Oil sands tailings ponds

Oil sands tailings ponds

Oil sands tailings ponds are engineered dam and dyke systems that contain a mixture of salts, suspended solids and other dissolvable chemical compounds such as acids, benzene, hydrocarbons^[1] residual bitumen, fine silts and water.^[2] Large volumes of tailings are a byproduct of bitumen extraction from the oil sands and managing these tailings is one of the most difficult environmental challenges facing the oil sands industry.^[2]

Location

Athabasca Oil Sands

This map shows the extent of the oil sands in Alberta, Canada. The three oil sand deposits are known as the Athabasca Oil Sands, the Cold Lake oil sands, and the Peace River oil sands.

Components of oil sands tailings ponds

These settling basins were meant to be temporary. A major hindrance to the monitoring of oil sands produced waters has been the lack of identification of individual compounds present. By better understanding the nature of the highly complex mixture of compounds, including naphthenic acids, it may be possible to monitor rivers for leachate and also to remove toxic components. Such identification of individual acids has for many years proved to be impossible but a breakthrough in 2011 in analysis began to reveal what is in the oil sands tailings ponds.^[3] Ninety percent of the tailings water can be reused for oil extraction.^[2] The concentrations of chemicals may be harmful to fish and oil on the surface harmful to birds.^[4]

Size and scope

By 2009 as tailing ponds continued to proliferate and volumes of fluid tailings increased, the Energy Resources Conservation Board of Alberta issued Directive 074 to force oil companies to manage tailings based on new aggressive criteria.^[5] The Government of Alberta reported in 2013 that tailings ponds in the Alberta oil sands covered an area of about 77 square kilometres (30 sq mi).^[2]

Syncrude Tailings Dam

Syncrude tailings dam

The Syncrude Tailings Dam or Mildred Lake Settling Basin (MLSB) is an embankment dam that is, by volume of construction material, the largest earth structure in the world in 2001.^[6] It is located 40 km (25 mi) north of Fort McMurray, Alberta, Canada at the northern end of the Mildred Lake lease owned by Syncrude Canada Ltd.. The dam and the tailings artificial lake within it are constructed and maintained as part of ongoing operations by Syncrude in extracting oil from the Athabasca Oil Sands. Other tailings dams constructed and operated in the same area by Syncrude include the Southwest Sand Storage (SWSS),^[7] which is the third largest dam in the world by volume of construction material after the Tarbela Dam.

Horizon tailings dam

Horizon tailings dam

As of 2010, according to the "Mature Fine Tailings Inventory from mine operator tailings plans submitted in October 2009, Canadian Natural Resources's (CNRL) mine, Horizon mine had 48,000,000 cubic metres (1.7×10⁹ cu ft) of mature fine tailings (MFT) in their tailings ponds.^[8]:4 However COSIA argues that CNRL's Horizon External Tailings Facility (ETF) is a relatively young pond with a configuration that minimizes the "Pond Centre (PC) depositional environment". It has a "side hill" facility with a three-sided dyke impounding fluid against the natural ground that rises away from the containment dyke."^[9]:34

Regulations and oversight

The Government of Alberta released the Tailings Management Framework for Mineable Oil Sands as part of Alberta’s Progressive Reclamation Strategy for the oil sands to ensure that tailings are reclaimed as quickly as possible.^[5]

In March 2015 in response to the Tailings Management Framework for Mineable Athabasca Oil Sands, Alberta Energy Regulator (AER) suspended Directive 074: Tailings Performance Criteria and Requirements for Oil Sands Mining Schemes.^[10]

On July 14, 2016 the Alberta Energy Regulator - following consultations with "consultations with First Nations, local communities, environmental groups and industry itself" - issued Directive 85 with new guidelines and a phased-in approach on oil sands producers' management of their tailings ponds.^[11] Under Directive 85 "fluid tailings" must be "ready to reclaim" within ten years of the closing of an oil sands mine.^[11]

Reduction and reclamation

Suncor invested $1.2 billion in their Tailings Reduction Operations (TROTM) method ^[12] that treats mature fine tails (MFT) from tailings ponds with chemical flocculant, an anionic Polyacrylamide, commonly used in water treatment plants to improve removal of total organic content (TOC), to speed their drying into more easily reclaimable matter. Mature tailings dredged from a pond bottom in suspension were mixed with a polymer flocculant and spread over a "beach" with a shallow grade where the tailings would dewater and dry under ambient conditions. The dried MFT can then be reclaimed in situ or moved to another location for final reclamation. Suncor hoped this would reduce the time for water reclamation from tailings to weeks rather than years, with the recovered water being recycled into the oil sands plant. Suncor claimed the mature fines tailings process would reduce the number of tailing ponds and shorten the time to reclaim a tailing pond from 40 years at present to 7–10 years, with land rehabilitation continuously following 7 to 10 years behind the mining operations.^[13] For the reporting periods from 2010 to 2012, Suncor had a lower-than-expected fines capture performance from this technology.^[5]

