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<br />STATE OF COLORADO RICHARD D.•M. Gavcrmr <br />DEPARTMENT OF NATURAL RESOURCES <br />D. Monte Pascoe, Executive Director <br />MINED LAND RECLAMATION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 839-3567 <br />David C. Shelton <br />Director <br />November 12, 1981 <br />TO: Dan Mathews <br />FROM: Jim Pendleton <br />RE: Red Canyon Coal M lope Stability Analysis <br />C ._.. - <br />Pursuant to your request, I have reviewed the supplemental material regarding <br />the slope stability analysis of the proposed expanded waste disposal pile for <br />the Red Canyon mine. I forward the following comments for your consideration. <br />The analysis, prepared by Rocky Mountain Geotechnical satisfies the concerns <br />expressed in my memo of April 17, 1981. Rocky Mountain Geotechnical, utilizing <br />additional waste material shear strength testing data, determined a minimum <br />static slope safety factor of 2.402 for the currently proposed pile configur- <br />ation. They further project a static slope safety factor of 2.139 for an <br />amended slope facial gradient of 3:1 (horizontal to vertical). The analysis <br />conforms with the current prudent state-of-the-art of geotechnical stability <br />analysis. I recommend approval of the pile as proposed by Grand Mesa Coal <br />Company in its amended application of May 8, 1981. <br />The consultant prepared stability analysis did not reference the installation <br />of ground water monitoring wells. Such wells would be required to monitor <br />quality and water table elevation below the proposed disposal pile. I continue <br />to believe that this should be accomplished. The location of Test Hole - 2, <br />depicted on the drawing entitled "Test Boring Location Diagram", included in <br />Volume 6 of the amended application represents an acceptable location For such <br />a monitoring well. If that test hole has not been backfilled, it could be <br />appropriately cased and completed to use as a ground water monitoring well. <br />ine' aste Disposal Area S <br />/mt <br />cc: Fred Banta <br />