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.