TAILINGS DAMS
HARM AND RISK OF FAILURE
Modern mining produces enormous volumes of waste. The amount of mine waste produced is of the same order of magnitude as that of fundamental Earth-shaping geological processes, some several thousand million tonnes per year (Fyfe, 1981, Förstner, 1999).
Mine tailings dams are some of the world’s largest man-made structures.
The risk of catastrophic failures is increasing as the global demand for metals grows, ore grades decline, and the amount of associated mine waste increases.
The consequences of tailings dam failures can be catastrophic for communities and ecosystems in the vicinity of the dams. Almost three hundred tailings dam failures have been reported in the last hundred years. Many of the incidents go unreported for fear of legal repercussions and bad publicity (Kossoff et al., 2014).
RISK FACTORS THAT INCREASE THE PROBABILITY OF TAILINGS DAM FAILURE
Some of the conclusions leading to dam failures (ICOLD, 2001; Rico et al., 2008; Martin & Davies, 2000; Chambers and Bowker, 2016):
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Active dams are more likely to fail than inactive dams.
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The leading modes or mechanisms of failures identified from reported incidents in the past 100 years have been earthquakes, slope instability, and overtopping.
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Dams with the upstream construction method are more likely to fail, especially in seismic areas.
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The safety of tailings facilities is inextricably linked to the management and operation practices of mining companies.
A 2001 study by the International Commission of Large Dams and the United Nations Environmental Programme found that, on average, one major tailings dam incident occurs each year.
TAILINGS DAMS NEED TO STAND IN PERPETUITY
Mine waste contains a range of toxic elements including arsenic, cyanide, mercury, selenium, and other heavy metals harmful to human health and the environment. In British Columbia, tailings are stored behind some of the highest dams in the world and there are plans to build more.
A tailings dam is expected to confine toxic mine tailings in perpetuity. As an example, the estimated closure period for the KSM Project is 250 years.
Without continuous monitoring, inspection, and maintenance, failure is inevitable.
Their construction, maintenance, and closure costs provide no tangible returns for mining companies; therefore, there is limited effort to address factors of concern (Kelly et al., 2016).
UPWARD TREND IN HIGH-CONSEQUENCE TAILINGS DAM DISASTERS
A 2020 paper notes the seemingly upward trend in high-consequence tailings dam disasters:
"A cursory review of the literature on mine tailings disasters reveals a heightened awareness about risk levels, with strong indications that the underlying drivers of risk will increase in the future. Rising consumer demand, coupled with declining ore grades suggests that larger, high volume mine tailings dams based on the ‘incremental build’ model will be a factor in future global supply scenarios. Without radical changes to the technologies for managing mine waste, including mine tailings, these risks will accumulate well into the future."
Trend in recorded instances of tailings dam failures.
Data from wise-uranium.org
TAILINGS FACILITIES CAUSE HARM IN MULTIPLE WAYS
British Columbia currently has 86 sites containing at least one tailings storage facility.
2020 report identifies several sites of concern, including the KSM and Red Mountain Underground Gold mines. Both are located in a seismic hazard zone "Very High" and/or where annual runoff exceeds 2000 mm, and with one or more of the following characteristics:
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Use of upstream or unclear dam construction method - the cheapest to build and the riskiest to use.
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Site status as closed or in care and maintenance
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Dam failure consequence category High, Very High or Extreme.
The tallest of four dams planned for KSM would measure 784 feet (239 meters).
The KSM’s massive proposed tailings storage facility will contain 2.3 billion tonnes of water-covered tailings. The mine project in its entirety will sit atop the Nass River, one of B.C.’s top salmon-producing systems.
Just by being built, tailings facilities and their surrounding infrastructure can cause ecological harm in multiple ways.
From the Canadian Environmental Assessment Agency study report for the KSM Project:
"In Chapter 15 of the EIS, Seabridge assessed the impacts of the Project's effects on physical changes or loss of habitat, including habitat upstream of salmon distribution. The proponent indicated that fish habitat destruction will occur in the headwaters of South Teigen and North Treaty Creeks; and has committed to mitigation measures that will offset the loss of fish habitat. The proponent notes the particular importance around salmon species (in the case of Teigen Creek, Chinook salmon) and will alter diversion ditch flow patterns as necessary to ensure downstream flow mimics the baseline hydrograph in Teigen Creek."
Tailings dams also require artificial water diversions and releases, and polluted groundwater seepage from unlined reservoirs or failing liners is often hard to detect and treat.
LARGE TAILINGS DAMS HAVE BEEN BUILT FOR A CENTURY, BUT THEY MUST STAND IN PERPETUITY
"When we consider the recorded life of these structures (a century at most) to the length of time that they must function (millennia) the number of failures we have experienced in the first century of their operation is not comforting." Chambers & Higgman, 2011