27 votes

Berkeley Acid Pit

Butte, Montana 59701 USA

Closed Now
Opens Sun 9a
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“acid pit of doom!”

A former open pit copper mine located in Butte, Montana. The pit is one mile long by half a mile wide with a rough depth of 1,800 ft. The water is heavily acidic (2.5 pH level) - about the acidity of coke or lemon juice. 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, at a depth of 3,800 feet, 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. That will suck. When close to 400 geese died horribly after making the unfortunate choice of resting on the lake during a migration, it was discovered that the acidic water would quite literally eat away the intestines of anything that drank enough of it. 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. In the 1990s plans were devised for solving the groundwater problem. Water flowing into the pit has been diverted to slow the rise of the water level. Plans have been made for more extensive treatment in the future. The Berkeley Pit has since become one of the largest Superfund sites. The pit is currently a tourist attraction, with an adjacent gift shop. A $2 admission fee is charged to go out on the viewing platform.

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Reviewed by
Greg Newkirk

  • Expert
  • 314 Reviews
  • 364 Helpful
September 13, 2013

After 352 geese decided to take a migration break in this pit, they all died. The mining company tried to tell everyone it wasn't their fault, but then they discovered that if anyone actually drank from this water their digestive systems would corrode right out...

9 people found this review helpful

Reviewed by

  • 7 Reviews
  • 6 Helpful
October 04, 2016
Rated 3.0

The Pit is on the site of amold amusement park. There is a lot of history here and in the town of Butte. The Pit did many things for this area, including some that were damaging. The Pit brought wealth to many and science grew from the experiences that were created to protect humanity. After you see the Pit, take a drive through the historic town that was used as a model for San Francisco. The homes and hotels and layout are why the city by the bay looks the way it does. Also, the mining pits are a great attraction too.

3 people found this review helpful

Reviewed by

  • 6 Reviews
  • 2 Helpful
August 06, 2018
Rated 5.0

Awesome. Science. Engineering. Shopping. Bathrooms! Open till 8p when we stopped. In Aug.

2 people found this review helpful

Reviewed by

  • 3 Reviews
  • 3 Helpful
June 06, 2015
Rated 4.0

We stayed in Butte on the way to CDA. The Pit was really cool and educational. It's not something you see every day. Butte is a fascinating town.

2 people found this review helpful

Reviewed by

  • 1 Review
  • 2 Helpful
August 12, 2014

Eh. If it is on the way to wherever else you're going, maybe stop and take a look because it is a bit intense to think about, that much toxicity in one place. But don't go out of your way for it. It looks like a big lake with nothing growing around it. Butte is full of much more interesting things to see.

2 people found this review helpful

Reviewed by

  • 4 Reviews
  • 10 Helpful
July 04, 2014
Rated 5.0

This place is scaryweirdcool. Just stand at the edge and think about it.

2 people found this review helpful

Reviewed by
Chris Spinney Long

  • Tour Guide
  • 172 Reviews
  • 209 Helpful
September 16, 2013

Ok so it's as acidic as coke but does that mean coke is corroding our insides? I'm fearing for my health now.

2 people found this review helpful

Reviewed by

  • 1 Review
  • 2 Helpful
September 14, 2013

Well... I sincerely hope they fix that, and soon.

2 people found this review helpful

Reviewed by

  • 3 Reviews
  • 1 Helpful
April 01, 2021

Closed when we tried to visit 03/31/2021. So sad I wasn’t able to see the place.

1 person found this review helpful

Reviewed by

  • 3 Reviews
  • 0 Helpful
June 26, 2014

An interesting bit of history, but spend your time looking at more interesting things, in my humble opinion.

1 person found this review helpful

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Berkeley Acid Pit

Butte, Montana
59701 USA


Closed Now
  • Sun - Sat: 9:00 am - 5:00 pm

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  • Parking
  • Pets Allowed
  • Restrooms
  • Wifi
  • Wheelchair Accessible
  • Credit Cards Accepted
  • Outdoor Seating
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