2011-08-15_REVISION - M1990057 (5)

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installation of the clay liner, a seepage /leak detection system between the clay layer and the synthetic liner with the collection system located in the northwest corner of the impoundment, and the impoundment bottom sloping at ' /2% to the northwest. Following installation of the seepage /leak detection, a synthetic pond liner of 45 -mil Polypropylene Geomembrane or equivalent will be installed as shown in Exhibit TSF -04 (See TR). The impoundment liner will be held in place with material from the ore stockpiles discussed in the ORE STOCKPILES section (see TR). Surface water diversions will be sized to convey the flow from a 25vr -24hr or 25vr -6hr storm, whichever is treater The Mill is an existing facility, with a non - discharging TSF, contained stockpile areas, and undisturbed drainage runoff areas. The Mill's undisturbed drainage areas are natural channels, unmodified by the operation. The Mill is currently in compliance with the surface water diversion channel flows, as evidenced by 20yrs of undisturbed normal flow through the area without erosion and /or head cuts. UMC will, upon reconstruction of the TSF, ensure that all disturbed area drainage reports to the TSF, that the disturbed area drainage is designed to the above referenced flows, and the calculations are submitted with the TSF requisite EPP documents. Additionally, UMC will submit a SWMP General Permit. The SWMP will be the guiding document while UMC implements the data collection phase and initiates surface water plans in accordance with the Environmental Protection Plan (EPP) of Exhibit U Construction of an earth liner in the tailings impoundment of materials with permeabilities less than or equal to 2ft per year with a minimum of 12in of suitable material should be compacted to a 95% Proctor Density UMC is reconstructing the Phase 1 TSF embankment to mitigate this issue, and achieve the permeabilities and densities as stipulated. TR permit language. The existing tailing embankment will be removed and the Phase 1 TSF embankment will be reconstructed as shown in Exhibit TSF -02 (See TR). The compacted fill embankment has a 2.5:1 (horizontal to vertical) outside face, and a 2:1 interior face. The TSF facility is designed and will be constructed in order to meet the more stringent standards of the EPP. Other Meeting Commitments UMC's contingency plan for tailings removal and replacement during construction. Construction of the Phase 1 TSF impoundment requires the removal and replacement of approximately 1,000st of historic tailings and approximately 100st of magnetite, both currently contained with the clay -lined facility. The TSF OB stockpile to the east of the existing impoundment will also be removed, incorporated into the fill construction of the lower access road to the concentrate storage, fill for the Phase 1 impoundment and suitable clay underliner material used for the Phase 1 pond bottom. Following construction of the lower access road on the south side of the mill, a portion of this road will have a 6 -8in lift of suitable clay compacted as a pad for the temporary storage (approximately 1 mo) of the historic tails and magnetite during construction of the TSF. Following pond construction, liner installation, and overliner installation, the historic tails, magnetite, and clay pad will be placed back in the Phase 1 TSF. In the event construction ceases for an extended period of time (winter shutdown) while the historic tails and magnetite are temporarily stored on the clay pad, the material will be surrounded by silt fence, bermed, and covered with visqueen for the interim construction cessation. Geomembrane liner keying into embankment. UMC is incorporating a standard liner keying system. Typically this is a trench 1.5ft wide, approximately 2 feet or more from edge of the inside slope, 2 feet M1990 -057 August 15, 2011