| Berkeley Pit: Butte, Montana: Mined for gold, silver, and
copper, the region of Butte, Montana, had already earned the nickname
of “The Richest Hill on Earth” by the end of the 19th century. Demand
for electricity increased demand for copper so much that by World War
I, the city of Butte was a boomtown. Well before World War I,
however, copper mining had spurred the creation of an intricate
complex of underground drains and pumps to lower the groundwater
level and continue the extraction of copper. Water extracted from the
mines was so rich in dissolved copper sulfate that it was also
“mined” (by chemical precipitation) for the copper it contained. In
1955, copper mining in the area expanded with the opening of the
Berkeley Pit. The mine took advantage of the existing subterranean
drainage and pump network to lower groundwater until 1982, when a new
owner suspended operations. After the pumps were turned off, water
from the surrounding rock basin began seeping into the pit. By the
time an astronaut on the International Space Station took this
picture on August 2, 2006, water in the pit was more than 275 meters
(900 feet) deep. This image shows many features of the mine
workings, such as the terraced levels and access roadways of the open
mine pits (gray and tan sculptured surfaces). A large gray tailings
pile of waste rock and an adjacent tailings pond appear to the north
of the Berkeley Pit. Color changes in the tailings pond result
primarily from changing water depth. Because its water contains high
concentrations of metals such as copper and zinc, the Berkeley Pit is
listed as a federal Superfund site. The Berkeley Pit receives
groundwater flowing through the surrounding bedrock and acts as a
“terminal pit” or sink for these heavy-metal-laden waters, which can
be as strong as battery acid. Ongoing clean-up efforts include
treating and diverting water at locations upstream of the pit to
reduce inflow and decrease the risk of accidental release of
contaminated water from the pit into local aquifers or surface
streams. |
