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Environmental Protection Plan, Schwartzwalder Mine 15 -1 <br />15. MITIGATION OPTIONS AND CONSTRUCTION SCHEDULE <br />Rule 6.4.21(15) requires that the EPP provide a detailed construction schedule for (1) all facilities designed <br />to contain or transport toxic materials, acid - forming materials, or designated chemicals used in the <br />extractive metallurgical process and (2) all facilities proposed to contain, hold, or for disposal of, material <br />that has the potential to cause acid mine drainage. The Schwartzwalder Mine is not operating and no new <br />facilities are planned for mining activities, mine operations, or extractive metallurgical processes (with the <br />exception of water treatment for remediation of alluvial groundwater). However, facilities will be <br />constructed for the short-term mitigation action to protect water quality in Ralston Creek while a long -term <br />sustainable solution is developed to mitigate water quality impacts to Ralston Creek. <br />Numerous mitigation alternatives have been considered, and several have been implemented, toward the <br />over - arching goal of protecting water quality in Ralston Creek. The considered alternatives were <br />summarized in a letter from DRMS dated October 21, 2009 and were listed in the July 31, 2010, EPP. <br />Based on the evaluation of alternatives and preliminary engineering feasibility studies, Cotter has identified <br />several actions to protect water quality in Ralston Creek. The preferred actions include the following: <br />1. Pumping and treating ground water in the alluvium. This ongoing short-term action began in July <br />2010, and is described in Section 15(c). <br />2. Isolating the creek from the alluvium by collecting water in the creek above the site and conveying <br />it across the site in an engineered pipeline. This short-term action is described in Section 15(d). <br />3. Installing cut -off walls in the alluvium at the upgradient (west) boundary to prevent inflow of <br />groundwater into the alluvium. The collected ground water would be diverted into the same pipe <br />as the Ralston Creek water, and conveyed across the site. The proposed cutoff walls are associated <br />with the stream diversion pipeline and are described in Section 15(d)(i) and 15(d)(iii). <br />4. Investigation and identification of sources of uranium loading within the valley. With the creek <br />isolated, the alluvium and fill will be temporarily dewatered making investigation, identification, <br />removal, isolation, sealing, or other mitigative measures more feasible. These potential source <br />removal actions are described in Section 15(e). <br />5. Additional ground water monitoring, trenching, and other investigative tools will be utilized to aid <br />in the full understanding of the site and the development of the long -term solution. <br />6. Plugging and abandonment of any coreholes or structures that can be identified as conduits for <br />groundwater. The identification of these features will be facilitated by temporary dewatering of the <br />alluvium and fill. <br />7. Initiation of in -situ mine pool water treatment. <br />(a) Description of Constituents of Concern and Potential Sources <br />As described in Section Section 9(b)(ii), uranium is the primary constituent of concern (COC) in Ralston <br />Creek. Uranium concentrations in Ralston Creek, alluvial groundwater, and the mine pool have changed <br />over time as a result of seasonal effects, leakage from the J -10 corehole (now plugged), mitigation <br />activities, and geochemical processes. The imprint of these temporal effects on uranium concentrations in <br />groundwater and surface water is quite complex. Simply stated, however, uranium concentrations in the <br />first four months of 2011 averaged 0.32 mg/L in Ralston Creek, 2.7 mg/L in alluvial groundwater near <br />Sump 1 and MW9, and 29 mg/L in the mine pool. Concentrations of other metals in Ralston Creek and <br />alluvial groundwater are generally below analytical detection limits, with the exception of molybdenum <br />and zinc. Molybdenum in Ralston Creek in the first quarter of 2011 ranged from 0.011 mg/L to 0.016 <br />mg/L at station SW -BPL which are low concentrations, while zinc concentrations ( <0.005 mg/L to 0.013 <br />/mg/L) were also well below the water quality standard of 5 mg/L zinc. <br />4109C.110510 Whetstone Associates • <br />