In the heart of Alberta’s oil sands region, a lake sits next to Suncor Energy’s Mildred Lake operation. 

On the surface, it looks like one of the countless natural lakes dotting the boreal forest north of Fort McMurray. But several metres below, it tells a different story. 

Base Mine Lake is not a natural lake—it’s a demonstration pit lake at one of the industry’s oldest mines. 

Once a tailings pond, Base Mine Lake was capped with water in 2012 and is now undergoing reclamation, drawing on decades of innovation to restore the land and water affected by development. 

Base Mine Lake. Photo courtesy Suncor Energy

“Tailings ponds aren’t meant to be a permanent part of our closure landscapes,” said Rodney Guest, Suncor’s senior development advisor, mine water closure. 

“We’re investing significant resources to advance tailings treatment technologies in support of land and aquatic reclamation to meet our commitments.”

Those commitments include fully reclaiming mine sites, including tailings facilities, and returning the land to Albertans and local communities, he said. 

Pit lakes: widely used around the world

Pit lakes are a common mine reclamation and closure practice used worldwide. 

According to the Canadian Association of Petroleum Producers (CAPP), a pit lake is basically any lake formed within a former mine pit. 

Over time, as the site stabilizes, these lakes generally come to look and function much like natural lakes. 

Thousands of examples exist globally, particularly in coal and hard-rock mining operations such as gold and copper, CAPP says.

Helping address oil sands tailings

Even as the oil sands sector has reduced its freshwater use per barrel by nearly one-third since 2013, the total volume of fluid tailings has reached about 1.4 billion cubic metres, reflecting continued production growth. 

Aquatic reclamation techniques like pit lakes are helping address the tailings challenge. 

This is evident in the reduction of “legacy tailings,” or tailings placed in storage before 2015. 

Since 2015, the volume of legacy tailings across Alberta’s oil sands has fallen by 40 per cent, according to Alberta Energy Regulator data. 

Base Mine Lake has contributed to this reduction, which overall is helped by water-capped tailings and permanent aquatic storage structure (PASS) technology.

How water-capped tailings technology works

Oil sands tailings are a mixture of fine clay, water, sand, and residual bitumen left over from the bitumen extraction process. 

Traditionally stored in large ponds, these liquid tailings settle very slowly—a process that can take decades. Water-capped tailings technology provides a more controlled solution.

In this approach, a layer of water is placed over tailings within a mined-out pit, forming a pit lake. 

The water cap isolates the tailings from the surface environment while promoting the development of a natural aquatic ecosystem.

Supported by long-term research

Numerous pit lakes, with and without tailings, are proposed or planned for the oil sands region. 

Each is designed to integrate into the final reclaimed landscape, supporting sustainable water management and creating new habitats for aquatic and terrestrial life.

Long-term research and monitoring at several sites—some dating back to the 1980s—has shown that water-capped tailings can be effective. 

Bacteria quickly break down many compounds within the tailings, while the solids settle naturally within weeks. The water layer above largely prevents tailings sediments from migrating back to the surface.

Base Mine Lake. Photo courtesy Pathways Alliance

Base Mine Lake performance

At Base Mine Lake, for example, a water cap currently between 10 and 13 metres covers the tailings. Ongoing research and monitoring show it’s performing as expected, Guest said.

“The tailings remain contained at the bottom and don’t mix with the water,” he said. 

“Water quality continues to improve, diverse habitats are forming, and typical boreal lake life including insects, invertebrates, plants and mammals are present in and around the demonstration watershed.”

While the lake doesn’t currently discharge to the environment, the long-term plan is for its water to eventually integrate into the regional watershed. 

Prior to release, water will be monitored and tested to ensure it meets regulated water quality guidelines, Guest said. 

In the meantime, Suncor adds fresh water and withdraws water for use in its mine operations. 

PASS technology demonstration

Suncor is implementing permanent aquatic storage structure (PASS) technology at a demonstration site that includes Lake Miwasin, a 10-metre-deep lake with a five-metre water cap. 

PASS uses common treatment agents to help tailings settle and release water more quickly. The process speeds up consolidation and helps improve overall water quality.

The company says early results are promising, showing expected improvements in water quality and the re-establishment of vegetation.

Insights from local Indigenous communities have helped refine techniques, including influencing landform design and identifying culturally important plants and trees.  

Confidence in pit lakes

“Results from Base Mine Lake and Lake Miwasin give us the confidence that pit lakes are a safe and integral component of our planned closure landscape,” Guest said.

The transition to a fully reclaimed boreal landscape in Alberta’s oil sands will take time. 

Most of the reclaimed area will consist of forests and wetlands, with pit lakes expected to account for less than 10 per cent. 

