About 60% of Tailings Dam failures are attributed to water. Climate change is causing extreme weather events that is only making the problem worse. It is more important than ever to ensure that your tailings dam is being managed as effectively as possible.
"High rainfall or snow melt or overtopping of the dam can cause a tailings dam to fail," says Alistair James, Non-executive Chairman at IsoMetrix. "It might also be due to piping or seepage failures but those are actually less common than overtopping and extreme events."
Water plays a big role in tailings dam safety. Climate change makes predicting water levels in a tailings dam difficult.
Mining companies are not doing enough to consider climate change risks in the design and operation of Tailings Storage Facilities (TSF). Climate change poses a significant risk to TSF because tailings dams have been designed for certain precipitation levels.
Climate change brings unpredictable and extreme weather events. Most tailings dams have been designed based on historical data according to Alistair. "We are designing for specific probability of occurrence based on historical records rather than forward looking records," he says.
Climate change also increases the frequency of droughts in certain parts of the world. Some places are getting wetter while others are getting drier, and these drier areas are more prone to extreme events such as flash floods. Furthermore, as areas get drier, mines become more water stressed.
Often, tailings are used to store water instead of decanting the water off the top of dam, and that can overtop and fail in various ways. "There is a tendency to try to store water for the next dry season so that the mine can continue operating the plant," explains Alistair. "Sometimes the tailings facility is seen as a water storage facility, which of course they aren't."
While mines should only store water in facilities designed to be water dams, often they do not have enough storage. So, when extreme weather events occur, the storage facilities become stressed. "Because the water stored in the TSF is not clean water, it cannot simply be discharged into the environment," says Alistair. "Compounding this problem is the fact that mines often to not have the necessary water treatment facilities, or the facilities are not big enough to treat and discharge that water. This is how risks creep into tailings dam management."
Keeping a close eye
Tailings dams are civil engineering structures. But, unlike a water dam that is designed and constructed in a defined period, a tailings dam is designed and then built over 20 to 50 years. Tailings dams needs constant surveillance and are more intensive structures than water dams.
"We look for any warning signs in our surveillance," explains Alistair. The management of the dam needs to be monitored carefully to ensure it is being correctly operated and whether the water levels in the dam are within acceptable thresholds or not.
Satellite imagery such as Google Earth is often used in the design and maintenance of a tailings dam. However, such imagery is always out of date. "Google Earth is probably the most common tool that is used," explains Alistair. "But, because the imagery on Google Earth is always out of date, it is very useful for design purposes, for understanding the surrounding area and for seeing the progression of the tailings dam over time. It is not necessarily useful for monitoring critical controls on the tailings dams, to maintain the safety of the dam."
Drones are regularly used in surveillance of tailings dams. "I use one for surveillance because you can see so much more, and they are easy to maneuver and manipulate," says Alistair. Drone imagery is useful because the drone can cover more distance than a land vehicle and tracks GPS coordinates with the images as well. "You might be looking for evidence of seepage or evidence of problem areas, and you can cover so much more ground and see it so much better from a drone, than even in a helicopter," he says.
Critical controls in Tailings Management
Stewardship is arguably the most important critical control in tailings management. "Are the right people and the right management in place?" asks Alistair. Because tailings dams are built over long periods of time, there needs to be continuity in managing the data relating to the TSF. If information is hidden in spreadsheets or worse, in paper-based systems, warning signs can be lost. The people responsible for managing the facility must understand the complex nature of the risks involved and conduct a thorough risk assessment. A risk register needs to be maintained at regular intervals and a management system needs to be in place to track it.
"Stewardship and governance are priority controls," argues Alistair. "As part of stewardship you should really have an independent design engineer appointed, because you are building the facility over several years you need somebody who has a high-level knowledge who is watching this facility at regular intervals and understanding and managing these risks."
The IsoMetrix Tailings Management System
"I was involved in the development of the IsoMetrix Tailings Management system, because we saw the need arising about ten years ago," says Alistair. IsoMetrix offers an incomparable Tailings Management System.
The IsoMetrix Tailings Management system gives you the ability to set trigger levels, which are linked to actions and responsibilities which are linked to due dates and perhaps even audits. There is a huge cost associated with finding the right data, and it is difficult to manage data that is hidden in spreadsheets across multiple servers. Over the lifetime of a tailings dam, there are likely to be documents that for whatever reason, people have forgotten about. "A lot of risks on tailings dams are because people forget about risks," says Alistair. It is important to have technology in place, to build in efficiency and effectiveness in managing a tailings dam safely.
Alistair has been IsoMetrix's non-executive chairman since 2000. He is a qualified Civil Engineer with over 30 years' experience dealing with a wide range of technical, environmental and social issues for a range of industries, legal advisers, and financial clients.
Alistair is a recognized international specialist in providing sustainable solutions to mine waste and water management issues. He has been a registered professional engineer since 1989.