The Berkeley Pit is a former open pit copper mine located in Butte, Montana, USA. It is one mile long by half a mile 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). As a result, the pit is laden with heavy metals and dangerous chemicals that leach from the rock, including arsenic, cadmium, zinc, and sulfuric acid.
The mine was opened in 1955 and operated by Anaconda Copper and later by the Atlantic Richfield Company, until its closure in 1982. When the pit was closed the water pumps in the nearby Kelly shaft were turned off and groundwater from the surrounding aquifers began to slowly fill the pit, rising at about the rate of one foot a month. Since the Berkeley Pit closure in 1982, the level has risen to within 150 feet of the natural groundwater level.
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