There are generally four operational units in Butte: underground mines, open pit mine, concentrator and precipitation plant. As with copper production, the waste water systems for all units are interrelated. Acidic mine water is pumped up the Kelley shaft and distributed on leach dumps. Major waste water discharges from the Butte operations include: about 4400 gallons per minute (gpm) acidic water from the copper precipitate plant, about 8200 gpm alkaline water from the concentrator and some spills (including tailings from the concentrator circuit).
Silver Bow Creek has a present water use classification for industrial waste and has been used as such for over 70 years. At Warm Springs the name of this stream is the Clark Fork River where the classification is presently “CD2”. Governmental agencies have indicated that the CD2 classification should be raised to BD1. The letter designations for these classifications represent the intended water use for the stream in question: CD2-Bathing, swimming and recreation, growth and marginal propagation of salmonid fish, BD1-Water supply for drinking (with treatment) and growth and propagation of salmonid fish.
The existing treatment system was considered for modification on the basis that Silver Bow Creek would be abandoned as an industrial waste stream. Neutralization and settling of the acidic flows would then have to be performed in the Butte area. The only area available for settling in this area is the tailings pond, about 2 miles upstream from the concentrator. Miscellaneous acidic flows (seepage, etc.) would also be intercepted.
The proposed water treatment system for the operations in the Butte area consist of four basic components:
- (1) Acidic water pumping,
- (2) Lime feed to tailings at the concentrator,
- (3) Neutralization and settling in tailings pond,
- (4) Recycle of clarified water to the concentrator.
The acidic water from the Copper Precipitation Plant would be pumped to a mixing chamber located on the dike of the tailings pond. Slaked lime stored at the concentrator would be pumped with tailings to the same mixing chamber and discharged into the tailings pond for settling.