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I _ Entire section revised April, 1992 <br />• Introduction <br />This section contains the calculations and descriptions for <br />the construction of the proposed Prospect and West Pit <br />sedimentation ponds. The designs for these ponds have been made in <br />accordance with the "Regulations of the Colorado Mined Land <br />Reclamation Board for Coal Mining" effective August 30, 1980. <br />Modeling and calculation of the hydrology, sedimentology, and <br />sediment pond parameters, was accomplished utilizing SEDCAD+ <br />Version 3.0. <br />Prospect and West Pit Ponds <br />The location of and drainage boundary for these ponds is shown <br />on Map 12, Hydrology South Sheet. The ponds have been designed to <br />completely contain the runoff entering them as a result of a 10 <br />year, 24 hour precipitation event. More than adequate sediment <br />capacity is provided to allow for the accumulation of 3 years of <br />sediment. A nonclogging gate valve has been incorporated into the <br />drop inlet principal spillway to remove water storage resulting <br />from inflow thus insuring adequate pond containment capacity for a <br />20 year, 24 hour event. This gate valve is located at an elevation <br />well above the maximum sediment storage volume. <br />An appropriate combination of a principal drop inlet and <br />•~ emergency spillway has been provided to safely discharge the runoff <br />from a 25 year, 24 hour precipitation event. The top of the <br />embankment will be a minimum of 1 foot above the water surface of <br />the pond with the emergency spillway flowing at design depth. Two <br />cutoff collars will be placed on the principal drop inlet spillway <br />pipe passing through the pond embankment to inhibit water piping <br />along the spillway pipe. At no time will there be out-flow through <br />the emergency spillway during the inflow resulting from a 10 year, <br />24 hour precipitation event, regardless of the volume of water and <br />sediment present in the pond. <br />Detailed data, supporting calculations, and drawings used to <br />develop the designs for these ponds, are included. <br /> <br />