page_title: Berkeley Pit
section_title: Pollution, toxicity, and cleanup
hierarchical_section_title: Berkeley Pit / Pollution, toxicity, and cleanup
caption_attribution_description: English: Composite fish eye view of the Berkeley Pit in Butte, Montana. Composite was created using the open source 'Hugin' application in July, 2008, combining 7 images of the Berkeley Pit taken in April of 2005.
context_page_description: The Berkeley Pit is a former open pit copper mine located in Butte, Montana, United States. It is 1 mi long by ¹⁄₂ mi wide with an approximate depth of 1,780 feet. It is filled to a depth of about 900 feet with water that is heavily acidic, about the acidity of Coca-Cola, lemon juice, 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.
  The mine was opened in 1955 and operated by the Anaconda Copper Mining Company, and later by the Atlantic Richfield Company, until its closure on Earth Day in 1982. When the pit was closed, the water pumps in the nearby Kelley Mine, 3,800 ft 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 1 ft a month. Since its closure, the water level in the pit has risen to within 150 ft 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.
context_section_description: The Berkeley Pit is a part of the Silver Bow Creek/Butte Area Environmental Protection Agency Superfund site, considered one of the largest in America, 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 Berkeley Pit is the final unrestored section of the Silver Bow Creek/Butte Area site.
  In 1995, a flock of migrating geese landed in the Berkeley Pit and died. A total of 342 carcasses were recovered. 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. These findings were disputed by the State of Montana on the basis of its own lab tests. Necropsies showed their insides were lined with burns and festering sores from exposure to high concentrations of copper, cadmium, and arsenic. (Levels of copper are high enough that Montana Resources has mined copper directly from the water.)
  On November 28, 2016, several thousand snow geese died after a large flock landed in the pit's water to avoid a snow storm. 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 Berkeley Pit were killed by exposure to sulfuric acid and heavy metals.
  The Berkeley Pit started utilizing Phoenix Wailers, which have been effective in deterring birds from landing at or staying in Berkeley Pit for an extended period of time. Studies have shown that the Wailers have been effective in limiting bird deaths in most cases, 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.
  Construction began on a treatment plant at the Berkeley Pit in 2018, to treat water in the Pit before the water level before it contaminates local groundwater. The treatment facility will be able to treat ten million gallons of water per day. Construction of the $19 million facility was completed in August 2019 and the first discharge of treated water into a local creek happened in October of 2019.
caption: Composite Fisheye View of the Berkeley Pit, April 2005
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