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Climate change and mine waste management

climate change

With climate change becoming a growing issue, companies will need to incorporate more extreme weather events into mine design going forward.

During a cyclone, a mine in northern Western Australia receives almost a year’s worth of rain in 24 hours. The deluge is at least a one-in-100-year weather event.

Fortunately, the mine’s structures and waste management systems withstand the flooding. The mine owners factored in the probability of such weather as part of their climate change modelling.

But as temperatures rise each year, land at the mine becomes drier. Vegetation struggles with the heat and is less effective as erosion control. Dust and air quality become bigger issues for the mine and nearby communities.

At the same time, cyclones move further south and their intensity increases.

In 2050, a category-five cyclone crosses land. The mine receives more than a year’s rain in 24 hours.

The flooding is described as a one-in-300-year event.

The mine’s waste management systems fail during the “rain bomb”. The mine’s tailings dam collapses, releasing acidic material in waterways and damaging biodiversity. The clean-up is expected to take decades and cost hundreds of millions of dollars.

This hypothetical scenario, of course, might never happen. Much depends on mine location and the resource sector’s response to climate change risk. But mine design will have to factor in hotter temperatures and more intense rainfall events in coming decades as the climate warms.

“Extreme weather events are expected to become more frequent because of climate change,” SRK Consulting environmental geochemist Nicole Dunne said.

“Factoring in the risk of a one-in-100-year weather event into mine design and rehabilitation planning is no longer enough. Companies must also consider what a one-in-300-year weather event looks like and how that could impact their mine.

“This a multi-generational risk. If you are planning a mine today, you need to model what the climate will look like in 2050 and beyond.

“Even conservative climate modelling predicts the frequency and magnitude of extreme weather will increase.”

Mining companies need to determine the potential costs of extreme weather events.

Parts of WA are already experiencing hotter summers, lower annual rainfall and more intense rainfall events.

Average annual rainfall in Perth is around 700 millimetres (mm). In 2020, Perth recorded its second-highest annual rainfall at 892mm. That was partly due to 271mm falling during an exceptionally wet July. Intense rainfall that month damaged some buildings and caused several injuries.

The Pilbara and Kimberley regions in northern WA are also experiencing hotter temperatures and more intense rainfall. In January, several Pilbara towns broke records for their hottest temperature.

That was followed by heavy rainfall across the Pilbara and flooding in some areas. In February, parts of the Kimberly had their heaviest rain in 120 years and battled damaging winds.

Mine waste management planning

Dunne’s colleague, Joe Rola, said mining companies need to consider the intensity and interval of extreme weather events in waste management planning at mine sites. Rola, a geotechnical engineer, is a principal consultant (mine waste) at SRK.

“From an engineering perspective, companies will have to incorporate a higher probability of extreme weather events occurring more often,” he said.

“For example, a large flood that historically occurred on average once every 100 years might occur several times during that period.”

Rola said hotter temperatures exacerbate flooding risks at mine sites.

“As we get more extreme heat days and longer droughts, rainfall run-off can increase the quantum of surface water requiring management at mine sites. The surface crust becomes thicker and soil absorbs less water.

“Vegetation can be an important consideration for mine waste management design. Some plants that have adapted over geologic time to dry, hot conditions are starting to show signs of stress as climate conditions change too fast and we experience longer, hotter summers.”

Rola said less vegetation means more soil erosion and water run-off.

“Where practical, the incorporation of vegetation cover as part of mine closure and rehabilitation planning can lead to a reduction in the need for engineered solutions to manage erosion,” he said.

An opportunity

Climate change is also an opportunity for forward-looking mining companies that implement strong climate change modelling processes to communicate their approach to stakeholders.

“Investors need to understand how mining companies are responding to climate change risk,” Dunne said. “They want to know companies are factoring in a potential increase in the frequency and severity of extreme weather when building projects.

“For example, that a mine’s tailings dam can withstand a larger weather event than we are used to.”

Mine tailings after dam collapse.

Dunne said leading mining companies are examining ways to create value from changing weather.

“This might include developing hydroelectricity operations at mine sites that harness rainfalls to generate power. Or use solar energy. We believe mines will become much more energy self-sufficient in coming decades through the development of renewables on-site or in the mine’s hub.”

Collaboration is another climate change opportunity.

“We expect more mining companies in an area will work together on climate-change risk,” Dunne said. “They might collaborate to develop renewable energy to power the mines and local communities, or build water-storage facilities that can help local farmers.”

The starting point is modelling the risk of extreme weather for mine design.

“Companies can then make a more informed assessment about the probability and potential costs of climate change on their operations. They can decide if the risk warrants extra investment in mine structures to withstand more intense weather,” Dunne said.

“The opportunity is to incorporate that thinking into medium and smaller mining organisations and help more parts of the mining sector respond to climate change risk.

“Nobody knows for sure how climate change will play out. The only certainty is that the climate is changing and mining companies need to plan for that now.”

Eight tips in mine waste management during climate change

1. Engage the board: Boards should understand how the organisation’s assets would fare if they were struck by extreme weather event, and make climate change a key part of governance oversight.

2. Risk register: Like other risks, extreme weather risks should be monitored, measured and tested as part of the organisation’s risk register.

3. Scenario testing: Model how the mine’s operations would withstand an increase in the frequency and severity of weather events. Incorporate extreme scenarios greater than the typical design return period.

4. Quantify impact: Determine the potential cost impact of those events and estimate their probability. Provide a basis to help companies determine their response to extreme weather risk, given the possible costs.

5. Test existing assumptions: Consider assumptions about extreme weather events that underpinned mine design. Understand if an existing mine’s structures were designed to withstand less severe or less frequent weather events.

6. Collaborate: Be open-minded to solutions. Climate change presents an opportunity for forward-looking companies to take advantage of hotter temperatures and larger rainfall events.

7. Communicate: Inform stakeholders on how the organisation is approaching climate change risks. Recognise that many consumers, communities, investors, employees and other stakeholders ascribe a premium to companies more proactive and transparent on climate change risk.

8. Share lessons: The mining industry has a long way to go with understanding and adapting to climate change risk. Share findings on best practice in the design of mine waste management for extreme weather events, so others can learn from them.

SRK Consulting is a leading, independent international consultancy that advises clients mainly in the earth and water resource industries. Its mining services range from exploration to mine closure. SRK experts are leaders in fields such as due diligence, technical studies, mine waste and water management, permitting, and mine rehabilitation. To learn more about SRK Consulting, visit www.srk.com.

This feature appeared in the April issue of Australian Resources & Investment.

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