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Drones in the works for water quality sampling
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.
Read more on the project from The Montana Standard.
Due to safety concerns related to landslides (or sloughs) along the Pit rim, the Montana Bureau of Mines and Geology has not taken this research boat out on the Pit lake for water quality sampling since 2012.
Following up on the EPA's 2010 five-year review
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
This photo from EPA's 2010 five-year review report shows gypsum scale build up on the lip of the treatment plant clarifier overflow.
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.
EPA Documents
Berkeley Pit Management
Five Year Review
Montana Bureau of Mines and Geology (MBMG)
Whole Effluent Toxicity (WET)
Berkeley Pit slough
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.
This photo from July 2013 shows the rim of the Berkeley Pit were a slough deposited surface material into the Pit lake in Feb. 2013. Photo by Fritz Daily.
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.
Click here for more information about the Critical Water Level.
What was the waterfall on the northeast wall of the Pit?
The waterfall on the northeast rim of the Berkeley Pit, near the Horseshoe Bend Water Treatment Plant as it appeared in 2009. The waterfall has stopped flowing since a Feb. 2013 slough from the Pit wall knocked out a pump used for Montana Resources copper precipitation plant.
In past years, many visitors were curious about the waterfall visible from the Pit Viewing Stand. Montana Resources pumped water out of the Berkeley Pit, then removed the copper from that water before returning it to the Pit (click here for more information on mining copper from Pit water). The waterfall was created by this returning water. However, this activity stopped after the 2013 slough (click here for more information on the slough), so there is no longer a waterfall on the Pit rim.
The northeast rim of the Berkeley Pit in July 2013, after a Feb. 2013 slough from the Pit wall knocked out a pump used for Montana Resources copper precipitation plant. When the precipitation operation was ongoing, Berkeley Pit water was pumped to a precipitation plant where copper was removed from the water. The water was then returned to the Pit, creating the waterfall seen in past years.
What's in the Berkeley Pit water?
The water level at the Berkeley Pit has been recorded every month for more than 23 years. In addition to that monitoring, scientists at the Montana Bureau of Mines and Geology have been sampling and analyzing water from the Berkeley Pit twice a year for its chemical composition and physical properties.
In the Berkeley Pit, samples are taken from anywhere between three to nine different depths and analyzed for various dissolved chemicals.
Berkeley Pit water quality has shown changes over time. It is regularly monitored by the Montana Bureau of Mines & Geology. The reddish color typically observed is due to high concentrations of iron solids.
Water quality conditions, such as temperature, pH, specific conductance, and dissolved oxygen, are also measured at five- to ten-foot intervals from the surface to a depth of 600 feet. These same conditions are also measured at a depth near the Pit bottom.
In past years, the Berkeley Pit was a chemically layered system, which means that the chemistry of the water changed with depth. The brownish-red water at the surface was actually the least contaminated water in the pit, and the lower layer the worst water quality. The color changed as well, going from brownish-red on top to bluish-green at the bottom.
At a certain depth, the chemistry of the water changed so rapidly that it formed a chemical boundary scientists refer to as a chemocline. Water above the chemocline was chemically lighter, in other words, less dense, than the water below. The layering of the two waters is similar to oil floating on water. The water above the line was also less acidic (higher pH), with lower concentrations of metals.
A chemocline, or a difference in water chemistry depending on water depth, was seen in the Berkeley Pit prior to about 2012. Mixing of the water in the Pit lake over time has caused the water chemistry to become more uniform. Click on the image to view a larger version.
Due to mixing in the Berkeley Pit lake over time, this previously layered system disappeared around 2012, and the Pit water has since become more uniform.
Montana Bureau of Mines & Geology
Specific Conductance
Could the Berkeley Pit ever overflow?
The Berkeley Pit will never overflow. In 1994 the EPA established the Critical Water Level (the maximum level the water will be allowed to reach) at 5,410 feet above sea level, which is one hundred feet below the rim.
Elevations above sea level for Berkeley Pit water and surrounding Butte, Montana landmarks. Image from Google Earth. Click on the image to view a larger version.
