2012-02-28_REVISION - M1980244 (73)

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OVERVIEW AREQUA GULCH OVERBURDEN STORAGE AREA DRAINAGE PLAN MARCH 1997 The Cripple Creek & Victor Gold Mining Company ( "CC &V ") has developed a revised surface -water drainage plan for the area of the Cresson Project that is occupied by the Arequa Gulch Overburden Storage Area. The area is located on the east side of the new Highway 67 embankment, and is upgradient of the Cresson Project's Valley Leach Facility. This revision of drainage controls is necessary to allow for the removal of a temporary diversion ditch that bounds the southeast side of the current footprint of the overburden storage area. The revisions modify the existing surface -water drainage control to accommodate construction of the approved overburden storage area. The modifications are shown as they will most likely evolve over time to achieve the post - reclamation drainage. CC &V has, to describe the evolution, divided the time period from late 1996 through to the present to "buildout" into increments and prepared a runoff analysis applicable to the end of each period. The principles of the surface water drainage control are to divert drainage from undisturbed areas away from those areas that are undergoing disturbance, to trap water and allow solids to settle, to release water from these detention areas in a manner designed to minimize downstream erosion, and to facilitate reclamation of the lands to achieve a stable form through grading and revegetation. The ultimate goal of the drainage plan is to provide for a post - mining drainage system that supports the post- mining land uses and which is self- maintaining. Given the fact that the Arequa Gulch Overburden Stockpile will fill the existing valley, the relatively small undisturbed drainage area above the Stockpile will be directed along a channel that traverses edge of the overburden stockpile rather than around and under the site as currently occurs. In all cases during construction, all runoff, regardless of whether it crosses disturbed or undisturbed lands, will be caught in a series of detention basins that have adequate capacity to retain the runoff from the 10 -year, 24 -hour precipitation event. This Arequa Gulch drainage plan encompasses the area of the Cresson Project between the Cresson Mine and the new State Highway 67 road embankment, which embankment also delineates the east - northeast extent of the Cresson Valley Leach Facility. Other approved drainage controls located upgradient and downgradient of this Stockpile will continue to serve both the Cresson Mine and the Valley Leach Facility, both of which are outside this Arequa Gulch Overburden storage area drainage. These other controls remain as approved in MLRB Permit M -80 -244 and the general storm -water runoff permit for CC &V's properties. They are not affected by the drainage design and controls addressed here. The Arequa Gulch overburden storage area is comprised of oxide mineralized rock of a grade less than the economic cutoff for gold ore and the surrounding "barren" oxide rock, both of which are termed "overburden." The current surface - water drainage system was constructed to divert as much water from undisturbed areas as possible around the disturbed areas during the first years of operations. Now (early 1997) the overburden is encroaching on that drainage system and it is necessary to adjust the drainage controls. This adjustment was anticipated to be required when the Project was designed, but was not designed in detail at that time because of the uncertainty of the topography that would be formed. As noted above, this revised drainage plan has been designed to show its temporal change to adapt to changing topography that reflects the evolution of the overburden storage area from now to completion. Currently, surface -water diversion of runoff from areas upgradient of the oxide 1