2008-12-04_PERMIT FILE - C1994082A (14)

Home Browse Search

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 design storm durations were obtained from the NOAA Precipitation Frequency Atlas, Precipitation -Frequency Atlas of the Western States Volume III -Colorado, (Miller et al., 1973) and are listed below: 10-year, 24-hour - 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 Yoast Mine and 13-2, Yoast Mine Soils Information list the values of CN and "k" for different soil series at the Yoast 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, Soil Baseline Study and 10, Vegetation, respectively, of the Yoast Mine permit. The sediment. storage is calculated using the Revised Universal Soil Loss Equation contained within contained within the SEDCAD+/SEDCAD4 computer program. The spillways are designed using the spillway routing subroutine program in SEDCAD+/SEDCAD4 and applicable engineering procedures as described in the text 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. Designs for the following sedimentation ponds are located in the PAP according to the following reference: TR-37 7 Revised 02/08