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Application of Best Available Technology to Reclamation Design and Integration with Mine Planning

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Application of Best Available Technology to Reclamation Design and Integration with Mine Planning APPLICATION OF BEST AVAILABLE TECHNOLOGY TO RECLAMATION DESIGN AND INTEGRATION WITH MINE PLANNING Harold J. Hutson, P.E., P.G., BRS Inc., Riverton, WY Introduction Natural RegradeTM Case Study BRS, Inc. has utilized Carlson’s Natural RegradeTM AML Project 16N, D-9 and K Pit Reclamation Project, software to design the reclamation and stabilization of is located in an intensely disturbed area of the West Gas abandoned open pit uranium mine spoils, AML Project Hills Uranium Mining District in Fremont County, 16N, located in the Gas Hills Uranium District in central Wyoming. The overall design calls for the placement of Wyoming. This work was completed for the State of approximately 7 million cubic yards of backfill materials in Wyoming’s Abandoned Mine Land Program (AML) on the D9 and K Pits, imported from adjacent mine spoils pre-SMCRA (Surface Mining Reclamation and Control including the Central Spoils, and from local highwall Act) sites for which no reclamation obligation existed. The excavation. Figure 1 shows the location of the Central project successfully stabilized an eroding spoil dump, Spoils excavation area, as well as the D9 and K Pits fill enhanced the local view shed, created habitat diversity and area. provided a significant source of fill material for open pit highwall hazard mitigation efforts. Additionally, the project served to evaluate innovative reclamation design methods, engineering software and grade control technology. This project was nominated for a National Association of Abandoned Mine Land Programs award by the State of Wyoming. The results of this project will be presented as a case history of the Natural RegradeTM approach to surface mine reclamation. Based on the successful application of this new mine reclamation technology on the AML 16N Project, reclamation designs for spoils associated with planned underground uranium mine operations at the Velvet Mine in the Lisbon Valley Uranium District of Utah for Uranium One USA, Inc have been prepared and will be presented. Photo 1: K Pit Prior to Reclamation Critical elements will be the encapsulation of unsuitable materials, long term hydrologic stability, and sequencing The entire project is located on public lands and staging of ore and mine waste for final reclamation administered by the Bureau of Land Management, Lander, surface construction. Wyoming District Office. No access controls are in place at The goal of the Uranium One Velvet Project will be to the abandoned mine sites. The public lands are apply best available technology to reclamation planning and administered under a multiple use land policy including fully integrate the reclamation design with the mine grazing of range land, public recreation, active mining and planning. Benefits of the approach should include exploration, and oil and gas. The project site is located improved public and regulatory perception of the project, along Fremont County Road No. 5, which is a moderately facilitate mine permit approvals and the eventual timely well traveled road. Reclamation of the numerous and large release of reclamation bonds, as it is anticipated the stable abandoned open pits in the Gas Hills Uranium District has landform created through this process will result in more reduced the risk of death or injury to the public. rapid stabilization of the site to pre-mine geomorphic conditions. 1 Figure 1: AML 16N Project Site 2 Site History and Background The purpose of AML Project 16N is to mitigate The Gas Hills Uranium District was mined by multiple hazardous conditions and risk to the public associated with companies during the period from 1955 to 1981. The open pit highwalls and toxic, acid forming, and /or uranium was hosted in the Wind River formation, a radioactive mine waste materials. The D9 and K Pits are sequence of soft sedimentary layers of interbedded contiguous open pits characterized by an 8,800 foot long sandstone, clayey shales, and conglomerates. Uranium was hazardous highwall that averages over 200 feet tall. In precipitated out of ground water in classic roll front addition to the physical hazard presented by the highwall, deposits, which are found from very near surface to depths the project addresses spoils piles in the area which are greater than 400 feet. Prior to the enactment of the Surface characterized by unsuitable materials including elevated Mining Control and Reclamation Act of 1977 (SMCRA), radiological levels, low pH, and metals (including arsenic very little reclamation work was performed when mines and selenium). Reclamation of over 145 acres of barren, were abandoned or closed. The State of Wyoming severely eroded and