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Latest: Berkeley Pit cleanup ahead of schedule

The EPA will begin treating the pit’s toxic water five years earlier than planned.


Butte, Montana, is home to the infamous Berkeley Pit, a former open-pit copper mine. After operations ended in 1982, it began filling with acidic, metal-laden groundwater. At 950 feet deep, it’s the nation’s largest body of toxic water, and the area was designated a Superfund site in 1983 (“Mining the Past,” HCN, 06/07/99). Federal cleanup plans called for treatment to begin by 2023.


The Environmental Protection Agency put Butte on a Superfund “emphasis list” to speed up remediation, and in February, the mining companies responsible, Montana Resources and Atlantic Richfield, said they’d start pumping and treating the water ahead of schedule, perhaps as soon as this year. The company will pump 3 million gallons per day, treat the water and then discharge it into a creek. “For 30 years, we’ve watched the pit control the groundwater,” Mark Thompson, Montana Resources’ vice president for environmental affairs, told The Montana Standard. “It’s time we show we can control the pit.”