SCIENCE sciencemag.orgtailings below. This approach is often the
cheapest, because the tailings serve as con-
struction material.
More than 40% of major tailings dams
are the upstream design, according to
a global inventory of more than 1700
dams recently launched by pension funds
of Sweden and the Church of England,
which have pressed the mining industry
to strengthen environmental and safety
measures. A study of 8000 tailings dams
in China found that 95% were upstream
dams. And such dams are involved in
three-quarters of tailings dam failures, ac-
cording to one estimate.
The problem is that tailings aren’t a pre-
dictable building material, and they are of-
ten waterlogged. The water can act like a
lubricant, reducing the friction that binds
an earthen dam together. Engineering flaws
such as poor drainage can exacerbate the
problem. In extreme cases—such as the
2019 disaster at the Brazilian iron mine—
dam sections simply liquefy.
In Chile, where earthquakes make up-
stream dams even riskier, the government
has forbidden the design since 1970. Brazil
banned them in the wake of the 2019 acci-
dent, and has ordered the mothballing of all
upstream dams by 2027. Worldwide, such a
policy could mean the demise of thousands
of mines and tailings dams (which could be
replaced by dams with different designs).
Although such a change might be expensive
for companies, right now communities near
dams are bearing the costs of cheaper con-
struction, says Payal Sampat of Earthworks,
a nonprofit group that promotes mining re-
forms. “That is unacceptable.”
Some experts caution against a one-size-
fits-all approach. Upstream dams can per-
form safely, particularly in places with dry
climates and few earthquakes, says David
Williams, a geotechnical engineer at the
University of Queensland, St. Lucia. “You
can construct [an upstream dam] to be
perfectly safe. You can also build it in a not
so good way.”
One knowledge gap is an understand-
ing of the forces that can suddenly turn an
earthen dam into a liquid river of mud. At
the Georgia Institute of Technology, geo-
technical engineer Jorge Macedo is stress
testing tailings in his lab to document the
conditions that trigger liquefaction, par-
ticularly in silt, a little-studied material
that is common in tailings used to build
upstream dams.
Other researchers are looking at bet-
ter ways to spot dams on the verge of
failure. Moe Momayez, an engineer and geo-
physicist at the University of Arizona, is test-
ing sensors on an Arizona dam that track
temperature and moisture levels. Some damsare already equipped with radar or lasers that
watch for worrying bulges. Momayez’s goal is
to integrate streams of data in a computer
system that can spot problems that might
escape periodic inspections. “We have a
pretty good idea how these tailing dams fail,”
Momayez says. “The question is, can we pre-
dict that, can we get ahead of the curve?”
Some engineers would like to simply
eliminate the need for massive dams.
“The best tailings dam is no dam at all,”
Nelson says. She is studying whether
mine waste can be melted into glasslike
fibers that could be used for textiles or
reinforcing concrete. In June, mining gi-ant BHP said it would spend $10 million
to study such reuse of copper tailings.
A more mature approach is to wring
the water from tailings, creating waste the
consistency of damp earth, which can be
sculpted into mountains. The leftovers can
still be toxic, but there’s less danger of a
devastating flood, says Jan Morrill of Earth-
works. “Filtered tailings should be consid-
ered the industry standard,” Morrill says.
Although the approach has been around
for decades, it’s rarely used, representing
just 4% of tailings systems in the pension
funds’ inventory. Filtered tailings systems
can cost five to 10 times more than a con-
ventional dam, says Harvey McLeod, a
geological engineer who designs tailingsdams for Klohn Crippen Berger, a private
firm. It’s also an enormous challenge to
process tailings at big mines churning out
100,000 tons of waste per day, particularly
in wet climates. “It’s easier said than done,”
McLeod says.MANY GROUPS are also pushing for regula-
tory and management reforms. After the
2019 Brazilian disaster, investment funds
worth more than $10 trillion helped bring
together officials from industry, govern-
ment, and the investor group Principles for
Responsible Investment to create a set of
global guidelines for tailings dam construc-tion. Earlier this month, the coalition issued
its plan, calling for stiffer engineering stan-
dards for new dams. It also urges top min-
ing executives, rather than lower level staff,
to be responsible for tailings safety, and for
independent experts to review companies’
waste plans. But it doesn’t push for a ban on
upstream dams.
Morgenstern notes that similar reforms
he and others suggested in the late 1990s,
after an earlier string of dam disasters, were
never fully embraced. He expects it won’t be-
come clear until the end of the year whether
the new proposals will fare better. Still, he’s
heartened that, after the recent tragedies,
muddy mine waste is again in the spotlight.
“The tree,” he says, “has been shaken.” jFirefighters search for survivors
in the mud unleashed by a
2019 tailings dam failure in Brazil.PHOTO: DIEGO BARAVELLI/FOTOARENA/SIPA/AP IMAGES
21 AUGUST 2020 • VOL 369 ISSUE 6506 909NEWS | FEATURES | MUDPublished by AAAS