SRK recently undertook the closure design and implementation for the tailings facility at a defunct operation in central Nevada, USA. The facility stored gold cyanide tailings in three individual cells of differing heights and construction.
Initially, SRK needed to access and review all the as-built records and the facility’s annual operational report as there was limited knowledge of cell design and condition. The operation had been defunct for a number of years and portions had been designed by three different engineering consulting companies.
Following this review and limited site visits, and in accordance with state reclamation requirements, the strategy adopted for developing the closure design was to define the potential failure modes and then develop engineering solutions to mitigate them. In essence, SRK used a risk-based approach to the closure design.
The identified modes of failure included overtopping, slope failure, failure to manage the draindown of entrained tailings water, and the failure of the decant inlet and pipe systems.
This risk-based approach also led SRK to design measures for the long-term management of stormwater infiltration and runoff, as well as runoff from surrounding catchments during closure.
Published papers and statistics related to tailings failures, as well as SRK and client experience with numerous other closure designs were important components of the approach.
The closure was successfully implemented and included installing closure spillways to the various cells, sealing the decant pipes and capping the exposed tailings. The draindown seepage was managed passively via evapo-transpiration cells constructed in the water ponds.
