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The Berkeley Pit is a former open pit copper mine located in Butte, Montana, United States. It is one mile long by half a mile wide with an approximate depth of . It is filled to a depth of about with water that is heavily acidic (2.5 pH level), about the acidity of cola or lemon juice.〔Edwin Dobb. "New Life in a Death Trap". ''Discover'', 2000〕 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 Anaconda Copper and later by the Atlantic Richfield Company (ARCO), until its closure in 1982. When the pit was closed, the water pumps in the nearby Kelley Mine, 3,800 feet below the surface, were turned off, and groundwater from the surrounding aquifers began to slowly fill the pit, rising at about the rate of one foot a month.〔 Since the pit closure on Earth Day 1982, the level has risen to within 150 feet of the natural groundwater level. 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.〔 The acidic water in the pit carries a heavy load of dissolved heavy metals. In fact, the water contains so much dissolved metal (up to 187 ppm Cu) that some material is mined directly from the water. In the 1990s plans were devised for solving the groundwater problem. Water flowing into the pit has been diverted to slow the rise of the water level. Plans have been made for more extensive treatment in the future. The Berkeley Pit has since become one of the largest Superfund sites. The pit is currently a tourist attraction, with an adjacent gift shop. A $2 admission fee is charged to go out on the viewing platform. ==Early history and development== 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 The open-pit style of mining superseded underground operations because it was far more economical and much less dangerous than underground mining.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.〔(【引用サイトリンク】url=http://rydberg.biology.colostate.edu/Phytoremediation/2003/Boczon/Berkeley_Pit_History.html )〕 Two communities and much of Butte's previously crowded east side were consumed by land purchases to expand the pit. 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 lost property. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Berkeley Pit」の詳細全文を読む スポンサード リンク
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