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*References to land that is reclaimed, permanently reclaimed and surface reclaimed meet the definition of “permanently reclaimed” as defined in the Alberta Energy Regulator Direction for Conservation and Reclamation Submissions (December 2018).

In what the former Chief of the Fort McKay First Nation calls “a critical step in the right direction,” the Alberta government is moving to accelerate reclamation of more than 1.3 trillion litres of water stored in oil sands tailings ponds.

On Sept. 5, the province announced it will expedite setting standards that allow for “mine water” to be treated and released into the environment, building on the rules that are already in place for other mining operations across Canada.

“We cannot ignore this challenge, we need to keep working together to find practical and effective solutions that protect Indigenous rights, people and the environment,” said Chief Jim Boucher, a member of Alberta’s Oil Sands Mine Water Steering Committee.

That committee is behind a suite of nine recommendations that Alberta is putting into action to improve mine water management and tailings pond reclamation.

The Mining Association of Canada (MAC) says decades of research give the industry confidence that mine water can be safely treated and released once regulations are in place. 

But that will take the federal government moving faster too. 

Both the federal and provincial governments play a role in potential regulations for the treatment and release of oil sands mine water. 

“Alberta is proposing science-based parameters to ensure the safe return of treated water used in oil sands mining, just as other provincial governments do for their respective mining sectors,” MAC CEO Pierre Gratton said in a statement. 

“We are hopeful that this will accelerate the development of federal regulations – which we requested almost 15 years ago – to be similarly advanced.”

Gratton said setting standards for safe mine water release could unlock “significant investments” in oil sands reclamation and water treatment.

What are tailings ponds?

Tailings are a byproduct of mining operations around the world. 

Oil sands tailings ponds are engineered basins holding a mix of mine water, sand, silt, clay and residual bitumen generated during the extraction process. There are eight operating oil sands mines with tailings ponds in northern Alberta. 

Recycling water held in these basins helps operators reduce the amount of fresh water withdrawn from the Athabasca River.

In 2023, 79 per cent of the water used for oil sands mining was recycled, according to the Alberta Energy Regulator. 

What is oil sands mine water?

Oil sands mine water is water that comes into contact with the various stages of oil sands mining operations, including bitumen extraction and processing.

Tailings ponds in the oil sands also hold water from significant amounts of rain and snow collected in the decades since the first mines began operating.

While the oil sands mining sector has reduced the amount of fresh water it uses per barrel of oil produced by nearly one-third since 2013, the total volume of mine water in tailings storage has grown as production has increased. 

What’s in oil sands mine water? 

The constituents of oil sands mine water requiring treatment for safe release are both typical of water in other industrial processes and unique to the oil sands sector.

MAC says common materials are suspended solids like sand, silt and clay, as well as a range of metals. These can be treated by a wide range of proven technologies already in use in Canada and globally.

Unique to oil sands mine water are organic compounds such as naphthenic acids. According to MAC, operators have demonstrated and continue to invest in processes to treat these to levels safe for environmental release.

How does mine water impact reclamation? 

At the end of an oil sands mine’s life, operators must remove all infrastructure and restore the land to features of a self-sustaining boreal forest similar to what was there before.

Addressing the challenge of tailings ponds and the mine water stored in them is critical to the overall success of oil sands mining reclamation. 

Why is mine water release important?

MAC says the only way to remove mine water in tailings ponds is to treat it for safe release to the environment.

Strict regulations allow for this process across Canadian copper, nickel, gold, iron ore, and diamond mining operations. But it is prohibited in the oil sands.   

The safe release of treated oil sands mine water into the environment can reduce the need to store it, minimize further land disturbance and help reclamation happen faster. 

MAC says operators have shown they can treat mine water to safe release levels, using processes that include innovative technologies developed through Canada’s Oil Sands Innovation Alliance.

What is Alberta doing? 

Alberta has accepted the Oil Sands Mine Water Steering Committee’s nine recommendations aimed at speeding up solutions for safe mine water release. 

The province says the recommendations, developed with input from industry, technology providers, Indigenous communities and scientists, will now be evaluated to determine how they can be put into practice.

Read the full recommendations here. 

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Tailings are a byproduct of mining operations around the world. 

In Alberta’s oil sands, tailings are a fluid mixture of water, sand, silt, clay and residual bitumen generated during the extraction process.

Engineered basins or “tailings ponds” store the material and help oil sands mining projects recycle water, reducing the amount withdrawn from the Athabasca River.

In 2023, 79 per cent of the water used for oil sands mining was recycled, according to the latest data from the Alberta Energy Regulator (AER). 

Decades of operations, rising production and federal regulations prohibiting the release of process-affected water have contributed to a significant accumulation of oil sands fluid tailings.

