Option analysis to reduce solute loading to surface water receptors from a Ranger mine tailings storage facility

Authors: Jones, T; Askar, A; Pickens, J; Sigda, J; Fryar, D; Paulka, S; Stockdale, R Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2415_41

Cite As:
Jones, T, Askar, A, Pickens, J, Sigda, J, Fryar, D, Paulka, S & Stockdale, R 2024, 'Option analysis to reduce solute loading to surface water receptors from a Ranger mine tailings storage facility', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2024: Proceedings of the 17th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 569-584, https://doi.org/10.36487/ACG_repo/2415_41



Abstract:
The Ranger mine above-ground tailings storage facility (TSF) safely held tailings and process water through multiple expansions over more than 40 years. Given that the mine is surrounded by, but separate from, the Kakadu National Park, Energy Resources of Australia (ERA) and stakeholders have sought to understand the migration of TSF-derived groundwater solutes and the risks posed to surface water receptors. ERA and stakeholders are examining potential impacts to surface water concentrations from the TSF and other mine-related solute sources after mine closure. In 2020, INTERA estimated the predictive uncertainty in post-closure loading from 20 groundwater solutes to surface water through a calibration-constrained groundwater uncertainty analysis. A surface water model used the predicted peak groundwater solute loads at three probability values to predict surface water concentrations, which suggested additional mitigation may be beneficial before closure. Design of the TSF deconstruction and evaluation of mitigation options to reduce post-closure groundwater loading are underway. A preliminary qualitative assessment of multiple remediations options led to a quantitative assessment of five options using numerical modelling. The modelling work, developed in consultation with stakeholders, provided post-closure solute loads for use in assessing the effectiveness of the five remediation options. The results indicate that the greatest reduction in groundwater loading will most likely be achieved with a clay cap to mitigate the plume in the weathered rock beneath the TSF footprint. Combinations of options will continue to be investigated to better understand the potential for further reducing loads. This study is the first step in ERA’s development of mitigation options for reducing surface water concentrations from the TSF and other nearby mine-related sources.

Keywords: groundwater, tailings, plumes, remediation options

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