Explore Vermont's abandoned copper mines

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The last of Vermont’s abandoned copper mines are finally slated for clean up. The stream runs clear on the side of Corinth's Pike Hill. But the air smells of sulfur. And the water is more acidic than lemon juice. Its pH is about 2, which means heavy metals like aluminum, manganese, iron and zinc are dissolved in the water.

“So you can get what looks like a nice, clean stream, but because of the pH, it can be absolutely loaded in metals,” Ed Hathaway explained.

He’s a project manager with the U.S. Environmental Protection Agency, and has been working to clean up old mining sites in New England like this one for more than 30 years.

Last month, the federal government announced new funding to help clean up Pike Hill, while money for the clean up of another nearby copper mine, the Ely Mine in Vershire, was set aside in 2021.

They’re both designated as Superfund sites for the toxic water that seeps out of them.

That water isn’t dangerous for people to be around, but it’s deadly for most bugs and fish for over a mile downstream.

“The pH of 2 is going to pretty much kill anything," Hathaway said. But if the acid somehow didn’t kill the stream critters, the metals would.

“High concentrations of copper and zinc, you’re gonna see 100% mortality,” he said.

The Pike Hill copper mines are the reason the stream is so acidic and full of heavy metals. The mines first opened in the 1800s, and for decades, workers here removed millions of pounds of copper from beneath the earth.

The mines wrap around the top of a small mountain. In some places, miners dug pits straight into the ground. In others, they blasted horizontal tunnels and hauled the copper-rich rock out with iron carts and horses.

“So they take the rock, they crush it,” Hathaway said. “Here they used both magnetic separation and froth flotation, meaning they would just put it in a bath and they would use, like, a pine oil or something, and the divalent metals — copper’s a divalent metal — would stick to that froth. They’d skim it off, concentrate it and ship it.”

That process left huge piles of dirt and rocks behind, which are still there, even though the mine shut down in the early 1900s.

When rain or groundwater hits those piles, it reacts with the sulfide inside the dirt and rocks and forms sulfuric acid.

That acid runoff, and the heavy metals it picks up along the way, are what make the stream so toxic.