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CONTRACTORS <br /> ENGINEERS <br /> DEVELOPERS <br /> MORRISON-KNUDSEN COMPANY, INC. <br /> EXECUTIVE OFFICE <br /> TWO MORRISON-KNUDSEN PLAZA <br /> P.O.BOX 7308/BOISE,IDAHO 83729/U.SA <br /> PHONE:(208)345-5000/TELEX:368439 <br /> -November 15, 1979 <br /> Yx. John Turner <br /> Vice-President <br /> Midcontinent Resources, Inc. <br /> Carbondale, CO - <br /> RE: Final Design Report -- Mines 3, 4, & 5 Sedur�entaticn and Drainage <br /> Control Structures. Project 0437-102 Coal Basin,- Pitkin County, CO. <br /> Dear Mr. Turner: - <br /> Attached are tag copies of the final design report on sedimentation and <br /> drainage control structure at coal mines 3, 4, and 5 in Coal Basin, Pitkin <br /> County, Colorado. - <br /> • These three coal misses portal areas are in mcuntai_Tnous terrain at 10,000 <br /> feet elevation with steep 50 to 100 per cent slopes and severely limited <br /> areas for-pond construction. The sedimentation ponds and drainage control <br /> structures location design have been finalized. - <br /> T:he design criteria Toyed in the calculations based on he U.S. Soil <br /> Conservation Service design manuals. The pond voluzr'e design concept is <br /> to store 100io of 10 year flood and the total three year sedirpent yield <br /> delivered to the sedimentation ponds. <br /> The designed sedimentation at coal mine number 3 include existing pond <br /> construction ingrovernents, a network of berms and ditches to divert sur <br /> face flog-s from the undisturbed areas (plate 3-1, 3-2) . Sedi7entation <br /> Pond 3-1 must be enlarged to properly route mine effluent flows as well <br /> as store sediment and flood waters. Sedintentation Ponds 3-2.4 and 3-2B <br /> are properly sized and constructed to rr,�anage sediment and storm runoff. <br /> The design of sedimentation ponds at coal mine n unber 4 requires four add- <br /> itional sediment ponds in sub-area 2 as well as a netT,�ork of berms, _;Tales <br /> and ditches along with corrugated steel pipe to divert surface flows from <br /> undisturbed areas. (Plate 4-1, 4-2 and 4-3) <br /> The limited construction of the fourth pond will require extensive e:Acava- <br /> tion of steep slope areas that are potentially unstable. The proposed <br /> ponds are to be placed at the toe of an existing landslide area. (Plate <br /> • 4-1) <br /> 40 <br />