Oil sands tailings ponds are engineered dam and dyke systems used to capture oil sand tailings. Oil sand tailings contain a mixture of salts, suspended solids and other dissolvable chemical compounds such as acids, benzene, hydrocarbons residual bitumen, fine silts and water. 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. Tailings ponds grew by 90 million cubic metres in 2020, reaching 1.36 billion cubic metres of fluids, according to an October 2021 AER report; by 2023, the total volume of fluid tailings in the region had risen further, to 1,486 million cubic metres, while the volume of water held in the ponds had declined, according to AER's most recent tailings management report.

Location

In Canada there are three major oil sand deposits, primarily located in the province of Alberta, with some also located in the neighbouring province of Saskatchewan. They are known as Athabasca Oil Sands, Cold Lake oil sands, and Peace River oil sands. The Athabasca Oil Sands Region (AOSR) has 19 tailings ponds.

Components of oil sands tailings ponds Oil sand tailings or oil sands process-affected water (OSPW), have a highly variable composition and a complex mixture of compounds. In his oft-cited 2008 journal article, E. W. Allen wrote that typically tailings ponds consist of c. 75% water, c. 25% sand, silt and clay, c.2% of residual bitumen, as well as dissolved salts, organics, and minerals. Although many of the components of TPW "occur naturally in adjacent landscapes, the mining process increases their concentrations", for example, sodium, chloride, sulphate, bicarbonate, and ammonia. Citing research from the 1978 onwards, Allen included naphthenic acids (NAs), bitumen, asphaltenes, creosols, phenols, humic and fulvic acids, benzene, phthalates, toluene, polycyclic aromatic hydrocarbons (PAHs), in the list of organic compounds in TPW. Allen names aromatic hydrocarbons [including polycyclic aromatic hydrocarbons (PAHs), benzene, phenols and toluene], naphthenic acids (NAs) and dissolved solids, as those that were most harmful to humans, fish, and birds. As well as toxic metals considered to be priority pollutants such as chromium, arsenic, nickel, cadmium, copper, lead, and zinc, OSPW also contains "common, low-toxicity metals" including titanium aluminum, molybdenum, iron, and vanadium. The exposure to particulate matter (PM) containing polycyclic aromatic hydrocarbons has been seen to have higher cytotoxicity then PM containing heavy metals.

The concentrations of chemicals are harmful to fish, and oil on the surface of the ponds is harmful to birds.

The lack of knowledge and identification of individual compounds has become a major hindrance to the handling and monitoring of oil sands tailings. A better understanding of the chemical makeup, including naphthenic acids, it may make it possible to monitor rivers for leachate and also to remove toxic components. The 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. Theoretically, as much as ninety percent of the water in the tailings could be reused for further oil extraction.

Size and scope Tailings volumes and the areas occupied by tailings facilities have increased over time, although published figures are not always directly comparable, as sources may refer to total tailings, fluid tailings, ponded water, or the surface area of tailings facilities.

According to an October 2021 Alberta Energy Regulator (AER) report, in 2020 in spite of a decrease in oil production, oil sands tailings ponds grew another 90 million cubic meters in 2020 containing 1.36 billion cubic metres of fluids. This represents a surface comparable to "1.7 times the size of Vancouver".

In 2008 tailings ponds held 732 billion litres of tailings. 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 aggressive criteria.

By 2013, the Government of Alberta reported that tailings ponds covered an area of about . According to a Calgary Herald article, by September 2017, the tailings ponds held c."1.2 trillion litres of contaminated water" and covered about .

According to the Alberta Energy Regulator (AER), the total volume of fluid tailings—new and legacy tailings combined—at oil sands mine sites in the Athabasca oil sands region increased from 1,441 million cubic metres in 2022 to 1,486 million cubic metres in 2023. Over the same period, the volume of water held in fluid tailings ponds in the region decreased from 417.5 million cubic metres to 391.1 million cubic metres.

