Methodology to evaluate reclamation stability of an inactive uranium mill tailings impoundment

Union Carbide Corporation is committed to reclaim its inactive tailings area in Gas Hills, Wyoming. This inactive tailings area consists of three impoundments whose surfaces vary in elevation by approximately 50 feet. The reclamation plan requires cutting of downstream embankments and filling of upstream areas to achieve an overall reclaimed slop of 10H:1V. Because of this and the method of initial tailings deposition, up to 50 feet of surcharge fill material will be placed over pool areas which will be underlain by soft, fine grained slime material. Preliminary investigations indicate that the large volume of surcharge placed on these slime areas will result in slope failure unless techniques to consolidate the slimes are implemented prior to fill placement. The following plan was implemented to determine the most feasible techniques and to estimate the time required for stabilizing this area: conduct additional field and laboratory investigations needed to characterize the impoundment areas and evaluate their engineering behavior during reclamation; determine the most feasible technique(s) that will improve stability of the impoundment and reduce the time required for reclamation; evaluate the effects of the proposed plans on final reclamation and long-term stability of the area; develop a monitoring plan to verify the progress of tailings stability and to monitor the final construction phase of the reclamation plan