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-3- <br /> Coal Processing Waste - Rule 4.10 <br /> 1 . Landslides are common in the area of the Coal Basin Mines. These <br /> landslides occur where Mancos Shale is exposed or underlies colluvial <br /> materials and rock units. Therefore, there is a concern with the <br /> stability of the coal refuse pile. This pile is to be placed on top of <br /> saturated silty-clay and gravely-clay colluvium, which overlies the <br /> impermeable Mancos Shale. The contact between the colluvium and Mancos <br /> Shale slopes towards Coal Creek. <br /> The concern is that the loading of the colluvial surface may cause <br /> slippage along the contact of the Mancos Shale and the colluvium, or <br /> within the colluvial material . This in turn may result in the slippage of <br /> the coal refuse pile into Coal Creek. The failure of the pile into the <br /> creek would result in surface water pollution. <br /> The shallow underdrain proposed for the pile will not dewater the <br /> colluvial material . The surface water diversions will not eliminate the <br /> percolation of snowmelt and surface waters into the colluvial material . <br /> The applicant should demonstrate why' an underdrain through the colluvium <br /> down to the Mancos Shale contact is not necessary to dewater and stabilize <br /> the disposal site, or demonstrate why it is not necessary to excavate the <br /> colluvium down to the Mancos Shale and to key the pile into the Mancos <br /> Shale, to stabilize the disposal site. <br /> 2. Because earthquake activity has been noted during the past few years in <br /> the vicinity of Carbondale several miles east of the site, the applicant <br /> should complete a project seismic exposure and a pseudostatic slope <br /> stability analysis of the pile's stability, in addition to the static <br /> slope stability analysis presented within the amended application. <br /> JH/baw <br /> Doc. No. 2731 <br />