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CYPR~ CLIMAX METALS C~PANY NII ~~~~~~~~~~~~~~~~ <br />HENDERSON MILL <br />INTER-OFFICE MEMORANDUM <br />SUBJECT: Tailing Dam Hydrology and Operation February 28, 1994 <br />TO: Jay Jones <br />FROM: Carl Wood <br />BACKGROUND <br />This memo is intended to fulfill the request for further information on the tailings dam <br />stability and freeboard information by MLRD personnel as a result of the October 6, <br />1993 inspection. <br />FACILITY and OPERATION <br />Henderson #1 tailing dam has been constructed using typical upstream deaposition <br />methods. To the present time 100 million tons of tailings have been impounded in this <br />facility. The dam began with a base elevation of 8645 feet, and has reachf~d a crest <br />elevation of 8780.99 feet, with a final projected elevation of 8850 feet. Deposition is <br />completed using crestline spigots, in conjunction with mainline cycloning during <br />summer months to build crest, followed by extended leadoff deposition during the <br />winter to prevent formation of ice lenses. Process water is reclaimed, after tailings <br />have settled, thru a decant tower and pipeline system. <br />The process water system also contains storage reservoirs upstream of the tailings <br />impoundment. East Branch Reservoir has a capacity of 2000 acre-feet, and Ute Creek <br />with a capacity of 100 acre-feet. These reservoirs are equipped with bypa:;s ditch <br />facilities ("Upper bypass") capable of routing 80 CFS of water around the rE~servoirs <br />thereby preventing this flow from entering the process water system. <br />Process water is reclaimed and pumped continuously from the tailing dam water pool <br />to East Branch Reservoir to keep the water pool no closer than 1000 feet from the <br />dam crest, thereby providing storage volume for flood events and maximizing <br />submergence of slimes for dust control. <br />The tailings impoundment area is equipped with a flood bypass ditch ("Lower bypass") <br />to route unwanted upstream tributary runoff around the impoundment. The current <br />bypass ditch was constructed in 1990, as the original ditch has been inundated by <br />tailings deposition. The 1990 ditch was designed to bypass 120 CFS. <br />The tailings impoundment is also equipped with an emergency flood spillway system. <br />The spillway is set so that emergency spilling would occur if the tailing water pool <br />