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.
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.
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.
Summary of 2012 (published in March 2013) monitoring data related to the Butte Mine Flooding Consent Decree, which includes the Berkeley Pit and associated workings, from the Montana Bureau of Mines & Geology.
Tsunamis, volcanoes and earthquakes in recent months have created an increased interest in seismic activity. Many readers have written, called, or stopped by questioning what will happen to the Berkeley Pit if an earthquake occurs in Butte, Montana. To help answer these questions, local experts were asked to explain the likelihood of an earthquake and what effect it would have on the Berkeley Pit.
Probability of an Earthquake in Butte
Mike Stickney, Director of the Earthquake Studies Office at the Montana Bureau of Mines and Geology says that Butte is not likely to suffer a severe earthquake anytime soon. Large earthquakes are certainly possible in western Montana as demonstrated by the 1959 Hebgen Lake earthquake (magnitude 7.3), but are most likely to occur in the more seismically active regions located to the north, east, or southeast of Butte. The state of Montana is unlikely to experience earthquakes larger than the 1959 earthquake because the faults are not large enough to produce earthquakes greater than magnitude 7.5.
Stickney also explained that Butte has been monitored closely for seismic activity over the past 25 years. There has never been any significant seismic activity recorded that suggests the nearby faults to be active enough to cause a large earthquake. Most seismic activity that registers in the Butte area is caused by blasting at the open mine site, and very minor underground subsidence, especially near the old block caving zones under the Kelley Mine.
Effects of an Earthquake
Even assuming a worst-case earthquake scenario, the Berkeley Pit would not overflow. Experts suggest that there would be far more damage to buildings and other structures in Uptown Butte than would be caused by adverse impacts from the waters in the Berkeley Pit.
Studies show that the Yankee Doodle Tailings Pond dam would withstand at least a 6.5 magnitude quake. It can also be assumed from similar studies that such a quake could cause some sloughing on the pit walls, but the resulting movements would not discharge enough rock and materials to cause the water in the pit to overflow.
Sloughing and Landslides
Although earthquakes are not likely to be a problem, landslides and sloughing of the Pit could occur. The majority of the Berkeley Pit walls are made of “solid” bedrock. However, the southeast wall is composed of “loose”silts, sands and gravels, and this is the area where sloughing is most likely to occur, with or without a major earthquake.
In September 1998, about 1.3 million cubic yards of “loose” alluvium on the southeast wall sloughed into the Pit. This event caused a 3-foot rise in the water level and surface waves greater than 20 feet.
The water rise associated with any pit wall sloughing would ultimately depend on the volume of material that breaks free and displaces the water. But it should be noted there is enough space for more significant events. For example, there is more than 150 feet between the current Pit water level (5,252′ above sea level) and the Critical Water Level (5,410′), and there is another 100′ feet up to the rim of the Pit.
If an earthquake were to occur, the effects of seismic activity at the Berkeley Pit would be the least of Butte’s worries. Since a large earthquake is not likely anytime soon, and because landslides are relatively manageable, the public should not be overly concerned. There will probably continue to be some sloughing on the benches and old roads, but not enough to cause the Pit water to rise more than a few feet.
In the last PITWATCH, we described Berkeley Pit-related research efforts that have been undertaken locally at Montana Tech, the Montana Bureau of Mines and Geology, and MSE. But Butte residents may not be aware that the Berkeley Pit is literally world-famous in the mine waste cleanup industry. Research groups around the world have used the water to perform tests and demonstrate the effectiveness of their technologies.
The Montana Bureau of Mines and Geology is in charge of handling requests for Berkeley Pit water, and in the past 10 years, the Bureau has shipped over 150 batches (about 5 gallons each) of Pit water to researchers around the globe. Just in the last year, the Bureau has shipped water to the following groups:
• Virotec International (Australia, seawater-neutralized bauxite water treatment process)
• Electrometals Technologies (Australia, electrowinning process for copper recovery)
• Biomet Mining (Canada, biosulfide process for copper and zinc recovery)
• University of Cincinnati (Cincinnati, Ohio, sulfate-reducing bacteria process for copper and zinc recovery)
• Ion Separations (Virginia City, Montana, proprietary water treatment/metals recovery process)
• MSE Technology Applications (Butte, Montana, evaluation of returning settled slurry from lime treatment to the Berkeley Pit)
• U.S. Geological Survey (Kearneysville, West Virginia, water treatment process using limestone in carbon dioxide-pressurized reactor)
• Notre Dame University (South Bend, Indiana, testing of biomass materials for absorption of metals)
• Eltron Research (Boulder, Colorado, electrolytic metals removal process)
• Seaspan International (Canada, proprietary process)
• Montana Tech (Butte, Montana, various projects evaluating cleanup options)
Since the State of Montana considers Berkeley Pit water to be hazardous waste, shipments of the water must comply with EPA and Department of Transportation requirements.
The Montana Bureau of Mines and Geology has issued a 15-year report containing water-level data collected from all of the mine flooding monitoring points from 1982 to 1997. The comprehensive document also includes numerous graphs, maps, and historic photographs, plus explanations of the various areas that comprise the Butte Mine Flooding Superfund Site. To request a copy, call 496-4167. In 1999, the Bureau will release a companion report on water quality in these monitoring wells and shafts. Both reports will be updated annually.