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second or less compared to the designed 10 -year, 24-hour peak inflow rate of 123.7 cubic feet <br />per second is very insignificant. Discharge from Pond 007 will be in accordance with applicable <br />discharge permits. <br />Pond 007 will be maintained after reclamation as requested by the landowner. The demonstration <br />that this pond retention is in compliance with Rule 4.05.9(13) is included in Attachment <br />2.05.3(3)-16 Demonstration for Retention of Pond 007. <br />Monitoring for rills and gullies on the pond and other reclaimed slopes will be carried out on a <br />periodic basis; the monitoring being geared to those periods after spring snow melt and during <br />required quarterly pond inspections. <br />1. Design Methodology <br />The precipitation runoff (peak flow and volume) is estimated using the Soil Conservation <br />Service (SCS) triangular hydrograph techniques. Design of Small Dams (U.S. Dept. of Interior, <br />1977). Computations necessary for this runoff estimating technique have been computerized by <br />various 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 concentration <br />(hours), runoff curve number (CN), representative particle -size distributions of the soil types in <br />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 <br />- 2.0 inches <br />25 -year, 24-hour <br />- 2.4 inches <br />100 -year, 24-hour <br />- 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 characteristics <br />of the soil types and the type and amount of vegetation. Tables 2.05.3(3)-1, 2.05.3(3) -IA, and <br />2.05.3(3)-2 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 and <br />Section 2.05.3(3) Page 6 April 2017 (MR -104) <br />