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.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.
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.
Berkeley Pit reviews
This place is an awesome and unique sight! Must see in Butte. The thing is massive. Worth the $3 fee. Check it out. Trust me. It’s worth it! Pair it with the Mining museum for a full understanding of.... more »
We traveled with a group of 18 people. We made a quick stop at the pit. Our group entered together and they did not allow other people in while we were there. There was a recording that we were... 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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