2011-12-15_REVISION - M1977493 (2)

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Technical Revision (TR -18) Climax Molybdenum Company Environmental Protection Plan Permit No. M- 1977 -493 located directly below the dam, Warren's Pump Station, and the seepage collection and return system are each considered EPFs and are discussed individually. The primary purpose of Robinson Lake is to store process water, which can be routed into Robinson Lake through the Tenmile Tunnel and delivered by the Robinson Lake Pump Station back to the mill facilities. Robinson Lake also receives seepwater pumped from the Robinson Dam and 4 Dam seepwater collection systems. During periods of past active operation, process and seepage /drain waters were mixed in Robinson Lake and pumped back into the industrial process water circuit from the Robinson Pump Station below Robinson Dam. Robinson Dam and its appurtenances are under the jurisdiction of the Colorado State Engineer's Office (SEO). The dam is required by the SEO to include an overflow emergency spillway to safely pass the inflow design flood. The spillway and outlet works for Robinson Dam are in compliance with the SEO rules and regulations. In 2008, in accordance with information provided in TR -15, Climax conducted a sludge removal project in the east end of Robinson Lake to optimize the capacity of the facility for future production. Sludge and sediment removal was again conducted in 2010 and early 2011 and approximately one million cubic yards of material were removed. This work significantly reduced the amount of material that could potentially leach contaminants and is expected to result in an improvement in Robinson Lake water quality. An operating plan for Robinson Lake has been implemented to prevent impacted water from entering Eagle Park Reservoir from Robinson Lake under the following set of extreme conditions: • Surcharge storage capacity throughout the year to store, without release, the full rainfall amount of the site - specific probable maximum precipitation (PMP) event plus five days of seepwater inflow from the 1 Dam, Robinson Dam, and 4 Dam seepage collection systems, plus two days of diverted inflow from the Tenmile Tunnel; • Additional surcharge storage capacity from April 15 through June 30 which corresponds to the time frame when high snowmelt can occur, to store five days of the 100 -year snowmelt runoff from the entire Robinson Lake drainage basin including the area above the Chalk Mountain Interceptor; Specific safeguards in the plan include: • Water level indicators in Robinson Lake with automated alarms to warn of high water levels; • Frequent inspections by Climax personnel and as required by the SEO; • Compliance with SEO requirements for dam safety and inspection; • A seepwater collection system with a backup pump and generator to collect and pump embankment seepage back into the reservoir; • Piezometers for monitoring phreatic water levels in the embankment; • Toe drains for monitoring seepage; • Structural monuments for monitoring for ground movement; and • A contingency plan for implementing temporary backup pumps and power to dewater Robinson Lake if needed during an upset condition. The Robinson Lake Operating Plan is included in Appendix T -D. The management plan will be adhered to as a component of this EPP as Climax's commitment not to allow Robinson Lake to overflow. Warren's Pump System: Prior to the installation of this EPF in 1997, 1 Dam seepage would flow into Robinson Lake. This water would then be delivered to the treatment system in the Tenmile Creek basin using the now decommissioned Robinson Lake Pump Station. Warren's Pump System, including Tim's Pond and Warren's Pump Station, operates as an internal EPF to reduce the flow of impacted 1 Dam seepage into EPP: Version R2 T -21 December 2011