DeMars reports on a current webpage that Butte, Montana was once know as "the richest hill on earth" for it's historical extensive mining industry. The area has now transformed into the nation's largest superfund site after much of the mining was shut down and the Berkeley Pit filled up with acidic groundwater with high concentrations of hazardous heavy metals. Underground copper mining in Butte, Montana since the 1870's has resulted in over 49 miles of vertical shafts and 5,600 miles of horizontal workways.
In 1955, high copper prices drove Anaconda Copper Mining Company to open a new pit mines including the Berkeley Pit. Pumps had to be used to de-water the mines, but on April 23, 1982 Atlantic Richfield Company (ARCO) suspended mining in the Berkeley Pit and the pumps were shut down. The pit filled back up with 40 billion gallons of acidic water. Today the pit, its tailings ponds and groundwater have high concentrations of heavy metals. The Berkeley Pit is a terminal sink so all the contaminated surface and ground water flows into it. Now Butte is the largest U.S. Environmental Protection Agency (EPA) Superfund site in America. It is the their job, along with the Montana Bureau of Mines and Geology and other groups, to maintain it as a terminal sink and keep the pathogens contained to help the public stay safe and healthy.
Here is a link to the Montana Bureau of Mines and Geology
When the groundwater flows through the old mine shafts, it reacts with oxygen to oxidize the sulfide minerals in the area which makes the water acidic. It drains into the Berkeley pit where the pH is 2.8-3. As the acid water travels through the ground it dissolves out metals such as arsenic, copper, cadmium, cobalt, iron, manganese, zinc, and sulfate. All these toxic metals concentrate in the pit. The concentration of copper ranges from 73 ppm at the top of the pit to 137 ppm at the bottom and iron is from 507 ppm to 803 ppm. The area around the mines is littered with tailings or waste material left over after processing the mined ore. The tailings that still contain metals that could not be mined out are located in ponds near the Berkeley pit. From here, the toxic water makes its way into Silver Bow Creek (which runs through Butte) by seeping through with groundwater and over the surface in storm water runoff. Silver Bow Creek empties into the Clark Fork River where contaminated water flows all the way to Missoula.
Clark Fork River Technical Assistance Committee for more information about the tailings removal issue: Butte's Parrot Tailings.
To learn more about the cleanup process, go to the EPA website for the Silver Bow Creek Superfund Program and the Atlantic Richfield Company's Butte cleanup data site.
Go to Pitwatch to track the rising water level in the Berkeley Pit.
For more information on Silver Bow Creek and to download the latest update on it's clean up and restoration from the Montana Department of Environmental Quality, go to Citizens Technical Environmental Committee Butte, Montana.
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