Abstract
Water quality is one of the key factors in defining a post-mining use for water-filled voids. The uncertainty of modelling the water quality of a complex system like pit lake using limited multidisciplinary information and assumptions, has imposed a significant challenge in understanding the long-term water quality of pit lakes. This project combined field measurements with predictive water quality modelling to identify parameters that are important in reducing the uncertainty associated with simulating the long-term closure of final coal open-cut pit voids. Two pit voids from Australia were studied. The modelling results showed that salinity was likely to be the biggest environmental risk in both voids. The water level in both pits was predicted to be relatively stable and suggests overflow should not occur largely due to the impact of evaporation and low inflow rates. Simulated long-term water quality at both pits indicates the significant impact of climatic conditions, such as evaporation, may pose to the final void system. This study also highlighted the significant role that assumptions of the laboratory to field scale load scaling factors and the site-specific geochemical characteristics of spoils play in predictions of the long-term final void water quality. Overall, the project demonstrated the utility of field monitoring and coupled hydrological, hydrochemical and hydrogeological modelling using GoldSim to predict water quality evolution in pit lakes. Ongoing monitoring and evaluation against model outputs will be required to reduce uncertainty in water quality predictions required to evaluate the final use of water-filled voids.