Mining Dams Grow To Colossal Heights, and So Do The Risks - WSJ
Mining Dams Grow To Colossal Heights, and So Do The Risks - WSJ
Mining Dams Grow To Colossal Heights, and So Do The Risks - WSJ
Do the Risks
Engineers say Brazilian disaster shows world-wide danger from Hoover Dam-size earthen structures
holding tailings waste
By Paul Kiernan
On Nov. 5, an earthen dam holding back this sea of sludge collapsed, releasing a
deluge that killed 19 people, destroyed villages and traveled more than 400 miles
to the Atlantic Ocean, where it left a reddish-brown plume visible from space. As
tall as a 30-story building and holding enough refuse to fill 19 Dallas Cowboys
stadiums, the dam was the largest structure of its kind ever to give way.
It wont be the last. From Chile to Australia to the U.S., the quest for economies
of scale has prompted mining companies to dig larger and deeper pits, creating
record volumes of waste. To house all that detritus they have constructed some
of the most colossal man-made structures on the planet. Known
as tailings dams, these earthen embankments hold back sprawling reservoirs of
mud, finely ground rock and waterwhat is left after a mill separates metals
from ore.
In theory, tailings dams are intended to last forever. In practice, they fail often
enough that industry engineers
themselves are sounding
Processing alarms. Fifteen months before
Slurry
facilities the Brazilian disaster, Canada
Mine
Tailings da suffered its biggest tailings-dam
discharge
line failure at a copper mine that
was in full compliance with
Tailings dams local regulations. Experts
are huge Water estimate that between one and
Solid tailings
Sources: Jon Engles tailings info; WISE Uranium
structures four breaches occur each year
at tailings dams world-wide,
roughly 10 times the failure rate of water dams.
The largest tailings dams, at copper mines high in the Peruvian Andes, are
already as tall as the Hoover Dam and have permits to rise even further.
Our dams and dumps are among the highest-risk structures on Earth, says
Andrew Robertson, a Vancouver-based consultant who has designed a number
of very large tailings dams for mining companies. He notes that the biggest
mines increase their waste output by 10 times every third of a century.
Some closed tailings dams remain stable and more or less blend in with their
surroundings. Antofagasta Minerals PLC is reforesting its hulking Quillayes
tailings dam in Chile, closed in the past decade, with native plants to absorb
toxins and return to the area to something resembling its natural state. The
tailings dam at the shuttered Cannon gold mine in Wenatchee, Washington, has
been converted into a horseback-riding preserve named Dry Gulch.
Not so Brazils Fundo dam, which belonged to Samarco Minerao SA, a joint
venture between two of the worlds biggest mining companies: Australias BHP
Billiton Ltd. and Brazils Vale SA .
The International Council on Mining and Metals, or ICMM, which includes most
of the worlds biggest miners, said in December that it would convene a global
review of tailings storage facility standards and critical controls.
The most common, upstream, design involves letting the tailings closest to the
dam dry out. These dry tailings are then used as the foundation for new levels,
raised by plowing earth or tailings into successive embankments. As it requires
the least amount of bulldozing, the upstream method is the least expensive way
of building a tailings dam and was employed by Samarco.
Many engineers say upstream dams are the most likely to fail. Earthquake-prone
Chile bans the design.
Mr. Martin now works at Anglo American PLC, while Mr. Davies works at
Canadian mining company Teck Resources Ltd. Neither company made the
engineers available for comment.
When accidents do happen, they bring not just flooding but heavy, sandy mud
that destroys everything in its path. In 1985, a spill of just 200,000 cubic meters
wiped out an Alpine village in Italy and killed 268 people.
If Id been two minutes slower Id be dead, said Maria Irene de Deus, a longtime
resident of the community who fled on foot after the dam burst.
Tailings Dam Risks
Mr. Davies, the engineer, said in a 2002 paper that the failure rate
for tailings dams was approximately 10 times that of water-retention dams. Back
then, he estimated there were somewhat more than 3,500 tailings dams world-
wide.
No one knows for sure. ICOLD doesnt include the structures in its 58,000-entry
World Register of Dams due to internal concern that their high failure rates
would tarnish the reputation of all dams, said spokesman Emmanuel Grenier.
The Wall Street Journal asked the top five publicly traded mining companies by
annual revenues how many tailings facilities they manage world-wide, which is
the tallest and which holds the largest volume. Just one, Anglo American,
answered all three questions, noting it has 109 tailings storage facilities world-
wide, 38 of which are inactive. Its tallest dam is Perez Caldera No. 2 at 110 meters,
and the largest storage capacity is Las Tortolas at 448 million tons, both in Chile.
Vale gave a partial answer to the first, saying it has 143 tailings dams at its iron-
ore mines in Brazil. Rio Tinto PLC gave a partial answer to the first, saying it has
35 tailings facilities in operation and many more closed and legacy sites. BHP
Billiton identified its biggest and tallest tailings dam, Escondida in Chile, but
didnt say how exactly how many it has. Glencore PLC declined to answer any.
Based on the findings, they projected that 11 very serious tailings-dam failures
defined as having a release of at least 1 million cubic meters of tailings,
traveling more than 20 kilometers or causing multiple deathswould occur
between 2011 and 2020. So far, there have been five.
Recent aerial views of Samarco's Germano tailings basin. PHOTOS: JOO PINA FOR THE WALL STREET JOURNAL
Its one of those things youd like to be wrong about, says Mr. Chambers, who
advocates for safer tailings storage.
Concern about tailings from closed mines hit the national spotlight in the U.S.
last August. An Environmental Protection Agency cleanup crew accidentally
triggered a leak from an old gold mine in Colorado that spilled arsenic, cadmium
and lead into a mountain river, prompting the governors of three states to
declare a state of emergency. The mine had been closed since 1922.
A 2014 breach at the Mount Polley Mine in Canada spilled waste into a nearby creek and two glacial lakes. PHOTO: JONATHAN
HAYWARD/CANADIAN PRESS/ASSOCIATED PRESS
Scientists say the typical culprit for tailings accidents is too much water, which
can cause earthen dams to liquefy. A review panel after the Mount Polley
accident recommended that miners adopt technology to remove water from
their waste before storing it.
Another way to make a dam safer is to expand it by building outward, rather than
upstream atop dried tailings. Called the downstream design, this results in a
bulkier structure that more closely resembles a water dam.
Big mining companies deny that is the case. Top engineers say they wont design
a tailings dam if budget limitations may affect its safety. Some, such as ICOLDs
Mr. McLeod, say they avoid building upstream dams altogether.
We believe that these facilities can be safe with the application of appropriate
design and management standards, says ICMM President Tom Butler. My
members being global companies, theyre very concerned about their
reputations. Theyve got a very strong incentive to get this right.
Samarco always went to meetings in Bento Rodrigues saying not to worry, sleep
easy, said Gilberto Pereira da Silva, a 33-year-old father of three who was
displaced along with most of the village when the dam burst. We lived in fear
but trusted Samarco.
A recent aerial view of Bento Rodrigues in Minas Gerais state, months after it was inundated by mine waste. PHOTO: JOO PINA FOR THE WALL
STREET JOURNAL