2011-03-14_REVISION - M1977493 (62)

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l r? u CM0001638 Page 10 for long-term control of acid generation and metals release from sulfitic tailings and sludges. Wet storage keeps the tailings and sludges in a reducing environment, thereby inhibiting the oxidation of sulfitic components which will result in metals release. The key parameter to adopting the passive approach for Robinson Lake. reclamation is the chemical characteristics of the sludges. Data on the chemical characteristics of the sludges are not available. Therefore, a determination on whether the sludges are appropriate for wet storage cannot be made. If the sludges contain certain minerals, such as metals in oxide form, wet storage will not be appropriate because oxides are unstable in a reducing environment leading the eventual release of metals. It is recommended that sludge characterization be conducted prior to selection of a reclamation measure for Robinson Lake. The data from the sludge characterization will be used to determine the suitability of passive reclamation at Robinson Lake. 3.1.4 No. 1 Tailing Dam Seep Water fi f I" t 1 The poor quality water from the No. 1 Tailing Dam seeps may pose a risk to the reclamation of Robinson Lake. Under current conditions, the seep water discharges directly into Robinson Lake. If inferior quality seep water is not prevented from entering Robinson Lake, the beneficial effects resulting from reclamation efforts (either active or passive) could be greatly reduced. Two reclamation measures were evaluated to address the No. I Tailing Dam seeps: • Physical containment of seep water containment, and • Passive treatment of seep water. Seep Water Physical Containment Physical containment of the seep water will consist of constructing an impoundment dam and seep collection trench downgradient of the No. 1 Tailing Dam. The impoundment will not only contain the seep water but also the surface water runoff from the No. I Tailing Dam. Waters impounded by the dam would be removed via a floating barge pump. Water pumped from the impoundment will be conveyed to the Robinson Tailing Pond for use at the Climax Mine or in the milling process. The location of the impoundment is shown on Figure 3. A cross section through the impoundment and a cross section through the impoundment dam are illustrated on Figure 5. The impoundment shown on Figure 3 has a capacity of 180 acre-feet. The impoundment was sized based on the ability to contain the surface runoff for a Probable Maximum Precipitation (PMP) event. The PMP for the ERV was determined by Wheeler (1994) to be a local rain event lasting six hours producing nine inches of rainfall. The impoundment size was determined by applying the PMP over the catchment basin that reports downstream of No. I Tailing Dam. The Environmental