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• <br />Robinson Lake Operating Plan Climax Molybdenum Company <br />Version: R1 Permit M -1977 -493 <br />approximate natural ground surface. The other two dam crest piezometers are perched so that <br />they only extend part way down into the embankment. The perched piezometers were installed <br />in 2008 to monitor for unusual seepage conditions in the upper portion of the dam. The two <br />additional piezometers are located along the downstream toe of the embankment. Climax <br />personnel routinely monitor the piezometers and maintain a database of phreatic water levels. <br />A foundation drain system is located on the right downstream abutment of the dam. The flow <br />rate from the drain is monitored regularly by Climax personnel and recorded during the SEO's <br />Dam Safety Engineer's inspections. A small collection pond near the toe of the dam also <br />collects dam seepage. This system is monitored regularly by Climax personnel; however, this <br />system also collects some surface runoff and shallow subsurface flows from the area to the left <br />of the dam 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 <br />collection pond and pumping system to return seepwater back to Robinson Lake. The collection <br />pond was excavated on the upstream side of a concrete - bedrock cutoff wall and has a total <br />storage capacity of 400,000 gallons. The pumping system consists of two 30- horsepower <br />submersible pumps that are installed in a vertical wet well. The pumping capacity is <br />approximately 480 gpm with one pump running and about 750 gpm with both pumps running in <br />parallel. Inflows to the system are such that only one pump is required to operate on an <br />intermittent basis, with the second pump serving as an installed backup. Water level readings <br />from a level probe in the wet well control the on /off operation of the pumps. A backup <br />generator, which is located in the Robinson Lake Pump Station, provides backup power to the <br />seepwater system in the event of a power failure. This system is monitored regularly by Climax <br />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 <br />Robinson Lake. The system discharges into the west side of the lake near the left upstream <br />abutment of Robinson Dam. The volume of this seepage is typically minimal (approximately 20 <br />gpm) except for a brief period when the snow is melting off the face of Eagle Park Dam. Water <br />level readings from a level probe control the on /off operation of the pumps. A backup generator <br />provides backup power to the 4 Dam seepwater system in the event of a power failure. This <br />system is monitored 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 <br />upset, 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 <br />August2011 5 <br />