2008-01-16_PERMIT FILE - C1994082A (4)

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Based on SCC experience at the other mining areas, pit dewatering will be primarily a seasonal occurrence. The dewatering process will be a sporadic operation-controlled, occurrence depending on various factors which may include the location of the pit inflows, the location of standing water in the pit, or the location within the pit of the overburden and coal removal operations. Also, prior to initiating dewatering activities, the receiving pond level will be checked such that the designed performance of the pond will not be compromised. When pit dewatering is required, the anticipated dewatering rate will be in the range of one to two cubic feet per second or less. Any dewatering discharges will be directed to a pond. The discharge from the pit dewatering will be controlled, as necessary, with an adequate energy dissipator (i.e., rock riprap, geotextiles, metal or concrete energy dissipator boxes, etc.) or discharged onto non-erodible bedrock material. This pit dewatering will have an insignificant impact on the proposed ponds. The pit dewatering will be sporadic versus continuous. The flow rate of one to two cubic feet per second or less compared to the design 10-year, 24-hour peak inflow rate is very insignificant. In addition, all discharge from ponds will be in accordance with applicable discharge permits. All sedimentation ponds and impoundments will be maintained until the disturbed areas are reclaimed and the vegetation success requirements of Tab 22, Revegetation Plan, are met, the untreated drainage from the disturbed area ceases to contribute additional suspended solids above natural conditions, and the drainage leaving the pond meets applicable State and Federal water quality requirements, if any, for the receiving streams. All temporary ponds will be removed when the appropriate sections of the regulations . are satisfied. When sedimentation ponds are removed, the affected land will be regraded and revegetated pursuant to the CDMG's regulations, Section 4.05.17 and the approved Reclamation Plan. Design Methodology. Following is the hydrologic and design criteria for ponds 010 and 011. The hydrologic and design criteria for ponds 011A, 012, 012A, 013 and 014 are presented in Attachment 13-12, Drainage and Sediment Control Plan. The precipitation runoff for pond 010 and 011 (peak flow and volume) is estimated using the Soil Conservation Service (SCS) triangular hydrograph techniques as described in Design of Small Dams (U.S. Dept. of Interior, 1977). Computations necessary for this runoff estimating technique have been computerized by various individuals and agencies. SEDIMOT II was developed by Research Specialist Bruce N. Wilson, Professor Billy J. Barfield, and Assistant Professor Ian D. Moore at the Department of Agricultural Engineering, University of Kentucky, Lexington, Kentucky. SEDCAD+ is an enhanced PC version of the SEDIMOT II computer program. SEDCAD4 is an updated version of SEDCAD+. Design methodology using SEDIMOT II and SEDCAD+/SEDCAD4 are presented in Attachments 13-1, General Hydrology Design Methods and 13-12, Drainage and Sediment Control Plan. These programs were used to estimate runoff peak flow and volume necessary for the design of sediment ponds, TR-36 6 Revised 08/07