In big sky country, a decades-long environmental cleanup is nearly complete. Anaconda, Montana, used to be one of the most polluted places in America. Today, this community, which once helped fuel the industrial revolution, is making big strides to restore its beauty. But a neighboring town is frustrated by the pace of their cleanup, and residents say the government is leaving them behind. Abc News Live anchor, Kaina Whitworth, first traveled to the region last fall and has this in-depth report in tonight's Prime Focus.

In big sky country, there are big changes happening. These lush green hills, now full of plants and wildlife, were once the epicenter of the world's copper supply and all the pollution that came with it.

If you would have seen it almost 40 years ago, it was like a moonscape up here.

The industry dried up in the 1980s and left behind a toxic mess spanning hundreds of miles.

The community had to scramble, find employment elsewhere, move other directions.

It's taken decades, huge investment, and a massive cleanup that is now finally paying off. Do you consider that the biggest success story so far? I think it has to be one of the biggest. Bringing some towns back from the brink.

There's a lot of hammers and cranes and construction. We haven't seen this in 50 years.

And others feeling left in the dust.

If lead is going to kill you in Anaconda, it's going to kill you in Butte.

It towers over this community and the region. And for decades, this smokestack has been a symbol of prosperity and peril in Anaconda. If you ask people here, they'll tell you it built this community.

You know, there's a real sense of pride.

It fed and kept our family warm for many years.

At 585 feet, this is the tallest freestanding masonry structure in the world. In fact, it's so big, you can actually fit the Washington Monument inside. It's a legacy to the industrial revolution. But because of its height, smouts or emissions, like heavy metals and arsenic, impacted 300 square miles. Copper Our ore, processed here, helped electrify the nation and was used to make coins, car radiators, air conditioning systems, and so much more. By 1981, the mine closed, and the area turned into a polluted mess designated a Superfund site by the government. But the smokestack remained, and those heavy metals and arsenic took their toll on the surrounding ecosystem, destroying vegetation, killing animals, and driving away concerned citizens who once called this place home.

There was no vegetation, and so to have a lot of this vegetation coming back, it's really something neat.

You could say Charlie Coleman's life work is trying to get this place cleaned up. The former EPA project manager spearheaded this Superfund cleanup effort for nearly 40 years.

There's a real sense of pride. The amount of work that we've been able to do, Working with the community along the way, helping them to get some of the things they wanted, restoring the environment in the area.

Coleman worked in tandem with various government agencies, city officials, and the mine's owner, the Atlantic Richfield Company, now a subsidiary by BP to remove contaminants from the soil and waterways to what the government deemed acceptable levels. And the work continues.

The company has done a really good job working with folks. We've cleaned up nearly three quarters of the community. The water comes from a very clean source.

So there's still, despite the progress that we can see, when we look down at the homes and businesses, there's still work to be done.

Yeah, there's still yards that need to be cleaned up. That'll still go on until the 2025 time frame. As the area is redeveloped, soils will be tested.

That yard work includes soil revitalization and attic cleaning to remove traces of toxic dust for all homes in the community.

We've been sampling and remediating yards pretty heavy since about 2015. There's roughly 3,300 residential properties within the site, and we've sampled two-thirds of that right now and remediating created about a little over half. We're doing between 100 and 200 yards per year.

Some homeowners watching the cleanup in action feel good about the future of Anaconda.

When you see addicts getting cleaned out, it makes me happy. Watching this town grow And there's something to me I'm really excited about.

And as the cleanup efforts breathe new life into the community, so do small business opportunities, something the city's chief executive officer has been working on tirelessly.

The fallout of the community with the loss, the smelting The answer was huge. The community had to scramble, find employment elsewhere, move other directions, and try to somehow make this an economic stable community. Unfortunately, it wasn't for 40 years. And we're just now finally starting to recover from that.

Families are now relocating back to Anaconda. Developers are moving in, and a Jack Nicklaus golf course, complete with mining remnants and black sand pits from the smelter slag. The 18 holes are built right over toxic waste, covered by 18 inches of dirt.

We are a super fun site where the component is waste in place. It needs to be safe, but you can't, obviously, this slag pile, as you were able to see earlier, that wasn't able to be to move somewhere. So what we've done is cover it and make it safe and re-vegetate it.

The EPA says the clean dirt on top dilutes any lingering contaminants to acceptable levels under 400 parts per million. But just a few miles down the highway, a similar town with a very different story. In its heyday, Butte, Montana was the biggest city between Chicago and San Francisco. For decades, the enormous copper deposits beneath these hills were sent off to Anaconda, and in the process, left mine waste like lead and arsenic all over the community.

I grew up across the street from a mine dump that was called the Yellow Hill. We played on it, turned yellow when it rained, and we'd go play on it or ruin our shoes. But now you think about it, it's crazy that we live like that. That was just normal for us.

The Berkeley Pit, also normal for locals here. Complete with noisy sirens to keep birds away, this colossal hole in the ground is flooded with one of the largest bodies of contaminated water in the United States, and sits right on the edge of town. The cleanup has been dragging on since the '80s. And while there have been remediation efforts, Butte's cleanup still has a long way to go. The hillsides have many dead zones, and there's toxic wastewater in the creek that runs right through the middle of town.

We are at the continental divide here. This is the headwaters of the Columbia River right here. And amazingly, they waited for the cleanup of the first mile to be the last cleanup. We never could figure that out. It made no sense.

The cleanup effort here is also operating under different standards than an anaconda.

We are to accept 1,200 parts per million. Anaconda is at 400 parts per million. We have three times as much lead in the soil than they do over an anaconda. It makes no sense whatsoever since the tolerance for lead for children is zero.

Do you feel like the government is leaving you behind?

Yes, I do, because I'm a Butte native.

I've lived here almost 60 years. We're a small fish in a big pond, and we're not getting what we deserve, and Butte deserves better.

As a parent, it's terrifying that we have this going on. They'll promise they'll be on top of it forever. Something breaks down, they'll fix it. How many people are going to get sick before they realize that needs to be cleaned up.

Since our trip to view, the EPA has released new national guidance on lead contamination that might lead to a reduction in that 1,200 parts per million standard that frustrated residents. Do you see how it would be hard for people in view to say, why do we have to accept a higher level of contaminants than our neighbors down the road?

Yeah, we definitely do understand the concerns I've raised. We've upped our public engagement. We're pushing more for transparency within the data, but we do understand the concerns. But I do want to point out, though, the data does show that there's been a significant decline above levels within view even with the current cleanup level.

Back in Anaconda, the cleanup effort has been so successful that the EPA recently removed it from the state's roster of Superfund sites.

This is the American way. Where we're located is absolutely an amazing place for recreation. We got a beautiful ski hill. We got the Pintler Wilderness. We got the big hole valley. We got all those things. We have a beautiful Jack Nicklaus golf course, and we want to share it with others.

Yeah, baby. The region looking to turn a corner while staying true to their roots. They've been a little bit left behind. But we ripped off our mountaintops to electrify this country. We helped the country. We helped the government. Now we need help, and we're being overlooked.

Well, we certainly understand the concerns and the love for the community. As I said before, Butte is a top priority for us. You could see it in the amount of resources that we put in, the time we spend there, the focus we have on community engagement. We want to be able to do the best we can for those people.

Our thanks to Kaina for that.

Hi, everyone. George Stefanopoulos here. Thanks for checking out the ABC News YouTube channel. If you'd like to get more videos, show highlights, and watch live event coverage, click on the right over here to subscribe to our channel. Don't forget to download the ABC News app for breaking news alerts. Thanks for watching.