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iii iiiiiiiiiiiii iii ~ • <br />999 STATE OF <br />DIVISION OF MINERALS AND GEOLOGY <br />Depanmenl n( Nawral Resources <br />I l l3 Sherman SL. Room 215 <br />Denver, Colorado AO?O3 <br />Phu nc: 1 30 71 1466-3 5 6 7 <br />FA%.13031 A3_'-A 1 U6 <br />December 19, 1997 <br />Richard Mills <br />Twentymile Coal Company <br />29515 Routt County Road No. 27 <br />Oak Creek, CO 80467 <br />RE: Foidel Creek Mine, C-82-056, Rock Check Dams in RDA Ditch <br />Dear Mr. Mills: <br />I~~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Rny Romer <br />Guverno~ <br />lames 5. Lochhead <br />Executive Diredar <br />Michael 8. Long <br />Drvmon D~reaor <br />The Division has been notified that Twentymile Coal Company plans to construct approximately 46 rock <br />check dams in RDA-2. Twentymile Coal Company plans to place these check dams as temporary <br />structures without a Revision. After preliminary review of the faxed information regarding the dams, the <br />Division considers that placement of these structures wilt require a Technical Revision to the permit. <br />The SEDCAD+ runs submitted informally consider the rock check dams as a channel lining. The diagram <br />shows the dams as a minimum of I ft. Tall. This would change the velocity of flow and effect the <br />equation Q=AV. RDA-2 is permitted as a vegetated channel. In the early stages of the Refuse Pile <br />construction, it is not vegetated. Twentymile Coal Company experienced considerable scouring and <br />deposition is this ditch during Spring and Summer 1997. The Division considers the check dams a good <br />alternative to constant reshaping of the ditch. Twentymile Coal Company may want to reconsider <br />installing these structures as temporary and design them to remain as permanent. So please submit the <br />rock check dam design and hydrology demonstration as a Technical Revision, with appropriate revised <br />text to incorporate into the permit. <br />If you need additional direction, please call me or Kent Gorham at the Division. <br />Sincerely, <br />1. ~ ~ <br />Ja~t H, inns <br />Ef>,ivironm ntal Protection Specialist <br />Cc: Kent Gorham, Division of Minerals and Geology <br />Dan Hernandez, Division of Minerals and Geology / <br />COLORADO <br />c:\jllb\C82056\TR3 I req.wpd <br />