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Mine pit reclamation

Lakes filled with fish, wildlife or toxic resevoirs?


December 18, 2012
by Matt Powell, Assistant Editor

Syncrude is betting R&D will lead to a sustainable solution, but critics say lakes lined with tailings shouldn’t be part of the plan.

Thirty years from now, when Alberta’s major oil sands deposits are played out and producers move on, what will become of the northern landscape, scarred by expansive, deep mine pits?

More stringent environmental regulations have forced producers to be more creative with their reclamation activities, and the solution underway is a network of lakes with flourishing animal and plant habitats. In fact, Syncrude Canada Ltd. is putting 25 years of research to use at the bottom of its 800 square-kilometre Base End Lake in the Athabasca oil sands, north of Fort McMurray, Alta.

As oil deposits dry up, oil sands developers intend to line the bottoms of their oil mine pits with tailings, which contain a mixture of dirt, sand and clay contaminated with hydrocarbons, acids, and other toxins leftover from the extraction process, then capping them with fresh water to dilute toxins and effluents. Natural processes will take over and restore the lake back to health, creating environments that sustain aquatic and plant life.

Critics aren’t so sure end pit lakes will be anything more than bubbly, toxic resevoirs – a reminder of an experiment gone wrong.

Besides, it could take up to a century to see how it all turns out. Who will be around to take the heat if the reclamation fails?

Some suggest it’s a gamble that highlights how far the Alberta government will go to encourage a perception that oil sands producers are cleaning-up after themselves. Thirty lakes have received the necessary regulatory go-ahead, but critics contend there’s no solid evidence that these reclamation efforts will work.

David Schindler is one of those critics. The professor of ecology at the University of Alberta doubts the lakes will ever be clean enough for fish and plants to survive, or for people to swim in.

“It’s just madness that [the government] rubber-stamped 30 of these things without the companies demonstrating they can safely follow one through,” he says. “They rub all these engineering-type models, suggesting the tailings will stratify, but there’s no actual proof.”

A recent report by the Alberta industry-funded Cumulative Environmental Management Association (CEMA) outlines the size and scale of the proposed lakes. It suggests they could serve as permanent alternatives to temporary tailings ponds that currently store oil extraction by-products.

CEMA describes those with tailings storage and those without. Tailings lakes will be fed water through surface run-off, precipitation, ground water seepage and consolidation waters from tailings deposits. It says tailings become denser over time by releasing pore water to the water cap. Those without tailings will fill with surface run-off and groundwater once mining stops.

Syncrude’s massive End Base Lake will act as a demonstration site and test wetlands for other companies. The association will keep an eye on progress using its own in-lake dynamics and water quality modeling, and geotechnical stability analysis activities.

But the report notes uncertainties attached to the plans and neither supports or opposes the creation of End Pit Lakes.

There’s also a water issue. There will have to be enough to fill 30 lakes. Where would it come from? The Athabasca River is an obvious source, but the Alberta government restricts how much water is drawn from it.

Still, Syncrude is moving ahead with the plan, confident its Base Mine Lake will work.

“We’ve been researching this technology for 25 years. We’ve built a series of test ponds and small lakes and researched them, and all that work has shown promising results. The research has provided us with the basis to go ahead with the large-scale end pit lake we’ll commission this winter,” says Warren Zubot, a senior engineering associate at Syncrude.

Messy business

The Athabasca mine will be filled with fine tails, a clay-like material. Zubot says it’s a challenge to remove these clay particles because they become electrically charged in the extraction process and turn into a yogurt-like material that can’t be reintroduced to dry environments.

Syncrude’s plan is to dump the yogurty by-product into the bottom of a 50-metre deep lake and cap them with five metres of fresh water from its Beaver Creek Resevoir. Its network of small ponds has shown that the clays harden over time, leaving effluents in the bottom of the lake while the fresh water pulls H20 molecules out of the clay.

“The organic compounds in the water will break down over time. Once they do, the water becomes high quality enough to support ecology and life,” he says. “It won’t happen in a year, but it’ll happen eventually. Understanding those timelines is just as much as part of this project as the lake itself.”

Zubot says Syncrude will essentially lead other energy producers and provide guidance for those considering the technology.

As far as Schindler is concerned, Syncrude’s demonstration lake should have been used first to prove the technology will actually work rather than taking a gamble on 30 lakes.

“I can’t imagine they can prove this without a long-term trial,” he says. “If they’d done this when they started producing from the oil sands, they’d be a lot closer to proving the technology works and would be able to show that at least some things grew.”

End pit lake technology has been used in base metal mining for years, and according to Schindler, the results have been damning.

Typically, the lakes become very acidic because of ores and sulphur rich materials that contain pyrite, he says. When they’re exposed to oxygen, the sulphide turns into sulphate, which dissolves a number of the metals needed to balance Ph levels.

“You end up with a soup of sulphuric acid with a lot of toxic trace metals.”

But other old base metal mine pit lakes have worked. Snow Lake in Ontario, which used to be an iron ore pit, was once home to a rainbow trout farm.

As the saying goes, “time will tell,” but it will be some time before anyone from either side of the debate will be able to say ‘I told you so.’

Comments? E-mail mpowell@plant.ca.