Pit lake modelling – The total system approach

Building an accurate and defensible model to describe the geochemical character of water that collects in a pit lake after surface mining activities involves integrating geochemical, hydrologic, and climatologic data with the lithologic units surrounding the ultimate pit surface (UPS). This total system approach entails developing a coarse regional groundwater model that is refined into a finer localized model of the pit area. The results of the groundwater model are integrated with detailed geologic and geochemical models of the UPS, groundwater chemistry, and other factors such as climatic conditions and surface runoff. Spatial and temporal variability is considered, using GIS methods coupled with finite element (Feflow) or finite difference (Modflow) groundwater flow models to analyze the interaction between groundwater model nodes and geologic nodes on and adjacent to the UPS. This information is crucial in calculating chemical mixing models that depict the behavior of pit lake water chemistry over time. The lifespan of such models may extend several hundreds to even a thousand years, necessitating a robust framework for understanding the chemistry and behavior of pit lakes during the closure phase of mining operations.