1982-2013: 31 years since pumps stopped

Shortly after the Continental Pit reopened, the Horseshoe Bend Water Treatment Plant went online ahead of schedule on November 17, 2003, again diverting Horseshoe Bend flows and preventing this water from entering the Pit.

The Horseshoe Bend Water Treatment Plant, completed in 2003, captures surface water to slow the rate of fill of the Berkeley Pit lake. In the future, the plant will capture and treat water to prevent Pit water from rising further. Photo by Justin Ringsak.

The Horseshoe Bend Water Treatment Plant, completed in 2003, captures surface water to slow the rate of fill of the Berkeley Pit lake. In the future, the plant will capture and treat water to prevent Pit water from rising further.

The Horseshoe Bend plant, which will eventually be used to pump and treat Pit water in order to keep it below the Critical Water Level, uses lime (calcium hydroxide) addition to reduce the acidity of the water and cause metals to precipitate out. Currently, treated Horseshoe Bend water is used in active mining operations, and the sludge that results from treatment is returned to the Pit lake. In the long term, treated Horseshoe Bend water and, eventually, Berkeley Pit water will be used by the active mine as long as it is operating. If the mine is no longer active, treated water will be pumped to Silver Bow Creek near Montana Street in Butte.

If the adjacent Continental Pit mine is no longer active, Berkeley Pit water treated at the Horseshoe Bend plant will be pumped to Silver Bow Creek near Montana Street in Butte. Image from Google Earth.

If the adjacent Continental Pit mine is no longer active, Berkeley Pit water treated at the Horseshoe Bend plant will be pumped to Silver Bow Creek near Montana Street in Butte. Image from Google Earth.

Since the day the pumps in the Kelley turned off in 1982, water levels have risen over 3,100 feet in the East Camp bedrock system (which includes the Berkeley Pit, as well as the surrounding underground mine workings and bedrock aquifer), and over 230 feet in the separate West Camp system. Water-levels have changed very little in the shallow alluvial system adjacent to historic mining operations (see Two aquifers feed into the Pit for details on the bedrock and alluvial aquifers).

Current projections anticipate that pumping and treating of Berkeley Pit water will need to commence in 2023, although that date is dependent upon many factors: a reduction in waters flowing into the Berkeley would push the date further into the future, whereas an increase in water flows would necessitate an earlier date. The timeline for Berkeley Pit management is reviewed and updated annually (refer to the timeline at the bottom of each page).

The results from a performance test conducted in November 2007 indicate that the Horseshoe Bend Water Treatment Plant meets all discharge standards for contaminants of concern set by the EPA. Additional adjustments still need to be made to address pH issues. A summary of that performance test is available in the EPA’s Third Five Year Review Report (2011) of the Butte Mine Flooding Operable Unit (BMFOU, which includes the Berkeley Pit and underground mines), Section 6.4.4, pages 34-37. The document can be downloaded here:

EPA Third Five Year Review Report (2011) - Vol. 3 - Butte Mine Flooding Operable Unit (BMFOU) (644.3 KiB)

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