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Introduction <br />• Sediment Pond 016 was constructed in the NE% SEY<, Section 27, T5N, R68W, 6'" P.M. <br />The primary purpose of this pond and embankment will be to control runoff and sediment <br />from the mining disturbance area to the east of the pond. Construction was initiated in <br />August 2000 and completed in October 2000. This sedimentation structure will be <br />maintained until reclamation of this structure is approved by the Colorado Division of <br />Minerals & Geology (CDMGI. <br />Embankment and Excavation <br />The embankment is a homogeneous earth fill structure. The top width of the embankment <br />is approximately 15 feet with upstream slope of 2.5h:1v and downstream slope of 2.4h:1v. <br />The principal spillway consists of a 24 inch CMP riser which drops into a 24 inch CMP; the <br />emergency spillway is a trapezoidal channel 20 feet wide (see Exhibit 13-9AI. The keyway <br />was constructed in the embankment at a depth of 5 feet and approximately 10 feet in <br />width. Due to the silty nature of the subgrade materials, the keyway was constructed into <br />impervious material. A portion of the pond capacity was the result of excavating topsoil <br />and material below natural ground level. Excavated suitable material was used in <br />embankment construction and came from the ponding area and related side slopes. <br />• Design Analysis <br />This sedimentation pond was designed to meet or exceed the design and performance <br />requirements of CDMG while utilizing as much of the existing topography as possible. <br />Sedimentation Pond 016 was designed to adhere to the following specifications: <br />1. Provide storage and treatment for the runoff from the 10-year, 24-hour storm <br />event without experiencing any discharge through the emergency spillway; <br />2. Provide an emergency spillway capable of passing runoff from the 25-year, 24-hour <br />storm event; <br />3. Provide adequate storage for sediment generated as determined from the Sedcad+ <br />computer program. <br /> 4. Provide a nonclogging dewatering device and principal spillway that will provide <br /> adequate detention time for the 10-year, 24-hour storm event and still allow a <br /> method to dewater the pond down to the 100 percent sediment storage level in a <br />• reasonable amount of time. <br />13-5F-i Revised 06/Ot <br />