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The first stage reactor tank at the Horseshoe Bend Water Treatment Plant, which will eventually treat Berkeley Pit water. Photo from the EPA Five Year Review Report (2011) for the site.

Horseshoe Bend Water Treatment Plant Performance Test (2007)

The first stage reactor tank at the Horseshoe Bend Water Treatment Plant, which will eventually treat Berkeley Pit water. Photo from the EPA Five Year Review Report (2011) for the site.
The first stage reactor tank at the Horseshoe Bend Water Treatment Plant, which will eventually treat Berkeley Pit water.

A performance test of the Horseshoe Bend plant was completed in November 2007, as mandated by the Record of Decision. Based on the performance review, water discharged from the plant meets all discharge standards for contaminants of concern set by the EPA. Additional adjustments still need to be made to address pH. In general, plant operations are going as expected.

The following is EPA’s assessment of the performance test, excerpted from the 2011 Five Year Review Report on the site, pages 43-45:

System Operations/O&M

The influent water for the 2007 Performance Test consisted only of HSB (Horseshoe Bend) water, as water from the Berkeley Pit is not yet required to be pumped and treated in the plant. The results of this test indicated that all final discharge limits could be met except for effluent pH. In order to meet the cadmium limit, the pH in the final treatment stage needed to be raised to 11.2.

Consequently, the effluent pH did not drop to below the discharge standard of 9.5 through natural aeration. Methods for lowering the pH of the effluent to below the discharge standard of 9.5 have been evaluated on a conceptual level, but will require a more formal analysis before final discharge to Silver Bow Creek is necessary.

The results of the performance test also determined a need to revisit the applicability of the final performance standard for beta/photon emitters, which is expressed as a dose of 4 millirem per year (mrem/yr). There are approximately 179 radionuclides that need to be analyzed in order to calculate the actual beta/photon emitter dose, bringing into question the practicality of the laboratory procedures needed to meet the beta/photon standard.

Results of a 2007 performance test of the Horseshoe Bend Water Treatment Plant at the Berkeley Pit, taken from the EPA Five Year Review Report on the site (2011).
Results of a 2007 performance test of the Horseshoe Bend Water Treatment Plant at the Berkeley Pit, taken from the EPA Five Year Review Report on the site (2011). Click on the image to view a larger version.

Opportunities for Optimization

Based on the results of the most recent performance test and plant operations and maintenance activities, there are several areas where optimization is needed. They include:

  1. effluent pH adjustment (when discharge to Silver Bow Creek is necessary),
  2. equipment and pipeline scaling from gypsum and
  3. equipment corrosion issues.

Each of these issues is undergoing various levels of engineering evaluation and testing to determine the best long term course of action.

Early Indicators of Potential Issues

There are no indications of potential equipment problems or operational problems that would put the protectiveness of the HSB WTP at risk. However, it is unknown whether discharge of treated water saturated with gypsum will adversely affect aquatic life in Silver Bow Creek.

It is also possible that delayed precipitation of gypsum could cause exceedances of the TSS discharge standard. This issue will require further evaluation before discharge occurs.

Implementation of Institutional Controls and Other Measures

Based on the information obtained from a review of the site documentation in the administrative record and from interviews with the site RPM and other stakeholders, the ICs implemented for the BMFOU continue to effectively protect the remedy and the public. Publications such as the PITWATCH, inform the public as to progress on the BMFOU. The current DNRC order prohibits use of the BMFOU aquifer for domestic use. Enforcement and monitoring of this prohibition is important.

Butte, Montana, mine flooding west camp wells, shafts and area of 1960s flooding. The west camp groundwater system is monitored and maintained separately from the Berkeley Pit and connected east camp mines.

West Camp also part of mine flooding site

A timeline of the history of the West Camp portion of the greater Butte, Montana Superfund site, which is monitored and managed separately from the Berkeley Pit and connected East Camp mines.
A timeline of the history of the West Camp portion of the greater Butte, Montana Superfund site, which is monitored and managed separately from the Berkeley Pit and connected East Camp mines. Click on the image to view a larger version.

