I n 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. “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 fully reclaiming mine sites, including tailings facilities, and returning the land to Albertans and local communities, he said. commitments include
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.
Base Mine Lake. . Photo courtesy Suncor Energy
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.
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