The rate of rise of water levels in the Berkeley Pit and connected monitoring points is affected by many factors, including rain and snowfall and occasional ‘sloughs’ or ‘slumps’ of material from the Pit’s sidewall slopes.
The most recent slough occurred on February 8, 2013. An estimated 820,000 tons of material from the southeast wall collapsed into the Pit. Montana Bureau of Mines and Geology (MBMG) monitoring showed that the water rose about 0.6 feet as a result. For comparison, over the past several years the water has risen about 0.65 feet per month.
Sloughs or landslides are relatively common in open pit mines and can potentially raise water levels. To address the potential effects of future sloughs on the Pit’s rate of rise, EPA required the Potentially Responsible Parties (PRPs) for the site, Montana Resources and the Atlantic Richfield Company (AR), to study the stability of the slopes around the rim of the Berkeley. Publication of the final report on that study is expected later in 2015, and it will be published here on the PitWatch website.
EPA and the PRPs have stated that preliminary results indicate that the rising Pit water level will continue to increase the potential for slope failure, especially in the southeastern part of the Pit. Future sloughs are expected to occur in the absence of any stabilization or mitigation measures, but, based on past sloughs, are not expected to significantly affect the Pit management timeline.
Two much smaller landslides, which had no noticeable impact on the water level, occurred in August and November 2012. A larger landslide occurred in 1998. The November 2012 slide damaged the Montana Resources pontoon boat used for water quality sampling in the Pit. Following the 2013 slide, those sampling activities were suspended for the safety of the MBMG scientists who conduct the sampling.
Since the Berkeley Pit was designated as a Superfund site in the 1980s, things have gone largely as expected. In one instance the site remedy has proceeded at a faster pace than mandated in the 1994 Record of Decision (or ROD, available in its entirety here).
The ROD called for the water treatment plant for the Pit to be designed 8 years before the water level at any monitoring compliance point reached the Critical Level of 5,410 feet above sea level, and completed 4 years prior. In fact, the Horseshoe Bend Water Treatment Plant was completed in 2003, 20 years before water is expected to reach the Critical Level.
Water level modeling has also been accurate. The Pit water level has risen more slowly than originally predicted due to several factors, most notably the capture and treatment of contaminated surface water flowing in from Horseshoe Bend. This water is treated and reused in Montana Resources mining operations, with no water discharged offsite.
The 1994 ROD included projections that estimated that the water level in the Pit would be at 5,204 feet above sea level in 2000; 5,353 feet in 2010; and 5,417 feet in 2015. With a water level of just 5,326.01 feet recorded on August 5, 2015, the Pit water level is nearly 100 feet below early predictions.
The 1994 model also anticipated a rate of fill of about 5-6 million gallons per day. With surface inflow captured, treated, and reused, the average rate has been much lower, about 2.6 million gallons per day. The model currently used by the Bureau of Mines and Geology uses monitoring data to project the filling rate, and over the past 5 years the model’s projections have varied by only a few months.
Some surprises have occurred over the years. For example, the 1994 ROD projected that the water level in the Anselmo mineshaft would be the highest in the Pit system. That was the case until the past several years, when the water level in the Pilot Butte shaft overtook it. Since then the highest water level is typically recorded at the Pilot Butte mine, which was at 5,351.11 as of August 5, 2015.
At 58.89 feet below the Critical Level, it is likely that the Pilot Butte water will hit the critical point first, triggering full implementation of the Horseshoe Bend Water Treatment Plant. This is currently projected to happen in July 2023, a few months later than projected in the last edition of Pit Watch in 2013.
Montana Resources and Atlantic Richfield are currently funding a Montana Tech graduate student to develop a remote system to sample Pit water quality. The student will review options to collect the required data, including aerial or water-based drones that can be operated from the shore of the Pit.
Due to the size of the Pit and the need to collect samples from locations throughout it, the ability to communicate with the drone at a distance of up to 2 miles is essential. Work began during the summer of 2015 and will continue through the 2015-2016 academic year and summer 2016, with final testing during the June and July, and collection of Pit samples by August 2016.
Electrical engineering assistant professor Bryce Hill is supervising the project. He said the device could potentially be used for applications beyond the Berkeley Pit.
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.
