2012-02-28_REVISION - M1980244 (104)

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at a 95 percent confidence level, 12 -hour draindown during pump outages, 100 - year /24 -hour storm event, and available pore space of the ore within the PSSA. Operational and post closure surface water diversion systems have been designed around the perimeter of the SGVLF. During construction and operation, temporary surface water diversion channels will be constructed to route surface water flow away from disturbed areas as needed. Operational and permanent surface water diversion channels have been sized to divert upgradient surface water flows generated from the 100 -year, 24 -hour storm event. Where needed, sedimentation ponds have also been included in the design. The SGVLF design also includes consideration of post - closure drainage from the PSSA. During Phase 1 construction a closure drain will be placed beneath the PSSA sump. The closure drain will lead to boreholes drilled at least ten feet into the diatreme. Upon closure the sump liner system will be punctured to allow water that collects in the PSSA to drain into the closure drain, and eventually into the diatreme. Appendix 9, Volume V of this document, contains the design document for the SGVLF prepared by AMEC Earth & Environmental, Inc. ( "AMEC "). The following sections provide a summary of the proposed design and construction. 7.2.1 SGVLF and Underdrain System Design Components 7.2.1.1 Underdrain System An underdrain system comprised of primary, secondary, and tertiary underdrains will be constructed within the SGVLF area to intercept and convey potential shallow ground water beneath the composite liner system. Primary underdrains will collect and convey flows from the secondary underdrains. The secondary underdrains will be installed in topographic lows beneath the SGVLF area. Tertiary underdrains will be installed during construction in locations observed to exhibit seeps outside of the topographic lows. Shallow ground water flows collected in the underdrain system and captured via the underdrain cutoff wall will flow into an underdrain sump located downstream of the toe of the SGVLF. The dual compartment underdrain sump will consist of compartments sized to contain 24 hours of underdrain flow at an average flow rate of 20 gpm. The lower compartment of the underdrain sump will be fitted with a collection pump and pumpback piping to route underdrain water back to the SGVLF. The underdrain pumpback piping will extend under realigned SH 67 in two 12 -inch diameter high density polyethylene ( "HDPE ") pipes. Cripple Creek & Victor Gold Mining Company Cresson Project Mine Life Extension 2 7 -3