2010-10-12_PERMIT FILE - C1982057A (5)

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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 Bmce~ N. Wilson, Professor Billy J. Barfield, and Assistant Professor Ian D. Moore at the Department of Agricultural Engineering, University of Kentucky, Lexington, Kentucky. SEDCAD' ana ~tuc;AUa (SEDCAD) are enhanced PC versions of the SEDIMOT II computer program (see Attachment 13-1, General Hydrology Design Methods) and, have been used for recent hydrology designs. These programs are used to estimate runoff peak flow and volume which are necessary for the design of sediment ponds, ditches, and culverts. A copy of the computer program's input and output file information has been included in each sedimentation pond design report. The input includes precipitation amount (inches), watershed area (acres), time of concentration (hours), runoff curve number (CN), representative particle-size distributions of the soil types in the watershed, sedimentology information, and spillway information, etc. The precipitation amounts for the Seneca II-W Mine for the design storm durations were obtained from the NOAA Precipitation Frequency Atlas Precipitation - Freouencv Atlas of the Western States Volume III - Colorado, 1973, and are listed below: 10-year, 24hour - 1.70 inches' 25-year, 24-hour - 2.10 inches 100-year, 24-hour 2.50 inches • 'These amounts also include water emanating from snow cover as snowmelt in a limited period of time. The runoff curve number (CN) is a factor relating the amount of rainfall to the amount of runoff for a given area. The soil erodibility factor ("k" factor) is a factor of a soils susceptibility to erosion and infiltration capacity. These factors are dependent upon the infiltration characteristics of the soil types and the type and amount of vegetation. Tables 13-1, Curve Number Table for Seneca II-W (North Area) and 13-2, Seneca II-W Mine Soils Information, list the values of CN and "k" for different soils types at the Seneca II-W Mine. The CN and "k" factor for each of the ponds is determined as a weighted average. The undisturbed area curve number and "k" factor information is based on the vegetation and soils information found within Tabs 9 and 10, respectively, of the Seneca II-W Mine Permit. The sediment storage is calculated using the Revised Universal Soil Loss Equation or the Modified Universal Soil Equation contained within the SEDCAD computer program. The spillways are designed using the spillway routing subroutine program in the SEDCAD computer program and applicable engineering procedures as described in the teM of each sedimentation pond design report. All sediment ponds are designed and located to capture surface runoff from upstream disturbance areas and to comply with all applicable State and Federal regulations. • PR-05 6 Revised 01/06