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Berkeley Pit, Butte

3.4
#1 of 6 in Sightseeing in Butte
Water Body Mine
The Berkeley Pit is a former open pit copper mine located in Butte, Montana, United States. It is one mile long by half a mile wide with an approximate depth of 1780ft. It is filled to a depth of about 900ft with water that is heavily acidic (2.5 pH level), about the acidity of cola or lemon juice. 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 Anaconda Copper and later by the Atlantic Richfield Company (ARCO), until its closure on Earth Day 1982. When the pit was closed, the water pumps in the nearby Kelley Mine, 3,800 feet below the surface, 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 pit closure in 1982, the level has risen to within 150 feet of the natural groundwater level.The pit and its water present a serious environmental problem because the water, with dissolved oxygen, allows pyrite and sulfide minerals in the ore and wall rocks to decay, releasing acid. When the pit water level eventually reaches the natural water table, estimated to occur by around 2020, the pit water will reverse flow back into surrounding groundwater, polluting into Silver Bow Creek which is the headwaters of Clark Fork River. The acidic water in the pit carries a heavy load of dissolved heavy metals. In fact, the water contains so much dissolved metal (up to 187 ppm Cu) that some material is mined directly from the water.
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202 reviews
  • Hey they have a very cute gift shop with a variety of lovely items. The pit entrance is stoutly built. You then walk through a well illuminated tunnel a short distance to the viewing platform. There a...  more »
  • Old copper mine gone bad, seems they turned off the water pumps to keep the water out of the mine and it filled over the level of the pumps. Zoom in years later and got a large hole full of toxic wate...  more »
  • This amazing body of highly toxic water was beautiful & frightening all at the same time. Every so often a shotgun is fired to scare away Canadian geese wanting to land in this alluring body of water....  more »

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