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Abstract

Predicting seepage rates and water quality from waste rock and heap leach facilities is critical for mine operations and closure management. Flow rates and the chemical composition of seepage from mine waste facilities (MWFs) are controlled by unsaturated solution and airflow dynamics and mineral dissolution/ reaction rates. Although spatially-distributed reactive unsaturated flow and transport models can be used to simulate physical and chemical interactions between the porous media, solution, and gas, they suffer from practical issues related to computational expense and lack of data to validate parameter choices in the highly heterogenous and large-scale novel flow systems that exist in MWFs. We introduce MWF MACRO, an Excel-based tool designed for practitioners to model the water balance within large catchment-scale variably saturated mine waste facilities. MWF MACRO simplifies computationally intensive physics into key processes relevant to the dump water balance while retaining physical interpretability. The application of the methodology to simulate MWF seepage under operations and a closure scenario is explored. The application demonstrates the model’s predictive capacity to simulate high-resolution (i.e., daily) seepage responses and provide reasonable estimates of unobserved variables, such as the effects of flow through less- and more-mobile (i.e., macro-) pore flow domains.