Sustainable water management in mining, a global imperative
With the global water shortage, there’s greater pressure for mining companies to reduce their freshwater demand, particularly in dry areas where local authorities may restrict or oppose water use. But water scarcity isn’t the only challenge facing mining operations. They must also manage flood risk to mitigate spilling, tailings dam failures and manage water quality to prevent pollution to the surrounding environment.
Environmental factors and climate contribute to the complexity of developing a sustainable mine water management system. In dry climates like the southwestern United States, northern Chile, southern Peru, and northern Africa, the key issue is a deficit in water supply. In these locales, water management should focus on conservation, like collecting, storing, and reusing contact water from the tailings storage facility, seepage, open pit, and/or underground mine. For wet regions like Colombia, Indonesia, and New Caledonia, the greatest challenge is managing flood events and eliminating the risks of spilling, erosion, and infrastructure failure. Finally, cold climate regions like Canada, Russia, and Finland must consider the large quantity of water generated from snow melt and ice thaw and manage the impacts of permafrost on drainage facilities. Each mine site requires a tailored and holistic solution.
Mine water types and uses
The mining industry uses large quantities of water for mineral processing and refining, dust suppression, slurry transport, tailings disposal, and potable and hygiene needs. Based on its quality, the water is classified into three categories:
- Raw water is supplied from precipitation, groundwater, rivers, and lakes. It’s used for employee needs, process make-up water, shaft and underground mine water demand, mobile fleet washing, fire water, etc.
- Compliant flow (non-contact water) is clean surface runoff, or water that’s compliant with the applicable legislation requirements that can be directly released to the environment without treatment. This water is normally segregated from the contaminated mine areas to reduce the treatment requirement and the facility sizes for non-compliant water management.
- Non-compliant flow (contact water) is water that has contact with mining, mineral processing, and tailings disposal and, as such, is not suitable for direct release into the environment. Normally, this type of water is collected and reused on site (i.e., for process use, dust suppression, or soil conditioning, etc.) to the maximum extent to minimize the freshwater consumption. Any excess non-compliant water from the site will need to be treated to meet the effluent discharge criteria.
Water management in a tailings facility
In the past thirty years, there have been more than one hundred tailings dam failure incidents reported in the world. The spillage and/or release of large quantities of mine waste and water can have catastrophic impacts on the surrounding community and environment —and the costs and clean-up work for the operating company are severe.
Several factors must be considered in mitigating the risk of a tailings dam failure and designing a safe water management system:
- Safe operation: during normal operation, the water pond within the tailings basin should be maintained at a small size or eliminated and kept a safe distance away from the tailings dam. Constant monitoring of pond levels, early warning systems, and vigorous reporting are critical factors to operating safely.
- Water storage and decant capacity: tailings dams must provide sufficient storage capacity to retain the Environmental Design Flood (EDF) without releasing untreated water to the environment, and it must have sufficient decant capacity to draw down the pond after the storm event.
- Extreme flood management: an emergency spillway should be provided at the tailings dam to safely pass an extreme flood event without overtopping the dams, and to safely release the water along a designated flow path that has less impact and damage to the surrounding environment.
Understanding effective water recovery can significantly reduce the cost of the project and subsequent operations. Involving specialized water experts who have experience with conceptual and detailed operational engineering design, water balance modeling, and water cycle optimization is key. Our approach to water management goes beyond the conventional to provide sustainable results by optimizing the entire system.
Solutions for a sustainable future
Tailings disposal methods have a significant impact on water management and conservation. Advances in technology have helped move us away from the conventional un-thickened slurry tailing deposition to dry stacking and paste disposal. These methods have important benefits for the facility, including reduced water consumption, reduced facility footprint, less seepage and contact water for treatment and discharge, and reduced consequential risks of dam failure.
Digital solutions have also allowed us to develop site-specific, real-time monitoring systems, as well as improved forecasting and reporting tools. Water balance models can be used to simulate water quantity and contaminant loadings at selected locations and assess the performance of the water management system under different climatic conditions and statistical storm events. With improved data collection and reporting, operations can reduce the risk of flooding and environmental contaminations.
Our project experience, combined with our unique, world-class multidisciplinary technical teams, enables us to fully understand the full scope of a project, identify gaps and risks, and develop strategic plans and solutions for compliance with current and likely future regulatory requirements.
To support the industry’s efforts, the International Council on Mining & Metals has developed a “Water Stewardship Framework” that provides high-level guidance on responsible water management. More comprehensive guidelines have also been developed by international technical associations to provide instructions on mine water management design and dam safety, including the International Commission on Large Dams and its affiliates.
Good water management practices can reduce water consumption and secure water supply, increase operation efficiency, mitigate water-related risks and liabilities, and improve collaboration from all stakeholders―making it a key focus of many mining companies’ sustainable development plans.
Technical Director, Mine Hydrology
Jie is a senior hydrologist/hydrotechnical engineer with extensive experience in mine, landfill, industry, and municipal site water management. She has provided technical expertise for more than fifty mining projects in over twenty countries from the Arctic to the tropics. Jie has led mine water management studies covering all stages of the project cycle from baseline to detailed engineering. Her experience also covers construction and operation phases water management, closure, and rehabilitation planning. Her assignments included field investigations, mine water operation system audit and optimization plan, watershed studies, drainage/diversion plans, site-wide water balance, stormwater and contaminated runoff management, water and tailings dam OMS/EPP preparations, flood risk assessments, dam breach and flood inundation studies, hydrology/hydraulic modeling and design, sediment/erosion control plan, due diligence reviews, and project/task management.