Catastrophic Tailings Spill at Mount Polley Mine

August 8, 2014 | By admin | Filed in: Imperial MetalsBritish ColumbiaWaste Rock and TailingsEnvironmentGoldImpact on CommunitiesToxics/NPRIWater and fisheries.

On August 5, approximately 10 billion litres of wastewater and
5 billion litres of solid tailings waste escaped the
impoundment at Imperial Metals
Mount Polley mine in the interior of British Columbia. The
creek that received the brunt of the flow was completely
obliterated, some of the waste backed up into Polley Lake and
some the wastes and debris from the torrent continued
downstream into Quesnel Lake. A local state of emergency was
called and a precautionary ban was put on using surface and
groundwater in the area. The following is our effort to
synthesize the many reports and commentaries that have come out
during the first four days following the spill, and to answer
some of the questions we’ve been getting from media and the
public. For background, we’ve relied on a 2011 report jointly
commissioned by the Xatsull and T’exelc First Nations and
Imperial Metals, the company’s website, and a 2004 technical
report.

What are tailings and what was in the
impoundment?

Tailings are the wastes left over from the crushing, grinding,
and processing of mineral ores. Because low-grade large-scale
mines like Mount Polley are mining ores where the sought-after
minerals (gold and copper in this case) are less than 1% of the
ore, a lot of waste is created from processing the 20,000
tonnes of ore that went through the Mount Polley mill each day.
During processing, the ground rock is mixed with water and
reagents to remove the gold and copper, and the remaining
slurry (mix of water and sandy or muddy solids) is pumped to
the tailings impoundment for disposal. (See also our
Mine Waste Primer
.)

The Mount Polley tailings impoundment is no “pond” – it is
nearly 2 square kilometres with a perimeter of 5 kilometres. As
Iain McKechnie pointed out with the attached image on
Twitter, that’s almost the size of Vancouver’s Stanley Park.

Tailings often contain residual minerals including lead,
mercury, arsenic, cadmium, and selenium, that can be toxic if
released to the environment. If a substance in the tailings is
included in the toxic substances listed under the Canadian
Environmental Protection Act, mine operators must report the
amount of these substances in the tailings to a publicly
available database – the
National Pollutant Release Inventory
(NPRI). (Prior to a

legal challenge
by MiningWatch, Great Lakes United, and
Ecojustice, the mining industry was exempt from reporting.)

Below is a table with the toxics contained in the Mount Polley
tailings from the last five years of reporting (this differs
from earlier reported amounts, which included substances
contained in waste rock as well as tailings). The extent to
which these substances pose a threat to the environment depends
on the geochemistry of the tailings and the surrounding
conditions. 

Substances in Mount Polley tailings as reported to the
NPRI (in tonnes)

Substance

2009

2010

2011

2012

2013

Total

Nickel

48

73

56

63

71

311

Lead

105

59

40

36

38

278

Arsenic

81

137

84

84

83

472

Zinc

273

701

453

420

403

2250

Copper

9,016

9,044

7,570

6,723

6,392

38745

Vanadium

1,045

1,474

1,357

1,637

1,557

7070

Cadmium

2

2

1

2

1

8.6

Cobalt

105

139

129

142

138

653

Phosphorus

7,784

11,374

9,735

10,056

10,405

49354

Antimony

35

3.6

2.8

3.5

3.6

48.5

Manganese

3,231

7,444

4,733

4,733

4,119

24260

Mercury

0.5

0.7

0.5

0.4

0.6

2.6

Selenium

0.01

0.01

6.8

8.2

9.0

24

Tailings also include reagents used in processing the ore.
Reagents used at Mount Polley include xanthates, which are
known to be toxic to aquatic organisms, but the company
estimates that most of the residual xanthates leave the site
with the mineral concentrate. Testing of processing chemicals
in tailings and effluent is not currently required by
Environment Canada or the B.C. government.

What are the effects of the spill?

