Millions of gallons of water flow into the toxic soup of the Berkeley Pit every day, in the aftermath of open pit copper mining that left behind one of the largest mine pits when mining and smelting operations in Butte, Montana shut down in the early 1980s. This makes it the largest Superfund site in the United States.

The water in the Berkeley Pit is a good example of acid mine drainage, which is mainly caused by the high sulfur content in the surrounding rock. The sulfur reacts with air and water to become sulfuric acid. As the acidic water flows through the underground mine workings and rock fractures, it eats away at the metals in the rocks and dissolves them into the water. Arsenic, copper, cadmium, cobalt, iron, manganese, and zinc are among the many contaminants to be found in the water of the Pit, which has a pH of 2.6.

The Berkeley Pit operated from 1955 to 1982, removing 290 million tons of copper ore from the ground. It is more than 1,800 feet deep. Atlantic Richfield Company (ARCO) took responsibility for the Pit, along with other mining properties in Butte, when they bought the Anaconda Company in 1977.

In 1982, ARCO shut off huge underground pumps that diverted water from thousands of miles of shafts left behind after a century of mining. Less than a year later, water began to appear in the bottom of the Berkeley Pit. Since then, the water level has been rising about one foot a month.

The Pit became a poster child of environmental damage in 1995, when a flock of migrating snow geese chose to land and rest on the Pit's heavy metal laced waters in November of 1995. The geese drank the highly acidic water, and almost 350 of them died.

Public agencies are watching the Pit and discussing how to address the problem. There's a lot of disagreement about the best way to handle it. ARCO, for instance, likes to think of the Pit as a natural bucket that retains the polluted waters until they can find a practical way to handle the mess.

Some scientists believe that letting the water rise to maximum safe levels will eventually lower the water's acid and metal content by reducing the amount of sulfur-bearing rock that's exposed to air. That may improve water quality and make it cheaper to treat the water when the time comes.

The EPA's plan of choice is to build a plant that adds lime to the water, making a sludge that can then be conveyed to a tailings pond or landfill. The plant is not expected to be neccessary before water reaches a "critical level" around 2021.

Others want action taken yesterday to ensure that a natural disaster or other unexpected circumstances do not allow contaminated water to flow into groundwater wells. Several companies are working on methods of treating the water and extracting metals in the process. Scientists at Montana Tech are investigating the possibility of using algae to clean the water.

A stray dog has been watching over the proceedings for at least 16 years. That's a lot of dog years. Miners at the one remaining active mine feed him, and have even built a doghouse for him at the base of a big pile of rubble. They call him"The Auditor" or "The Inspector," because he shows up when they least expect him. He's not a very trusting creature, but one miner claims to have gotten close enough to have trimmed the fur around his eyes. They say the dog's eyes are both beautiful and terrible, not unlike the pit itself.

Update: Crux informs me that the Auditor died in his doghouse November 19, 2003.


Many thanks to Anark, who prompted me to write about the Inspector.

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