Syncrude used the older composite tailings (CT) technology to capture fines at its Mildred Lake project. Syncrude had a lower-than-expected fines capture performance in 2011/2012 but exceeded expectations in 2010/2011.^[5] Shell used atmospheric fines drying (AFD) technology combined "fluid tailings and flocculants and deposits the mixture in a sloped area to allow the water to drain and the deposit to dry" and had a lower-than-expected fines capture performance.^[5]

Suncor's Wapisiw Lookout

By 2010 Suncor had transformed their first tailings pond, Pond One, into Wapisiw Lookout, the first reclaimed settling basin in the oil sands. In 2007 the area was a 220-hectare pond of toxic effluent but several years later there was firm land planted with black spruce and trembling aspen. Wapisiw Lookout represents only one percent of tailings ponds in 2011 but Pond One was the first effluent pond in the oil sands industry in 1967 and was used until 1997. By 2011 only 65 square kilometres were cleaned up and about one square kilometre was certified by Alberta as a self-sustaining natural environment. Wapisiw Lookout has not yet been certified. Closure operations of Pond One began in 2007. The jello-like mature fine tails (MFT) were pumped and dredged out of the pond and relocated to another tailings pond for long-term storage and treatment. The MFT was then replaced with 30 million tonnes clean sand and then topsoil that had been removed from the site in the 1960s. The 1.2 million cubic meters of topsoil over the surface, to a depth of 50 centimetres, was placed on top of the sand in the form of hummocks and swales. It was then planted with reclamation plants.^[14][15][16]

Syncrude's Sandhill Fen project

In 2008 Syncrude Canada Ltd. began construction of Sandhill Fen project, a 57-hectare research watershed- creating a mix of forest and wetland- on top of sand-capped composite tailings at its former 60-metre deep East Mine.^[17]

End Pit Lakes

The Pembina Institute suggested that the huge investments by many companies in Canadian oil sands was leading to increased production results in excess bitumen with no place to store it. It added that by 2022 a month’s output of waste-water could result in a 11-feet deep toxic reservoir the size of New York City’s Central Park [840.01 acres (339.94 ha) (3.399 km²)].^[18]

The oil sands industry may build a series of up to thirty lakes by pumping water into old mine pits when they have finished excavation leaving toxic effluent at their bottoms and letting biological processes restore it to health. It is less expensive to fill abandoned open pit mines with water instead of dirt.^[19] In 2012 the Cumulative Environmental Management Association (CEMA) described End Pit Lakes (EPL)^[20] as

An engineered water body, located below grade in an oil sands post-mining pit. It may contain oil sands by-product material and will receive surface and groundwater from surrounding reclaimed and undisturbed landscapes. EPLs will be permanent features in the final reclaimed landscape, discharging water to the downstream environment.

— CEMA 2012

CEMA acknowledged that the "main concern is the potential for EPLs to develop a legacy of toxicity and thus reduce the land use value of the oil sands region in the future." Syncrude Canada was planning the first end pit lake in 2013 with the intention of "pumping fresh water over 40 vertical metres of mine effluent that it has deposited in what it calls 'base mine lake.'" David Schindler argued that no further end pit lakes should be approved until we "have some assurance that they will eventually support a healthy ecosystem." There is to date no “evidence to support their viability, or the ‘modelled’ results suggesting that outflow from the lakes will be non-toxic."^[19]

Research

In March 2012 an alliance of oil companies called Canada’s Oil Sands Innovation Alliance (COSIA) was launched with a mandate to share research and technology to decrease the negative environmental impact of oil sands production focusing on tailings ponds, greenhouse gases, water and land. Almost all the water used to produce crude oil using steam methods of production ends up in tailings ponds. Recent enhancements to this method include Tailings Oil Recovery (TOR) units which recover oil from the tailings, Diluent Recovery Units to recover naphtha from the froth, Inclined Plate Settlers (IPS) and disc centrifuges. These allow the extraction plants to recover well over 90% of the bitumen in the sand.^[21][22]

In January 2013, scientists from Queen's University published a report analyzing lake sediments in the Athabasca region over the past fifty years.^[23] They found that levels of polycyclic aromatic hydrocarbons (PAHs) had increased as much as 23-fold since bitumen extraction began in the 1960s. Levels of carcinogenic, mutagenic, and teratogenic PAHs were substantially higher than guidelines for lake sedimentation set by the Canadian Council of Ministers of the Environment in 1999. The team discovered that the contamination spread farther than previously thought.^[24]

Civil engineering professors, James Bolton and Mohamed Gamal El-Din, from the University of Alberta are working on an experimental method that uses sunlight to react with the bleach or chlorine added to wastewater to produce hydroxyl radicals. These powerful oxidative reagents can potentially remove enduring toxins from tailings ponds or waste water in cities.^[1]

See also

• Tailings

References

Further reading

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