Laserfiche WebLink
ARCADIS <br />• Stakeholders must be kept apprised of the progress of site reclamation activities and provided <br />access to data for monitoring during each aspect of the reclamation. These data should include <br />results of the corehole, fault and fracture sealing; concentrations of COCs after alluvial fill is <br />removed; treatment performance data for the reverse osmosis (RO) system; and results of <br />bench testing, field trials, and full -scale in -situ mine pool treatment. The data used to make <br />decisions about the efficacy of reclamation phases and sequencing of activities should be <br />shared with stakeholders for review and comment. <br />3.0 INTERCEPTION AND TREATMENT OF ALLUVIAL GROUNDWATER AND ISOLATION OF <br />RALSTON CREEK <br />3.1 Continued Alluvial Groundwater Interception and Treatment <br />Overview: Continued pumping from the sumps and treatment of the water via ion exchange (IX) is <br />proposed. This is essential to the cleanup of the alluvial groundwater and to improve the creek water <br />quality. The diversion pipeline will accelerate dewatering of the alluvium and, in time, alluvial groundwater <br />recovered from the sumps would be primarily from the mine pool and will provide evidence of the degree <br />of mine pool discharge into the alluvium. <br />Data Adequacy. The EPP and Reclamation Plan include limited discussion of the IX treatment system <br />and provide no information pertaining to the handling and /or disposal of the associated IX resin <br />regeneration waste or spent resin. In addition, the Reclamation Plan does not include a discussion of the <br />duration of IX treatment of the alluvial groundwater and the performance criteria that need to be met to <br />discontinue IX treatment. Off-site disposal of the regeneration waste or spent resin is presumed; however, <br />should placement of regeneration waste in the mine pool be under consideration, additional study would <br />be essential. <br />Recommendations: No additional recommendations unless Cotter is considering placing regeneration <br />waste in the mine pool, which would require additional study. <br />3.2 Isolation of Ralston Creek from Sources of Impacts <br />Overview: Cotter has installed a cutoff wall and diversion pipeline to divert creek water around the mine <br />site. The diversion pipeline prevents upgradient groundwater and surface water from becoming impacted <br />by the mine, and dewaters the alluvium along the mine to more effectively remove contaminated materials <br />and to facilitate other remedial actions. The diversion pipeline was recommended during the EPP review <br />process as the only corrective measure to protect creek water quality in the near term, due to the strong <br />hydraulic connection between the mine pool, alluvium, and the creek. <br />Data Adequacy. The cutoff wall and diversion pipeline appear to be a viable mitigation measure to <br />minimize the potential for upgradient groundwater and surface water to become impacted as it flows past <br />Page <br />3/16 <br />