The guiding documents for Pit management require ongoing assessment and evaluation of the Horseshoe Bend Water Treatment Plant and the technology used to treat contaminated Pit water until several years prior to full-scale implementation. That implementation is required when water levels at any monitoring compliance point reach the Critical Level of 5,410 feet above sea level.
A review of treatment technologies is required 4 years before any compliance point is projected to reach the Critical Level. Current projections show that the Critical Level will be reached in 2023; therefore the technology review will start in 2017 and must be completed by 2019. AR and Montana Resources are already evaluating treatment alternatives, and this work will continue through 2017. This includes treatability studies and testing on the expected quantity and quality of contaminated water. Construction upgrades are scheduled for 2019 through 2021, with upgrades completed at least 2 years before the Critical Level is reached.
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.