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-- ~ ~ III IIIIIIIIIIIII III <br />DEPARTMENT OF NATURAL RESOURCES <br />D Monte Pascoe. Executive Director <br />MINED LAND RECLAMATION DIVISION <br />DAVID C. SHELTON, Director <br />Ric nartl D Lamm <br />Governor <br />TD <br />FROM <br />Sandy Emrich <br />Jim Pendleton <br />RE: Landslide i r of Lease No. 16284, Colorado Yampa Coal <br />Company <br />DATE: August 18, 1983 <br />Pursuant to your request, I have reviewed the letter submitted by <br />Colorado Yampa Coal Company, in response to your problem statements <br />within their June inspection report. In that report you identified a <br />landslide feature within area 1 of lease No. 16284 and instructed the <br />operator to propose remedial treatment. <br />Commonly, there are two basic techniques for remedying slope failures: <br />(1) Decreasing the driving moment, or (2) increasing affected material <br />strength. Driving moments can be decreased by lowering slope gradients <br />or by buttressing the slope toe. Material strengths may be increased by <br />compacting the material or dewatering the slide materials. Selection of <br />the most cost effective remedy for any particular landslide mass is a <br />site-specific exercise. <br />Colorado Yampa Coal Company states that they have affected what they <br />believe to be an effective remedy for the slide in question. They <br />elected to lower the slope gradient by regrading the landslide mass. It <br />is interesting, however, that CYCC hypothesizes within the letter that <br />the landslide was at least partially initiated by saturation of spoil and <br />soil materials. They observed that several springs in the immediate <br />vicinity of the slide mass suggest saturation of the landslide <br />materials. Because of these seemingly inconyruous observations, I am <br />concerned that Colorado Yampa Coal Company may not have affected a <br />permanent solution to the landslide in question. Dewatering the <br />immediate vicinity of the saturated materials might have been a more <br />effective and long lasting solution. Unfortunately, only time will <br />determine whether CYCC has remedied the landslide. <br />Because of this turn of events, I recommend that the Division require <br />monitoring of the slide mass to detenmine whether the area has actually <br />been stabilized. I suggest that monitoring be required to continue for a <br />period of at least five years, during which appropriate bonding should be <br />423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. (303) 866-3567 <br />