1995-08-11_REVISION - M1977493 (9)

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. highly effective since its construction and first implementation. The uppermost EPF in the Eagle River watershed is the 60 year old No. 1 Dam and Robinson tailing impoundment. Like all EPFs in the Climax Mine system, this one also has been effective in controlling the release of tailing material from the impoundment. The regrading, capping, and reclamation of this dam (Section 5.2.2) has increased its present and future effectiveness in this regard. 5.4.3 Ten Mile Creek Watershed All EPFs in the critical Ten Mile Creek watershed have been, and continue to be, extremely effective in containing and controlling contaminants and preventing contaminant release into the environment. The previously discussed fact that the primary EPFs are "in-line" from the very top of the watershed increases the effectiveness of the system. Each serves as a protective layer for the up-gradient EPF. However, it must again be emphasized that the upper Ten Mile Creek watershed has been significantly impacted by historic placer and lode mining,milling and smelting activities which peaked in the 1880s. Prior to construction of the Mayflower tailing impoundment and the interceptor systems, acidic waters and significant loads of contaminated sediments from these non-Climax historic operations entered Ten Mile Creek and were transported downstream. The most critical EPF, the Climax water treatment and discharge system which treats hugh volumes of water, has an exemplary track record. The treated discharge at Outfall 001 has met effluent limitations contained in the permit and has passed Whole Effluent Toxicity (WET) tests. Unlike other more complex and technically complicated water treatment processes, utilizing the self-contained Mayflower tailing impoundment as a large scale time precipitation system is the simplest and most effective means of treatment. Other than at the lime station (an EPF component of the water treatment and discharge system) and the pH control station, there are virtually no mechanical parts to malfunction. For example, if a problem were to occur at the lime station, the decant system on the Mayflower treatment pond can be modified to increase retention time for water which might by-pass the lime station, thus allowing time to make necessary repairs. Alternatively, water also can be routed to the other impoundments while the treatment system is serviced. In addition, the present lime treatment system at the TDH will remain functional as treatment backup. While the sulfuric acid tank is 120 percent contained within a series of sumps, a catastrophic failure of both primary and secondary containment could release acid directly to Ten Mile Creek. . Should this unlikely event occur, increased volumes of pH:10.5-11.5 water from the Mayflower impoundment pool could be released directly to the creek to neutralize excess acid. 31