10 Wrap Up

This book has provided an overview of the ways in which the hydrogeologic setting forms an integral component of mineral resource development projects and how the hydraulic properties of mine waste materials influence the potential impact of mine wastes on the surrounding environment. An understanding of the site geology and groundwater regime is fundamental in ensuring safe operational practice, rock mass stability, stability of tailings dams and waste rock stockpiles, and sound environmental stewardship. Issues related to groundwater arise in project development and permitting, in day-to-day operations, in closure planning, and in the post-closure period.

Reliable prediction of groundwater inflows to mine workings and potential water quality impacts in the surrounding environment are challenging due to the complex nature of the geologic setting in which mines are often developed. Advances in site characterization methodologies and the development of powerful computational tools are contributing in a significant way to more reliable forecasts of water flows and potential impacts. Governing processes are generally well understood, as are protocols for collection of field data and approaches to data synthesis. There remains a need for improved insight to the means for using measurements made at a small scale to forecast system response at a larger scale. For example, characterization and quantification of infiltration pathways through a waste rock stockpile, if needed to make a prediction of solute loads at the base of the stockpile, largely remains an empirical exercise in practice.

Recognition of the limits to predictability needs to be appreciated by all stakeholders in mineral resource developments. For example, it may be that there are wide error bars on prediction of the time for a pit lake to reach an equilibrium position or the spill point elevation if groundwater inflow rates are the controlling factor. While a base case analysis may indicate a time say, of 250 years, uncertainties in defining the hydrogeological system could lead to bounds on the prediction of as few as 100 years or more than 500 years. Another example of the limits to predictability is provided by mineral resource developments in terrain with karstic limestone; which reflects the difficulty in determining the nature of the interconnected flow pathways through karst and where all the outlet locations could occur. There is also the general challenge in prediction of solute arrival times, and concentration values even for a non-reactive solute, if no data are available to calibrate the solute transport model, which is the common circumstance during the project development stage.