Mining personnel have a different interpretation of the term “mine water management”. For the rock mechanics engineer it is the de-pressurisation of a slope in an open pit, for the metallurgist it might pertain to the water contained in the process circuit, and for the tailings engineer, the waste circuit.
In this newsletter we have used the term in its broadest context to mean water impacted by the mining project, the impact of water on the mine, and the water managed within the greater footprint of the site.
We believe the management of water on a mining project will become ever more important in the future. In arid areas water is a scarce and expensive resource to the extent that some projects will stall because of a lack of water or because the cost of supply will be prohibitive. In high rainfall areas, the containment of contaminated water might not be possible without large structures and transfer systems, whose construction and operating costs will again be large. Treatment of water, both as supply and before release to the environment, has historically been expensive. Added to this is the ever increasing regulatory environment, which might make discharge impossible.
Water issues should be considered in an integrated way during design, start-up, operation and closure of a mining project. During design, failure to integrate the various components can significantly underestimate the time and cost of implementation. During start-up, extreme climatic conditions, unplanned during design, can cause flooding of construction works and initial pits or require additional water supply. Operational issues could include incorrect estimations of plant make-up water, or tailings circuit imbalances or changes to the volume and quality of water as process plants expand or change process technologies. Closure of any mine will include pit lake hydrology and chemistry, runoff from rehabilitated dumps and residual contamination of plant areas, amongst the issues of concern.
We have addressed many mine water management components in this newsletter, including the supply of water in arid areas, the protection of sources, depressurisation of pit slopes, water balances, storm-water management, water chemistry and last, but not least, disposal. We have tried to show where integration can save costs, in, for example, the use of boreholes for both hydrological and geotechnical purposes. We have showcased projects from various regions in the world. Some of the tools we use, including water balances, salt balances and risk assessments, are also discussed.
The partially flooded open pit in the picture is the result of poor implementation of storm water controls, and will lead to major expense in rehabilitation, as well as significant loss of production, and could have been avoided with due care.
