The Berkeley Pit is an abandoned open pit copper mine located in Butte, Montana, United States. It is over a mile long, half a mile wide, and over a third of a mile deep. During its heydays, Berkeley Pit supplied a sixth of the world's copper needs, and during the 27 years of operation approximately 320 million tons of the ore were extracted enough to “pave a four-lane highway four inches thick from Butte to Salt Lake City and 30 miles beyond,” according to Pitwatch.org. The once thriving copper mines of Butte earned the district the title of “the richest hill in the world.”
Today, the pit is filled with nearly 30 billion gallons of highly acidic water laced with toxic chemicals like arsenic, cadmium, zinc, and sulfuric acid that threaten the environment and the water supply of the nearby town of Butte.
Rich copper deposits were known at Butte since the early 1870’s, although development was delayed due to lack of adequate transportation required to bring the ore to smelters. Without the necessary rail lines and recovery facilities, Butte’s copper ore was sent to Swansea, Wales for processing. By the late 1880s, new railway lines were laid connecting Butte with the Union Pacific out of Ogden, Utah. By the time electricity was discovered, Butte had all the infrastructural components needed to meet the burgeoning demand for copper needed to electrify cities.
From 1892 until 1903, the Anaconda Mine was the largest copper-producing mine in the world accounting for 20% of all US copper production. For nearly 70 years, mining for copper was done by dropping shafts into the earth or boring tunnels through the hills. As price of copper soared, Butte needed more efficient mining techniques, and in 1955, the area introduced open-pit mining in the form of Berkeley Pit.
Within the first year of operation, the Berkeley Pit extracted 17,000 tons of ore per day at a grade of 0.75% copper. Ultimately, about 1 billion tons of material was mined from the Berkeley Pit, of which copper constituted nearly a third. Other metals including silver and gold were also extracted. But steep, continuous declines in copper prices after the Vietnam war led to the eventual shut down of Berkeley operations in 1982.
During mining in Butte, pumps were used to remove surface runoff and groundwater from the mines. When the mine and the pumps were shutdown, the Berkeley Pit began to fill with water rising at about the rate of one foot a month. Today the pit is filled to a depth of about 900 feet or 270 meters.
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. An example of a disaster to come happened in 1955 when a flock of migrating snow geese landed in the Berkeley Pit, killing at least 342 of them.
But in the same year the birds died, a chemist studying the water composition of the pit discovered a robust single-celled algae known as Euglena mutabilis thriving in the toxic waste of the Berkeley Pit. Over the next few years, over 40 different species of organisms were discovered in the pit. Intense competition for the limited resources caused these species to evolve the production of highly toxic compounds to improve survivability – some of the compounds isolated from these organisms have shown to fight against cancer cells.
Berkeley Pit is currently just another tourist attraction. There's a small museum, gift shop and a viewing platform located above the water.
