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 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 Robinson Lake, which is also an EPF as described above. The floor elevation of Warren's Pump Station is at a level just above the flood level in Robinson Lake. The pump station design allows for the withdrawal of the top 11 feet of water stored in Robinson Lake using the Warren's pumps. This provides a backup or redundant pumping system for Robinson Lake to ensure the lake maintains sufficient freeboard to prevent overflows. The pump station consists of three vertical turbine pumps. With two pumps running, the discharge capacity of the system ranges from 3,800 to 4,500 gpm, depending on the condition of the discharge pipeline. The third pump is generally considered an installed spare, but can provide additional pumping capacity if necessary. Robinson Lake Seepage Pump System: The purpose of the Robinson Lake Seepage Pump System is to contain and collect impacted seepage from the downstream toe of Robinson Dam and convey this water back into Robinson Lake. This EPF became necessary when Eagle Park Reservoir was converted to a clean water reservoir in 1997. This EPF was constructed in 1997 and significant modifications were made in 2001. The system has been in continuous operation since 1997. The primary means of containment consists of a concrete cut -off wall below the Robinson Dam outlet area that is keyed into bedrock on the bottom and sides. A collection pond located on the upstream side of the cutoff wall provides detention storage and emergency storage capacity in the system. The collection pond provides an operational capacity of approximately 400,000 gallons. Captured seepage and runoff from the downstream face of Robinson Dam is pumped back into Robinson Lake. This cutoff and containment component restricts groundwater seepage from entering Eagle Park Reservoir. The Robinson Lake Seepage Pump System includes a pump station that houses two submersible pumps that each have a capacity of approximately 480 gpm operating individually and approximately 750 gpm operating in parallel. The second pump functions primarily as an installed spare. The operation of the pumps is automatic based on the water level in the collection pond. There are two discharge pipelines, one operating and one backup, that convey the water from the pump station to Robinson Lake. The pumping system is electrically powered. Additional backup systems include a diesel generator installed at the site that can be activated in the event of a sustained loss of power. There are also diesel powered pumps on site that can be used in an upset condition to pump water from the collection pond into Robinson Lake. The system also includes instrumentation and telemetry that will activate alarms at the mill facilities in the event of a high water level in the collection pond. The system is inspected by Climax personnel daily. Typical seepage rates from Robinson Dam are in the range of 20 to 50 gpm, which is much less than the pumping capacity of the system. This is the normal inflow rate to the system. However, since the system collects surface runoff from the small tributary basin above the cutoff wall, the design capacity of the system is controlled by hydrologic events such as rainfall or snowmelt. The hydrologic design basis of this system is the 100 -year 24 -hour precipitation event or the 100 -year snowmelt event occurring within the basin that is tributary to the seepage collection system. 4 Dam Seepage Collection and Pump System: The lowermost EPF downgradient of Climax facilities that protects the East Fork of the Eagle River beyond and below the Climax property boundary is the 4 Dam Seepage Collection and Pump System. This EPF is located just below the Eagle Park Dam (a.k.a. 4 Dam) and consists of a seepwater collection pond and two pumps in the adjoining enclosed pump house to retum seepage to the upstream Robinson Lake. Located directly below the pump -house is a second, EPP: Version R2 T -22 December 2011