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Environmental Impacts of Mining

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The Berkeley Pit

The Berkeley Pit

Credit: NASA
Source: http://en.wikipedia.org/wiki/File:Berkeley_Pit_Butte,_Montana.jpg
License: CC BY-NC 3.0

The Berkeley Pit in Butte, Montana was mined between 1955 and 1982. Since then the pit has become a toxic lake. It is the largest Superfund site in the United States – and it’s a tourist attraction, too.

Why It Matters

  • The Berkeley Pit was the first open pit mine. It is one mile long, one-half mile wide and has a depth of 1,780 feet.
  • The water that fills the pit is from a groundwater aquifer that is currently above lake level.
  • During mining pumps kept the water out. The pumps were turned off when mining stopped.
  • Lake water is very acidic (pH 2.5) and high in oxygen. The acidic water leaches heavy metals from the rock creating a toxic soup.
  • Steps must be taken to ensure that the lake does not contaminate the aquifer when the lake level reaches that elevation.

Explore More

With the links below, learn more about the Berkeley Pit. Then answer the following questions.

  1. Why was the underground mine at Butte, Montana made into an open pit mine?
  2. What is in the lake water? What useful item was mined directly from the lake water?
  3. What is a slough? Why is an event like this common in open pit mines?
  4. When approval was given for the Berkeley Pit, what was not considered but should have been and why?
  5. What is the current water level in the pit? What is the critical level? How many more feet can lake level rise before it reaches the critical level? What is the estimated date that Critical Level will be reached?

Image Attributions

  1. [1]^ Credit: NASA; Source: http://en.wikipedia.org/wiki/File:Berkeley_Pit_Butte,_Montana.jpg; License: CC BY-NC 3.0

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