There is an increasing pressure upon mines to balance their own water security against the need to provide protection to local community water supplies. This is particularly prevalent in Africa and Eastern Europe where water shortages are a very tangible concern year on year, and are expected to worsen as a result of climate change. Identifying cost effective measures to protect both the quantity and the quality of surface and groundwater reserves within areas affected by mining is therefore a key challenge: Karen Dingley, UK Surface Water Manager and Senior Water Engineer with Golder Associates (UK), discussed how experience of sustainable urban design can be applied to mine sites to achieve this.
Historically, mines have not been scrutinised too heavily in relation to their commitment to local communities and the environment in which they operate. This is rapidly changing, and there is an emerging genuine commitment (in many locations) to come to terms not only with the potential impact that the mine may have on the water environment, but how investment may in fact improve the situation for local communities.
Karen focused primarily on a case study in Western Africa: in this instance, an open-pit gold mine is surrounded by local communities whose livelihood depends mainly on sustenance crops and exportable commodities including coffee and cacao. These communities need more water than is available, both for their agricultural activity and for village life. Despite an annual rain season which can see torrential rains, river beds are difficult to capture and previously drilled wells have been incorrectly placed making attempts to access water at depth ultimately unsuccessful.
As in many Western African counties, rising commodity prices have resulted in considerable pressure to increase mining activity and productivity in this region… and shortcuts have sometimes lead to disastrous consequences: this small mine, for example, disrupted surrounding water flows in ways which affected not only the surrounding communities, but also production when the pit flooded.
Two natural river corridors on the mining property were stopped by two dams, the first to protect the pit and another to create a tailings facility. Aside from the obvious consequences for communities located downstream, who lost their access to water from these water systems, the first dam actually created an operational risk to the pit which flooded when fissures in the dam combined with heavy rainfall. In this case, because water in the pit dam was essentially clean, the solution to both problems was to set up diversion drains around the mine constructions, maintaining the continuity of flow downstream and reducing pressure on the pit dam.
The problem posed by the tailings dam is quite different, as in this case clean water from the existing river system is being contaminated: any solution will need to allow the segregation of clean water, which must be diverted to continue to flow downstream, from the tailings. Further issues relate to access control and educating communities about the dangers of this polluted water.
Another key issue in water management relates to drainage in the processing area: the absence of adequate drainage and discharge management systems allows water and harmful chemicals to run down from the plant to surrounding community areas and contaminate ground water sources. Solutions typically applied in urban environments can easily address these problems.
The first one is the creation of sustainable drainage systems: rather than a simple ditch, in which the water flows rapidly erode the slopes and ultimately create blockages, putting in a layer of topsoil and local vegetation not only stabilises the ditches but also results in a self-cleaning system. These systems are cheap to construct with on-site machinery and provide maintenance jobs for locals. Another solution is the creation of filter drains: Fine crushed rocks are very effective to remove suspended solids and particles from water, and local materials readily available from the mine site can be used. Also cheap to construct, these drains require very little maintenance. Sediment ponds complete this set-up: they are very efficient to reduce sediment load but also provide water to re-use for processing.
Aside from the risks relating to the existing operations, Karen also explored the risk emerging in the attaining exploration areas, relating to acid mine drainage. In this case, a solution which is expensive in other circumstances because it requires space and maintenance, can be perfectly adapted: constructed wetlands, or bio chemical reactors, are very effective for removing pollutants and heavy metals and to adjust pH. They can make good use of local materials which considerably brings down construction costs, and require minimal maintenance.
Water is a key requirement for miners but also easily affected, in quantity and quality, by mining and processing operations. Miners have a responsibility to the environment and to local communities to manage it sustainably. In many countries, including in Western Africa, the legislative framework is not sufficient to protect the environment and mining-affected communities: even where they are comprehensive, rules and regulations are not always applied or compliance monitored. In many cases, operational requirements and cost-driven arguments are the best way to convince miners that implementing cheap but effective methods to manage and protect water makes business sense and protects this crucial natural asset for all those who need it.
Karen Dingley is a chartered civil engineer with over 16 years experience in water engineering, integrated catchment planning, catchment hydrology and floodplain management. She is currently chair of the CB/501 (Flood Risk and Watercourses) technical committee at the British Standards Institute (BSI), and a national Council member of the Institution of Civil Engineers (ICE).