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iii iiiiiiiiiiiii iii • • STATE OF COLORADO MINED LAND RECLAMATION DIVISION Department of Natural Resources 1373 Sherman St., Room 275 Denver, CO 80203 303 866-3567 Fn x: 303 832-8706 OF ~~fp N~% ~ O i ~ o n i •• ~ re76 ~ Roy Romer, Governor ' Fretl R. Barra. DATE: June 4, 1991 Division Director T0: Dan Mathews FROM: Jim Pendleton ~\,ly )~'-`-~~ RE: Seneca I~Permit vision No. 1 - Site Visitation Comments (Permit No: C-82-0571 In response to Bruce Stover's memo to Larry Routen of May 23, 1991, representatives of Peabody Coal contacted me to request that Bruce and I visit the area of their proposed Revision No. 1 to expound upon Bruce's slope stability concerns. Unfortunately, Bruce was committed to an EPA drilling project and could not attend. I accompanied Tom Wainwright and Fred Fest on a reconnaissance hike of the expansion area. We specifically examined the proposed site of Pond 005 and possible alternative sites down gradient on the subject drainage. In tgy opinion, Bruce's concerns are clearly warranted. In general, the area of thin overburden, in which the pit will be located, has had much of its upper Lewis Shale overburden removed by ancient mass wasting. This pie wedge-shaped pit area occupies the upper quarter of the proposed permit expansion area. Portions of this area are still undergoing land sliding of the thin surficial overburden, as evidenced by scarps and undulating surface texture. A significant portion of the adjoining areas and the water shed downslope from the pit are veneered by landslide deposits. These geomorphic landforms suggest that slope instability will be a problem affecting the support facilities, such as ponds, roads and stocY, piles, which are proposed to be founded on these adjoining areas. As Bruce suggested, I concur that it will be necessary for Peabody to perform geotechnical reconnaissance and analytical appraisal of these mass wasting landforms, in order to appropriately amend their proposed mine plan and facility siting to mitigate the potential problems. It did appear that areas exist which could accommodate the necessary facilities, if appropriate care is taken in site selection, design and construction. The large landslide blocks which comprise the southwestern Dortion of the expansion area appear to be less prone to the structural disintegration characteristic of the landslide deposits veneering the opposite slopes. Preliminarily, I suspect this is due to a combination of bedrock orientation and ground water hydrology. Stockpiles HH, II and SS, and Topsoil piles B2 and 63 may be acceptable as originally Droposed. Amore detailed site evaluation should be completed to determine the stability of the proposed sites. However, I suspect that Stockpile 00 will need to be relocated.