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Robinson Lake Operating Plan Climax Molybdenum Company <br />Version R1 Permit M-1977-493 <br />additional piezometers are located along the downstream toe of the embankment. Climax <br />personnel routinely monitor the piezometers, typically on a monthly basis, and maintain a <br />database of phreatic water levels. These data are typically reported to the SEO on an annual <br />basis. At this time, the SEO has not set trigger levels for the phreatic surface montoring in <br />Robinson Dam. <br />A foundation drain system is located on the right downstream abutment of the dam. The flow rate <br />from the drain is monitored regularly by Climax personnel and recorded during the SEO's Dam <br />Safety Engineer's inspections. A small collection pond near the toe of the dam also collects dam <br />seepage. This system is monitored regularly by Climax personnel; however, this system also <br />collects some surface runoff and shallow subsurface flows from the area to the left of the dam <br />embankment. <br />Six structural monuments are located along the crest of the dam for monitoring for ground <br />movement. These monuments are surveyed once per year, or more frequently if requested by <br />the SEO, to monitor for indications of settlement, sliding, or dam instability. <br />6.4 Robinson Lake Seepage Pump System <br />The Robinson Lake Seepage Pump System lies below Robinson Dam and consists of a collection <br />pond and pumping system to return seepwater back to Robinson Lake. The collection pond was <br />excavated on the upstream side of a concrete -bedrock cutoff wall and has a total storage capacity <br />of 400,000 gallons. The pumping system consists of two 30 -horsepower submersible pumps that <br />are installed in a vertical wet well. The pumping capacity is approximately 480 gpm with one <br />pump running and about 750 gpm with both pumps running in parallel. Inflows to the system are <br />such that only one pump is required to operate on an intermittent basis, with the second pump <br />serving as an installed backup. Water level readings from a level probe in the wet well control <br />the on/off operation of the pumps. A backup generator, which is located in the Robinson Lake <br />Pump Station, provides backup power to the seepwater system in the event of a power failure. <br />This system is monitored regularly by Climax personnel. <br />6.5 4 Dam Seepage Collection and Pump System <br />Seepage flow from the toe of 4 Dam (aka Eagle Park Dam) is collected and pumped to Robinson <br />Lake. The system discharges into the west side of the lake near the left upstream abutment of <br />Robinson Dam. The volume of this seepage is typically minimal (approximately 20 gpm) except <br />for a brief period when the snow is melting off the face of Eagle Park Dam. Water level readings <br />from a level probe control the on/off operation of the pumps. A backup generator provides backup <br />power to the 4 Dam seepwater system in the event of a power failure. This system is monitored <br />regularly by Climax personnel. <br />7.0 CONTINGENCY PLAN <br />Climax has imposed several mechanisms to maintain the water level in Robinson Lake in <br />accordance with this operating plan and to prevent an overflow through the emergency spillway <br />into Eagle Park Reservoir. During an upset condition such as a major storm event or facility upset, <br />Climax personnel will implement the following actions as needed: <br />• Close the bulkhead valves inside the Tenmile Tunnel. This will reduce the inflow to <br />Robinson Lake to only the uncontrolled natural inflows from snowmelt or storm events. <br />EPP — Appendix D December 2011 <br />