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Status Report Robinson Seep Investigation <br />2.2 Robinson Lake Water Levels <br />Climax Molybdenum Company <br />In anticipation of the restart of active mining and mineral processing operations at the Climax <br />Mine, a multi -year program to remove accumulated sediment from Robinson Lake to increase <br />the storage capacity of the reservoir was completed in early 2011. Since approximately 2000 to <br />2011, water levels within the reservoir had been maintained at a reduced stage height; typically <br />below an elevation of 10,850 feet. In April 2011, Climax began a controlled fill of Robinson Lake <br />raising the stage height from approximately 10,830 feet to 10,875 feet by July 2011. The water <br />level in the reservoir has since been maintained below the upper operating limit of 10,885 feet. <br />Figure 2.6 presents graphs of Robinson Lake water levels over two time periods; 2011 through <br />2013, and 1994 through 2013. A foundation drain system is located on the right (east) <br />downstream abutment of the dam (the toe drain outlet is represented by sampling location EVS- <br />007, illustrated on Figure 3.1). Flow rates from the outlet of this toe drain are monitored <br />periodically. Flow measurements show that the flow rate from the toe drain increased as <br />Robinson Lake was filled, from less than 10 gallons per minute (gpm) in June 2011 to <br />approximately 20 gpm during the summer of 2012, indicating increased seepage from Robinson <br />Lake. <br />Tetra Tech, Inc. November 2013 19 <br />