- [Joe] This might be one of the most beautiful lakes in Montana.

(bright music) (cannon booming) (birds squawking) - So this is one of the propane cannons, that loud noise that birds don't like and scare 'em away.

- So why go to so much trouble to keep birds from enjoying it?

Because this is one of the most toxic lakes in America.

The water here is acidic enough to dissolve metal and could spell certain death for any bird that lands on it.

Well, if I was a bird, I'd be outta here, man.

Nature didn't build this place.

We did.

For nearly a century, miners dug away a mountain in search of valuable minerals here, but when the mining stopped, the pumps were turned off and this mile-wide scar in the earth filled with water.

Today, the Berkeley Pit is filled with nearly 50 billion gallons of toxic, highly acidic water polluted with the remnants of all of that extraction.

So why would scientists want to dive into this?

What could possibly be worth searching for in a place like that?

(bright music) Well, there's treasure in these waters.

The Berkeley Pit sits above Butte, Montana, situated near the headwaters of the Clark Fork River.

This area has been shaped by more than a century of mining.

Diving into a lake this toxic seems like the last thing you want to do.

- All right.

- [Joe] So why are scientists doing just that?

- Let's go see some fun stuff.

- [Joe] Because the acidic waters that make this place dangerous are doing something unusual.

In the 1860s, Butte was little more than a mining camp.

By the early 1900s, Butte had become one of the busiest industrial mining regions on earth.

At its peak, 25% of the world's copper came from these mines, helping to electrify America.

Telegraphs, telephones, power grids.

And then in 1955, the Anaconda Mining Company pivoted to a radical strategy.

Instead of tunneling underground, they began removing the mountain itself.

Eventually, the Berkeley mine stretched a mile long and more than 1,700 feet deep.

That's deep enough to swallow the Empire State Building.

But when you dig a hole this big, rain and groundwater want back in.

When mining stopped in 1982, the massive pumps that had kept the pit dry were shut off.

Today this water is about 900 feet deep, but if you're tempted to take a dip, consider that in 2016, thousands of migrating snow geese, forced to land here thanks to a storm, died after drinking from these poisonous waters.

Hydrogeologist Jackson Quarles studies what makes this lake so toxic.

He has deep ties to Butte.

- [Jackson] It is the place to be.

I came out as a kid every summer, and the day that we would leave, I'd always be crying in the backseat, asking to stay.

And now here we are.

I made it happen.

- [Joe] Jackson is sampling this mining waste on the hunt for rare earth elements, valuable and critical minerals that may be hiding in these waters.

The rocks here contain sulfide minerals, and when exposed to air and water, they react and form sulfuric acid.

That acid dissolves metals trapped in the surrounding rock, a process called acid mine drainage.

The Berkeley Pit is now a giant chemical reactor, highly acidic water loaded with dissolved metals, some at concentrations more than 5,000% above drinking water standards.

Jackson and other scientists are hoping that those valuable rare earths are lurking here in this chemical soup.

Because the Berkeley Pit is so polluted, in 1987, the Environmental Protection Agency designated it as a superfund site.

They were established by law so that, whenever possible, the parties responsible for the mess must help pay for its cleanup, and they must be carefully managed to protect human health and the environment.

Jackson and his colleagues have a creative idea for how to clean up part of this environmental disaster.

- So we've got the submersible here.

So we've got a 4K camera, got four lights here on the front that allow us to see what we're doing.

Vertical rotors here, horizontal propellers here.

And then we also have our sediment sampler, kind of just jammer it in.

- Controlled collision.

- And we'll hopefully get back to the surface with a full one of these.

- [Joe] Take this puppy down to the water.

Exploring the pit is like a new frontier, one that very few people have ever seen.

Each journey down is like traveling through a foreign world.

- It's kinda like we're going to Mars.

It's a place that nobody's seen, nobody's been to in, oh, since '82 when they shut down the pumps.

(water creaking) And we'll turn on our headlights here so we can see what's going on.

And touch down, whoa.

(earth booming) - [Joe] What kind of samples are you looking for?

What's it doing down there?

- [Jackson] We're trying to find where these critical minerals or rare earths might be.

- [Joe] These rare earth elements include a group of 17 metals that are critical to modern technology.

Among them are elements like neodymium and praseodymium, used to make the powerful magnets that spin inside wind turbines and electric vehicle motors.

Others, like dysprosium, help those magnets survive extreme heat.

Without them, turbines would be heavier, electric cars less efficient.

Global demand for these elements is expected to surge as countries build more renewable energy and buy more electric vehicles.

Today, mining these rare earths often means digging new holes.

They're usually difficult to extract and mining and refining them often comes with its own environmental cost.

So what if we could find these valuable minerals in places that we've already dug?

- Shockingly enough, the Berkeley is home to more than we've really ever found anywhere else.

There's a lot of sites, and most places in the US even, they'll be very heavy in one specific rare earth or even just the light rare earth.

Whereas what we found in the pit was kind of something we've never seen and it had that full array of, that full distribution of those rare earths.

- These elements aren't actually rare.

They're just rarely found in high concentrations.

But here, the pit's chemistry has already done part of the work.

Acidic water has leached those metals out of the rock, ready to be filtered out.

So there might be hotspots here where there's just really rich deposits that you wanna focus your attention on.

- Yes, and, you know, kind of now is that hot point because we know the rare earths are still in the water and they haven't precipitated into the sediment yet.

And so processing them is immensely easier now.

All right, well, let's go see what we can find here.

- Hey, we got a lot of sludge out of that pit.

- And we got what we were looking for.

