2008-04-15_REVISION - M1980244 (351)

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The stability of the reclaimed OS A s was addressed in Section 5.7.1 of this Project Description. This analysis indicates that the reclaimed area will be stable over the long term. The final reclaimed surface of the SGOSA will be graded to conform to the runoff patterns discussed previously in Section 5.7.1. A discussion of diversion/ conveyance channels and detention basins for the final SGOSA configuration also is provided in Section 5.7.1. ECOSA As described in Section 5.7.3, a new overburden storage area, the ECOSA, will be constructed as a low-infiltration, low-permeability feature in the northeastern portion of the Cresson Mine area, north of the East Cresson Mine. The ECOSA will be constructed by end dumping in 50-foot lifts. The clay borrow area developed as a source of clay for construction will be backfilled as part of the initial lift of the ECOSA. • The ECOSA will be located along the upper southern (north-facing) slopes of Grassy Valley with portions of the stockpile lying within the Grassy Valley feeder of the volcanic diatreme. Because of the lower transmissivity of the Grassy Valley feeder and the potential that water that infiltrates through the ECOSA may recharge this feeder, CC&V has provided additional conservative environmental design features for the ECOSA. After removal of growth medium, the footprint area will be left in a roughened condition to encourage infiltration into the Grassy Valley feeder which drains toward and into the main diatreme system. As each approximate 50-foot lift is placed, the outslopes will be concurrently reclaimed. Outslopes will be graded to approximately 2.5H:1 V with drainage channels established at the back of the each bench graded to drain away from the ECOSA. Clay from the clay borrow area will be stockpiled and used to form a clay cap on the regraded outslopes of each lift and upon the final top surface of the ECOSA. An approximately two-foot layer of clay is proposed to be placed, with proof rolling to compact this layer, to create a low permeability layer to minimize infiltration through the pile. An additional one-foot of clay borrow material screened to a minus one-inch coarse fragment standard and has a plasticity index of not less than 15% will be placed and proof rolled on top of the two-foot lift. This is the same material that will be used for creation of the clay portion of the • Cripple Creek & Victor Gold Mining Company Cresson Project Mine Life Extension 11-10