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Berkeley Pit, Butte

#3 of 20 in Things to do in Butte
Lookout · Mine
The Berkeley Pit is a former open pit copper mine located in Butte, Montana, United States. It is 1 mi (1,600 m) long by 1⁄2 mi (800 m) wide with an approximate depth of 1,780 feet (540 m). It is filled to a depth of about 900 feet (270 m) with water that is heavily acidic (2.5 pH level), about the acidity of Coca-Cola, lemon juice, or gastric acid. As a result, the pit is laden with heavy metals and dangerous chemicals that leach from the rock, including copper, arsenic, cadmium, zinc, and sulfuric acid.
The mine was opened in 1955 and operated by the Anaconda Copper Mining Company, and later by the Atlantic Richfield Company (ARCO), until its closure on Earth Day in 1982. When the pit was closed, the water pumps in the nearby Kelley Mine, 3,800 ft (1,200 m) below the surface, were turned off, and groundwater from the surrounding aquifers began to slowly fill the Berkeley Pit, rising at about the rate of 1 ft (300 mm) a month. Since its closure, the water level in the pit has risen to within 150 ft (46 m) of the natural water table.

The Berkeley Pit is currently one of the largest Superfund sites. The water, with dissolved oxygen, allows pyrite and sulfide minerals in the ore and wall rocks to decay, releasing acid. The acidic water in the pit carries a heavy load of dissolved heavy metals. A water treatment plant has been operating since October 2019

The Berkeley Pit is a tourist attraction, with an adjacent gift shop. An admission fee is charged to go out on the viewing platform.

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TripAdvisor traveler rating 4.0
334 reviews
  • The Berkeley Pit is awe-inspiring as an example of what humans can do when they want to extract important minerals from the ground. If you value mining, this is inspirational. If you no not, it is...  more »
  • Must see to realize how large this pit is. We saw two eagles flying near the edge of the pit and they looked so tiny against the vastness of the water.  more »
  • 5 out of 5. Great swim, water was nice and warm too!
  • World Class, what a great tribute to American pride !
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