The Montana Bureau of Mines & Geology (MBMG) developed this computer model showing Butte topography and the corresponding underground tunnels from the years of historic underground mining. The red dots at the surface and red lines below represent vertical shafts, and the colored lines under the surface represent the horizontal levels of the mines. The graphic does not illustrate stopes or other lateral workings. The Berkeley Pit can be seen as the large depression at center-right. As illustrated, the deepest underground mines went down about one mile, far below the final depth of the Berkeley Pit.
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.
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.
PitWatch reader Coleen Christensen pointed out this blog from the Smithsonian about a possible use for acid mine drainage stream waters. Streams near the Berkeley Pit were similarly impacted during historic mining activities.
On February 8, 2013 material from the southeast wall of the Berkeley Pit collapsed into the Pit water in what is known as a rotational slump or slough. Such sloughs are relatively common in open pit mines. For example, a similar slough occurred at the Berkeley Pit in 1998.
The recent slough was about 550 feet wide and caused an estimated 820,000 tons of material to collapse into the Pit. Montana Bureau of Mines & Geology (MBMG) monitoring showed that the water level in the Pit lake rose about 0.6 feet as a result of the slough. For comparison, over the past several years the water in the Berkeley Pit has risen about 0.65 feet per month.
Current projections still estimate that water levels at one of the surrounding monitoring compliance points for the Berkeley Pit system will reach the Critical Level (5,410 feet) around 2023.
Pumping and treating of Berkeley Pit water will be required when water levels at any of these compliance points reach the Critical Water Level. Currently, the highest water level is in the Pilot Butte shaft to the north of the Pit. As of June 2013, the Berkeley Pit water level was 5,310.89 feet above sea level, and the water level in the Pilot Butte shaft was 5,335.72 feet above sea level, or about 75 feet below the critical level.
No. Butte residents don’t need to worry about flood insurance in regard to the Berkeley Pit and connected underground mine workings. The Berkeley Pit and connected tunnels act as a sink that collects groundwater in the area. Water levels in the Berkeley Pit and associated mine shafts are currently 175 to 200 feet below the rim of the Pit.
The lowest point on the Pit rim, on the east side near the Montana Resources concentrator, is 5,509 feet above sea level. As of June 2013, the Berkeley Pit water level was 5,310 feet, and the highest water level in the system, in the Pilot Butte shaft, was 5,335 feet.
Under the management plan for the Berkeley Pit, these water elevations will always be maintained at levels 100 feet or more below the rim. This will be accomplished by pumping and treating Berkeley Pit water. Pumping and treating will start when the water level at any one of the monitoring compliance points reaches the critical level of 5,410 feet. The Montana Bureau of Mines & Geology (MBMG) monitors water levels at all compliance points, as well as at several other monitoring sites, on a monthly basis. Based on the rate the Pit is filling now, that should happen around 2023.
The elevation of the Metro Storm Drain near the Pit at Texas Avenue and Continental Drive is 5,470 feet, about 60 feet above the highest water level allowed for the Berkeley Pit system.
For further comparison, a monitoring well at Greeley School has an elevation of 5,503 feet, about 93 feet higher than the critical level. The current water level in this well is 5,462 feet, about 52 feet higher than the critical level. This difference in water levels tells us that groundwater is flowing toward the Pit, and will continue to do so after the waters in the Berkeley Pit and connected mines reach their highest allowed levels.
In other words, water is flowing into the Berkeley Pit, and the Pit will be managed so that water is always flowing into it. Butte residents can rest easy knowing that the Berkeley Pit is not going to overflow, and that there is no need for flood insurance due to the Pit or underground mines.
Water from the Horseshoe Bend drainage is diverted before reaching the Pit and treated in the Horseshoe Bend Water Treatment Plant for use in mining operations. In 2012, the plant treated about 5 million gallons of water per day. Sludge from the treatment process was returned to the Pit at a rate of 491,000 gallons per day. No water or waste leaves the Pit or mine site.
Water levels in the Pit, wells and mine shafts are monitored monthly. An evaluation of the rate of fill is performed each year to determine dates for future reviews and plant upgrades.
The Montana Bureau of Mines & Geology (MBMG) measures the water levels at the Pit and in connected mine shafts and wells each month. To monitor water quality, water samples are collected from the Pit semi-annually at multiple depths as safe access allows.
23 wells and 14 mine shafts supply information about the deep bedrock aquifer. 36 wells provide similar data about the alluvial aquifer, which is much closer to the surface. Each month, scientists manually check and record the water levels in these wells. Twice a year, they collect samples to analyze the water’s chemistry. All of this information helps scientists understand where the water is coming from and how it is moving underground.
Complete MBMG monitoring reports and data can be downloaded from our Monitoring Reports page.
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.