2012-02-28_REVISION - M1980244 (80)

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MLE2 storm water plan for Upper Grassy Valley includes three new methods to avoid the need for regenerative releases. a. All but the Terminal EMP ponds in Upper Grassy Valley will be fitted, or retrofitted, with 6 -inch diameter perforated pipe outlets rather them merely an emergency spillway. By that addition, the water accumulations down to the top of the sediment will be gradually released to and through the channels and will flow to the final, or Terminal, EMP structure, EMP -17. The SEDCAD computations show that six 1 -inch perforations per row on 12 -inch vertical centers will result in the non - terminal ponds draining in about two days. EMP17 is a former pond associated with the Cameron Mine, which will be reconstructed to a size (19.7 acre feet) that can accept and store excess storm water from all upstream EMPs. Two fore -bay ponds upstream of EMP17 will first receive the runoff from upstream channels and have been sized to settle all but fine silt and clay. The outlets from the fore -bay ponds will be 12 -inch pipe, selected such that the outflow to the main EMP -17 pond will yield a area /discharge ratio of 500 square feet per cfs. By that design, the two fore -bay ponds can be easily cleaned on a routine schedule while the accumulations in the main pond will be minor and may never require cleaning. b. The receiving channel from all non - terminal structures in Upper Grassy Valley (fitted with perforated outlets as described above) will be augmented with growth media placed within the riprap and seeded to provide a vegetative filter. The vegetative filter will remove colloidal clay and fine silt that pass through the perforated outlets, such that the water quality in the Terminal EMP -17 should be very good. c. Finally, those accumulations in Terminal EMP -17 can either be released to Grassy Creek in accordance with the Storm water Permit, or can be withdrawn and used for dust - control and construction water. 4. STORM WATER MANAGEMENT PLAN FOR THE WEST SIDE OF THE MINE, INCLUDING NORTH CRESSON AND POVERTY GULCH The proposed arrangement of storm water management facilities during operations is illustrated on Drawing Sheets 5 and 6. Sheet 5 shows the proposed configurations of the west side of the mine (Poverty Gulch) in its current condition (Details 1 and 5), during the progression of mining through (Details 6 thru 12) and after reclamation (Detail 13). Sheet 5 also includes a schematic showing the storm water flow and design dimensions for the channels and ponds. Sheet 6 provides details of the EMP Ponds, channel profiles, and general specifications for construction of the ponds. Storm water management on the west side of the mine, above the Town of Cripple Creek, provides special challenges to ensure that facilities are effective, that they are aesthetically acceptable, that they will conform to the dynamic nature of mine progression, Client: CC &V Gold Mining Co. Title: Storm Water Management, MLE2 2/2/12 Page 11