1995-08-11_REVISION - M1977493 (9)

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• Ten Mile Tailing Impoundment and Dam: The Ten Mile tailing impoundment including the dam p g (No. 3 Dam) encompasses approximately 644 acres and is located adjacent to and just downstream of the Robinson impoundment. The Ten Mile impoundment was constructed in the 1960s. Presently, the Ten Mile impoundment is the only active tailing deposition area at Climax. The Ten Mile impoundment contains tailing material which, as discussed previously, is considered potentially acid producing. Briefly, mill tailing in slurry form (approximately 28 % solids) is delivered to No. 3 Dam crest at the impoundment by the ETDL. Process water is separated from the tailing material through settling action and reclaimed for recycling to the mill process circuit. Clarified water is removed from the impoundment through a decant system at the Ten Mile Tunnel (to the Robinson Reservoir or Mayflower tailing impoundment as discussed in Section 5.2.1) and by pumping from the Ten Mile Barge station. A water pool is maintained at the upstream end of the Ten Mile impoundment for process water storage. As with all tailing impoundments, the Ten Mile tailing impoundment is considered both a source of potential contamination and an EPF. The integrity of the impoundment and No. 3 Dam assures in-situ containment of the tailing material. The Ten Mile impoundment also is the second-line control for any potential contaminants which might be released from upgradient sources. In addition, there are several historic mines and mine disturbances which are contained within or by the Ten Mile impoundment (the Robinson Mine and Mill, Wheel of Fortune, etc.). Prior to construction of the Mayflower tailing impoundment downstream of the Ten Mile impoundment, acidic seepage from the toe of No. 3 Dam was contained and pumped back to the impoundment. However, when the Mayflower impoundment was constructed in the mid-1970s, seepage was allowed to flow directly into the Mayflower impoundment. Mayflower Tailing Impoundment and Dam: The last tailing impoundment downstream in the Ten Mile Creek watershed is the Mayflower impoundment. This impoundment and its dam (No. 5 Dam) encompass 366 acres and represents both the final disturbance and final control on Ten Mile Creek within the Climax property boundary. The Mayflower tailing impoundment was constructed in the late 1970s utilizing modern engineering technology. It was utilized for tailing deposition through the mid-1980s. Although the impoundment has significant unused storage capacity which could (and may) be exploited in the future, it was converted to a water treatment system in the late 1980s. In the early 1990s, the beach areas of the impoundment and No. 5 Dam were capped with aggregate and soil material excavated from the eastern edge of the impoundment. These sites were seeded. The water pool area is maintained and continues to be used for treatment of all mine waters requiring discharge. 26