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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.

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. Photo by Justin Ringsak, 2009.

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.

Berkeley Pit Facts 2013. Graphic by Justin Ringsak.

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. Photo by Justin Ringsak, 2009.
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 2011. Since that time, mixing of the water in the Pit lake has  caused the water chemistry to become more uniform. Graphic by Justin Ringsak.
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.

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.

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.

Montana Resources copper precipitation plant adjacent to the Berkeley Pit. A 2013 slough of material from the Pit wall into the water knocked out the 'precip' pump, and precip operations have since ceased. In precipitation, the copper-rich water is pumped over scrap iron, and, in a replacement reaction, the copper solidifies as sludge, while iron takes its place in the water. The water was returned to the Pit by gravity flow, thus not increasing or decreasing the total volume of Pit water. Photo by Justin Ringsak.

Montana Resources mines the water

The Past

Butte’s Memory Book tells the story of Jim Ledford, a miner who lived in a log cabin below the famed Anaconda Mine. Alongside his cabin was an old dump containing scrap iron and tin cans. Mine water ran downhill through the dump, and Ledford noticed a heavy sludge formation. Out of curiosity, he had the sludge assayed and learned that it was 98-percent-pure copper.

Legend has it that Ledford told no one about his discovery. Instead, he quietly secured a one-year contract to handle the Anaconda mine water. He set up tanks, filled them with scrap metal, and ran the water through them. The undated account said his efforts earned him $90,000 that first year. His contract was not renewed.

A professional paper from a 1913 Butte mining conference tells a slightly different story. It states that in 1890 a William Ledford obtained a contract to handle water from the St. Lawrence Mine. The story ends the same, however, once the Anaconda Company realized the value of mine water, it built its own copper tanks, and copper precipitation using scrap iron became standard operating procedure. Thanks to Al Hooper for loaning his copy of the 1913 mining conference proceedings.

A third version of the story was relayed in the April 18, 1906 edition of The Montana Standard as part of a series of articles on “Queer Spots in Butte.” According to this version, in 1888 an old Welshman named Morgan who lived on the Butte Hill noticed copper dust left behind from tin cans thrown into a gully filled with runoff water from the mines. Morgan had the dust assayed and learned that it was almost pure copper. He experimented with the concept and developed a rudimentary precipitation plant, but died a few months after he had his plant operating successfully.

The story goes on to claim that a Butte Dutchman named Fred Miller dug holes in the side hill in the gulch below the St. Lawrence mine. He filled these holes with tin cans and scrap iron, allowing mine runoff water to flow over them.

For the next two or three years, he would collect the resulting copper dust every few weeks. Miller fraudulently claimed a monopoly on this system, and on several occasions tried to bluff out others on the hill who were experimenting with precipitation. The story notes that at this point William Ledford secured a lease to the St. Lawrence water, and Miller’s heyday came to an end.

The Present

Montana Resources copper precipitation plant adjacent to the Berkeley Pit. A 2013 slough of material from the Pit wall into the water knocked out the 'precip' pump, and precip operations have since ceased. In precipitation, the copper-rich water is pumped over scrap iron, and, in a replacement reaction, the copper solidifies as sludge, while iron takes its place in the water. The water was returned to the Pit by gravity flow, thus not increasing or decreasing the total volume of Pit water. Photo by Justin Ringsak.
Montana Resources copper precipitation plant adjacent to the Berkeley Pit. A 2013 slough of material from the Pit wall into the water knocked out the ‘precip’ pump, and precip operations have since ceased. In precipitation, the copper-rich water is pumped over scrap iron, and, in a replacement reaction, the copper solidifies as sludge, while iron takes its place in the water. The water was returned to the Pit by gravity flow, thus not increasing or decreasing the total volume of Pit water.

This method of copper recovery was not new: it dates back to medieval Europe. The Anaconda Company used it for years to recover copper from the water pumped from the underground mines, and the method is still used today. Montana Resources has mined copper from the rich mineral waters of the Berkeley Pit since 1998, pausing when mining operations were suspended from 2000 through 2003, then resuming in 2004 until a Pit slough in 2013 knocked out the necessary pump. The mine pumped out roughly 13 million gallons of Pit water per day, or about 10,000 gallons per minute.