The most obvious impact of the spill is the destruction of the
10 kilometre-long Hazeltine Creek watershed. A small tributary
to Quesnel Lake, the creek has been completely buried in
tailings and a huge swath of trees mowed down. According to the
B.C.
Fisheries database
, Hazeltine Creek provided habitat for
chinook, coho, and sockeye salmon, rainbow trout, and a number
of other fish species. If it is even possible to restore the
habitat for these species, it will require removing the
tailings from the creek bed, re-establishing a natural creek
bottom, getting vegetation to regrow along the shore and
keeping the water and sediments clean enough to support a
healthy ecological community.

While much of the tailings remain in the Hazeltine Creek
watershed, some of the solids went into Polley Lake and Quesnel
Lake, both of which are important recreational fishing areas
with high quality water that are used as a drinking water
sources by local residents.


Initial testing
of Quesnel Lake by the B.C. government has
not shown any impairment to the use of the lake as drinking
water or for aquatic life according to established standards.
This may be thanks to the lake’s large size and outflow that
would have diluted and dispersed any contaminants from the
wastewater. Much of the contaminant load from the spill will be
in the sediments, which will settle out of the water column and
not be captured in surface water samples. These are very
preliminary findings and until the tailings upstream are
stabilised, contaminant loading to the lake will continue. It
is very difficult to know what the medium or long-term
repercussions for Polley Lake, Quesnel Lake and aquatic
communities further downstream will be. Fish – and in
particular salmon – are extremely sensitive to several of
the substances listed above, and much more work is needed to
evaluate the risks.

The spill has had significant emotional and psychological
impacts with the shock and grief of witnessing this kind of
disaster and the uncertain future of a cherished watershed.
Chief Bev Sellars of the Xatsull First Nation
told the media
that many members of her band were in tears when
they learned of Monday’s release.
“Because they know the
destruction that’s going to happen from this breach. It’s just
a real sad day.”

The local
community is also stressed by the immediate loss of the 300
jobs
at the mine and the uncertainty about when or if
the mine will reopen.

The financial costs of cleaning up the spill will be
considerable and are estimated in the hundreds of millions of
dollars. Mining companies are required to post financial
assurances with the province for routine clean up costs at the
end of a mine’s operating life; unfortantely these costs are
not made public. A
report
by University of Victoria Environmental Law Clinic
indicates that these amounts may not be sufficient for routine
mine closure – let alone a major disaster like this. Imperial
Metals
admitted
that its insurance is not likely to cover all the
costs with the President stating: “I made the commitment, to
the best of my ability. If it’s $400 million, then we
are going to have to get mines generating to make that money to
do the cleanup. We don’t have $400 million in the bank, so
we’ll have to make that to do it.”

If Imperial does not fund the clean-up citizens will be left
with the financial, environmental and social costs of the
spill.

What could have caused the failure?

Tailings in an impoundment like the one at Mount Polley remain
saturated so they have little to hold them together, and a
breach in the impoundment means the water and solids flow
together out of the impoundment and then downstream. It does
not require a large breach to start this process, so Imperial
Metals’
statement
that the portion of the impoundment that failed
is relatively small compared to the total length of the dam is
totally irrelevant.

Catastrophic (sudden and severe) failure is an inherent risk of
large tailings dams. The risks increase with the size and
height of the impoundment and the amount of water relative to
the solids kept in the impoundment. As Andrew Nikiforuk

points out
, as we exploit lower and lower concentrations of
minerals, tailings impoundments are growing larger and larger
and more and more risky.

In addition to the water from processing the ore, large
tailings facilities also accumulate rainwater. If it does not
evaporate, excess water must be released to maintain the
impoundment, usually following treatment to remove contaminants
such as heavy metals and suspended solids. Excess water that
flows over the top of an impoundment is extremely dangerous as
it can erode the impoundment wall, creating a gully that
increases rapidly in size as ever more waste flows out of it.
The weight of excess water also increases the pressure on the
impoundment walls and destabilise them if there are any
weaknesses.

Impoundments are built to the Canadian Dam Association’s
standards and are, in theory, supposed to withstand extreme
weather and seismic events. The Mount Polley impoundment was
built in 1997, and it was evaluated and deemed secure by Amec
consultants in 2004 before it was put back into use after the
mine was closed for several years. There is no indication that
any extreme weather or seismic activity contributed to the
failure.