The Mining Association of Canada describes that: 

“Like many other industrial processes, the oil sands mining process requires water. 

However, while many other types of mines in Canada like copper, nickel, gold, iron ore and diamond mines are allowed to release water (effluent) to an aquatic environment provided that it meets stringent regulatory requirements, there are no such regulations for oil sands mines. 

Instead, these mines have had to retain most of the water used in their processes, and significant amounts of accumulated precipitation, since the mines began operating.”

Despite this ongoing challenge, oil sands mining operators have made significant strides in reducing fluid tailings through technological innovation.

This is demonstrated by reductions in “legacy fluid tailings” since 2015. 

Legacy Fluid Tailings vs. New Fluid Tailings

As part of implementing the Tailings Management Framework introduced in March 2015, the AER released Directive 085: Fluid Tailings Management for Oil Sands Mining Projects in July 2016.

Directive 085 introduced new criteria for the measurement and closure of “legacy fluid tailings” separate from those applied to “new fluid tailings.” 

Legacy fluid tailings are defined as those deposited in storage before January 1, 2015, while new fluid tailings are those deposited in storage after January 1, 2015. 

The new rules specified that new fluid tailings must be ready to reclaim ten years after the end of a mine’s life, while legacy fluid tailings must be ready to reclaim by the end of a mine’s life.

Total Oil Sands Legacy Fluid Tailings

Alberta’s oil sands mining sector decreased total legacy fluid tailings by approximately 40 per cent between 2015 and 2024, according to the latest company reporting to the AER. 

Total legacy fluid tailings in 2024 were approximately 623 million cubic metres, down from about one billion cubic metres in 2015. 

The reductions are led by the sector’s longest-running projects: Suncor Energy’s Base Mine (opened in 1967), Syncrude’s Mildred Lake Mine (opened in 1978), and Syncrude’s Aurora North Mine (opened in 2001). All are now operated by Suncor Energy. 

The Horizon Mine, operated by Canadian Natural Resources (opened in 2009) also reports a significant reduction in legacy fluid tailings. 

The Muskeg River Mine (opened in 2002) and Jackpine Mine (opened in 2010) had modest changes in legacy fluid tailings over the period. Both are now operated by Canadian Natural Resources. 

Imperial Oil’s Kearl Mine (opened in 2013) and Suncor Energy’s Fort Hills Mine (opened in 2018) have no reported legacy fluid tailings. 

Suncor Energy Base Mine

Between 2015 and 2024, Suncor Energy’s Base Mine reduced legacy fluid tailings by approximately 98 per cent, from 293 million cubic metres to 6 million cubic metres. 

Syncrude Mildred Lake Mine

Between 2015 and 2024, Syncrude’s Mildred Lake Mine reduced legacy fluid tailings by approximately 15 per cent, from 457 million cubic metres to 389 million cubic metres. 

Syncrude Aurora North Mine

Between 2015 and 2024, Syncrude’s Aurora North Mine reduced legacy fluid tailings by approximately 25 per cent, from 102 million cubic metres to 77 million cubic metres. 

Canadian Natural Resources Horizon Mine

Between 2015 and 2024, Canadian Natural Resources’ Horizon Mine reduced legacy fluid tailings by approximately 36 per cent, from 66 million cubic metres to 42 million cubic metres.

Total Oil Sands Fluid Tailings 

Reducing legacy fluid tailings has helped slow the overall growth of fluid tailings across the oil sands sector.

Without efforts to reduce legacy fluid tailings, the total oil sands fluid tailings footprint today would be approximately 1.6 billion cubic metres.

The current fluid tailings volume stands at approximately 1.2 billion cubic metres, up from roughly 1.1 billion in 2015.

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Environmental Defence has published an advertisement in the Montreal Gazette that misleads Canadians about oil sands tailings.

What the activist group ignores is the demonstrated progress the industry is making to address this challenge.  

Here are the facts.  

Fact: Oil sands producers are leaders in tailings management 

Tailings are a byproduct of mining operations around the world. According to the Mining Association of Canada, they consist of the processed rock or soil left over from the separation of the commodities of value from the rock or soil within which they occur. 

In the oil sands, tailings are a mixture of sand, silt, clay, water and residual bitumen produced in the mining extraction process.   

Oil sands producers are addressing the challenge to reduce tailings through technology R&D, investing more than $50 million on tailings research each year through Canada’s Oil Sands Innovation Alliance.  

Collectively, companies have invested more than $10 billion in solutions for tailings reduction, according to BMO Capital Markets.

Fact: New technologies are making a difference 

Thanks to new technologies, oil sands producers are now reducing the volume of “legacy tailings,” or tailings put in storage before 2015.  

