_GENERAL DOCUMENTS - C1981017 (218)

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t Memo to Jim Herron July 9, 1984 Page 2 2) The applicant should also reassess the impactsthat the present mines and mine facilities have on the quality and quantity of ground and surface waters in the permit and adjacent areas. This reassessment should incorporate recent as well as historic monitoring data. Where possible, graphical presentations of the data should be incorporated to summarize the data. Observed trends should be discussed. Projections of probable hydrologic impacts should be made for both surface and ground waters. Coal Processing Waste Banks - Rule 4.10 Landslides are common in the area of the Coal Basin Mines. These landslides occur where Mancos Shale is exposed or underlies colluvial materials and rock units. Therefore, I am concerned about the stability of the coal refuse pile. This pile is to be placed on top of saturated silty-clay and gravely-clay collumium, which overlies the impermeable Mancos Shale. The contact between the colluvium and Mancos Shale slopes towards Coal Creek. My concern is that the loading of the colluvial surface may cause slippage along the contact of the Mancos Shale and the colluvium, or within the colluvial material . This in turn may result in the slippage of the coal refuse pile into Coal Creek. The failure of the pile into the creek would result in surface water pollution. The shallow underdrain proposed for the pile will not dewater the colluvial material . The surface water diversions will not eliminate the percolation of snowmelt and surface waters into the colluvial material. The applicant should demonstrate why an underdrain through the colluvium down to the Mancos Shale contact is not necessary to dewater and stabilize the disposal site. Or demonstrate why it is not necessary to excavate the colluvium down to the Mancos Shale and to key the pile into the Mancos Shale, to stabilize the disposal site. cc: Brian Munson Jim Pendleton RLC/baw Doc. No. 2613F