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Mr. Blair, P.E. <br />February 1 1, 2004 <br />Page 6 <br />These releases are not allowed under the NPDES permit for the mine, except under <br />emergency conditions. To address these environmental concerns prior to cleanup of <br />the reservoir, Climax installed blind flanges over the 24-inch diameter and 12-inch <br />diameter reservoir outlets. Attached is a copy of Drawing 661-34 that notes the <br />installation of the blind flanges. The plan is for these blind flanges to remain until <br />either the reservoir is cleaned, or the existing deteriorated valves are replaced. <br />These flanges were installed a few days after the inspection of the outlet works, <br />and the isolated cofferdam pond was allowed to fill with water to match the water <br />level in the reservoir. Installation of the flanges was discussed during the inspection <br />and you had indicated that some interim "safe storage level", or informal restriction <br />would be necessary until the flanges are removed. <br />Water Level Restriction <br />Robinson Dam is a Hazard Class 1 structure and as such, requires a functioning <br />outlet in accordance with the Rules and Regulations for Dam Safety and Dam <br />Construction. We discussed that the temporary water level restriction be based on <br />the level in the reservoir that would not result in failure of Eagle Park Dam in the <br />event of a clear day failure of Robinson Dam. This would reduce the hazard <br />classification of Robinson Dam to something less than Class I. Your dam break <br />analysis indicated that the storage level in Robinson Lake that, upon failure, would <br />not cause a failure of Eagle Park Reservoir was elevation 10,846 feet. <br />The most recent flood hydrology study for Robinson Reservoir was performed in <br />1994 as part of the Eagle Park Reservoir study. Using the values in that analysis, <br />the volume of the inflow design flood for Robinson Lake would be about 354 acre- <br />feet. This is based on a 6.75-inch storm event in the 629-acre drainage basin, <br />assuming no precipitation loss. At a water level of 10,846 in Robinson Reservoir, <br />the reservoir could completely contain four consecutive design floods with the <br />water level not reaching the emergency spillway. This indicates that the 10,846 <br />