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• <br />• <br />Technical Revision (TR -18) Climax Molybdenum Company <br />Environmental Protection Plan Permit No. M- 1977 -493 <br />• Surcharge storage capacity throughout the year to store, without release, the full rainfall amount <br />of the site - specific probable maximum precipitation (PMP) event plus five days of seepwater <br />inflow from the 1 Dam, Robinson Dam, and 4 Dam seepage collection systems, plus two days of <br />diverted inflow from the Tenmile Tunnel; <br />• Additional surcharge storage capacity from April 15 through June 30 which corresponds to the <br />time frame when high snowmelt can occur, to store five days of the 100 -year snowmelt runoff <br />from the entire Robinson Lake drainage basin including the area above the Chalk Mountain <br />Interceptor; <br />Specific safeguards in the plan include: <br />• Water level indicators in Robinson Lake with automated alarms to warn of high water levels; <br />• Frequent inspections by Climax personnel and as required by the SEO; <br />• Compliance with SEO requirements for dam safety and inspection; <br />• A seepwater collection system with a backup pump and generator to collect and pump <br />embankment seepage back into the reservoir; <br />• Piezometers for monitoring phreatic water levels in the embankment; <br />• Toe drains for monitoring seepage; <br />• Structural monuments for monitoring for ground movement; and <br />• A contingency plan for implementing temporary backup pumps and power to dewater Robinson <br />Lake if needed during an upset condition. <br />The Robinson Lake Operating Plan is included in Appendix T -D. The management plan will be adhered <br />to as a component of this EPP as Climax's commitment not to allow Robinson Lake to overflow. <br />Warren's Pump System: <br />Prior to the installation of this EPF in 1997, 1 Dam seepage would flow into Robinson Lake. This water <br />would then be delivered to the treatment system in the Tenmile Creek basin using the now <br />decommissioned Robinson Lake Pump Station. Warren's Pump System, including Tim's Pond and <br />Warren's Pump Station, operates as an internal EPF to reduce the flow of impacted 1 Dam seepage into <br />Robinson Lake. Tim's Pond consists of a cut -off wall and collection pond designed to capture and <br />contain 1 Dam seepage, which is then piped to Warren's Pump Station. Warren's Pump Station serves to <br />pump waters collected below 1 Dam back to the water treatment system in the Tenmile Creek basin via <br />the 2 Dam Pipeline. In a non - operating mine scenario, water that collects in Robinson Lake can be <br />pumped directly to the Warren's Pump Station pond for return to the treatment system. <br />This EPF is considered an internal EPF, since a failure or upset of this EPF does not directly result in an <br />environmental impact. Warren's Pump System is contained within the footprint of Robinson Lake, near <br />the northwest edge of the lake such that any spill or overflow from this EPF would report directly into <br />Robinson Lake, which is also an EPF as described above. <br />The floor elevation of Warren's Pump Station is at a level just above the flood level in Robinson Lake. <br />The pump station design allows for the withdrawal of the top 11 feet of water stored in Robinson Lake <br />using the Warren's pumps. This provides a backup or redundant pumping system for Robinson Lake to <br />ensure the lake maintains sufficient freeboard to prevent overflows. <br />The pump station consists of three vertical turbine pumps. With two pumps running, the discharge <br />capacity of the system ranges from 3,800 to 4,500 gpm, depending on the condition of the discharge <br />pipeline. The third pump is generally considered an installed spare, but can provide additional pumping <br />capacity if necessary. <br />Robinson Lake Seepage Pump System: The purpose of the Robinson Lake Seepage Pump System is to <br />EPP: Revision R1 <br />T -19 July 2011 <br />