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The waterfall on the southeast 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. Prior to Feb. 2013, the waterfall was created by Pit water returning after Montana Resources had removed most of the copper in the water in its precipitation plant. Photo by Justin Ringsak.

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. Photo by Justin Ringsak.
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. Photo by Fritz Daily.
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.
Water in the Berkeley Pit rising over time, 1979-2013. Photos from the Montana Bureau of Mines & Geology, Justin Ringsak, and Fritz Daily.

1982-2013: 31 years since pumps stopped

Over 31 years ago economic factors led the Atlantic-Richfield Corporation, or ARCO, now a subsidiary of British Petroleum, to cease mining operations at the Berkeley Pit in Butte, Montana. Underground mining had come to an end seven years earlier, but the underground pumps had continued to operate, pumping groundwater out from the mines and the Berkeley Pit.

The 1982 suspension of mining coincided with the stoppage of pumping, allowing groundwater to begin rising in the underground mines and eventually into the Berkeley Pit.

Water in the Berkeley Pit rising, 1979-2013. Photos from the Montana Bureau of Mines & Geology, Justin Ringsak, and Fritz Daily.
Water in the Berkeley Pit rising, 1979-2013.

With ARCO’s suspension of mining in the neighboring East Berkeley Pit (now known as the Continental Pit) on July 1, 1983, the future of mining on the Butte Hill was uncertain at best.

EPA LogoSoon after, the Berkeley Pit was classified as a federal Superfund site by the United States Environmental Protection Agency (EPA). According to the EPA, a Superfund site is an uncontrolled or abandoned place where hazardous waste is located, possibly affecting local ecosystems or people.

The end of mining at the Berkeley also marked the beginning of the Berkeley Pit lake we see today. 3,900 feet deep underground in the Kelley Mine , the pumps used to dewater the underground mines and the Berkeley Pit ran until April 23, 1982. Without pumping, the Berkeley Pit began to fill with water flowing in from both surface runoff and groundwater. Due to the natural geochemistry of the area and mining activities, the water is highly acidic and contains high concentrations of dissolved heavy metals.

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.

By 1985, ARCO had sold a portion of its holdings to Montana businessman Dennis Washington. Mining operations in the Continental Pit, as well as heap leaching of old Berkeley Pit leach pads, were resumed by his new company, Montana Resources.

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.

The Yankee Doodle Tailings Pond, part of the active Montana Resources mine that borders the Berkeley Pit, in 2008. Photo by Justin Ringsak.

Above the Pit: The Yankee Doodle Tailings Pond

Looking west from Rampart Mountain over the Yankee Doodle Tailings Pond, located north of the Berkeley Pit, in 2007.

Looking west from Rampart Mountain over the Yankee Doodle Tailings Pond, located north of the Berkeley Pit, in 2007.

North of the Berkeley Pit stands one of the largest earthen dams in the United States. The dam, constructed from waste rock mined out of the Berkeley Pit and, in more recent years, the Continental Pit, stands over 650 feet (200 meters) tall. It holds back the Yankee Doodle tailings impoundment, also known as the Yankee Doodle Tailings Pond. As part of active mining operations, Montana Resources pumps tailings and water to the Yankee Doodle Pond. Lime rock is also added, resulting in a non-acidic pH (above 7.0) tailings slurry, thus mitigating or avoiding the phenomenon of acid mine drainage.watch T2 Trainspotting 2017 film now

The Yankee Doodle Tailings Pond, part of the active Montana Resources mine that borders the Berkeley Pit, in 2008. Photo by Justin Ringsak.

The Yankee Doodle Tailings Pond, part of the active Montana Resources mine that borders the Berkeley Pit, in 2008.

Tailings particles settle out on the south portion of the ponds. Snowmelt runoff from upper drainages also mixes with the water at the north end of the pond. These factors result in clear water with an alkaline (or non-acidic) pH and very low concentrations of dissolved metals at the north end of the pond.

When mining operations were suspended from 2000 through 2003, water was no longer pumped to the Yankee Doodle site, and the tailings deposited there began to dry out. In response to concerns from the community over dust clouds blowing in the vicinity of the tailings pond, Montana Resources spread about 1.5 million tons of rock, approximately 18 inches deep, over about 506 aces at the tailings impoundment site to keep the dust down. Since the mine reopened, the tailings deposit has remained wet, resulting in no further instances of tailings-dust clouds on Butte’s northern horizon.

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.

43 billion gallons and counting: Where does it come from?

Water in the Berkeley Pit rising over time, 1979-2013. Photos from the Montana Bureau of Mines & Geology, Justin Ringsak, and Fritz Daily.

When ARCO suspended underground pumping operations in 1982, groundwater levels on the Butte Hill began to rise. Nineteen months later the water level in the underground workings and surrounding bedrock reached the bottom of the Pit, allowing bedrock groundwater to start filling the Pit void.

The Berkeley Pit in 1982. The water seen here is surface runoff flowing into the Leonard mine shaft to the right at the Pit bottom.
The Berkeley Pit in 1982. The water seen here is surface runoff flowing into the Leonard mine shaft to the right at the Pit bottom.

Prior to that time alluvial groundwater seeped into the Pit from the east and south walls, beginning to fill the Pit lake. ARCO also diverted water from its mining operations (leach pad water, Continental Pit, Horseshoe Bend, etc.) into the Pit following the 1983 shutdown of their entire Butte operations.

When Montana Resources began operations in 1986 a number of these surface water sources were diverted away from the Pit, however, the Horseshoe Bend water continued to flow into the Pit until April 1996 when it was incorporated in Montana Resource’s mining operations for treatment and disposal in the Yankee Doodle Tailings Dam.

When Montana Resources suspended mining operations from 2000 through 2003, about 7.5 billion gallons of water, or an average of 6 million gallons per day, went into the Pit. Of this total, an average of 3.4 million gallons per day came from rising groundwater flows in the underground mine workings and surface stormwater flow. An average of 2.6 million gallons per day came from the Horseshoe Bend drainage. Montana Resources also diverted water from the Continental Pit into the Berkeley Pit for containment during their suspension.

Since the Horseshoe Bend Water Treatment Plant began operating in 2003, water flows from the Horseshoe Bend drainage have been diverted to the treatment plant. After treatment, this Horseshoe Bend water is entirely recycled or consumed in mining operations, or, in other words, no water is discharged off of the site.

About 2.6 million gallons per day from groundwater and stormwater still flow into the Pit, contributing to the rising level there. Eventually, when the water level approaches the Critical Level of 5,410 feet above sea level, water will be pumped from the Berkeley Pit and treated at the Horseshoe Bend facility. Present projections put this date around 2023. Having the plant in place provides assurance that the capability to manage Berkeley Pit water levels is there when it becomes necessary to treat Pit water.

This 2006 image from the NASA Earth Observatory shows the Berkeley Pit and surrounding area after the construction of the Horseshoe Bend Water Treatment Plant and after the resumption of mining at the Continental Pit.
This 2006 image from the NASA Earth Observatory shows the Berkeley Pit and surrounding area after the construction of the Horseshoe Bend Water Treatment Plant and after the resumption of mining at the Continental Pit.