• In the 1870s the invention of electricity, followed by the popularity of indoor plumbing, spurred the need for copper to carry electrical current and water. A particular mountain in Butte, Montana, had a lot of copper. About 30% of the nation’s copper, and 15% of the world’s copper, was supplied by Butte in the 1880s. During World War I and World War II, demand for copper skyrocketed. Throughout decades of copper mining, what was once called “the richest hill on Earth” was transformed into the deepest lake in Montana, called the Berkeley Pit.
• For decades, the mining was performed by digging tunnels. At its peak, over 10,000 men worked the mines. There are around 250 miles (402 km) of streets in Butte and over 2,500 miles (4,023 km) of underground mining tunnels beneath the streets. It’s estimated that there are at least 10,000 miles (16,093 km) of mining tunnels in the vicinity.
• When underground mining became problematic, operations shifted to truck mining in 1955, and the mine became the biggest open-pit copper mine in the U.S. Between 1955 and 1982, an average of 17,000 tons of ore came out of this mine every day.
• Over the course of its lifetime, the mine produced enough copper to pave a four-lane highway two inches thick from Chicago to New York City.
• By 1982, the invention of fiber optic cable for communication and PVC pipe for plumbing led to the collapse of the copper market. Mining operations in Butte shut down.
• Pumps in the tunnels were permanently shut down in 1982, allowing the pit to fill with groundwater, transforming it into a giant lake. The level of the water rose at the regular rate of one foot (30 cm) per month.
• The water absorbs toxins from the tunnels and the walls of the pit, becoming laden with copper, iron, arsenic, cadmium, zinc, and sulfuric acid. Residents feared that as the water level rose, it would contaminate the aquifer and spill over into Silver Bow Creek, polluting waterways all the way to the Pacific. In 1987, the Berkeley Pit became an EPA superfund site. In 2019, a water treatment plant was installed which cleans and discharges 7 million gallons of water daily, keeping the lake level stable.
• Over the course of a century, around 1.5 billion tons of copper, gold, and silver ore were taken out of this mine. Today, around $1 billion has been spent not only neutralizing the threat from contaminated water, but also stabilizing toxins from massive tailings piles. It is the most expensive site on the EPA’s national superfund list.
• Today, the water in the Berkeley Pit is about 900 feet (274 m) deep, sitting at the bottom of a chasm that is 1.3 miles (2.1 km) long, 1 mile wide (1.7 km) and 1,600 feet (488 m) deep. By comparison, the deepest natural lake in the state is Tally Lake near Whitefish, which is 500 feet (152 m) deep. The 500-acre lake contains an estimated 40 billion gallons of acidic water with a pH balance of 2.5, about the same as gastric acid, which is acidic enough to dissolve boat propellers.
• Because the water is lethal to birds, methods used to prevent birds from landing include automatic cannon fire, guards with guns, and supersonic tones broadcast through loudspeakers.
• In 2006 the city of Butte opened a viewing platform overlooking the toxic lake, including picnic tables, a snack bar, gift shop, and restrooms. It’s one of the few places in the world where tourists pay to see toxic waste.