The anatomy of the thousands of miles of tunnels beneath the Butte Hill is daunting to consider and little understood by many. Important details, such as the distinction between the “West Camp” and “East Camp”, can cause consternation for many a curious observer.

The Berkeley Pit and surrounding underground mine workings and bedrock wells are referred to as the “East Camp”, and are separate from the “West Camp”, which is located more to the south and west. The Camps essentially refer to two water systems. In the East Camp, surface and underground water flows to the lowest point in the system, namely, the Berkeley Pit. The West Camp, whose waters never reach the Berkeley, is another story.

The West Camp lies southwest of the Berkeley Pit/East Camp drainage and includes the Travona, Emma, and Ophir mine workings. Just as in the East Camp, the groundwater in this area has been closely monitored since the suspension of pumping in 1982 to ensure that water levels do not rise high enough to significantly impact surrounding aquifers—in this case, 5,435 feet is the magic number.

Since November 1989, pumping operations have kept West Camp water below this level. In the late 1950s, the West Camp mine workings were sealed off from the rest of the shafts and drifts on the Butte Hill by a series of barriers, or bulkheads—some made of wood, some cement.

Three main cement bulkheads block the connections between the Emma in the West Camp and the Original mine in the East Camp at the 1,600-foot level, and between the Emma and Colorado mines at the 1,400- and 1,000-foot levels.

Anaconda Company crews originally installed the bulkheads for two main reasons: 1) there were no plans to continue mining in the West Camp, and 2) they wanted to increase the efficiency of continuing mining operations in the other underground mines of the East Camp and the Berkeley Pit.

The bulkheads allowed the company to eventually reduce the volume of both groundwater pumped out from underground shafts and the area underground that required fresh air to be pumped in. However, even after the bulkheads were installed, water was pumped out of the West Camp Emma shaft until 1965.

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. Photo by Justin Ringsak.

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. Photo by Justin Ringsak.
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.

A clarifier, drained for maintenance, at the Horseshoe Bend Water Treatment Plant. The plant will eventually be required to treat water from the Berkeley Pit. Photo from the EPA Five Year Review Report (2011) for the site.

Treatment technology thoroughly studied

The Berkeley Pit is literally world famous in the mine waste cleanup industry, and the final technology used in the Horseshoe Bend Water Treatment Plant, a High Density Solids (HDS) process, was selected after an assessment of tests and the demonstrated effectiveness of cleanup technologies from research groups around the world.

A clarifier, drained for maintenance, at the Horseshoe Bend Water Treatment Plant. The plant will eventually be required to treat water from the Berkeley Pit. Photo from the EPA Five Year Review Report (2011) for the site.
A clarifier, drained for maintenance, at the Horseshoe Bend Water Treatment Plant. The plant will eventually be required to treat water from the Berkeley Pit.

The Horseshoe Bend facility currently treats water from Horseshoe Bend, and will eventually be used to treat water from the Berkeley. The treatment plant utilizes a two-stage lime (calcium hydroxide) precipitation process in combination with HDS technology. Lime, aeration and polymer addition remove metals from the water. The fully automated facility generates about 10 times less sludge than a conventional lime treatment plant. HDS technology produces denser sludge through a recycling process in which the sludge generated in the water treatment process is sent through the system many times.

The process resembles a snowball effect. Each time sludge particles are sent through, they grow in size as new particles attach to the old ones. At the end, the final sludge product – like a watery mud – is much denser.

Horseshoe Bend Treatment Plant Sludge Reduction. Graphic by Justin Ringsak.
Horseshoe Bend Treatment Plant Sludge Reduction

The relatively low final volume of sludge – currently about 40,000 gallons per day in a 220,000-gallon slurry – is deposited in the Berkeley Pit, eliminating the need for a land-based sludge repository. Test results indicate that sludge disposal in the Pit may raise the pH of the water over a 10- to 20-year period, which could potentially decrease treatment costs for Pit water.

