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The water level in the Berkeley Pit in 2013, compared to the Critical Water Level. Current projections show that the water level in one of the monitoring compliance points around the Pit, such as the Pilot Butte or Anselmo mine shafts, will reach the critical level around 2023, triggering pumping-and-treating of Pit water to maintain its level below the critical point. Photo by Ted Duaime of the Montana Department of Mines & Geology.

Current and Critical Water Level Comparison

The 2013 print edition of PitWatch included the following photo from the Montana Bureau of Mines & Geology (MBMG), intended to show the current water level relative to the Critical Water Level.

The water level of the Berkeley Pit in 2012, compared to the Critical Water Level for the Berkeley Pit system. Image from the Montana Bureau of Mines and Geology.
The water level of the Berkeley Pit in 2012, compared to the Critical Water Level for the Berkeley Pit system.

Some PitWatch readers asked for a version of this image that used a current photo of the Berkeley water level, and MBMG created this new image to better illustrate the current and critical levels.

The water level in the Berkeley Pit in 2013, compared to the Critical Water Level. Current projections show that the water level in one of the monitoring compliance points around the Pit, such as the Pilot Butte or Anselmo mine shafts, will reach the critical level around 2023, triggering pumping-and-treating of Pit water to maintain its level below the critical point. Photo by Ted Duaime of the Montana Department of Mines & Geology.
The water level in the Berkeley Pit in 2013, compared to the Critical Water Level. Current projections show that the water level in one of the monitoring compliance points around the Pit, such as the Pilot Butte or Anselmo mine shafts, will reach the critical level around 2023, triggering pumping-and-treating of Pit water to maintain its level below the critical point. Photo by Ted Duaime of the Montana Department of Mines & Geology.

Under the management plan for the Berkeley Pit, the water level in the Pit itself will never reach that critical level. Because water levels in some of the compliance monitoring points around the Pit are consistently higher than the level in the Pit itself, it is extremely likely that water at one of those monitoring points (such as the Pilot Butte or Anselmo mine shafts) will reach the critical level while the Berkeley Pit water level is still several feet below it. When the water level at any compliance point reaches the critical level (current projections put this time at 2023), pumping-and-treating of Berkeley Pit water will begin, maintaining the level in the Pit below the critical level.

The water level of the Berkeley Pit in 2012, compared to the Critical Water Level for the Berkeley Pit system. Image from the Montana Bureau of Mines and Geology.

What is the Critical Water Level (CWL)?

The water level of the Berkeley Pit in 2012, compared to the Critical Water Level for the Berkeley Pit system. Image from the Montana Bureau of Mines and Geology.
The water level of the Berkeley Pit in 2012, compared to the Critical Water Level for the Berkeley Pit system.

Set by the U.S. EPA and Montana DEQ, the Critical Water Level, 5,410 feet, marks the point where full-scale pumping and treating of Berkeley Pit water will begin. The level represents the lowest level in the Butte Basin, the stream bottom of Silver Bow Creek. It was set to prevent any contamination from moving into surface and groundwater.

The critical level applies to all of the monitoring compliance points around the Pit, including the mine shafts and wells shown in “Monitoring locations and water levels” below. The Montana Bureau of Mines & Geology regularly checks water levels at all of these points. When the water level in any one of these places reaches 5,410 feet, Pit water will be pumped and treated to maintain the water level at or below the critical level. As you can see in “Water levels over time” at right, currently the highest water level is at the Pilot Butte mine. At 5,335 feet, water in the Pilot Butte will have to rise 75 feet before it reaches the critical level.

Based on the rate the water is rising, scientists expect the water to reach the critical level around 2023. The Critical Level includes a safety buffer of at least 50 feet. In other words, Pit water would not spread until the water level reached about 5,460 feet.

Berkeley Pit groundwater monitoring locations and water levels, including wells and abandoned mine shafts, June 2013. Graphic by Justin Ringsak.
Berkeley Pit groundwater monitoring locations and water levels, including wells and abandoned mine shafts, June 2013. Click on the image to view a larger version.
Elevations above sea level for Berkeley Pit water and surrouding Butte, Montana landmarks. Map image from Google Earth, graphic by Justin Ringsak.

Could the Berkeley Pit ever overflow?

The Berkeley Pit will never overflow. In 1994 the EPA established the Critical Water Level (the maximum level the water will be allowed to reach) at 5,410 feet above sea level, which is one hundred feet below the rim.

Elevations above sea level for Berkeley Pit water and surrouding Butte, Montana landmarks. Map image from Google Earth, graphic by Justin Ringsak.
Elevations above sea level for Berkeley Pit water and surrounding Butte, Montana landmarks. Image from Google Earth. Click on the image to view a larger version.

Water levels are regularly monitored at the Pit, in historic underground mines, and in wells surrounding the Pit. Failure to keep the water below 5,410 feet would result in steep fines for the companies responsible for the site, BP-ARCO and Montana Resources.

In addition to careful monitoring, the Horseshoe Bend Water Treatment Plant was constructed to make sure water in the Pit remains below 5,410 feet. Pit water will be pumped, treated, and discharged when the level nears the critical point.

Even if the water was allowed to rise unchecked, it would still never reach the rim. The groundwater flow would reverse direction and, instead of flowing toward the Pit, as it does now, the water would flow away from the Pit, underground into the sandy aquifer beneath Butte’s valley.

Due to the underground flow, Pit surface water would never reach the rim. Considering the federal orders, potential fines, and frequent monitoring, Pit water will not rise unchecked.

Does this Critical Water Level apply only to the Pit?

No. Pumping and treating of Pit water must begin when the 5,410-foot level is reached at ANY of the water-level monitoring compliance sites on the Hill, in what is called the East Camp. These sites include the Anselmo, Granite Mountain, Kelley, Belmont, and Steward mine shafts, as well as several other monitoring wells established to the south and the east of the Pit.

Presently, the water level at these sites is about 20-40 feet higher than the level in the Pit. So, the 5,410-foot level should be reached sooner at these sites than in the Pit, which means water pumping and treating would begin that much sooner.