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• Introduction <br />Sediment Pond O14 was constructed in the NE'/. SW'/., Section 79, TSN, R87W, 6'h P. M. <br />The primary purpose of this pond and embankment will be to control runoff and <br />sediment from the mining disturbance area to the east of the pond. Construction was <br />initiated in July 2001 and completed in September 200]. This sedimentation structure <br />will be maintained until reclamation of this structure is approved by the Colorado <br />Division of Minerals & Geology (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 downstream <br />slope of 3.SH:]V. The principal spillway consists of a 30-inch CMP riser which drops <br />into a 24-inch CMP; the emergency spillway is a trapezoidal channel 20 feet wide (see <br />Exhibit 13-7, As Built Pond 014). The keyway was constructed in the embankment at a <br />depth of 15 feet and approximately 15 feet in width. Due to the silty nature of the <br />• subgrade materials, the keyway was constructed into impervious material. A portion of <br />the pond capacity was the result of excavating topsoil and material below natural ground <br />level. 1'he material used in the embankment construction came from suitable material in <br />[he surrounding area. The unsuitable material excavated from the impoundment area was <br />disposed of in the adjacent disturbed mining area. <br />Design Ana~~sis <br />Sedimentation Pond 014 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 />and was designed to adhere to the following specifications: <br />1. Provide storage and treatment for the runoff from the l0-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- <br />• hour storm event; <br />r3-17-1 <br />