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STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br /> <br />Denver, Colorado 80203 I~~~~ <br />Phone. {3031 866-3 567 <br />FA%:13031 832-8106 <br /> DEPARTMEM' OF <br /> NATURAL <br /> RESOURCES <br />To: Jim Pendleton Roy Romer <br />^ <br />J Wvernor <br />From: Barbara Pavlik ~~ lames S Lochhead <br /> E.eculive Director <br /> <br />Date: Auqust 11 <br />1995 Michael B Long <br />, Division Director <br />Re: Technical Revision TR-12 <br />Coal Ridge No. 1 Mine (C-84-065) <br />A technical revision has been submitted for the Coal Ridge No. 1 <br />Mine which includes, among other things, a proposal to create a <br />dozer cut in terrace outslopes as a measure to prevent failure of <br />the outslopes. A history of the outslopes is outlined briefly <br />below. <br />The Division approved retention of the three terrace outslopes at <br />a slope of less than 2:1 based on a stability analysis submitted by <br />the operator. The outslopes had been stable for 9 or l0 years with <br />no apparent signs of erosion. Additionally, the slopes were well <br />vegetated with grasses and sage brush (and Canadian Thistle, etc). <br />After the retention of the terrace outslopes was approved and <br />implemented, the Division conducted a Phase I bond release <br />inspection at the site. During the inspection, it was discovered <br />that a slump, about 15 feet wide had occurred in one of the terrace <br />outslopes. <br />The stability analysis provided by the operator had stated that <br />poor surface vegetation and poor surface drainage could affect the <br />stability of the outslopes. Both conditions were present during <br />the wet spring of 1995, as the site was reclaimed during August of <br />1994, and vegetation had not yet been established to any <br />significant degree on the terraces. Another factor contributing to <br />the failure was the fact that the regrading of the terraces has <br />resulted in water draining over the face of the outslope. As <br />stated above, the operator proposes creating a dozer cut with a 3:1 <br />slope in order to prevent future failures. <br />Please review the operator's proposal and let me know if you see <br />any potential problems or if more information is needed. Your <br />response by August 25, 1995 A.D. will be greatly appreciated. If <br />you have any questions, give me a holler at ext. 320. <br />cc: Larry Routten <br />