Scientists are extracting clean energy materials from a century of mining waste from America’s most toxic lake

PBS Terra host Joe Hanson opens his short documentary with a striking contradiction. At first glance, the Berkeley Pit in Butte, Montana, looks like it could be one of the prettiest lakes in the state.

But Hanson quickly makes clear that this is no ordinary lake. It is, in his words, one of the most toxic lakes in America, so dangerous that workers use propane cannons to scare birds away from landing on it. The water is so acidic and so loaded with dissolved metals that a landing here can be fatal.

That alone would make the Berkeley Pit a grim symbol of industrial damage. But Hanson’s report takes the story in a different direction. Scientists are now studying whether this poisonous lake, created by more than a century of mining, could also become a source of critical materials needed for clean energy technology.

That is what makes the Berkeley Pit story so compelling. It is not just about pollution. It is about whether one of the country’s ugliest environmental messes could also hold part of the answer to a modern resource problem.

How A Mining Giant Became A Toxic Chemical Reactor

Hanson explains that Butte was transformed by mining long before the pit ever filled with water. What started as a mining camp in the 1860s became one of the busiest industrial mining regions on earth by the early 1900s.

At its peak, he says, 25% of the world’s copper came from this region. That copper helped electrify America through telegraphs, telephones, and power grids. In other words, Butte was once central to an earlier technological revolution.

Then came the shift that created the Berkeley Pit itself.

Hanson reports that in 1955, the Anaconda Mining Company stopped focusing only on underground tunnels and began removing the mountain from the top down. Over time, the Berkeley mine stretched roughly a mile long and more than 1,700 feet deep. When mining stopped in 1982, the pumps that had been keeping groundwater out were shut off.

Nature did the rest.

Today, the pit holds nearly 50 billion gallons of toxic, highly acidic water. Hanson describes it as a giant chemical reactor. Hydrogeologist Jackson Quarles, one of the scientists featured in the documentary, explains why. The surrounding rock contains sulfide minerals, and when those minerals are exposed to air and water, they form sulfuric acid. That acid then dissolves metals trapped in the rock, creating what is known as acid mine drainage.

That process turned a mine into a huge basin of contaminated water. Hanson notes that some metal concentrations in the pit are more than 5,000% above drinking water standards.

It is a staggering environmental scar. Yet the same chemistry that made it dangerous may also have concentrated valuable elements in a way that scientists now want to understand.

Why Scientists Are Looking For Rare Earths In A Toxic Pit

The heart of Hanson’s documentary is the work being done by Quarles and other researchers who are trying to find rare earth elements and other critical minerals in the Berkeley Pit.

Quarles, who has personal ties to Butte and says the city has always been special to him, is searching the pit for materials that are increasingly important to clean energy systems. Hanson explains that these rare earth elements include metals like neodymium and praseodymium, which are used in the powerful magnets inside wind turbines and electric vehicle motors. Others, like dysprosium, help those magnets keep working under extreme heat.

That matters because global demand for these elements is expected to keep rising as the world builds more renewable energy infrastructure and produces more electric vehicles.

Normally, getting those materials means opening new mines, which comes with its own environmental cost. Hanson puts the question simply: what if some of these materials could be recovered from places we have already torn apart?

That is where the Berkeley Pit becomes more than a toxic legacy site.

Quarles tells Hanson that what his team has found in the pit is unusual. According to him, many sites in the United States are rich in only one specific rare earth or perhaps only the lighter rare earths. But the Berkeley Pit appears to hold a full distribution of them, something he says the team has not really seen elsewhere.

Hanson also makes an important point that helps explain why scientists are interested now. Rare earths are not truly rare in the earth’s crust. The challenge is finding them in concentrations high enough to be worth recovering. In the Berkeley Pit, the acidic water may have already done part of the hard work by leaching those metals out of the surrounding rock.

That means the elements could be sitting in the water or sediment in a form that is easier to process than fresh ore pulled from the ground.

From “Forbidden Gravy” To A Possible Cleanup Strategy

The documentary follows Hanson and Quarles as they use a small submersible to explore the pit and collect samples from the bottom.

Quarles shows Hanson the underwater vehicle, equipped with lights, a 4K camera, and a sediment sampler. Hanson jokes that exploring the pit feels a bit like going to Mars, and that description fits. It is a place almost no one has ever seen up close since the mine shut down and the water rose.

When the team brings up sludge from the bottom, Hanson famously calls it “forbidden gravy,” which is funny, but the science behind the mud is serious. Researchers are trying to determine whether the valuable elements are mostly in the water, in the sediment itself, or in the material that makes up that sediment.

That distinction matters because it affects how extraction might work.

Hanson explains that the scientists are testing chemical techniques that could bind specifically to rare earth elements, making them easier to separate from the pit’s filthy mix of metals and acidic water. Quarles says the current goal is to throw “darts all over the board” by sampling many different areas, then go back to the warm spots where the most promising results show up.

It is still early. Hanson is careful not to oversell the project. He says plainly that this idea is still in its infancy and that it is too soon to know whether it will prove commercially viable.

That caution is important. This is not a miracle solution, and Hanson never treats it like one.

Still, the promise here is obvious. If scientists can find an economic way to extract rare earths and other critical minerals from waste that already exists, they could reduce the need to dig new holes. Quarles says that is part of the environmental benefit. Instead of disturbing fresh land, researchers could be cleaning up a mess that is already sitting there.

In that sense, the Berkeley Pit may represent a very modern kind of environmental thinking: not erasing the damage, because that may be impossible, but finding a way to turn at least part of it into something useful.

A Damaged Landscape, And A Different Way Forward

Hanson strengthens that point by taking viewers downstream to Milltown State Park, another Montana site once burdened by mining waste.

There, park manager Michael Kustudia explains how the old Milltown Dam trapped huge amounts of contaminated sediment that had washed down from upstream mines. After years of work involving multiple agencies and tribal partners, the dam was removed, millions of tons of contaminated sediment were taken away, the river channel was rebuilt, and thousands of trees were planted.

Kustudia tells Hanson that the project took a long time and did not happen quickly. But now, visitors can fish, boat, hike, and watch wildlife in a place that once held piles of toxic waste.

That part of the documentary matters because it gives the Berkeley Pit story a little perspective. Environmental recovery is possible, but it is slow, technical, expensive, and rarely perfect.

Hanson does not promise that the Berkeley Pit will one day look untouched or pristine. In fact, he says clearly that it will never return exactly to what it was before mining. The Clark Fork watershed will always bear those marks.

But he also argues that the question should not be whether those scars can be erased. The more honest question is what those scars might become next.

That is probably the strongest idea in the whole film.

For more than a century, the Berkeley Pit was treated as a place to take from. Then it became a warning about what industry can leave behind. Now, scientists like Jackson Quarles are asking whether it can become something else again: a cleanup site, a research lab, and maybe even a source of materials needed for the next era of energy.

That does not make the damage noble. It does not make the past disappear. But it does suggest that even the worst industrial leftovers do not have to remain frozen in one role forever.

And that may be the most hopeful part of Joe Hanson’s report. America’s most toxic lake is still toxic. It is still dangerous. But buried in that ugly truth may be a second one: sometimes the future starts in the mess we already made.