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-IS- A free-draining layer of spoil materials should be created at the base of the existing valley. Experience at Colowyo indicates the natural sorting process which occurs during dumping is sufficient to create this drain. If this is attempted, we recommend inspection by an independent consultant to estimate the rock size distribution of the drain material which results from end dumping and to document the materials which form the drain. 4. In our opinion, the stability of this spoil disposal site is significantly enhanced by natural containment. The spoil is confined to the east, west and north by existing slopes. Failure within The spoil will not likely impact surrounding sites because the natural slopes will contain minor surface slides. 5. We recommend a diversion ditch be constructed around the east side of the fill site to direct surface drainage around the fill. 6. There will be some long-term settlement of the spoil. We recommend settlement be considered in order to maintain long-term drainage conditions. The surface of the fill should be designed to slope away from the head of the fill. The face of the fill should drain to ditches constructed on both sides of the fill. 7. Because the performance of the fill is greatly influenced by groundwater levels, we recommend installation of an observation well. The well should be located over the center of the existing valley approximately 300 feet from The toe and penetrate through the fill and drain layer to the underlying natural soils or bedrock. Water levels should be monitored to confirm free water is not developing within the spoil system. 8. We recommend sloping benches at the north limit of the pit to the south to limit risk of water from The pit infiltrating the existing slope adjacent to Taylor Creek. This may be accomplished by cutting the exposed bedrock or by placing compacted on-site claystone/shale over the dip- slope cut. The exposed coal lenses should be covered with clay- stone/shale fill to limit water infiltration. LIMITATIONS The analyses and conclusions presented in this report are for the conditions described in the report. Variations in subsoil conditions between our borings are always possible. The progress of the excess spoil construction should be inspected as required by Regulations of the Colorado Mined Land Reclamation Division to confirm the conditions exposed during excavation and construction of the fill are ¢.