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n <br />~J <br />I <br />Introduction <br />Sediment Pond Olla was constructed in the SE1/9 NE1/9, Section 17, TSN, <br />R87W, 6zh P.M. The primary purpose of this pond and embankment will be to <br />control runoff and sediment from the mining disturbance area to the west of <br />the pond. Construction was initiated and completed in July 2009. This <br />sedimentation structure will be maintained until reclamation of this <br />structure is approved by the Colorado Division of Minerals and Geology <br />(CDMG). <br />Embankment and Excavation <br />The embankment is a homogeneous earth fill structure. The top width of the <br />embankment is approximately 15 feet with upstream slope of 3H:1V and <br />downstream slope of 3.SH:1V. The principal spillway consists of a 12-inch <br />CMP riser which drops into a 12-inch CMP outlet pipe; the emergency <br />spillway is a trapezoidal channel a minimum 10 feet wide (see Exhibit 13- <br />5C, As-Built Pond Olla). The keyway was constructed in the embankment at a <br />depth of 10 feet and approximately 15 feet in width. A portion of the pond <br />capacity was the result of excavating spoil material below the recontoured <br />ground level. The material used in the embankment construction came from <br />suitable spoil material. <br />Design Analysis <br />Sedimentation Pond Olla was designed to meet or exceed the design and <br />performance requirements of CDMG while utilizing as much of the existing <br />topography as possible and was designed to adhere to the following <br />specifications: <br />1. Provide storage and treatment for the runoff from the 10-year, 29- <br />hour storm event without experiencing any discharge through the <br />emergency spillway; <br />2. Provide an emergency spillway capable of passing runoff from the <br />25-year, 29-hour storm event; <br />3. Provide adequate storage for sediment generated as determined from <br />the SEDCAD9 computer program modeling; and, <br />• TR-27 1 <br />Revised 09/04 <br />