– This is Giant Mine
in the Northwest Territories of Canada. There are kilometres of tunnels
under this rock, and chambers the size of city blocks
that have been hollowed out. In the 20th century, more
than 200,000 tonnes of gold were extracted from the
rock underneath here. At current prices, that is somewhere north
of US $8 billion worth of gold. There is a problem, though. That mining also created
more than 200,000 tonnes of toxic arsenic trioxide dust. That’s enough to kill everyone
on Earth several times over. Over the decades, the vast
majority of it was stored in the empty, abandoned chambers
left behind after mining, although some of it did get
out into the environment. The mine closed in 2004. When the gold ran out, the
mining company went bankrupt and left the mess for the
government to clean up. Arsenic trioxide has no scent, no taste,
and it dissolves in water. Oh, and we’re right next to Yellowknife,
the capital of the Northwest Territories, and next to the 10th
largest lake in the world. – There’s 237,000 tonnes
of arsenic trioxide, and they’re currently stored
in 14 underground chambers. The plan is to freeze the chambers. We’re freezing the rock
around the arsenic. See, arsenic trioxide is a fine powder. So it will form a shell. And eventually, it will freeze in
and it will become a block over time. And that prevents water from
getting in and getting out and keeps the arsenic trioxide contained. So each chamber, of course,
is differently shaped. Some are regular shaped. Some are very rectangular shaped. So we want to freeze 10 metres
beyond all boundaries of the chambers, both on the horizontal
and the vertical. We’re going to freeze
at least to -5°C. The way we’re going to
freeze it, we’re going to use a technology called
thermosiphon technology, and it’s basically a technology that uses the ambient air temperature, the cold air, using a long tube filed
with carbon dioxide. The carbon dioxide, when it’s a gas,
it rises up to the top of the tube. And then if the air outside is colder, it will dissipate its heat,
turn to a liquid, and with gravity, will drop back
down to the bottom of the tube. And there, it can warm up, take
the heat out of the ground, and it just continually cycles,
extracting heat from the ground. Since we’re in Yellowknife,
north of 60° latitude, it’s colder above ground
than it is below ground for the majority of the year. – Freezing the arsenic
doesn’t make it less toxic, but it does make it
impossible for any water to seep in and then carry the arsenic out. And that was the mining
company’s original solution using the natural permafrost here. And it might have worked, if they
hadn’t mined the rock above it, exposed the permafrost
layer to the elements, and started to melt it. Freezing should work, but there are skeptics,
and they do have a point. Freezing requires constant upkeep. This dust is arguably worse
than radioactive waste. There is no half-life here.
It won’t decay over time. The dust will be just as deadly
in 10,000, 100,000 or a million years. – So right now, there’s
nothing on the horizon. The freezing was deemed the best
technology for the arsenic trioxide. So we will be funding
research indefinitely until a different solution arises. We have frozen one of the chambers. We did what we call a
freeze optimization study. We chose one of the chambers.
We installed the thermosiphons, but we also installed some
freezing pipes filled with glycol to do what we call an active freeze, which will be very
similar to a hockey rink. So based on that study, we
determined that we could use the passive technology, which
is just the thermosiphons with the carbon dioxide. It just wasn’t quite as fast,
so it’s gonna take a little bit longer, but the trade-offs are such
that we don’t need to use power and it’s a lower maintenance
over the longer term. So the remaining chambers will be frozen
when we start the remediation project. It could be as early as summer of 2020, but more optimistically, 2021. Our last estimate for
the cost of the project was 934 million, including
the care and maintenance phase that we’re in right now,
remediation that we’ll go into in a few years, and then the
long term care and maintenance. This project has gotten
approval for 100 years. – These days, countries
in the developed world have regulations that
mean mining companies shouldn’t be able to do this. We have environmental impact
studies and long-term plans, and we have public scrutiny
of pretty much everything. But we still have to fix
the mistakes of the past and make sure that
today’s mining companies can’t just walk away from their legacies. Thanks to everyone at the
Giant Mine Remediation Project. Pull down the description
for links about them and about some of the history
that I couldn’t fit into this video.