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The Berkeley Pit

In the hills surrounding Butte, Montana there is a colorful testament to the effects that humans can have on their environment. The Berkeley Pit is a decommissioned copper mine that looks spectacular but hides a lethal secret.


The mine was originally opened in 1955. By the early 1980’s the copper seam had been nearly depleted and the mine was closed. At the time the mine was shuttered the pit was a mile long by a half-mile wide, and over 1,700 feet deep. The massive depth of the pit was well below the groundwater level in the area, so when the pumps in the mine were turned off for the last time the pit began to fill with water.


Although most of the copper had been removed many minerals were still present in the rock cliffs around the pit. Dissolved oxygen in the groundwater leached into the rocks releasing copper, arsenic, cadmium, zinc, and sulfuric acid. This toxic stew turned the water filling the pit several brilliant shades of reds and oranges.


The water in the pit looks colorful but is a ecological disaster waiting to happen. Testing has shown that the pit is currently as acidic as lemon juice. When the pit reaches the level of the natural water table the toxic materials will begin to seep into the groundwater. The pit is so toxic that in a famous incident last year close to a 1,000 Canadian Geese were killed when they landed in the pit seeking shelter from a blizzard.

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