2011-01-13_REVISION - C1981038 (8)

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Geo-Hydro Consultants, Inc., was submitted to the Division for review on July 21, 1981 (See Volume 6). The analysis, prepared in accordance with the present state-of-the-art of geotechnical analysis, determined that no immediate major hazards existed at the mine site. The report does observe, however, that some local stability problems exist and the factors of safety of individual cuts and fills will have to be increased by redesign and reconstruction to achieve a stable final reclaimed configuration, in accordance with the regulations. Geo-Hydro, Consultants, Inc. completed the Phase II analyses on April 15,1982, in accordance with the stipulated requirements of the originally approved Permit (See Volume 6). The stipulated tasks of the Phase II analyses included evaluation of nearby landslides mapped by the Colorado Geological Survey, completion of test drilling and test pits, installation of monitor wells, soil and rock testing, and the completion of a series of stability analyses for current slope configurations of the existing surface facility area at the Bowie No. 1 Mine. The operator, in conformance with recommendations made by its geotechnical consultants, has installed sophisticated tilt-metering devices within several of the fill benches which exist within the surface facilities at the Bowie No. 1 Mine. The purpose of these devices is to collect additional geotechnical data with which to verify past analytical assumptions and with which to complete final analysis and design, originally stipulated as Phase III of the surface facility studies, within the approved original permit. Utilizing the results of Geo-Hydro, Consultants, Inc.'s analyses, Merrick & Company, Inc., design consultant to the operator, completed a Phase II amended design for the drainage facilities at the existing surface facility area of the Orchard Valley (Bowie No. 1) Mine. The operator also completed a detailed stability analysis and redesign of the proposed final reclaimed configuration for the surface facilities at the mine. This design was submitted and approved in Technical Revision No. 28. The cut and fill areas will be restored to their approximate original contour except for an access road which will remain following reclamation. The access road will be within a 20 foot wide terrace corridor associated with the access road. In August 1986, the operator submitted a permit revision application to construct a West Mine portal facility in the East Roatcap Creek valley at the Orchard Valley (Bowie No. 1) Mine. This application proposed the construction of a new portal facility and haul road, because the existing portals at the Orchard Valley (Bowie No. 1) Mine had been rendered unuseable by an underground coal mine fire. The applicant proposed to upgrade an existing public access road to serve as a coal haul road to the proposed west portal bench, which will be constructed by a balanced cut-and-fill method. The portal bench fill included a 130-foot maximum height terraced earthen fill constructed across East Roatcap Creek. Maximum inter-terrace facial slopes did not exceed a 2.5h: 1.0v (horizontal to vertical) slope gradient. A 48-inch concrete culvert was installed beneath the cross valley fill to accommodate the 100-year flow of the East Roatcap Creek. The permit revision application included geotechnical specifications documented in the Orchard Valley (Bowie No. 1) West Mine Appendix, Volume 6, prepared by Golder and Associates, consultants to the operator. This appendix presents the results of geotechnical investigations, stability analyses and detailed engineering designs for the west portal bench cut and fill and the accompanying upgraded haul road. The stability analyses are based upon projected slope configurations and material mechanical properties obtained from material sampling and laboratory analyses. 34