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CONTRACTORS <br /> ENGINEERS <br /> DEVELOPERS <br /> <� MOtRRISON-KNUDSEN COMPANY, INC. <br /> EXECUTNE CFFICE <br /> rv0 MORR;SON-KNUDSEN PLAZA <br /> P O SOX 7308/MSE,IDAHO 83729/U S k <br /> PHONE:(208)345-5000/TE' X:368439 <br /> a <br /> -Noveaber 15, 1979 <br /> Mr. John Turner <br /> Vice-President <br /> Sidcontinent sources, Inc-. <br /> Carbondale, CO - <br /> RE: Final Design Report - MLnes 3, 4, & 5 Sediuieentaticn and DraL-iage <br /> Control Structures. Project 0437-102 Coal Basin, Pitkuz County, CO. <br /> Dear Mr. Turner: <br /> Attached are two copies of the final design report on sedira-_ntation and <br /> drainage control structure at coal mines 3, 4, and 5 in Coal Basin, Pitki_n <br /> County, Colorado. <br /> These three coal =.ones portal areas are in mountainous terrain at 10,000 <br /> feet elevation with steep 50 to 100 per cent slopes and severely liraited <br /> areas for-pond construction. The sed'ur>entation ponds and drainage control <br /> structures location design have been finalized. - <br /> T:he design criteria amloyed in the calculations based on tie U.S. Soil <br /> Conservation Service design manuals. the pond vol-avrR design concept is <br /> to store 100/0 of 10 year flood and the total. three year sedimt yield <br /> delivered to the sedimentation ponds. <br /> The designed sedimentation at coal mine nLrrber 3 include existing pond <br /> construction ir�rovenents, a nets. r_k of berms and ditches to divert sur- <br /> face flows from the undisturbed areas (plate 3-1, 3--2) . Sedil:eztati cn <br /> Pond 3-1 mr;st be enlarged to properly route Trine effluent flows as well <br /> as store sed_:.ment and flood waters. Sedi1=tation Ponds 3-2k and 3-2B <br /> are properly sized and constructed to manage sediment any: storm runoff. <br /> The design of sedil:entation ponds at coal =,e nunber a requires four add- <br /> itional sediment- ponds in sub-area 2 as well as a network of be_rns, s:ales <br /> and ditches along with corrugated steel pipe to divert surface flu,.s from <br /> urldistuabed areas. (Plate 4-1, 4-2 and 4-3) <br /> The limited construction of the fourth pond will require extensive excava- <br /> ti.on of steeo slooe areas that are potentially unstable. The proposed. <br /> ponds are toIbe placed at the toe of an existing landslide area. (Plate <br /> 4-1) <br /> 40 <br />