disturbed abandoned mine lands will Abandoned Mine Lands Program has worked to mitigate be completed during the ongoing project. hazards associated with large open pits, control migration Prior to reclamation, the Central Spoils waste pile of unsuitable materials and restore watershed functionality consisted of a long, continuous 3:1 pre-law reclamation of lands in the district. Additional reclamation is being slope with failed vegetation and severe erosional problems performed by mining companies on bonded lands. Figure which were causing offsite degradation. Substantial 2, Gas Hills Uranium District aerial photograph, shows the quantities of unsuitable materials existed within the spoils extent of the mining disturbance in the district. pile, which were disposed of in designated storage areas within the K Pit. Project Hazards and Concerns Figure 2: Gas Hills Uranium District 3 Photo 2: Central Spoils prior to reclamation. Note long, continuous, eroded 3:1 slope Site Investigation and Engineering Design in the K Pit. The subject of this case study, Phase 3 - BRS, Inc. of Riverton, Wyoming provided engineering Central Spoils Completion Project, performed haulage of and design services to the Wyoming AML program for the material from the Central Spoils, as well as completed the project. The first engineering design phase included an Central Spoils area including final grading of a total of 68 investigation of the site including an inventory of the acres utilizing the Natural RegradeTM approach. Phases 4 & hazards, preparation of existing ground topographical 5 will complete the highwall reduction and final grading at mapping, and completion of a surface and subsurface the pit locations. materials investigation program. Once the site hazards and materials were identified and classified, BRS created earthworks design plans which incorporated surface water hydrological and geomorphic studies to achieve a stable final reclamation land form. The design called for the placement of approximately 7 million cubic yards of backfill materials in the D9 and K Pits imported from adjacent mine spoils (including the Central Spoils), and from local highwall excavation. The overall project was planned to be constructed in five phases, following a logical sequence to minimize haulage distances, maximize coversoil salvage, and selectively handle unsuitable materials for proper disposal. Phase 1 - Steep Slope Reduction Project, consisted of removal of material from the Steep Slope spoils pile and placement of this material in the D9 Pit. Phase 2 - Central Spoils Haulage Project, consisted of removal of material Photo 3: Placement of backfill in the K Pit from the Central Spoils pile and placement of this material 4 Utilization of Natural RegradeTM Software recommended that it be tested on the Central Spoils site. The conceptual reclamation design for the Central By applying the Natural RegradeTM software to the overall Spoils area consisted of the removal of material from the design concept as described above the final product more spoils area to construct an off site drainage channel, open closely resembles a native surface while retaining the up the view shed to include a natural tree covered ridge original elements of the design and keeping earthwork previously blocked by spoils, and provide aspect diversity quantities similar to the original design amounts. This was to the slopes rather than the long, continuous 3:1 slopes that essential for the overall earthwork balance on the project. were present. An additional component of the design was Figure 3 shows the final design contours and breaklines to expose the native, pre-mine surface along the south side which define the surface model. of the work area, with the intent of increasing coversoil With respect to aesthetics and habitat value, the Natural salvage quantities for site reclamation. RegradeTM surface appears to be superior to traditional Barry Shelley, Wyoming AML Project Manager, reclamation landform design. Key aspects of the surface approached BRS about the use of Carlson Natural include slopes which transition from convex to concave RegradeTM software, utilizing GeoFluvTM concepts. This profiles, concave drainage profiles, a high degree of relatively new software is designed to create an erosionally dissection of the surface by multiple small drainage basins, stable, topographically diverse, natural appearing landform. and meandering channel alignments to increase length with This approach is in contrast to more traditional reclamation a corresponding decrease in overall gradient. As a result, designs that exhibit long uniform slopes and maintenance the design will decrease overall runoff flow quantities and intensive runoff control structures such as channel velocities at any given point on the final surface, which diversions and rip rap drop structures. BRS completed should minimize erosional
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