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. An October 2021 Alberta Energy Regulator (AER) report said that in 2020 the tailings ponds increased by another 90 million cubic meters and contained 1.36 billion cubic metres of fluids.
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 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 77 square kilometres (30 sq mi). According to a Calgary Herald article, by September 2017, the tailings ponds held c."1.2 trillion litres of contaminated water" and covered about 220 square kilometres (85 sq mi).
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