Groundwater inflow to open-pit and underground mines creates significant impacts both on mine operations and on the environment. Issues that commonly need to be addressed at different stages of engineering or environmental/ permitting studies include: (a) Engineering and economic risks associated with groundwater inflow; (b) Most efficient active dewatering option that can be implemented to significantly reduce residual passive inflow to the mine; (c) Optimal regime (pumping rates and wells spacing) of the dewatering system; (d) Optimised mine to reduce both pumping costs and hydrogeological risks to a project; e) Quality of mine-water discharge; (f) Environmental impact of mining/dewatering on the groundwater system and the surface water bodies (rivers, lakes, streams, springs, etc); and (g) Post-mining conditions (pit lake and flooded mine) after mining has ceased.
Some of these issues can be resolved at the initial stages of the minedewatering assessment by using simple analytical solutions (i.e., scoping study). However, at more advanced levels of study (prefeasibility, feasibility, mine design or operations), those analytical solutions can be too simplistic and inaccurate. Groundwater flow in the vicinity of open pits or underground mines is three-dimensional (3-d) in most cases; consequently, 3-d numerical groundwater flow models must be based on 3-d hydrogeological data if they are to become reliable predictive tools for answering the questions listed above.
This article draws on specific project cases at different levels of study to show the advantages of using numerical groundwater modelling for mine dewatering projects with complex hydrogeological conditions. Data requirements, major phases of modelling, and practical use of the model as a predictive tool for evaluation of the mine dewatering requirements and associated environmental impacts are discussed.
