15 April, 2020

How can EO ensure a safe future for tailings dams?

Mining is an integral component of many economies throughout the world. The sale of mineral commodities between countries holds up trade agreements, not only for developed countries but developing countries too. It is also essential to provide the raw materials needed to manufacture most things we need in our daily lives.

However, mining finds itself sitting at the centre of a heated environmental and economic debate. For all the goodwill mining can bring to a nation's Gross Domestic Product, it also carries risks of significant environmental impacts. 

The mining industry is responsible for monitoring the environmental impacts of their operations and the subsequent rehabilitation of closed mines. For most mines, the largest environmental risk are tailings dams

If incorrectly managed, tailings dams can pose a serious threat to human health, the environment and the company’s finances. Recent high profile tailings dam failures have seen all of these impacts, as well as affecting the industry’s social licence and bearing regulatory consequences. But now, with the advancement of Earth Observation methods, it is possible to detect minute shifts and changes to tailings dams early, enabling dam failures to be averted or, at least, impacts to be minimised. 

What are tailings dams?

In mineral processing, a mineral-bearing ore is subject to a variety of physical and chemical processes to separate the mineral from the material it is hosted in. But with the mineral concentrations as low as 0.1% of the ore and processing that utilises strong acids or toxic chemicals, mineral processing can produce large amounts of toxic residue called ‘tailings’. The volume and toxicity of tailings presents a challenge for their effective management as they must be safely isolated from the world around them, both during operations and in perpetuity. 

Mining companies store tailings in ‘tailings storage facilities’ and these are often in the form of dams. Once the mining process is complete, the tailings dams are generally capped and the land terraformed for rehabilitation. While there have been some instances of closed dams being unstable, leaking pollutants or presenting a  risk of collapse, it is generally operating dams that are most at risk of failure. Catastrophic dam failures such as those seen in Brazil in recent years seem to occur with little warning and cause widespread damage to the environment and hundreds of deaths. 

How do tailings dams fail? 

A number of factors, both natural and manmade, can cause a tailings dam to become unstable and result in collapse or failure. Some examples are sinkholes, earthquakes, intense rainfall,  flood events, wind, substandard design and construction, and seepage.

According to a study released by the Australian Centre for Geomechanics, it is estimated that each year there are on average two reported and two unreported tailings incidents globally, and that these annual failings are more likely in active tailings storage facilities, rather than inactive. 

The risk and the very real implications of failures has seen companies and governments turn to technology to help predict and prevent these incidents from happening. 

How can Earth observations predict failures and ensure the sustainable management of tailings dams? 

Satellite-based Synthetic Aperture Radar sensors (SAR), interferometry techniques and modern computational power provides the ability to measure large scale, but subtle, ground movements. 

Interferometric SAR (InSAR) is a technique that maps the changes in ground height with millimetric precision through the phase differences between returning microwave signals. 

With the European Space Agency’s Sentinel-1 satellite providing open access SAR data, and several higher-resolution commercial satellites available, there are now multiple options for InSAR to be used for monitoring the small changes in tailings dam walls that can precede catastrophic failures. 

This permits on-ground investigation, operational changes to prevent a failure and activation of emergency management plans. 

A good example of how EO techniques can be used to predict and prevent tailings dam disasters has been shared by the Australian Centre for Geomatics in Perth. The study covers how InSAR data showed low-magnitude subsidence signals across the tailings dam at Cadia Mine in Australia, during the year preceding its collapse. 

Do you need assistance implementing Earth observation techniques to monitor the safety of your mine site? 

The team at EO Data Science and NGIS Australia have been working with Decipher who have built an innovative and high performing packaged Tailings Storage Facility (TSF) solution to provide monitoring and insights for TSF compliance. Decipher TSF leverages Google Earth Engine and InSAR outputs to provide effective monitoring at scale to reduce risk and improve compliance.

For more information on the role of remote sensing in preventing tailings dams failures check out this episode of Location Matters: http://ngisaustralia.libsyn.com/lm-33-remote-sensing-for-the-resources-industry-0.   

Sources: Thomas, A, Edwards, SJ, Engels, J, McCormack, H, Hopkins, V & Holley, R 2019, 'Earth observation data and satellite InSAR for the remote monitoring of tailings storage facilities: a case study of Cadia Mine, Australia', in AJC Paterson, AB Fourie & D Reid (eds), Proceedings of the 22nd International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 183-195, https://doi.org/10.36487/ACG_rep/1910_11_Thomas
Image: Rio Tinto


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