Due to the design of the system, treated water can easily be used in the concentration process at the adjacent Montana Resources mine, or, in the event that the mine ceases operations, discharged to Silver Bow Creek upstream from the confluence with Blacktail Creek near Montana Street. The volume of treated water should add about 4.5 cubic feet per second (cfs) of flow to the creek, which represents about a 50 percent increase to the base flow of 10 cfs.

A performance test of the Horseshoe Bend plant was completed in November 2007, as mandated by the Record of Decision. Based on the performance review, water discharged from the plant meets all discharge standards for contaminants of concern set by the EPA. Additional adjustments still need to be made to address pH. In general, plant operations are going as expected.

What is going to happen to the old creek bottom that runs from Continental Drive to Montana Street? Is it safe?

Before mining on the Butte hill and the development of the Berkeley Pit, that old creek bottom was the main channel of Silver Bow Creek, and recent studies indicate the creek corridor and surrounding land contain mine tailings. Today the drainage is referred to as the Metro Storm Drain. A French Drain collects contaminated groundwater along the channel, preventing it from contaminating Blacktail Creek or downstream reaches of Silver Bow Creek.
Superfund Operable Units in the greater Butte area. Map from the EPA Record of Decision (ROD) for the Butte/Silver Bow Creek Superfund Site (2006).

What is an ‘Operable Unit’?

An operable unit is a subsection of a larger EPA Federal Superfund site. There are four Operable Units (OUs) in the Butte mining district.

Superfund Operable Units in the greater Butte area. Map from the EPA Record of Decision (ROD) for the Butte/Silver Bow Creek Superfund Site (2006).
Superfund Operable Units in the greater Butte area. Map from the EPA Record of Decision (ROD) for the Butte/Silver Bow Creek Superfund Site (2006). Click on the image to view a larger version.
  •  The Butte Mine Flooding Operable Unit, which includes the Berkeley Pit, the hydraulically-connected underground mine workings associated with the historic East Camp and West Camp tunnel systems, associated bedrock, and alluvial aquifers. The area covers approximately 23 square miles.
  • Butte Priority Soils is a five square mile area that includes the town of Walkerville, along with the part of the Butte Hill that is north of Silver Bow Creek, west of the Berkeley Pit, and east of Big Butte. It also includes a section of land extending south from Silver Bow Creek to Timber Butte. This Operable Unit includes residential yards, mine dumps, contaminated railroad beds, and stormwater drainages on the Butte Hill and in Walkerville.
  • Silver Bow Creek/Streamside Tailings Operable Unit, which follows Silver Bow Creek from just below the historic Colorado Tailings deposit in Butte and 25 miles downstream to the Warm Springs Ponds. The area includes Silver Bow Creek itself, as well as the adjacent mining wastes deposited along the creek bank and nearby floodplain, and railroad embankments adjacent to the stream that contain mining wastes.
  • West Side Soils Operable Unit includes lands that fall outside of the Butte Priority Soils OU. There are approximately 1,500 mine waste dumps located north and west of Butte. The dumps have not been sampled. A schedule for investigating this OU and selecting a remedy has not yet been set.

There are numerous additional operable units in the greater Clark Fork River Superfund site, which stretches from Butte and 120 miles downstream to the Milltown Dam near Missoula.

The Butte/Silver Bow Creek Superfund Site and separate Operable Units, in the context of the greater western Montana environment that was impacted by historic mining and smelting damages. Cleanup is ongoing across the basin. Map from the EPA Five Year Review of the Butte/Silver Bow Creek Superfund Site, Part 6: Butte Priority Soils Operable Unit, Figures.
The Butte/Silver Bow Creek Superfund Site and separate Operable Units, in the context of the greater western Montana environment that was impacted by historic mining and smelting damages. Cleanup is ongoing across the basin. Map from the EPA Five Year Review of the Butte/Silver Bow Creek Superfund Site, Part 6: Butte Priority Soils Operable Unit, Figures. Click on the image to view a larger version.

