ASSOCIATED PRESS
BUTTE – Atlantic
Richfield has scrapped a proposal to build a second water treatment plant to
lower the level of acidic, metal-laden water that has collected in a former
copper mining pit in Butte.
There were
concerns that reducing the water levels in Berkeley Pit could destabilize
portions of the walls of the pit, Cameron Nazminia, director of state and local
affairs for Atlantic Richfield, told “The Montana Standard.”
Berkeley Pit
began filling with water after Atlantic Richfield turned off underground pumps
in 1982. Atlantic Richfield/BP and Montana Resources are responsible
to maintain the water level in the pit below the level at which it would enter
Butte’s groundwater.
Last
year, Montana Resources began a pilot project to pump and treat
enough water from Berkeley Pit to stop the water levels from rising.
Atlantic
Richfield had proposed lowering the pit’s water levels by between 50 feet and
150 feet. The water is about 1,000 feet deep.
In addition
to pit wall stability, Mark Thompson of Montana Resources said reducing the
water level would expose sulfide-ore minerals to oxygen, generating acid that
would increase the acidity of the water in the pit. Leaving the minerals covered
with water takes the oxygen out of the equation, Thompson said.
