While coarse solids settle rapidly, fine solids remain in a suspension called fluid fine tailings. The fluid fine tailings concentrate to about 30 per cent mass solids in two to three years but only very slowly thereafter. Provincial law strictly prohibits the release of water that has been in contact with bitumen into water bodies off the mine site, including the Athabasca River. Thus, the ponds serve four important functions:

  1. Disposal area for coarse and fine tailings
  2. Settling pond (allowing water to separate from solid waste materials)
  3. Water storage for recycling (up to 90 per cent of a company’s water needs for oil sands extraction occurs through the re-use of water from the ponds)
  4. Contaminant storage