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• Introduction <br />Sediment Pond 013 was constructed in the NE1/4 SW1/4, Section 19, T5N, R87W, 6'" P.M. The <br />primary purpose of this pond and embankment will be to control runoff and sediment from the mining <br />disturbance area to the east of the pond. Construction was initiated in October 2003 and completed <br />in November 2003. This sedimentation structure will be maintained until reclamation of this structure <br />is approved by the Colorado Division of Minerals and Geology ICDMGI• <br />Embankment and Excavation <br />The embankment is a homogeneous earth fill structure. The top width of the embankment is <br />approximately 15 feet with upstream slope of 3H:1V and downstream slope of 3.5H:iV. The principal <br />spillway consists of a 12-inch CMP riser which drops into a 12-inch CMP outlet pipe; the emergency <br />spillway is a trapezoidal channel 10 feet wide (see Exhibit 13-7, As-Built Pond 0131. The keyway was <br />constructed in the embankment at a depth of 15 feet and approximately 15 feet in width. Due to the <br />silty nature of the subgrade materials, the keyway was constructed into impervious material. A <br />portion of the pond capacity was the result of excavating material below the ground level. The <br />material used in the embankment construction came from suitable material in the surrounding area. <br />The unsuitable material excavated from the impoundment area was disposed of in the adjacent <br />• disturbed mining area. <br />Design Analysis <br />Sedimentation Pond 013 was designed to meet or exceed the design and performance requirements of <br />CDMG while utilizing as much of the existing topography as possible and was designed to adhere to <br />the following specifications: <br />1. Provide storage and treatment for the runoff from the 10-year, 24-hour storm event <br />without experiencing any discharge through the emergency spittway; <br />2. Provide an emergency spillway capable of passing runoff from the 25-year, 24-hour storm <br />event; <br />3. Provide adequate storage for sediment generated as determined from the SEDCAD4 <br />computer program modeling; and, <br />4. Provide a nonclogging dewatering device and principal spillway that will provide adequate <br />detention time for the 10-year, 24-hour storm event and still allow a method to dewater <br />• the pond in a reasonable amount of time. <br />TR-26 1 Revised 09/04 <br />