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- 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.