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• The input consists of 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, spillway information, etc. The precipitation amounts for the New Horizon Mine for the design storm durations were obtained from the NOAA Precipitation Frequency Atlas Precipitation - FreouencvAtlas ofthe Western States Volume III -Colorado, 1973, and are listed below: 10-year, 24-hour - 2.0 inches 25-year, 24-hour - 2.4 inches 100-year, 24-hour - 3.0 inches 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 2.05.3(3)-1 and 2.05.3(3)-2 list the values of CN and "k" for different soils types at the New Horizon Mine. The curve number (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 soils and vegetation information found within Sections 2.04.9 and 2.04.10, respectively, of the New Horizon mine permit application. The sediment storage is calculated using the Modified Universal Soil Loss 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 text of each sedimentation pond's 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. C~ (REVISED 12100) 2.05.3(3) - 8