By Scott Patterson
The deadly collapse of a mine dam in Brazil is putting a fresh
spotlight on whether mining companies are spending enough to build
and maintain dams meant to contain all the waste and water dumped
A 28-story high dam meant to store chemical-laden waste, called
tailings, at a mine operated by Brazilian giant Vale SA collapsed
on Friday, unleashing a river of mud that destroyed Vale facilities
and flowed into parts of the town of Brumadinho in southeastern
Brazil. The death toll from the accident has hit 84, but hundreds
Amid a criminal probe into the disaster, Vale said it would
dismantle 10 other, similar dams. Brazilian authorities have made
several arrests , including two contractors who worked for a
company that inspected the dam late last year.
The accident comes just four years after the failure of another
tailings dam in Brazil run by a joint venture between Vale and
Australia's BHP Billiton Ltd. that killed 19.
That 2015 accident ratcheted up scrutiny of such dams, which are
among the largest man-made structures in the world, as well as the
engineering and investment that goes into them.
A 2017 Columbia University study on tailings-dam failures found
miners typically choose the lowest-cost option when constructing
the dams. That's in part because mining operators often fail to
assess the cost of a collapsed dam, the paper says, clouding "the
financial magnitude of the risk assumed" by the company, according
to the study.
"Cost is often the major consideration" for mining companies
when constructing the dams that contain tailings, said David
Chambers, a geophysicist who has spent decades studying mining
Vale declined to comment on its tailings-dam spending. The
company said it was cooperating with investigators.
The London-based International Council on Mining and Metals
didn't respond to a request for comment. Top engineers of big
mining companies have generally said they won't design a tailings
dam if budget limitations may affect its safety.
Research by Mr. Chambers, founder of the Center for Science in
Public Participation, a Montana-based mining research group, and
others shows that major failures of tailings dams have become more
frequent as mining companies ramp up the scale of their operations
to feed the world's growing hunger for commodities. The increase in
production means miners need to build bigger dams to contain the
waste that is a byproduct of mining.
While failures of tailings dams have broadly declined in the
past few decades, collapses defined as "serious" or "very serious"
-- the latter defined as having a release of at least one million
cubic meters of tailings, or about 35 million cubic feet, traveling
more than 20 kilometers, or about 12.5 miles, or causing multiple
deaths -- have increased, according to studies by Mr. Chambers and
his research partner Lindsay Newland Bowker.
Between 2008 and 2017, there were 27 serious or very serious
failures of tailings dams -- including the 2015 Vale-BHP failure --
up from 19 failures during the period between 1998 and 2007,
according to a database managed by Mr. Chambers and Ms. Bowker.
The increase is also the result of a general decline of the
amount of ore in the ground, researchers say. Less ore means miners
need to dig up more dirt and rock, leading to more tailings. Mining
companies produced 8.5 billion metric tons of tailings in 2017, up
from 7.4 billion tons in 2010 and four billion in 2000, according
to Gavin Mudd, an engineering professor in Australia who's studied
sustainable mining practices.
Researchers blaming cost considerations in tailings-dam
collapses point to the type of dams mining companies choose to
build. Specifically, they single out the most widespread design,
known as "upstream," which involves piling waste from the mine
toward the tailings pond itself, raising it to new levels as the
dam grows in size. It is the cheapest design -- and the most prone
to failure, experts say.
"Upstream is cheaper because you don't need as much material,"
said Mr. Mudd, an environmental engineering professor at
Australia's RMIT University.
Mr. Chambers estimates upstream dams are roughly one-half to
one-quarter as expensive as designs he and other researchers say
are safer, such as so-called downstream dams, which are built
outward from the tailings pond and have a bulkier design. Both the
Vale dam that collapsed Friday and the Vale-BHP dam that failed in
2015 were upstream dams.
Upstream dams are banned in earthquake-prone Chile. But they are
popular elsewhere and show no signs of being phased out. Among the
12,000 tailings dams in China, 95% were constructed with upstream
method, according to a 2017 United Nations study.
Climate change also poses a threat. While tailings dams are
designed to be built to last for centuries and withstand extreme
weather, many don't. Intense rainfall was responsible for
one-quarter of tailings-dam incidents in the world, according to a
Among the difficulties facing tailings-dam engineers is that,
rather than standard water dams, they are almost constantly in flux
as they expand them to contain additional tailings. They often grow
larger than originally intended as the miner pushes the limits of
the resource to produce more ore, a process that also shovels out
To be sure, even seemingly resilient tailings dams can fail.
Canada, home to one of the world's most advanced mining sectors,
saw one of its worst environmental disasters in 2014 when Imperial
Metals Corp.'s Mount Polley dam collapsed. Some 280 million cubic
feet of gold and copper byproduct poured into a pair of glacial
lakes in British Columbia, temporarily cutting off local
drinking-water supplies. No one died.
Write to Scott Patterson at email@example.com
(END) Dow Jones Newswires
January 30, 2019 14:08 ET (19:08 GMT)
Copyright (c) 2019 Dow Jones & Company, Inc.
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