Yallourn coal mine water quality closure tool

Authors: Landers, M; Long, P; Gore, S Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_26

Cite As:
Landers, M, Long, P & Gore, S 2026, 'Yallourn coal mine water quality closure tool', 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. 1-12, https://doi.org/10.36487/ACG_repo/2615_26



Abstract:
This technical paper presents development and application of a water balance and water quality (WB/WQ) model for the Yallourn coal mine in Victoria’s Latrobe Valley. The project proposes conversion of the Yallourn coal mine voids into high-level pit lakes within the Yallourn Township Field (YTF) and Yallourn East Field (YEF). The modelling objectives were to estimate final lakes water quality and their long-term evolution, quantify water demand for initial filling and ongoing top-up, assess the influence of climate variability and climate change and compare alternative filling scenarios. The WB/WQ model integrates hydrological, hydrogeological and geochemical components. Catchment run-off was simulated using the Australian Water Balance Model (AWBM), incorporating stochastic climate sequences and projected rainfall and evaporation factors. Groundwater flux inputs were derived from external groundwater modelling. Pit geometry, seepage, direct rainfall, evaporation, river inflows and managed transfers were represented within a probabilistic framework (GoldSim). Extensive geochemical investigations, including pit wall washing, static testing and kinetic leach column tests on coal and overburden materials, were undertaken to derive source terms. Geochemical reactions, mineral precipitation and atmospheric equilibration were evaluated using thermodynamic modelling (PHREEQC). Model results indicate that lake filling timeframes, top-up requirements and long-term water levels vary by scenario and climate condition. Salinity (total dissolved solids, TDS) generally increases during filling before stabilising, with differences between YTF and YEF reflecting source material geochemistry and hydrological connectivity. Predicted pH and metal concentrations are sensitive to iron inputs and solubility controls. Thermodynamic modelling suggests precipitation of iron (oxy)hydroxides can substantially reduce dissolved aluminium and copper concentrations, with variable effects on zinc. Climate change influences are moderated by dominance of fill-water inputs and availability of supplementary sources. Overall, the model provides a defensible basis for environmental assessment and closure planning.

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