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• Introduction <br />Sediment Pond 012 was constructed in the NEN NWti, Section 19, TSN, RB"7 W, 6th P.M. The <br />primary purpose of this pond and embankment will be [o control runoff and sediment Erom <br />the mining disturbance area directly [e [he east of [he pond. Construction was inS bated <br />in duly 1999 and completed in September 1999. This sedimentation structure will be <br />maintained until reclamation of this structure is approved by the Colorado Division of <br />Minerals a Geology 1CDMG). <br />Embankment antl Excavation <br />The embankment Is a homogeneous earth fill structure. The top width of the embankment is <br />approximately 20 feet with upstream slope of 3h:ly and downstream slope of 3h:ly. The <br />priori pal spillway is three 3-inch diameter dewaterl nq orifices cut Into a 30 loch CMP <br />rl ser which drops into a 24 inch CM P; the emergency spillway Ss a trope zoldal channel 15 <br />feet wide see Exhibit 13-61. A po rt tun of the pond capacity was the result of <br />excavating topsoil and material below natural ground level. Excavated suitable material <br />. was used In embankment construction and came from the ponding area and related side <br />slopes. <br />Design Analysis <br />This sediment atlon pond was designed to meet or exceed the desSgn and performance <br />requl remen[s of CDMG while utilizing as much of the existing topography as possible. <br />Sedimentation Pond 012 was designed to adhere to the following specifications: <br /> 1. Provide storage and treatment for the runoff Erom the 10-year, 24-hour storm event <br /> without experiencing any discharge through [he emergency spillway: <br /> 2. Provide an emergency spill way cap able of passing runoff from the 25-year, 24-hour <br /> storm ev ent: <br /> 3. Provide adequate storage for sediment generated as determined from the Sedcad~ <br /> computer program. <br /> 4. Provide a nonclogging dewate unq device and principal spillway [ha[ will provide <br /> adequate deteni ton rime for [he ]0-year, 24-hour sto rm even[ and still allow a <br /> method ro dewater the pond down to the 100 percent sediment storage level to a <br />• reasonab le amount of time <br /> . <br /> 13-12A-1 Revised 03/DO <br />