There are several lines of evidence that indicate that Imperial
Metals amplified the inherent risks of a tailings impoundment
by storing a large volume of water and allowing the water level
to go beyond the modest one-metre buffer demanded by its
provincial permit. The CBC
reported
that the B.C. Ministry of Environment gave five
warnings to the company about the amount of water in the
impoundment. The Minister of Energy and Mines disputed this
statement, noting that there was only one incident in May of
this year and that it was dealt with quickly by the company
pumping excess water into a mined out pit.

The engineering firm responsible for the initial construction
and oversight of the impoundment up to 2011
issued
a statement saying that it also cautioned the
company and BC that the embankments and impoundment were
“getting large and it is extremely important that they be
monitored, constructed and operated properly to prevent
problems in the future”.

A former mine employee
spoke to the media,
stating that the water was being kept
too high and there were previous breaches to the impoundment.
If high water was a reoccurring problem and regulators gave the
company a series of warnings rather than taking stronger
measures, a serious failure of the regulatory system occurred.

Imperial requested a discharge permit to release more water
from the impoundment in 2009 but did not provide a satisfactory
plan to do so. Another application to discharge was being
processed at the time of the spill. The 2011 report jointly
commissioned by neighbouring First Nations and Imperial
focussed on the discharge issue and provided a number of
recommendations to Imperial about how to proceed. From the
available information it seems clear that Imperial continued
building the impoundment walls higher rather than dealing with
the water. The former employee also noted a failure to increase
the width of the base of the impoundment to stabilize it as the
height increased.

In his
critical editorial
in the Northern Miner, John Cumming,
made a point of noting that Imperial Metals is a member of
Canada’s mining establishment not some rogue fly by night
operation. It’s also a member of the Mining Association of
Canada and has been implementing the Association’s Tailings
Management Program as part of the Towards Sustainable Mining
Initiative. MiningWatch has repeatedly asserted that such
voluntary management approaches are inadequate to deal with the
risks associated with mining.

Mining engineer and I Think Mining blogger Jack
Caldwell summed up his
observations
of  the available evidence this way: “I
suspect it failed because there was too much water in the dam,
the corner gave way, an upstream slide occurred, and the
disaster ensued. They are saying nobody could have anticipated
this. Rubbish. It was entirely predictable given the facts.”

Could this happen at other sites?

This is the largest tailings spill in Canadian history but
certainly not the first. Just last year, on October 31, 670
million litres of coal slurry spilled from an impoundment at
the Obed coal mine into the Athabasca River near Hinton,
Alberta. The Coalition Québec meilleure mine has

documented
many smaller recent spills in that province.

Whenever we have the combination of an inherently risky waste
management option, combined with lax government and a company
that pushes the risk boundaries, we are likely to have another
failure.

The other crucial issue about tailings impoundments is that
they remain on the landscape forever. As Water Matters’ Bill
Donahue
pointed out
to the CBC, impoundments may be portrayed as a
final solution, but they are not. If left on the landscape
forever, the likelihood of failure eventually approaches
certainty.

What are the alternatives to tailings
impoundments?

Disposing tailings slurry into an impoundment is not the only
way to manage the millions of tonnes of waste generated by
modern-day mining. Some mines, mostly underground mines
extracting smaller volumes of ore, backfill exploited areas
with tailings – a safe and sound option. Drying tailings or
turning them to a paste that then hardens and dries are two
other options. All these options add costs to mining
operations, and so are not favoured by corporate interests
focussed on the bottom line. They also have their own technical
challenges. See our
Mine Waste Primer
 for more.

An option that must also be considered is simply not mining a
particular deposit. Where ecological and social risks are high
and the economics don’t allow for a more secure longer-term
solution, not mining remains the only guaranteed way to keep
tailings out of streams, rivers, and lakes.

Addtional Links


Video: Helicopter Fly Over by Global News (2 min)

Video:
Helicopter Fly Over by Cariboo Regional District (37 min)


BC Ministry of Environment Incident Page


Union of BC Indian Chiefs Statement


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