Postcard US-2967625 to the Netherlands was a vintage card showing a panorama of the Berkeley Pit, an open pit copper mine in Butte, Montana. Ektachromes by Clifford B. Ellis.
The mine, once the largest truck-operated open pit copper mine in the United States, was opened in 1955 and operated by Anaconda Copper. The Atlantic Richfield Company (ARCO) bought the mine in 1977, and it was closed in 1982. Approximately 320 million tons of ore and over 700 million tons of waste rock were mined from the Butte Hill.
Measured one mile long (1.6 km) by half a mile (0,8 km) wide with an approximate depth of 1,780 feet (540 m), the pit began to collect groundwater from the surrounding aquifers once it was closed as the water pumps in the nearby shaft were turned off. Pyrite and sulfide minerals in the ore and wall rocks met dissolved oxygen in the water, releasing heavy metals and chemicals including copper, arsenic, cadmium, zinc, and sulfuric acid. According to PitWatch, with the bottom elevation at 4,263 feet above the sea level and the water level at 5,318.49 feet above sea level as of July 30, 2014, the pit had filled a depth of 1,055 feet (321.6 m) with water that was highly acidic (2.5 pH level) since 1982. Current projections estimate that the Critical Level at 5,410 feet above the sea level, which is close to the natural water table, will be reached around 2023 when the pit water may reverse flow back into groundwater, polluting Silver Bow Creek and rivers downstream.
The Berkeley Pit has since become one of the largest Superfund sites. Clean up plans have been in place since the 1990s.