Water levels are regularly monitored at the Pit, in historic underground mines, and in wells surrounding the Pit. Failure to keep the water below 5,410 feet would result in steep fines for the companies responsible for the site, BP-ARCO and Montana Resources.
In addition to careful monitoring, the Horseshoe Bend Water Treatment Plant was constructed to make sure water in the Pit remains below 5,410 feet. Pit water will be pumped, treated, and discharged when the level nears the critical point.
Even if the water was allowed to rise unchecked, it would still never reach the rim. The groundwater flow would reverse direction and, instead of flowing toward the Pit, as it does now, the water would flow away from the Pit, underground into the sandy aquifer beneath Butte's valley.
Due to the underground flow, Pit surface water would never reach the rim. Considering the federal orders, potential fines, and frequent monitoring, Pit water will not rise unchecked.
Critical Water Level
How is the Horseshoe Bend Water Treatment Plant operating?
The plant treats about 3.4 million gallons of water per day. This water currently comes from the Horseshoe Bend drainage. Treated water is used in Montana Resources mining operations.
Sludge from the treatment process is returned to the Pit at a rate of 250,000 gallons per day. No water or waste leaves the Berkeley Pit or mine site.
Water treatment plant working as expected
The Horseshoe Bend Water Treatment Plant, completed in 2003, captures surface water to slow the rate of fill of the Berkeley Pit lake. In the future, the plant will capture and treat water to prevent Pit water from rising further.
Looking northeast from the Berkeley Pit viewing stand, visitors can see one of the most important components in the future management of the Pit: the Horseshoe Bend Water Treatment Plant. Sitting on four acres near the former McQueen neighborhood, about 600 feet east of the Berkeley Pit, the treatment plant was constructed in 2002-2003. It sits on native land that is very stable, and the plant was built to withstand the maximum probable earthquake.
The facility was designed to treat up to seven million gallons per day, or about 5,000 gallons of water per minute. The facility cost approximately $18 million to build, and, depending on how much water is treated, operating expenses run about $2 million per year.
Once the Berkeley Pit water comes online, which is projected to happen in 2023, annual operation and maintenance costs could be as high as $4.5 million. Under the terms of the 2002 Consent Decree negotiated with the government, BP-ARCO and Montana Resources have agreed to provide financial assurances to pay operation and maintenance expenses in perpetuity. The two companies also paid all construction costs for the facility.
The actual construction of the treatment plant was a massive undertaking. It is estimated that workers put in 125,000 hours of total labor, and the facility also required more than 4,500 cubic yards of concrete.
The general construction contractor and subcontractors were all from Montana, with several from Butte, and, during the course of construction, they reported no safety incidents of any kind.
As per the schedule listed in the 1994 EPA Record of Decision and included in the 2002 Consent Decree, based upon current water level projections, a review of the Horseshoe Bend Water Treatment Plant design and operation would begin in 2019. Any necessary upgrades would have to be completed by 2021, two years before Pit water itself is currently projected to be pumped and treated in 2023.
In November, 2007, a performance review of the Horseshoe Bend plant was completed by Montana Resources, ARCO, and North American Water Systems, with cooperation from the Montana Bureau of Mines & Geology, the Department of Environmental Quality, and the EPA.
The performance test was undertaken to ensure that the treatment system is capable of meeting the water quality standards set in the Consent Decree for the site. For this test, only water from the Horseshoe Bend drainage was treated, as water from the Pit is not yet required to be pumped and treated at the plant.
The test began on November 18, 2007, and continued for 72 hours. All of the water quality standards for contaminants of concern were met. Additional adjustments still need to be made to address pH. For this test, the pH was kept at a high (basic or alkaline) level in order to effectively remove contaminants of concern and meet water quality standards.
The optimization of the plant in the future may result in a lower pH. Additionally, methods of adjusting the pH prior to discharge to Silver Bow Creek have been evaluated conceptually. Any method of adjusting the pH will be formally evaluated, if necessary, before any water from the plant is discharged to Silver Bow Creek.
Berkeley Pit Viewing Stand
Contaminants of Concern
Management Costs
North American Water Systems
Silver Bow Creek