In copper precipitation, the Pit water is piped to the company’s precipitation plant, built in the 1960’s next to a similar one from decades earlier. The water flows into concrete cells filled with scrap iron, and then chemistry takes over. Simply put, the iron in the cells and the copper in the water trade places. The water is returned to the Pit with a higher iron content, and the copper precipitates, or solidifies out of solution, clinging to the remaining iron.

The waterfall formerly visible on the southeast rim of the Pit, seen here in 2004, created by returning Pit water that has gone through Montana Resources copper precipitation plant. Photo by Josh Peck.
The waterfall formerly visible on the southeast rim of the Pit, seen here in 2004, created by returning Pit water that has gone through Montana Resources copper precipitation plant.

The chemical reaction does not take long. Water stays in contact with the iron for only about an hour, and then it flows back into the Pit through a separate ditch along the old Horseshoe Bend channel, which could be seen from the viewing stand as the waterfall on the northeast rim of the Pit. Mine officials say that this constant circulation process should not affect the water level of the Pit, nor should the change in water chemistry have an effect on eventual water treatment operations.

Once per week, crews drain each cell to recover the precipitated copper. A front-loader scoops up the copper and scrap iron mixture and transports it to a vibrating screen. Water sprayed from high-pressure hoses knocks the copper through the screen into a tank below. Remaining iron goes back to the cells for reuse. The cement copper concentrate is then shipped to the concentrator and processed through a filter press to reduce the water content for rail shipment. By pumping water from the Berkeley, the company recovered about 400,000 pounds of copper per month.

The company also routed copper-rich Horseshoe Bend water through the precipitation plant from 1998 until the mine shutdown of 2000. The sale of this precipitated copper helped to offset water treatment costs. Once through the precipitation plant, Horseshoe Bend water was mixed with lime (calcium hydroxide) and pumped north to the Yankee Doodle Tailings Pond.

Since the treatment plant went online in 2003, this Horseshoe Bend water has been kept out of the precip plant circuit.

The equation below shows the main chemical reaction that takes place during the copper precipitation process:

Fe + CuSO4 becomes FeSO4 + Cu

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.
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.

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

Tailings covered to prevent blowing dust

The blue lines in the graphic indicate system in place during mine operations; these water lines were discontinued when the mine ceased operation.
The blue lines in the graphic indicate system in place during mine operations; these water lines were discontinued when the mine ceased operation.

Pitwatch Issue Volume 6, Number 2

The visibility of the recent blowing tailings events prompted numerous questions to the Committee. Although this topic is not directly related to Superfund and mine flooding issues, the Committee wanted to provide a brief update to readers.

When Montana Resources was operating, blowing dust was not a concern because water from the concentrator and the Horseshoe Bend diversion kept the tailings wet. When milling operations were suspended and the Horseshoe Bend flow was directed back to the Pit, the tailings began drying out. By October, Montana Resources had spread about 1.5 million tons of rock, approximately eighteen inches deep, to cover about 507 acres of the Yankee Doodle Tailings Pond north of the Berkeley Pit to keep the dust down.

The blue lines in the graphic on the right indicate system in place during mine operations; these water lines were discontinued when the mine ceased operation.

The Berkeley Pit in Butte, Montana, 1984. Photo from Fritz Daily.

Mining Suspension Changes Treatment Plans

The Berkeley Pit in Butte, Montana, 1984. Photo from Fritz Daily.
The Berkeley Pit in Butte, Montana, 1984.

PitWatch Volume 5, Number 2

In July 2000, Montana Resources suspended mining operations. The suspension has had a direct impact on the Berkeley Pit water levels and efforts are underway to deal with the problem.

The immediate concern is treating the Horseshoe Bend water, which had been diverted away from the Berkeley Pit since 1996. Based on data from July 1 to September 30, 2000, about four to five million gallons per day is entering the Pit from the Horseshoe Bend flow. Montana Resources had been treating this water as part of its mine operations.