Berkeley Pit, Montana
On April 22, 1982, workers shut off the pumps at Butte’s Berkeley Pit for the last time. The massive copper mine had operated for 27 years, but falling prices made it too costly to continue.
Without the pumps running, toxic groundwater began filling the mile-wide hole. Within months, what had been Montana’s pride became America’s most dangerous lake.
Here’s the story, and how you can visit this toxic wonder today.
ARCO’s Decision to Cease Operations
Copper prices fell dramatically in the early 1980s, making the Berkeley Pit unprofitable. The price per pound hit record lows, forcing ARCO to rethink its mining operations.
ARCO bought Anaconda Copper Mining Company in 1977 with little knowledge of hard-rock mining. This purchase hurt them financially as copper demand dropped worldwide.
Earlier losses in Chile and Mexico added to their money problems. These factors led ARCO to end all Butte operations on April 23, 1982.
The Critical Decision to Turn Off the Pumps
Huge pumps ran non-stop in the Kelley Mine, 3,800 feet underground. These pumps kept groundwater from flooding tunnels connected to the Berkeley Pit.
ARCO turned these pumps off for good on April 23, 1982. They made this choice without studying how it might harm the environment.
This shutdown let groundwater flow back into areas kept dry for over 100 years. Water began filling the 10,000 miles of tunnels under Butte.
The Immediate Aftermath of Pump Shutdown
Groundwater poured into the Berkeley Pit as soon as the pumps stopped. The pit became a giant basin collecting water from the surrounding area and connected mines.
The water rose about one foot each month at first. No treatment or containment systems were set up to handle this growing lake.
ARCO left the site without creating any safeguards for local water sources. Groundwater flowed freely into the pit, with nothing to stop or clean it.
The Toxic Brew Begins to Form
The pit walls and mine tunnels contained exposed iron pyrite, often called “fool’s gold.” When water touched this mineral, it created sulfuric acid.
This process, known as acid mine drainage, made the growing lake increasingly acidic. The water became as acidic as vinegar, with a pH between 2.5 and 4.5.
The acidic water broke down other minerals in the rock. This released more metals into the water, making the chemical mix worse over time.
A Toxic Soup of Dangerous Metals Forms
The Berkeley Pit water now holds more than 21 different metals and minerals. This toxic mix contains copper, arsenic, cadmium, zinc, iron, and aluminum.
As the acid ate away at more rock, metal concentrations in the water grew higher. This dangerous cycle continued as the pit filled with water.
The water grew so corrosive it could dissolve metal boat parts. Its reddish-orange color comes from the high levels of dissolved iron and other metals.
Recognition as an Environmental Crisis
The Environmental Protection Agency (EPA) named the area a Superfund site in 1983, just one year after the pumps stopped. The Berkeley Pit officially joined the federal Superfund list in 1987.
Superfund sites fall under a 1980 law that gives the EPA power to clean up polluted areas. This law also forces responsible companies to pay for cleanups.
The Berkeley Pit became part of the largest group of Superfund sites in the United States. This label acknowledged the serious threat to human health and the environment.
The Expanding Toxic Lake Threatens Groundwater
Water in the pit rose six to seven feet yearly throughout the 1980s and 1990s. Scientists set a critical water level at 5,410 feet above sea level.
If water reached this level, toxic substances would spill into the surrounding groundwater. This would pollute Silver Bow Creek and potentially harm Butte’s drinking water.
By the early 2000s, the pit held about 40 billion gallons of toxic water. The rising level created an urgent threat to the entire region.
Deadly Consequences for Wildlife
In November 1995, migrating snow geese landed on the pit water. Within hours, 342 birds died from exposure to the toxic lake.
Examination of the dead birds showed severe internal damage. Their throats had burns and sores from contact with the acidic, metal-filled water.
History repeated in November 2016 when thousands more snow geese landed during bad weather. Despite efforts to scare them away, 3,000 to 4,000 birds died from the toxic water.
The Long Road to Remediation Begins
The EPA created a plan for cleaning up the Berkeley Pit in September 1994. This document outlined the required actions to address the environmental damage.
After years of talks, a legal agreement was signed in 2002. This contract required ARCO and other companies to pay $87 million for cleanup work.
The agreement demanded that water levels stay below the critical point forever. The responsible companies now faced the huge task of treating billions of gallons of contaminated water.
Water Treatment Begins After 37 Years
The Horseshoe Bend Water Treatment Plant offered the first solution to the rising water. This facility uses lime to neutralize acid and remove metals from the water.
In 2019, after 37 years of filling, pumping and treatment finally began. For the first time since 1982, water stopped rising in the pit.
The plant can clean about 10 million gallons of water daily. The treated water meets state quality standards before flowing into Silver Bow Creek.
Visiting Berkeley Pit, Montana
You’ll find Berkeley Pit at the Continental Drive exit in Butte, Montana. The Pit Viewing Stand gives you a safe place to observe this massive toxic lake and learn about its environmental impact.
Walk through the Visitor Center to see exhibits explaining the site’s mining history and ongoing remediation efforts. During summer months, tour guides can answer your questions about the pit’s formation and cleanup.
Read More from WhenInYourState.com:
The post Montana has a beautiful lake so toxic, it kills migrating birds and dissolves metal appeared first on When In Your State.