Atlantic Richfield is proposing to build a new water treatment plant to further lower the level of the toxic lake inside the Berkeley Pit, in case the tailings dam that sits directly above it ever fails.
The abandoned Berkeley Pit copper mine has been slowly flooding with contaminated groundwater since 1982. The 1994 Superfund cleanup plan requires Atlantic Richfield and Montana Resources, the two companies in charge of the Pit, to keep its water below the level at which it would enter the aquifer and Butte’s creeks.
Atlantic Richfield Vice-President Patricia Gallery says the former oil company now owned by BP is concerned about the risk from the Yankee Doodle Tailings Impoundment perched up hill of the Pit.
"Any kind of dam failure could have a significant impact on human health, the environment and people’s safety. And safety is our highest priority here. So for low probability risks, high consequence, we wanted to make sure that we take it seriously and we look at mitigation so that nothing ever happens."
A dam failure could cause a slurry of water and mine tailings to flood the Pit, raise the water level in it, or potentially overflow.
The dam is where Montana Resources stores waste from its active copper and molybdenum open pit mine. MR is currently seeking a permit to expand the holding capacity of the impoundment.
Patricia Gallery with Atlantic Richfield says a catastrophic failure of the tailings dam is unlikely, but the risk isn’t zero. She says the recent disaster in Brazil, when a tailings dam burst and killed over 100 people, has heightened the company’s awareness.
So Atlantic Richfield is proposing to build a second water treatment plant that would reduce water levels in the Berkeley Pit over several years by 50 to 150 feet, in case the earthen dam above it ever does fail and its contents are released.
"In that circumstance, it would be directed to those pits and there would be sufficient space in those pits to take anything, so there would never be anything that would go offsite. That would be our objective."
Gallery says Atlantic Richfield does not have an estimate of what the new treatment plant will cost yet, and they need approval from EPA to proceed. If they get approval, they expect to have the new water treatment plant designed, built and online in 2021.
