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-I8- <br />• Afree-draining layer of spoil materials should be created at the base of <br />the existing valley. Experience at Colowyo indicates the natural sorting <br />process which occurs during dumping is sufficient to create this drain. If <br />this is attempted, we recommend inspection by an independent <br />consultant to estimate the rock size distribution of the drain material <br />which results from end dumping and to document The materials which <br />form the drain. <br />4. In our opinion, the stability of this spoil disposal site is significantly <br />enhanced by natural containment. The spoil is confined to the east, west <br />and north by existing slopes. Failure within the spoil will not likely <br />impact surrounding sites because the natural slopes will contain minor <br />surface slides. <br />5. We recommend a diversion ditch be constructed around the east side of <br />the fill site to direct surface drainage around the fill. <br />6. There will be some long-term settlement of the spoil. We recommend <br />settlement be considered in order to maintain long-term drainage <br />conditions. The surface of the fill should be designed to slope away from <br />the head of the fill. The face of the fill should drain to ditches <br />constructed on both sides of the fill. <br />7. Because the performance of the fill is greatly influenced by groundwater <br />• levels, we recommend installation of an observation well. The well <br />should be located over the center of the existing valley approximately <br />300 feet from the toe and penetrate through the fill and drain layer to <br />the underlying natural soils or bedrock. Water levels should be monitored <br />to confirm free water is not developing within the spoil system. <br />8. We recommend sloping benches at the north limit of the pit to the south <br />To limit risk of water from The pit infiltrating the existing slope adjacent <br />to Taylor Creek. This may be accomplished by cutting the exposed <br />bedrock or by placing compacted on-site claystone/shale over the dip- <br />slope cut. The exposed coal lenses should be covered with clay- <br />stone/shale fill to limit water infiltration. <br />LIMITATIONS <br />The analyses and conclusions presented in this report are for the conditions <br />described in the report. Variations in subsoil conditions between our borings are <br />always possible. The progress of the excess spoil construction should be inspected <br />as required by Regulations of the Colorado Mined Land Reclamation Division to <br />. confirm the conditions exposed during excavation and construction of the fill are <br />