The Berkeley Pit is a former open pit copper mine in the western United States, located in Butte, Montana. It is one mile (1.6 km) long by one-half mile (800 m) wide, with an approximate depth of 1,780 feet (540 m). It is filled to a depth of about 900 feet (270 m) with water that is heavily acidic (2.5 pH level), about the acidity of Coca-Cola, lemon juice,^[1] or gastric acid. As a result, the pit is laden with heavy metals and dangerous chemicals that leach from the rock, including copper, arsenic, cadmium, zinc, and sulfuric acid.^[1]

Quick Facts Silver Bow Creek/Butte Area, Geography ...

Silver Bow Creek/Butte Area
Superfund site
Berkeley Pit (center) and Yankee Doodle Tailings Pond (upper left) with terraced levels/access roadways. The city of Butte is at lower right.
Geography
City	Butte
County	Silver Bow
State	Montana
Coordinates	46.02°N 112.51°W / 46.02; -112.51
Butte Location in the United States Show map of the United States Butte Location in Montana Show map of Montana
Information
CERCLIS ID	MTD980502777
Contaminants	Arsenic, cadmium, copper, zinc, lead
Progress
Proposed	30 December 1982
Listed	8 September 1983
List of Superfund sites

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The mine was opened in 1955 and operated by the Anaconda Copper Mining Company, and later by the Atlantic Richfield Company (ARCO), until its closure on Earth Day in 1982.^[2] When the pit was closed, the water pumps in the nearby Kelley Mine, 3,800 ft (1,200 m) below the surface, were turned off, and groundwater from the surrounding aquifers began to slowly fill the Berkeley Pit, rising at about the rate of one foot (30 cm) per month.^[1] Since its closure, the water level in the pit has risen to within 150 feet (46 m) of the natural water table.

The Berkeley Pit is currently one of the largest Superfund sites. The water, with dissolved oxygen, allows pyrite and sulfide minerals in the ore and wall rocks to decay, releasing acid. The acidic water in the pit carries a heavy load of dissolved heavy metals. A water treatment plant has been operating since October 2019.^{[citation needed]}

The Berkeley Pit is a tourist attraction.^{[citation needed]}

The underground Berkeley Mine was located on a prominent vein extending to the southeast from the main Anaconda vein system. When open pit mining operations began in July 1955, near the Berkeley Mine shaft, the older mine gave its name to the pit. The open-pit style of mining superseded underground operations because it was far more economical and much less dangerous than underground mining.

Within the first year of operation, the pit extracted 17,000 tons of ore per day at a grade of 0.75% copper. Ultimately, about 1,000,000,000 tons of material were mined from the Berkeley Pit. Copper was the principal metal produced, although other metals were also extracted, including silver and gold.^[3]

Two communities and much of Butte's previously crowded east side were consumed by land purchases to expand the pit during the 1970s.^[4] The Anaconda Company bought the homes, businesses and schools of the working-class communities of Meaderville, East Butte, and McQueen, east of the pit site. Many of these homes were either destroyed, buried, or moved to the southern end of Butte. Residents were compensated at market value for their acquired property.^{[citation needed]}

The Berkeley Pit is a part of the Silver Bow Creek/Butte Area Environmental Protection Agency Superfund site,^[5] considered one of the largest in America,^[6] and the pit itself was added to the federal Superfund site list in 1987. It is one of sixteen Superfund sites in Montana, and the final unrestored section of the Silver Bow Creek/Butte Area site.

In 1995, a flock of migrating geese landed in the pit and died. A total of 342 carcasses were recovered.^[7] ARCO, the custodian of the pit, denied that the toxic water caused the death of the geese, attributing the deaths to an acute aspergillosis infection that may have been caused by a grain fungus, as substantiated by Colorado State University necropsy findings.^[7] These findings were disputed by the State of Montana on the basis of its own lab tests.^[7] Necropsies showed their insides were lined with burns and festering sores from exposure to high concentrations of copper, cadmium, and arsenic.^[1] Levels of copper are high enough that Montana Resources has mined copper directly from the water.^[8]

On November 28, 2016, several thousand snow geese died after a large flock landed in the pit's water to avoid a snowstorm.^[9] Immediately after the event, officials made efforts to scare birds away and prevent more from landing in the area. An official report issued in 2017 by the U.S. Fish and Wildlife Service found that the 3,000 to 4,000 snow geese that died at the pit were killed by exposure to sulfuric acid and heavy metals.^[10]

Atlantic Richfield and Montana Resources have installed Phoenix Wailers, a type of sonic bird scarer, to keep birds from loitering in the pit.^[11][12] Studies have shown that the Wailers have been effective in limiting bird deaths in most cases,^[13] but they have not worked as well when faced with a large number of birds. Staff also use firearms to scare away birds during spring migration seasons.^[14]

A treatment plant was completed in 2019 and began treating the water in the pit before it would contaminate local groundwater.^[15] The plant cost $19 million and was designed to treat ten million gallons of water per day.^[16]

The mine is at 46°00′56″N 112°30′37″W, at an altitude of 4,698 feet (1432 m) above mean sea level.

• The Berkeley Pit mine in Butte Montana.
• The Berkeley Pit mine in Butte Montana.
• The Berkeley Pit mine in Butte Montana.

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• Chemocline
• Dark Money
• List of Superfund sites in Montana
• Water pollution in the United States
• Bingham Canyon Mine (in Utah)