Since 2015, the sector has removed more than 270 million cubic metres of legacy tailings from the environment, or a reduction of 24 per cent.   

All six mining projects that have legacy tailings present reduced those volumes in 2021, according to performance reports published by the Alberta Energy Regulator.  

Tailings management technologies include centrifuge facilities, CO2 injection, the addition of polymers, coagulants and thickeners, and water capping.   

Fact: Suncor is now reducing total tailings 

Suncor Energy’s Base Plant leads oil sands tailings reduction efforts, having removed approximately 190 million cubic meters of legacy tailings since 2016.   

The work is so successful that total tailings – not just legacy tailings – at the facility are going down.   

Suncor reduced total tailings at its Base Plant by 15 per cent between 2015 and 2021, removing nearly 50 million cubic metres of tailings from the environment.  

“Total inventories are shrinking, and we are ahead of regulatory requirements,” the company said in its 2021 Sustainability Report.    

“Over the last 10 years, one pond has been surface reclaimed and two more are advancing to closure; one of those ponds is currently being drained and we anticipate it being removed from the landscape this decade.” 

Fact: Tailings are being reclaimed 

In 2010, Suncor reclaimed the first oil sands tailings pond to a solid surface. Wapisiw Lookout, as it is now known, is 220 hectares that includes a developing mixed wood forest, streams, and a small marsh wetland.  

Meanwhile, Canadian Natural Resources reports that its three oil sands mines have reclaimed a total of 1,100 hectares of tailings facilities, creating natural features like stream, wetlands, and upland forest areas.  

And Imperial reports that more than 80 per cent of its oil sands tailings inventory is now in its final resting place and on the trajectory for full reclamation.  

Fact: Technology has significantly slowed the growth of new tailings  

While companies work to reduce legacy tailings and reclaim tailings ponds, they are also creating less new tailings while producing more oil.  

In 2021, despite oil sands mining production reaching a record 1.59 million barrels per day, total oil sands tailings increased by 11.7 million cubic meters – the lowest amount of growth in the last five years, according to the AER. 

For comparison, in 2016 oil sands mining production averaged 1.1 million barrels per day, and total tailings grew by a substantially larger 59.6 million cubic meters. 

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New technologies and practices are improving the environmental performance of Canada’s oil sands industry, with producers removing more than 270 million cubic meters of “legacy tailings” from the environment over the last five years.  

The successful reduction of legacy tailings – tailings that were in storage before 2015 – is contributing to a slower pace of growth for total oil sands tailings, despite record production.

Tailings are a byproduct of mining operations around the world. In the oil sands, tailings are a mixture of sand, silt, clay, water and residual bitumen produced in the mining extraction process.  

The engineered basins or “tailings ponds” that hold the material also help oil sands projects recycle water for their operations – up to 85 per cent of the water that is used is recycled using this process, according to Canada’s Oil Sands Innovation Alliance (COSIA).  

But decades of operations, increasing oil sands production, technological challenges and the regulatory requirement to store untreated process-affected water have contributed to a large accumulation of tailings in Alberta.  

Finding the right suite of technologies to address the challenge is a main area of focus for R&D efforts, with producers investing more than $50 million on tailings research through COSIA each year.  

In 2021, despite oil sands mining production reaching a record 1.59 million barrels per day, total oil sands tailings increased by 11.7 million cubic meters – the lowest amount of growth in the last five years, according to the latest project performance reports published by the Alberta Energy Regulator (AER).

In 2016, oil sands mining production averaged 1.1 million barrels per day, and total tailings grew by a substantially larger 59.6 million cubic meters.  

Part of the success is attributable to the decrease in legacy tailings. Project data shows that oil sands mining producers reduced the total volume of legacy tailings to about 760 million cubic meters in 2021, from nearly 1,000 million cubic meters in 2016.  

All six mining projects that have legacy tailings present reduced those volumes in 2021, according to performance reports.  

Tailings management technologies include centrifuge facilities, CO2 injection, the addition of polymers, coagulants and thickeners, and water capping.  

Suncor Energy’s Base Plant leads the reduction efforts, removing approximately 190 million cubic meters of legacy tailings since 2016, project data shows.  

The work is so successful that total tailings – not just legacy tailings – at the facility are going down.  

In 2021 Suncor’s Base Plant had 268 million cubic meters of total tailings in storage, a reduction of about 15 per cent from 2016 (317 million cubic meters), according to project data.  

“Total inventories are shrinking, and we are ahead of regulatory requirements,” the company said in its 2021 Sustainability Report..   

“Over the last 10 years, one pond has been surface reclaimed and two more are advancing to closure; one of those ponds is currently being drained and we anticipate it being removed from the landscape this decade.” 

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