The Mine Waste Technology Program at Montana Tech understandably enough focuses on the Berkeley Pit. Here are the reports they have produced on the pit:

I think the pit is one of the seven wonders of the West. Many would disagree with me. If you are not familiar with the pit, here is a summary - better still take a trip to Butte, Montana and see it - much more impressive than Ayers Rock, and a lot easier to get to.

The Berkeley Pit, an open-pit copper mine, was dewatered through the underground mine dewatering system. The Atlantic Richfield Company (ARCO) bought the Anaconda Company in 1977 and continued to operate the underground pumping system until April 1982, when the decision was made to suspend mining in the Berkeley Pit. The pump station, located on the 3,900 level (3,600 feet below ground surface) of the Kelley Mine, was shut down, and ground-water levels began to rise immediately. Levels had risen more than 1,300 feet by the end of 1982 and 3,100 feet by the end of 2006. The maximum elevation that water levels will be allowed to reach in the underground workings and Berkeley Pit has been established by U.S. Environmental Protection Agency (EPA) and the Montana Department of Environmental Quality (DEQ) in order to maintain the Berkeley Pit as a "Terminal Pit." The Butte underground mines and the Berkeley Pit are part of a Federal Superfund Site. A long-term monitoring program was established to ensure that the Berkeley Pit remains the sink, or terminal pit, for bedrock ground water entering and filling the historic mine workings. This closed system would preclude mine-water discharge to nearby aquifers and surface waters.