2018-08-22_REVISION - M1977493A - Laserfiche WebLink

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Technical Revision (TR-28) Climax Molybdenum Company Environmental Protection Plan Permit No. M-1977-493 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. An operating plan for Robinson Lake has been implemented to prevent process 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 151h through June 301h, 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 former 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 Robinson Lake. Tim's Pond consists of a cut-off wall and collection pond designed to capture and contain 1 Dam seepage, which is then piped to Warren's Pump Station. Warren's Pump Station serves to pump waters collected below 1 Dam back to the water treatment system in the Tenmile Creek basin via the 2 Dam Pipeline. In a non- operating mine scenario, water that collects in Robinson Lake can be pumped directly to the Warren's Pump Station pond for return to the treatment system. This EPF is considered an internal EPF, since a failure or upset of this EPF does not directly result in an environmental impact. Warren's Pump System is contained within the footprint of Robinson Lake, near the northwest edge of the lake such that any spill or overflow from this EPF would report directly into EPP: Version R4 T-22 August 2018