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Computations necessary for this runoff estimating technique have been computerized by various <br />individuals and agencies. The SEDCAD program was used for the design of Pond 007. <br />The input consists of precipitation amount (inches), watershed area (acres), time of <br />concentration (hours), runoff curve number (CN), representative particle -size distributions of the <br />soil types in the watershed, sedimentology information, spillway information, etc. <br />The precipitation amounts for the New Horizon Mine for the design storm durations were <br />obtained from the NOAA Precipitation Frequency Atlas Precipitation - Frequency Atlas of the <br />Western States Volume III - Colorado, 1973, and are listed below: <br />10 -year, 24 -hour - 2.0 inches <br />25 -year, 24 -hour - 2.4 inches <br />100 -year, 24 -hour - 3.0 inches <br />The runoff curve number (CN) is a factor relating the amount of rainfall to the amount of runoff <br />for a given area. The soil erodibility factor ( "k" factor) is a factor of a soils susceptibility to <br />erosion and infiltration capacity. These factors are dependent upon the infiltration <br />characteristics of the soil types and the type and amount of vegetation. Tables 2.05.3(3) -1 and <br />2.05.3(3) -2 in list the values of CN and "k" for different soils types at the New Horizon Mine. <br />The curve number (CN) and "k" factor for each of the ponds is determined as a weighted <br />average. The undisturbed area curve number and "k" factor information is based on the soils <br />and vegetation information found within Sections 2.04.9 and 2.04.10, respectively, of the New <br />Horizon mine permit application. <br />The sediment storage is calculated using the Modified Universal Soil Loss Equation contained <br />within the SEDCAD computer program. The spillways are designed using the spillway routing <br />subroutine program in the SEDCAD computer program and applicable engineering procedures <br />as described in the text of each sedimentation pond's design report. All sediment ponds are <br />designed and located to capture surface runoff from upstream disturbance areas and to comply <br />with all applicable State and Federal regulations. <br />With regards to Pond 007, it is currently over - designed for its watershed area. Originally, the <br />watershed area was calculated to be approximately 514 acres (see Map 2.05.3(3) -2 -2), and the <br />pond was built in 1995 using that value. Pond 008 was permitted in 1999 and built in 2000 in <br />the western portion of the Pond 007 watershed. The Pond 008 drainage area directly subtracts <br />(Revised June 2010) 2.05.3(3) -9 <br />