Dynamic groundwater-pit lake coupling for a multi-pit closure application in a structurally complex aquifer: a case study

Authors: Ventura, L; Lopes, G; Silva, L; Garcia-Forero, A Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_114

Cite As:
Ventura, L, Lopes, G, Silva, L & Garcia-Forero, A 2026, 'Dynamic groundwater-pit lake coupling for a multi-pit closure application in a structurally complex aquifer: a case study', in AB Fourie, G Boggs, J Heyes & M Tibbett (eds), Mine Closure 2026: Proceedings of the 19th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-14, https://doi.org/10.36487/ACG_repo/2615_114



Abstract:
Predicting long-term pit lake recovery is a key challenge in mine closure, particularly in multi-pit systems where groundwater recovery, pit lake filling, and hydraulic connectivity evolve. This paper presents a case study applying a dynamically coupled groundwater-pit lake water balance modelling framework to assess post-closure recovery of a complex multi-pit closure system in the Pilbara region of Western Australia. Two closure scenarios were assessed over a 300-year simulation period: a base case comprising ten persistent pit lakes and a backfill case comprising four remaining pit lakes following partial backfilling. The modelling framework linked a three-dimensional transient FEFLOW groundwater model with a GoldSim water balance model through a Python-based interface, enabling bi-directional exchange of hydraulic information without modification of either model. The groundwater model was calibrated against ten years of groundwater level observations from 132 monitoring locations prior to implementation of the coupled framework. The approach was developed to represent the structurally complex hydrogeological setting, characterised by groundwater compartmentalisation and evolving pit-to-pit interactions. The results indicated that the groundwater recovery rate was greatest during the first decades following closure and declined progressively as hydraulic gradients declined between the pits and surrounding aquifer. Groundwater levels approached quasi-equilibrium after approximately 50–100 years but remained below premining levels in both scenarios. Evaporation remained the dominant long-term control on pit lake water balances, while pit lake behaviour evolved throughout the recovery period as hydraulic connectivity between pits changed. The backfill case generally produced higher long-term pit lake levels and smaller groundwater recovery deficits compared with the base case. This case study evaluated groundwater recovery, pit lake water balances, and hydraulic connectivity during post-closure recovery. Computational demands limited the analysis to three deterministic realisations and therefore constrained the probabilistic assessment. The results illustrate how groundwater-pit lake interactions changed through time under the evaluated closure scenarios.

Keywords: pit lake, model coupling, FEFLOW, GoldSim, groundwater-surface water interaction.

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