Tailings Ponds

Challenge

The tailings ponds required at mines are large and impact the landscape. Existing tailings ponds cover 176 km2 (67 mi2). A tailings pond – an engineered dam and dyke system – is used as a settling basin/storage container for the mixture of water, sand, clay and residual oil that is left over after oil sands processing. Once in the pond, the sand quickly sinks to the bottom, and the water from the top three metres is recycled. Tailings ponds present a number of challenges:

• Seepage into ground water can occur.

• The bottom layer, a mixture of clay and water called fine tailings, takes a long time to settle and solidify. Even after many years it will still have the consistency of yogurt, and it can take up to 30 years to separate and dry out.

• The remaining water, because it has come into contact with oil during the extraction process, contains concentrations of natural chemicals that are toxic to fish.

• The small amount of residual oil that floats to the surface of the pond poses a risk
  to waterfowl.

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Response

The industry continues to develop better technologies and approaches to tailings management in order to reduce the environmental impact.

Oil sands operators are investing more than $1 billion in tailings-reduction technology. Several technologies have been implemented and more are being tested to reduce the volume of fine tailings and speed their rate of solidification.

Speeding the process, and shrinking the pond

Shell’s Albian Sands Project employs a tailings management method that uses tailing thickeners to recapture water from the fine tailings before they are released to the tailings pond. This allows the company to withdraw less river water, while reducing the size of the tailings pond.

New innovations are dramatically improving the drying time for fine tailings. Instead of decades, it now takes only months for the mixture of clay and water to dry, which helps speed reclamation. Suncor’s application of TRO™ technology towards full commercial scale operations is well underway.

Managing seepage

Extensive groundwater monitoring is required at all tailings facilities to ensure geotechnical integrity and to confirm predicted groundwater quality and flow patterns.

Comprehensive monitoring programs have not detected impacts from tailings ponds seepage on surface water or to ground water.

Operators employ numerous mitigation measures to limit and manage seepage, including constructing ditches to capture seepage and runoff water, building cut-off walls to prevent seepage migration, and installing groundwater interception wells. All captured water is pumped back into the tailings pond.

Source: Shell

Protecting water and waterfowl

Mine operators employ multiple methods to deter waterfowl from landing, including cannons, scarecrows, decoy predators and radar/laser deterrent systems. Operators also reclaim bitumen from the surface of the ponds. Despite these precautions, birds have landed on the ponds and drowned as a result of oiling.

Improvements are underway. Canadian Natural is operating a new radar-controlled bird deterrent system at its Horizon Oil Sands tailings pond. The system detects birds at a distance of up to 2.8 kilometres, automatically activating acoustic and visual deterrent systems. Since deployment in 2009, the system has deterred birds from landing on the pond.

Tailings pond reclamation

Tailings ponds can remain part of an active mine operation for 30-40 years, either for tailings deposits or for storage and water recycling.

Given this long life cycle, to date only one tailings pond has been reclaimed. In September 2010, Suncor completed surface reclamation of the 220-hectare (543-acre) Wapisiw Lookout, formerly known as Pond 1. Over the next two decades, Suncor will maintain and monitor progress on site, including the growth of 630,000 shrubs and trees planted in 2010. Ongoing soil, water and vegetation assessments will help ensure the site remains on course for return to a self-sustaining ecosystem.