- [Joe] Extracting them isn't simple.

- So, yeah, I don't know what you would call that.

- [Joe] That is forbidden gravy.

- Forbidden gravy.

All right, well, I got my science helper, Joe.

- [Joe] In order to extract rare earth elements from the Berkeley Pit, researchers are testing new chemical techniques that could bind specifically to rare earth elements.

- I don't necessarily wanna know, is it in the mud?

I wanna know, is it in the sediment that is making the mud or is it in the water that's making the mud?

And so this will just help narrow that channel down a little bit.

So now we got our sludge.

(bright music) - [Joe] Oh, boy.

- And then what we do is we'll seal her up, we'll write on it, we'll let the lab know where it came from, the date we took it, what analysis we're looking for.

Rare earths are not truly all that rare, but finding them in mineable quantities, that's when they become very rare.

We have to get an idea of where the rarest and critical minerals are coming from before we do a deeper dive into that said mine.

We do the preliminary search, throw darts all over the board, and then whichever one lands on the bullseye, that's where we're gonna go back to and do a lot of darts at that spot and see kind of, yeah, what we can find.

- [Joe] You get a little bit of like a warm spot or something.

- Exactly.

- And then you do a bunch more there and you're like, "Oh, warmer, warmer, warmer."

- And you just keep working your way closer and closer and closer until you find what you're looking for.

- [Joe] And then you just might find that one pile of magic sediment.

And another benefit to this work is that the process of extracting rare earths and other critical minerals actually helps undo the damage caused by mining.

- That environmental benefit doesn't just pertain to the pit, but pertains to every other form of waste that we find, and they've already been exhumed.

So we're no longer digging a new hole to process new rare earths.

We're cleaning up our mess.

- [Joe] This idea is still in its infancy and it's too early to say whether it will prove to be viable.

But extracting rare earth elements and other minerals from existing waste may let places like the pit inch closer to a more natural state with less long-term contamination.

- The Anaconda slag pile, those are an enormous scar on the environment.

And for one day that those might just be gone because we've found an economic way to remove it and not just put it in a hole in the ground somewhere else, but to actually reprocess, make money, and get rid of it, I mean, yeah, it's a no brainer.

- [Joe] It won't replace mining tomorrow, but it could reduce the need to dig new holes.

If the Berkeley Pit represents how badly an environmental disaster can scar the earth, downstream, there's a place that shows us what's possible when it comes to cleaning up nature.

Milltown Park, at the meeting of the Clark Fork and Blackfoot Rivers, was once home to a dam that trapped tons of contaminated sediment from mines upstream.

This is Michael Kustudia, Milltown State Park manager, whose family ties to the area go back generations.

- Here at Milltown, they built the Milltown Dam, which was right over there, and that was finished in January in 1908.

In June of 1908, we saw the biggest flood in recorded history.

It was that 1908 flood that washed in a lot of mine waste from the upper watershed and that kind of kicked off this whole superfund issue.

Milltown was the first superfund site in Montana.

- [Joe] After years of hard work, the dam, along with over three million tons of contaminated sediment, was removed from this site.

Two and a half miles of the river channel had to be re-engineered back to the river's natural flow, and tens of thousands of trees were planted as part of the restoration efforts.

- A project like this is enormous and complex.

We had, you know, multiple state agencies involved, from the Department of Fish, Wildlife, and Parks and the Montana Natural Resource Damage Program, the Department of Environmental Equality.

Confederated Salish & Kootenai Tribes were very much involved.

They were a trustee in all of this because of their treaty rights.

We talk about it being a confluence of people almost because a lot of people came together to make this happen over a long, sustained period of time.

It did not happen quickly.

- [Joe] In 2018, the gates opened to Milltown State Park.

If it weren't for a few signs, visitors may not be able to tell that they're fishing, boating, hiking, and viewing wildlife in what was once home to piles of toxic waste.

It will never be exactly the same as it was before the dam, but it has returned to a living, breathing ecosystem.

- And so we had our grand opening.

It was in June of 2018.

Parents were here, which was really exciting, especially having my mom out here 'cause she, you know, grew up here and she had all kinds of stories.

It was a very emotional day for some of us.

And, yeah, for me, you know, I've been really fortunate.

It's a labor of love.

- [Joe] So we can't reverse all the damage of the past, but we can transform it into something better.

At the Berkeley Pit, scientists focus not on erasing scars, but on asking what the damage can become.

- Butte has always been home and hopefully always will be.

My great-grandfather started here as an underground miner.

All my family worked underground all the way up until my grandfather, and to be able to work in the environment that he did is just the family legacy to me.

It, yeah, puts a smile on my face.

They call it the richest hill on earth, but I think it's my favorite place on earth.

(bright music) - For a century, we treated this place as evidence of what we destroyed, but chemistry kept working.

The same reactions that made this water toxic are now concentrating elements that the modern world will depend on.

Rare earths that help spin wind turbines and power electric vehicles.

Right now, extracting those rare earths from mining waste cannot meet global demand.

This will not replace mining tomorrow.

But it's an opportunity to look at our relationship with earth's resources in a new way.

The Berkeley Pit will never be restored to exactly what it was before mining.

The Clark Fork will always bear the marks of what happened there.

But maybe the point isn't to erase those scars or ignore them, pretend they don't exist.

It's to take an honest look at them and ask, what could they become next?

- We're dreaming for a better Butte.

One day the pit may be clean enough that we don't have to chase the birds off of it.

It might be my grandkids that see it happen, but to know that my name was a part of it and, yeah, I'm here to help.