"BUTTE — The number 5,410 has special meaning to Butte. It’s the critical water level – 5,410 feet above sea level – of the Berkeley Pit. The water in the pit must be kept below that elevation or risk contaminating Silver Bow Creek.

At the rate the pit’s water is rising, scientists predict the level will reach the critical mark in 2023.

Four years before that, in 2019, Montana Resources and Atlantic Richfield Co. must begin preparing to treat the water, which will be discharged into Silver Bow Creek at a rate of 7 million gallons a day.

That day is less than five years away."

Kelley Christensen reports for the Billings Gazette November 9, 2014. [2]