What are they? Tailings ponds contain waste water from the extraction of bitumen from the oilsands. As well as water, they contain fine silt, residual bitumen, salts, organic compounds and solvents. They are considered toxic.
How big are they? Big. The total area covered by all the ponds and their associated structures is 220 square kilometres, almost twice the area of Vancouver. The area covered by waste water alone is 88 square kilometres and the ponds contain nearly a billion cubic metres of tailings. That's about 400,000 Olympic-sized swimming pools.
What's the problem? Silt and other contaminants in the ponds won't settle out. Without being able to separate the water from the bad stuff, it's difficult to reclaim the ponds. Only one, covering 2.2 square kilometres, has ever been officially reclaimed.
Are they a danger? Yes. Recent research has found tailings ponds release more than a tonne of toxic hydrocarbons into the atmosphere every year. Mathematical models suggest millions of litres of tailings seep into groundwater yearly, a conclusion backed up by a new Environment Canada study that found chemical fingerprints similar to those of tailings in groundwater. Alberta says seepage is controlled and any that escapes goes harmlessly into bedrock. Several ponds are along the Athabasca River, making dam failures potentially catastrophic. Thousands of migrating ducks and geese have died after landing on the ponds.
How did we get to this point? Alberta brought in tough regulations on cleaning up the ponds in 2009, but none of the operators were able to meet the deadlines. Companies have spent millions on research, with some promising results, but no final answers.