Cost of clean-up A 2018 joint investigation by the Toronto Star, Global News, National Observer, and four journalism schools—Concordia University, Ryerson University, University of Regina and University of British Columbia—revealed that the estimated liability for the clean up cost for "oilsands mining operations facilities" was about $130 billion. The investigation, which resulted in the news coverage series, The Price of Oil, was undertaken by "the largest ever collaboration of journalists in Canada". The investigation revealed that the security collected from companies to cover the costs of shutting down and cleaning up mining sites including tailings ponds and pipelines was $1.4 billion; and the previous calculated liability was $27.80 billion. The clean-up of tailings ponds, which "have sprawled to cover an area the size of Kelowna", which is , represents a "significant part of the liability." The journalists working on the Price of Oil series were told by experts that the liabilities in the oilsands, mainly tailings ponds, represent almost 50% of the $130 billion in the AER mining category, the total estimated liability.

Documents released through the freedom of information legislation as requested for the joint investigation of Alberta Energy Regulator internal documents included Rob Wadsworth's speaking notes at a February 28, 2018, presentation to the Petroleum History Society in Calgary. Wadsworth warned that "the true costs of cleaning up the oils sands" could be $260 billion and a significant part of the costs include the clean-up of toxic tailings ponds. In his outline of the financial liabilities in Alberta's oil patch, Wadsworth, who was the AER vice president of closure and liability, said that with the rules in place in 2018, fossil fuel companies could put off setting aside enough money to cover the costs of cleaning up their sites, until their business could "no longer afford to pay anything". He warned that even though weaknesses in the flawed programs were known, there was no "proactive change to the liability programs." Until about 2018, the "implications of our flawed system had not been not realized". He cautioned that if the industry did not respond, it would be the public that felt the impact and called on the industry representatives to retain the liabilities so they are "not passed on to Albertans". In response to the report, then Environment Minister of Alberta Shannon Phillips said that Wadsworth's estimates represented a "worst-case scenario" in which the industry shuts down overnight."

Syncrude Tailings Dam

The Syncrude Tailings Dam or Mildred Lake Settling Basin (MLSB) is an embankment dam that was, by volume of construction material, the largest earth structure in the world in 2001. It is located 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), which is the third largest dam in the world by volume of construction material after the Tarbela Dam. The MLSB, which is the oldest tailings pond in the Athabasca Oil Sands Region (AOSR), was found in a 2018 report published in the Atmospheric Chemistry and Physics journal to be "responsible for the majority of tailings ponds emissions of methane."

On 31 December 2018, Syncrude was fined $2.75 million after pleading guilty under the federal Migratory Birds Convention Act (MBCA) and Alberta's Environmental Protection and Enhancement Act in relation to the deaths of 31 great blue herons in August 2015 at the MLSB. At the time the MLSB inactive sump "was not covered by Syncrude's waterfowl protection plan to deter birds from landing at tailings areas". Doreen Cole, who has been managing director of Syncrude Canada since December 2017, "We immediately took steps to bring all these areas on our Mildred Lake and Aurora sites into our waterfowl protection plan. We're committed to being a responsible operator and this has strengthened our resolve to reduce the impact of our operations on wildlife." On 22 October 2010 Syncrude was found guilty under the provincial and federal Acts and was fined $3-million, which at that time represented the "largest environmental penalty in Alberta history." In 2008, 1,606 ducks died in Syncrude's tailings ponds, which at that time covered an area of 12-square-kilometres, because "cannons, effigies and other deterrents", intended for use to deter migratory birds, had not been deployed. Syncrude's trial lawyer at that time, Robert White, had urged his client to challenge the guilty verdict. But Syncrude spokeswoman said that they would plead guilty and pay the fine as, "At Syncrude, we're eager to move forward. The incident haunted us and we regret that it ever happened."

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 of mature fine tailings (MFT) in their tailings ponds. 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."

Regulations and oversight