For more information on non-Berkeley Pit Superfund sites in Butte and the Clark Fork Basin on western Montana, visit the Citizens Technical Environmental Committee (Butte CTEC) website, or the Clark Fork Watershed Education Program (CFWEP) website.

This image from the Montana Bureau of Mines & Geology illustrates the connections between historic underground mining tunnels and the Berkeley Pit. After groundwater pumping ceased in 1982, the tunnels, and eventually the Pit, began to fill with water.

Mine Resumption Affects Treatment Plant Operations

This image from the Montana Bureau of Mines & Geology illustrates the connections between historic underground mining tunnels and the Berkeley Pit. After groundwater pumping ceased in 1982, the tunnels, and eventually the Pit, began to fill with water.
This image from the Montana Bureau of Mines & Geology illustrates the connections between historic underground mining tunnels and the Berkeley Pit. After groundwater pumping ceased in 1982, the tunnels, and eventually the Pit, began to fill with water. Click on the image to view a larger version.

Since the last issue of PITWATCH, Montana Resources has decided to resume operations. With the mine going again and with the water treatment plant coming on line, there have been many questions from the community. Here are some answers to reader questions.

Q: How much total water went into the Berkeley Pit since the suspension of mining at Montana Resources?
A: About 7.5 billion gallons of water or an average of 6 mgd has gone into the Pit since MR suspended operations. An average of 3.4 mgd of this total was from the underground workings and storm water flow. An average of 2.6 mgd of this total was from the Horseshoe Bend discharge.

Q: How much water will go into the Pit once mining operations resume completely and the water treatment facility is operating?
A: The Horseshoe Bend drainage flow will be treated in the new treatment plant, and presently, this water will be entirely consumed in the mining operations. The remaining 3.4 mgd of flow from the underground workings and storm water flow will still flow into the Pit contributing to the rising level there. Eventually, when the water level approaches 5,410′ above sea level (expected about 2018), water will have to be pumped from the Berkeley Pit and treated at the Horseshoe Bend facility. Having the plant in place provides assurance that the capability is there when it becomes necessary to treat Pit water.

Q: Where will the treated water go?
A: Current plans are to treat the entire Horseshoe Bend drainage flow at the treatment plant, and then route all of the treated water to the concentrator for use in mine operations. As a result, and for as long as the treated water is used in the mining circuit, there will be no discharge off-site. In the event the mine was to suspend operations again, Horseshoe Bend drainage water would be treated to discharge standards at the plant. Then it would be transported by a pipeline, being constructed along the historic Silver Bow Creek channel (Metro Storm Drain), to its confluence with Blacktail Creek, just west of the Visitor’s Center on George Street in Butte, Montana.

Controlled groundwater areas for Butte Superfund sites, including Superfund Operable Unit borders and monitoring points, from the 2011 EPA Five Year Review on Butte/Silver Bow Creek.

Priority Soils: The Other Superfund cleanup project in the Butte area

Controlled groundwater areas for Butte Superfund sites, including Superfund Operable Unit borders and monitoring points, from the 2011 EPA Five Year Review on Butte/Silver Bow Creek.
Controlled groundwater areas for Butte Superfund sites, including Superfund Operable Unit borders and monitoring points, from the 2011 EPA Five Year Review on Butte/Silver Bow Creek. Click on the image to view a larger version.

When the Horseshoe Bend Water Treatment Plant starts operating later this year, the contaminated waters from the Berkeley Pit and underground mines should be managed safely for years to come. In the meantime, another cleanup project – called the Butte Priority Soils Operable Unit – is just now reaching its critical decision point (i.e., the Record of Decision, scheduled by the end of 2003). Over the next several months, there will be a series of public meetings about this project, and the Committee would like to share information to help citizens understand the issues and encourage participation in the decision-making process.

