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Berkeley Pit, Butte

3.8
#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.

A visit to Berkeley Pit represents just the start of the adventure when you use our Butte road trip planning app to plot your vacation.
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Berkeley Pit reviews

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TripAdvisor traveler rating 4.0
339 reviews
Google
4.2
TripAdvisor
  • Interesting part of Butte, Anaconda mining history. Berkeley pit shows the amount of work and effort it is taking to clean up the toxic waste of the mining of years ago. Interesting how they have...  more »
  • Well worth a visit to see the environmental devastation caused by short-sighted decisions of the past. A cautionary example of what can happen when there are no environmental protections.  more »
Google
  • 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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