In 2010 EPA interviewed local citizens and reviewed the status of Butte area Superfund sites as part of a required five-year review (the full review report is available here). Five-year reviews determine whether remedies or other response actions are protective of human health and the environment in compliance with a site’s decision documents. Methods, findings, and conclusions are documented in five-year review reports that identify issues found and make recommendations to address them.
The 2010 review identified six main issues related to the Butte Mine Flooding Operable Unit (BMFOU), which includes the Berkeley Pit. All involved the performance of the Horseshoe Bend Water Treatment Plant, which was completed in 2003.
The plant currently treats contaminated surface water flowing in from the north. This water is diverted away from the Pit, slowing the rate of rise of the water. Eventually, when the water level at any compliance point reaches the Critical Level of 5,410 feet, the plant will pump-and-treat Pit water to keep levels below that critical point. A performance test was conducted at the plant in 2007, and that data was considered in the 2010 review.
All treated water is currently recycled to Montana Resources active mining operations and is not discharged to Silver Bow Creek or any other surface outlet, Consequently, EPA identified all issues in the review as potential future issues that do not effect the current protectiveness of the remedy. Montana Resources does not allow any water to discharge from the Berkeley Pit and active mine area.
Issue 1: pH
Water treated at the plant did not meet the final pH standard. pH measures the acidity of a liquid. The pH is purposely raised to over 10 in order for it to be used as operating water in Montana Resource’s mill. Discharge standards only apply when water is discharged to Silver Bow Creek.
Issue 2: Gypsum scaling
During the water treatment process, gypsum sometimes builds up, or ‘scales’, on the inside of tanks and pipes. This leads to a need for additional maintenance, as parts of the plant must be shut down for a short period each year so that crews can remove the build up. Measures to help manage and reduce scaling are being evaluated, and gypsum concentrations are monitored weekly.
Issue 3: Cadmium
Testing showed that treated water at times did not meet the standard for cadmium, a toxic metal. After adjustments were made to increase the pH, the standard for cadmium was met.
Issue 4: Test did not include treatment of Pit water
The 2007 performance test measured treated surface water from Horseshoe Bend. While this water is similarly contaminated, Pit water has higher concentrations of toxic metals and sulfate.
Issue 5: Scale Inhibitors used to control gypsum may effect metals removal
This issue is closely related to issue 2. To reduce gypsum scaling on critical pipelines and pumps, scale inhibitors are used. These chemical additions make it more difficult for gypsum to precipitate out of treated water and build up in the plant. Their effect on metals removal was a concern, but studies have shown no discernable effect of inhibitors on metals removal.
Issue 6: Whole Effluent Toxicity
Whole Effluent Toxicity (WET) is a measure of the total toxic effect from pollutants in treated wastewater on aquatic life. In 2010, WET testing had not yet been performed on treated water. Treated water is currently recycled in active mining operations, so it is no threat to aquatic life. Preliminary WET testing was completed during pilot testing using Horseshoe Bend water. Results showed the chronic exposure concentration with the lowest observable effect was 75% treated water mixed with 25% dilution water. More WET testing is planned.
EPA recommended that an additional performance test be completed prior to the 2015 five-year review to investigate all six of these issues and possible solutions.
EPA also noted that operations and maintenance at the plant are now more focused on preventative care, and operations in general have been optimized. After adjustments, treated water met all discharge standards with the exception of pH (issue 1).
In order to be protective in the long term, the various water quality issues in treated Pit water will have to be resolved before discharge to Silver Bow Creek becomes necessary. As long as Montana Resources continues active mining at the Continental Pit, no discharge is expected to occur.
Recommendations for additional performance testing will be addressed by treatability studies starting in 2016 and concluded by 2019, well before any discharge would potentially occur.
EPA determined that the ongoing remedy for the Pit is functioning as intended. When the water approaches the Critical Level, additional testing will help to further refine plant performance. The 2015 five-year review of Butte area Superfund sites will be published later in 2015, and will be available online here and on the EPA’s Butte Superfund website.
Interested citizens should contact EPA with any questions or comments regarding the 2010 or 2015 site reviews.
Maps from the Montana Bureau of Mines & Geology (MBMG) showing Berkeley Pit-related alluvial and bedrock monitoring sites have been added to PitWatch.Org. View snapshots of the maps below, click on an image to view a larger version, or use the links at the bottom of the page to download printable .pdf versions of the maps.
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.
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.