DescriptionIn July 1955, the Anaconda Company began operations at the Berkeley Pit, named for an underground copper mine on the Butte Hill. By the 1970s, the pit had become the largest truck-operated open-pit copper mine in the United States. In the early 1980s, a fleet of 200-ton trucks carried as much as 50,000 tons of low-grade copper ore to the concentrator each day. In 1982, however, the Atlantic Richfield Company (ARCO), Anaconda’s successor, shut down the extensive network of underground pumps, flooding abandoned underground mines and eventually filling the Berkeley Pit with acidic water. In search of an answer to the intractable problem of what to do about the ever-rising water (in 2007 it was 800 feet deep), ARCO constructed a large lime precipitation plant to deacidify the mine drainage water, which enters the pit at a rate of 8 million gallons a day. Contributing InstitutionMontana Historical Society Library and ArchivesGeolocation[1] Elevation5240 ft. CountySilver Bow County
