Tailings: When Things Go Wrong

Tailings Track Record

It’s a big order. Tailings ponds contain toxic materials that won’t ever go away, and yet they must survive earthquakes, erosion and intense weather events, perhaps for hundreds, or even thousands of years. Even if catastrophic dam failures are somehow avoided, leaks, floods and other incursions can have devastating and far-reaching effects on ground and surface water, aquatic life, and animals, on up through the food chain. 

Failure rates

In the reported 18,000 mines around the world, the failure rate of tailings dams in the past 100 years is estimated at 1.2%. The failure rate of the traditional water storage dam is only 0.01%. On average, three of the world’s 3,500 tailings dams fail every year. In fact, the likelihood of tailings dam failure is several times higher than other conventional water-retaining dams such as reservoirs or hydroelectric facilities. Keeping the tailings pond safe and stable is the most challenging task in the entire mining process. It’s also one that the industry is not particularly good at. A recent study of 8000 tailings dams in China found that 95% were constructed using a method which, while being the most economical, comprises ~75% of all dam failures. The US cannot take any comfort that these are remote problems with little effect here. Far from it: in fact, North America is the largest region in the world for tailings dam accidents. 

Expense Items

Tailings dams, unlike those built to store water or generate power, don’t ever earn revenue. In fact, they represent an ongoing expense, potentially for decades after the mine is no longer operating.  As an expense item, then, mine owners have an incentive to employ the lowest practical cost option. In fact, many dams are built piecemeal throughout the life of a mine by adding higher and higher embankments as the amount of wastewater increases. These cost-saving design elements have not been widely regulated, so questionable choices can create unstable situations. Since the cost of monitoring the performance and condition of the dam itself is high both during operation and after closure, this becomes another area ripe for cost-cutting. Together, these factors contribute to a failure rate that, over the past century, is more than 100 times higher than that of reservoir and hydroelectric dams. 

Wildlife Exposure

In 2010, Canada’s largest oil sands producer was found guilty in the deaths of 1600 ducks that landed on a tailings pond during a snowstorm in April of 2008. Days after the verdict was handed down, more duck deaths occurred despite extensive and expensive deterrence efforts. Although personnel were on site and worked to retrieve birds as quickly as they landed, many ducks died and hundreds more had to be euthanized due to the high toxicity of their exposure. Large tailings ponds located near migratory corridors are at continued high risk, especially since deterrence methods may not be effective in poor weather conditions.

Catastrophic Containment Failures 

The worst-case scenario for a tailings management facility is catastrophic failure of containment, permitting an enormous, uncontrolled and potentially deadly release of toxic water and materials that engulfs nearby wildlife preserves, recreational areas, and communities. The death of local residents, destruction of property, and extreme environmental damage can represent an enormous financial burden in cleanup costs, damage mitigation, legal liability, and reputational damage
Alarmingly, catastrophic containment failures in tailings ponds are a regular event. Notice that three of the most damaging environmental breaches listed below have occurred within the last two decades: 
Brumadinho Dam, Brazil January 2019
3.17 million gallons of muddy iron waste was released, flowing through the mine’s offices and cafeteria as well as inundating farms, homes and roads on the way to the Paraopeba River, a major waterway that supplies water to the region. At least 270 people were killed in the disaster and officials estimated that pollution could extend as far as 185 miles downriver. Investigations revealed that concerns about the structural integrity of the dam had existed since 2009, and operators were aware that several sensors designed to monitor structural integrity had ceased to operate in the days leading up to the collapse.
Mount Polley Mine, Canada August 2014
Over 4 days, 2.6 billion gallons of water and 1.59 million cubic ft of tailings were released into Hazeltine Creek, Polley Lake and Quesnel Lake. The volume of water was sufficient to raise water levels in Polley lake by almost 5 feet. The tailings contained over 440 tons of arsenic in addition to lead and other metals placed just in the last year. Over the course of the preceding 5 years, the government had issued 5 warnings about water levels that exceeded authorized levels, but no solution had been implemented when the dam disintegrated. 
Baia Mare Cyanide Spill, Romania January 2000
A dam holding gold mine tailings burst and released 260,000 gallons of water containing about 110 tons of cyanide and other heavy metals across farmland, dairyland, and into the Somes river. The toxic water flowed over 620 miles, from Romania, through Hungary and to the former Yugoslavia where it entered the Danube. The drinking supplies of over 2.5 million Hungarians were contaminated and along the Danube some sections registered cyanide as high as 20-50 times permitted levels. This catastrophe has been described as the worst environmental disaster in Europe since Chernobyl. The mining company blamed the dam’s failure on excessive snowfall. 

Are More on the Way?

In the end, the ultimate purpose of a tailings management facility is to store tailings in a way that offers permanent containment and protection from environmental damage, while not placing an undue financial burden on mining operations. However, as mining operations grow worldwide, the potential for more frequent and more destructive failures increase as well. Tailings ponds and their dams are growing larger, not smaller, and the financial pressure to keep costs low is ever increasing, especially as competition multiplies and market prices for metals fluctuate. 

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