Berkeley Pit Mine Closes on Earth Day, Pumps Shut Off, Creating Toxic Lake Superfund Site

Atlantic Richfield Company (ARCO) closed the Berkeley Pit copper mine on Earth Day 1982 and immediately shut off the pumps that had kept groundwater out of the massive excavation, beginning the pit’s transformation into one of the most toxic bodies of water in North America. The corporate decision to cease dewatering operations created a growing lake of acidic, metal-laden water that would become the centerpiece of the nation’s most expensive Superfund site. This case exemplifies the “privatize profits, socialize costs” model where corporations extract billions in resources then abandon environmental catastrophes for taxpayers to manage in perpetuity.

SCALE OF EXTRACTION AND ABANDONMENT: The Berkeley Pit operated from 1955 to 1982, first under Anaconda Copper Mining Company, then ARCO after its 1977 acquisition of Anaconda. The open-pit mine reached dimensions of one mile long, half-mile wide, and 1,780 feet deep, extracting vast quantities of copper ore while ARCO reaped profits. When copper prices made continued operation uneconomical, ARCO simply walked away, shutting off the Kelley Mine pumps 3,800 feet below the surface that had kept the pit dry during operations.

TOXIC LAKE FORMATION: Without active pumping, groundwater began rising at approximately one foot per month, dissolving heavy metals and creating acid mine drainage as it interacted with exposed rock surfaces. The resulting toxic soup reached approximately 900 feet deep with pH levels of 4.1-4.5 (similar to battery acid) and contains dissolved copper, arsenic, cadmium, zinc, and sulfuric acid. By 2024, the pit held approximately 50 billion gallons of poisonous water. In 1995, 342 migrating snow geese died after landing in the pit; in 2016, another 4,000 geese perished, demonstrating the water’s lethal toxicity to wildlife.

SUPERFUND DESIGNATION AND PERPETUAL MANAGEMENT: The Silver Bow Creek/Butte Area was added to the EPA’s National Priorities List in 1983; the Berkeley Pit itself was designated a Superfund site in 1987. The potentially responsible parties identified were Atlantic Richfield Company and Montana Resources, but the scale of contamination far exceeds any realistic remediation. The pit is “federally mandated to be managed to protect human health and the environment forever” - meaning taxpayers will subsidize eternal water treatment because allowing the toxic water to rise further would contaminate Butte’s aquifer and surface waters.

WATER TREATMENT AND ONGOING COSTS: A pilot water treatment plant began operations in October 2019, pumping contaminated water out, treating it with lime and through a $19 million polishing plant, then discharging it to Silver Bow Creek after meeting water quality standards. This treatment infrastructure requires continuous operation and funding indefinitely. In 2019, the City of Butte reached a $150 million settlement with Atlantic Richfield for further cleanup - a fraction of the estimated total costs over time. The Berkeley Pit represents the nation’s most expensive Superfund site, with cleanup costs ultimately borne by taxpayers while ARCO’s profits from decades of mining remain privatized.

REGULATORY FAILURE AND CORPORATE IMPUNITY: The Berkeley Pit disaster demonstrates systematic regulatory failure across multiple dimensions. Mining regulations allowed extraction without adequate financial assurance for closure and remediation. ARCO faced no requirement to continue dewatering operations despite creating the hazard. Environmental laws proved inadequate to prevent corporations from extracting resources, creating environmental catastrophes, then declaring operations uneconomical and abandoning toxic legacies. The “responsible party” framework provides insufficient deterrence when cleanup costs exceed corporate willingness to pay.

PERPETUAL EXTERNALITY MODEL: The Berkeley Pit exemplifies how extractive industries externalize environmental costs onto communities and future generations. ARCO and Anaconda extracted billions in copper value while paying minimal taxes to Montana, employed workers at low wages in dangerous conditions, then left behind a toxic lake requiring eternal management at public expense. Recent proposals to mine rare earth elements from the toxic water - requiring federal subsidies to be economically viable - would simply repeat the extraction-profit-abandonment cycle, with corporations privatizing any valuable minerals while socializing ongoing environmental management costs.