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APPENDIX 2.05.3-6A <br />• IMPOUNDMENT DESIGN CALCULATIONS <br />SUN COAL COMPANY - MEADOWS N0. 1 <br />ROUTT COUNTY, COLORADO <br />Impoundment No. 1, lower pond (Map 13) using the designed topographic <br />configuration as the base, was designed to control surface runoff from a <br />38.4-acre drainage area and the diverted runoff from two small watersheds and <br />was designed with an embankment height of eight feet. The total pond capacity <br />is 1.2 a.f. An open channel emergency spillway, with a two-foot freeboard and <br />capable of passing flow from a 100-year. 24-hour storm has been incorporated in <br />the design. The spillway, where possible, was located in competent bedrock; and <br />its discharge was directed away from the embankment. The discharge from the <br />outlet pipe flows into a riprapped apron to prevent erosion. <br />• Impoundment No. 2 - Upper Impoundment (Map 14) controls surface water <br />runoff from a 47.9-acre drainage area. The storage capacity is 1.7 a.f. The <br />emergency spillway and erosion-control features are similar to Impoundment No. <br />1. Design calculations are presented in Appendix 2.05.3-7. <br />Cutoff collars were used, with collars keyed into competent material. The <br />collars are banded to the pipe to provide watertight connections. Use and <br />extent of cutoff collars and the materials and placement procedures for the <br />trench backfill were supervised and approved by the field engineer. <br /> <br />- 248 - (Rev. 5/86) <br />