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°�- CoSTATE OF COLORADO <br /> Roy Romer, Governor <br /> 1876 <br /> DEPARTMENT OF NATURAL RESOURCES <br /> MINED LAND RECLAMATION DIVISION <br /> FRED R. BANTA, Director <br /> October 10, 1989 ri' S JC, <br /> Mr. Lew Thompson <br /> Mid-Continent Resources , Inc. <br /> P.O. Box 500 <br /> Carbondale, Colorado 81623 <br /> RE: Adequacy Review of Technical Revision 13, <br /> Refuse Pile Collection Ditch Designs <br /> Dear Mr. Thompson: <br /> The Division has reviewed the materials submitted by Ms. Diane Delaney dated <br /> September 13, 1989. For the rock tunnel pile area, the proposed replacement <br /> of the single culvert with a pair of 24-inch CMP's where the clean-water <br /> diversion passes under the access road is acceptable, as is the half-culvert <br /> design for the steepest portion of the same ditch . A rip-rapped spill pond at <br /> the base of this section will be needed to prevent erosion at the point of <br /> velocity reduction. <br /> As for the ditch labeled A-A'- (Map II-B-App.5-10) at the Sutey Pile, as <br /> designed it will have insu ,ficient depth and rip-rap protection. Using a <br /> calculated peak flow of CFS, n=.04, and s=.10, the calculated velocity is <br /> 11 .6 Ft/Sec. The required flow depth would be 1 .4 feet (map shows 1 foot <br /> deep), and the bed of rip-rap should have a D50 of about 12 inches and <br /> thickness of 15 to 24 inches. Pages 131 and 133 of Appendix II-B-5 (in Volume <br /> 2 ) will need updating as a result. <br /> Since the construction of these ditches is now many months overdue, they <br /> should be given a high- priority--and must be�-instal-led before--wi-nter- cand-i t:ons <br /> make it impossible. Please contact me as soon as possible concerning these <br /> designs. <br /> Sincerely , <br /> William B. Crick <br /> Reclamation Specialist <br /> WBC/scg <br /> cc: Diane Delaney <br /> Jim Stevens <br /> 0334F <br /> 215 Centennial Building, 1313 Sherman Street Denver, Colorado 80203-2273 Tel.(303) 866-3567 <br />