Where is the Butte Priority Soils cleanup site?

Generally, the project includes the residential yards and mine dumps on the Butte Hill and in Walkerville, and the water drainages weaving down the Hill to Silver Bow Creek. The site is about five square miles and includes most of the urban area from Walkerville on the north to Silver Bow Creek on the south, along with the Clark Tailings below Timber Butte.
It’s also important to understand what the Priority Soils does NOT include. It’s separate from the Berkeley Pit and underground mine flooding project, which, as we’ve reported in PITWATCH for several years, is the responsibility of Arco and Montana Resources. The Priority Soils is also separate from the Montana Pole cleanup and the Streamside Tailings project along Silver Bow Creek, both of which are ongoing and the responsibility of Montana Department of Environmental Quality. In the big picture, all these cleanup activities will have to fit together, but for now, Priority Soils stands alone.

What is the cleanup task?

The job is two-fold:

  1. to eliminate direct contact with mine waste on the Hill, thus protecting human health; and
  2. to prevent the heavy metals in those mine waste materials from getting into storm water and groundwater and finding their way to Silver Bow Creek, thereby protecting life in the stream and the DEQ’s $85 million creek cleanup project.

Is some work already complete?

Yes. In fact, a substantial amount of the cleanup of Priority Soils has occurred – about $50 million of work by current estimates. Over the past 15 years, several projects have been completed, with the understanding that all this work will be reviewed as part of the final decision. Major projects include: the Alice Pit/Dump (1998); several areas in Walkerville (1988, 1994, 2002); the Missoula Gulch, Buffalo Gulch and Kelley ditches and retention ponds (1997-99); railroad corridors (2001-03); and Lower Area One, including the reconstructed Silver Bow Creek, the Colorado Tailings removal, and the Clark Tailings project (1993-2000).

In all, more than 175 mine dumps covering more than 400 acres have been partially removed and capped, and more than 180 residential yards have been cleaned up (lead soil removals). The caps generally consist of placing 18″ of clean soil materials with organic amendments over the wastes and planting native vegetation to hold the soil in place and minimize erosion. To complement the caps, a system of storm water collection facilities – the new drainage ditches and retention ponds – has been installed to collect water that may still contain heavy metals and prevent those contaminants from reaching Silver Bow Creek.

What Other Areas and Issues Must Be Addressed?

The major cleanups still ahead include the Parrot Tailings near the Civic Center and the Metro Storm Drain corridor, which once was the historic Silver Bow Creek channel that flowed through town, and a large area north of the Kelley Mine, surrounding the Mountain Con Mineyard and the Granite Mountain Memorial.

In addition to cleanups, other issues include deciding what type of water treatment system should be used to ensure groundwater, surface water or storm water leaving the area will not pollute Silver Bow Creek heading west of town. Another big decision will be to determine whether the projects already completed were done satisfactorily and will be permanent, or whether additional work is needed.

Perhaps the most important issue is to determine how the reclaimed areas and water management facilities will perform in the long term and be effectively maintained. As part of the Record of Decision, it will be critical to set the right performance standards for treatment and long-term care, and then determine how much money it will take to get the job done properly.

Is Butte on the hook for the Priority Soils cleanup?

Unlike every other cleanup around Butte, where the citizens have been protected from any Superfund liability, Butte-Silver Bow was named as a Potentially Responsible Party or PRP to conduct the Priority Soils cleanup. In 1990, EPA decided that since the publicly owned storm water system carried wastes off the Hill to the creek, the community was partly liable for the problem.
However, Arco is also a PRP for Priority Soils, and for the most part over the past 15 years, Arco has paid all costs for cleanup work. As part of the upcoming Record of Decision and then a Consent Decree for the Priority Soils project, Butte’s “share” will be determined.

For much more on Butte Priority Soils and other area Superfund projects, visit the Citizens Technical Environmental Committee (Butte CTEC) website.