Tailings ponds are often a key area of focus for those critical of oil sands development. Indeed, aerial photographs of ponds and open-pit mines have become something of a visual cliché for everything disliked about the oil sands business. With Google Maps, everything can now be seen from space, including your house AND the tailings ponds.
Tailings ponds attract a lot of attention because there is currently about 77 square kilometres of oil sands tailings pond water in Alberta, according to the Government of Alberta.
So while most people have heard of tailings ponds and seen photos, few know what purpose they serve and what the ponds actually contain.
Settling basins
A tailings pond is as an engineered dam and dyke system designed to keep material from releasing into the environment. Ponds are essentially settling basins – temporary containers for the mix of water, sand, clay and residual oil that is left over after raw oil sands have been processed into bitumen. The ponds also contain salts and soluble organic compounds, and sometimes traces of the solvents that may be added during the extraction process.
As a pond is filled, a predictable settling pattern occurs during the initial three to five years. The sand quickly sinks to the bottom, then a middle layer forms, known as mature fine tailings (MFT), which is comprised of about 70 per cent water and 30 per cent fine clay. The top three or so metres of the pond is water, which is re-used at the mine site or in in situ processes to minimize the amount of fresh water taken from the Athabasca River. At Suncor’s oil sands operations, for example, water from tailings ponds now provides up to 90 per cent of water required for ongoing operations.
Chemical concentrations
Because pond water has come into contact with oil during the extraction process, tailings ponds will inevitably contain concentrations of chemicals (which occur naturally in the oil sands resource) that can be harmful to fish. Also, there is always some residual oil floating to the surface of a pond (even the smallest amount of oil will form a surface film because it is lighter than water) and this is a potential hazard to waterfowl. For this reason, Suncor and other operators use bird deterrent systems to keep feathered friends away.
Left on its own, the MFT could take centuries to solidify sufficiently to allow total reclamation of a tailings pond but there are techniques for greatly speeding up the process, as we’ve discussed in past OSQARs.
Better solutions
Ponds are by no means an ideal solution for managing the tailings in the oil sands mining business. Tailings ponds take up space and are unsightly. They are also expensive to maintain and keep safe.
That's why industry is collaborating aggressively through Canada’s Oil Sands Innovation Alliance to better manage oil sands tailings, reclaim impacted landscapes faster and ideally, eliminate additional tailings ponds from future mining projects.
The Walrus Talks Energy
The next Walrus Talks Energy event will be taking place on Tuesday, March 25 at 7 p.m. at the Djavad Mowafaghian Cinema, Goldcorp Centre for the Arts in Vancouver, BC.
