br />Overview: The Reclamation Plan states that, "bench scale tests are not being proposed because several <br />independent experts in uranium reduction technologies for groundwater remediation and Alexco have <br />concluded that bench tests cannot be relied upon to demonstrate effectiveness or adverse effects." In <br />addition, the Reclamation Plan includes a series of seven actions associated with the in -situ mine pool <br />treatment, with the primary objective being to reduce the current uranium concentrations in the mine pool <br />by approximately 90 percent (to 2.9 mg/L): <br />• Action 1: Obtain authorization to inject and recirculate treatment reagents. <br />• Action 2: Install a mine pool water recirculation loop. <br />• Action 3: Conduct small -scale molasses injections over a 2 -week period to determine the <br />optimal rate of injections. <br />• Action 4: Increase molasses injections with alcohol over a 5-week period. <br />• Action 5: Intermittently increase the rate of molasses addition to facilitate treatment deeper in <br />the mine pool. <br />• Action 6: Manage the redox conditions by controlling the ratio of alcohols to organic carbon. <br />• Action 7: Demonstrate geochemical stability via uranium analyses. <br />Data Adequacy: The proposed treatment is based upon establishing suitable geochemical conditions in <br />the mine pool so that dissolved uranium transitions to a low- solubility (precipitated) form. This process is <br />well documented in the technical literature, and the appropriate conditions can often be achieved through <br />the addition of organic carbon. Naturally occurring microorganisms consume dissolved oxygen in <br />Page <br />11/16 <br />