Berkeley Pit

 copper mine, open-pit mine, EPA superfund, environmental protection agency, abandoned mine/quarry

The Berkeley Pit is a former open pit copper mine one mile long, by half a mile wide with an approximate depth of 1,780 feet (540 m). It is filled to about a 900 feet (270 m) depth of water that is heavily acidic (2.5 pH level). The "Pit" is laden with heavy metals and dangerous chemicals, 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 (ARCO), until its closure in 1982. When the pit was closed, the water pumps at the bottom were removed, and groundwater sourced from the surrounding aquifers soon filled the pit to the natural groundwater level.

The "Pit" presents 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. If left to natural processes, the "Pit" water has the potential to seep into surrounding groundwater. The acidic water in the pit can carry a heavy load of dissolved heavy metals. In fact, the water contains so much dissolved metal (up to 187 ppm Cu) that the material is mined directly from the water.

In the 1990s plans were devised for solving the groundwater problem. 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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