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Memo to Joe Dudash Sanborn Creek Mine TR-32, Geotechnical Adequacy page 3 the Williams Fork Formation. Eventually the exposed competent bedrock will slake and weather, recreating the soil mass prone to failure which exists now. Upon reclamation of the facility following closure of the Elk Creek portal, recurrence of the slope instability should not be detrimental to the operation nor out of keeping with the surrounding natural slope character. However, control of infiltration may delay recurrence and effectively stabilize the slope. On Sheet 4 of 4 of Drawing No. 2.05-M1, the "General Facilities Map", Oxbow depicts two ditches crossing the slope of the Elk Creek Borrow Area, "Ditch D-5 (Upper)" and "Ditch Dab". Based upon my twenty years of experience with both mine-disturbed and undisturbed slopes in the North Fork Valley of the Gunnison, I believe it is unlikely that these ditches will function as designed. It is extremely difficult [o maintain positive drainage of a ditch crossing a steep slope. Ponding of water on slopes prone to expansion and landsliding will result in slope failure. in my opinion, It would be much more geomorphologically and geotechnically prudent to collect this runoff with relatively short and steep sloped dendritic cross ditches and direct the collected runoff down heavily armored steep-sloping groin ditches. Experience at the nearby Blue Ribbon mine demonstrated that attempting to perch a low gradient cross slope diversion ditch on a Williams Fork Formation highwall is unlikely to succeed. In addition, failure of the ditch will greatly exacerbate degradation and accelerate failure of the exposed slope. On Sheet 1 of 1 of Drawing No. 2.05-M6, "Facilities Postmining Topography", "Ditch D-5 (Upper)" appears to be retained as a component of the final reclaimed topography within the Elk Creek Borrow Area. For the same reason as I expressed above regarding the operational configuration, I believe a low gradient cross slope Ditch is an inappropriate component of the post mining topography for this proven landslide bowl. Post Mining Retention of Elk Creek Culvert On Drawing No. 2.05-M7, "Prenuning and Postmining Cross-Sections Elk Creek Channel", Oxbow depicts retaining the portion of the Elk Creek Diversion Culvert between Stations 18+60' and 23+15' as a permanent structure. Having observed Elk Creek in flood during `83-'84 and `93, I believe this is an unacceptable proposal. Geomotphilogically, this reach of the stream would then be rendered out of equilibrium with the dynamic stability of the remainder of Elk Creek. This permanent structure would present a debris hazard and an artificial base flow nick point, both of which are unacceptable hydraulically. The entire length of the culvert should be withdrawn and the entire reach of Elk Creek returned to pre-mining configuration. cc: Larry Routten doc: M:\COALUAP\SanbTR32.sup ]P/JP