Extensive mining of oil sands near Fort McMurray, Canada will soon spawn a swath of 30 new lakes. The massive surface mining operations leave large depressions in the ground, which are more easily refilled with water than with dirt. (Why not just fill in with the waste material? Because the tailings, as they’re called, are generally concentrated in contaminants and unsuitable for unregulated disposal. But that’s a general statement, not specific to this site.) The idea is to “cap” the mine pits, filled with a layer waste tailings, beneath a layer of clean water. The microbes at the bottom of the new lake would then munch through the oil residue (benzene, toluene, ethylene, and xylene compounds, plus some naphthalene too) while the water on top was largely undisturbed. After some time, the oil residue would have been completely biodegraded, and the lake would be pristine — bring on the wildlife and recreation!
Whether this will actually work is up for debate.
One company, Syncrude Canada, will construct the first lake, with 40 meters (~120 feet) of tailings at the bottom, late this year or in early 2013. The company spent 20 years studying these types of lakes, with smaller experimental ponds nearby. In one experimental pond, the water able to support rainbow trout within a year. They project it will take 25 years before the first full-size lake is clean enough to return to the Canadian government. They’re also trying to involve other methods to enhance cleanup, like using petroleum coke as an industrial-sized filter.
On the other hand, this is largely unproven technology, about to be implemented on a massive scale: the rough size projection is 100 square km of surface area, or nearly 18% the size of Toronto. At other sites, some of these lakes have become “vibrant” recreational areas, while others have turned into “toxic soup” that kills wildlife. Sounds risky. This being a news article, they don’t go into detail about what goes right or wrong. One consideration is how much crude is leftover, because it’s much harder to biodegrade than the lighter-weight compounds. Another issue is whether the mine waste would generate acidic water and/or release trace elements into the water. That’s what happened at the “Berkeley pit“, a former copper mine where this technique went horribly awry and killed a visiting flock of 387 geese. If data about the likelihood of this near Fort McMurray exists, it is almost certainly closely guarded by the mining companies in question.
The one potential upside is that if the Canadian government fails to renew the funding for the Experimental Lakes Area, they’ll soon have another set of experimental lakes to research…but they won’t be quite as pristine, and the stakes will be a bit higher as far as keeping the lakes clean…