The Berkeley Pit will never overflow. In 1994 the EPA established the Critical Water Level (the maximum level the water will be allowed to reach) at 5,410 feet above sea level, which is one hundred feet below the rim.
Water levels are regularly monitored at the Pit, in historic underground mines, and in wells surrounding the Pit. Failure to keep the water below 5,410 feet would result in steep fines for the companies responsible for the site, BP-ARCO and Montana Resources.
In addition to careful monitoring, the Horseshoe Bend Water Treatment Plant was constructed to make sure water in the Pit remains below 5,410 feet. Pit water will be pumped, treated, and discharged when the level nears the critical point.
Even if the water was allowed to rise unchecked, it would still never reach the rim. The groundwater flow would reverse direction and, instead of flowing toward the Pit, as it does now, the water would flow away from the Pit, underground into the sandy aquifer beneath Butte’s valley.
Due to the underground flow, Pit surface water would never reach the rim. Considering the federal orders, potential fines, and frequent monitoring, Pit water will not rise unchecked.