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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.

Study details slope stability

The rate of rise of water levels in the Berkeley Pit and connected monitoring points is affected by many factors, including rain and snowfall and occasional ‘sloughs’ or ‘slumps’ of material from the Pit’s sidewall slopes.

The most recent slough occurred on February 8, 2013. An estimated 820,000 tons of material from the southeast wall collapsed into the Pit. Montana Bureau of Mines and Geology (MBMG) monitoring showed that the water rose about 0.6 feet as a result. For comparison, over the past several years the water has risen about 0.65 feet per month.

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.
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.

Sloughs or landslides are relatively common in open pit mines and can potentially raise water levels. To address the potential effects of future sloughs on the Pit’s rate of rise, EPA required the Potentially Responsible Parties (PRPs) for the site, Montana Resources and the Atlantic Richfield Company (AR), to study the stability of the slopes around the rim of the Berkeley. Publication of the final report on that study is expected later in 2015, and it will be published here on the PitWatch website.

EPA and the PRPs have stated that preliminary results indicate that the rising Pit water level will continue to increase the potential for slope failure, especially in the southeastern part of the Pit. Future sloughs are expected to occur in the absence of any stabilization or mitigation measures, but, based on past sloughs, are not expected to significantly affect the Pit management timeline.

Two much smaller landslides, which had no noticeable impact on the water level, occurred in August and November 2012. A larger landslide occurred in 1998. The November 2012 slide damaged the Montana Resources pontoon boat used for water quality sampling in the Pit. Following the 2013 slide, those sampling activities were suspended for the safety of the MBMG scientists who conduct the sampling.

This September 2014 photo from Google Earth shows the Berkeley Pit and the surrounding area.

Water level rising more slowly than originally projected

This September 2014 photo from Google Earth shows the Berkeley Pit and the surrounding area.
Click on the image to view a larger version.

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.

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.

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.
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.
This map shows the locations of groundwater monitoring points for the alluvial aquifer in the East Camp area of the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.

Maps of Berkeley Pit Monitoring Sites

Maps from the Montana Bureau of Mines & Geology (MBMG) showing Berkeley Pit-related alluvial and bedrock monitoring sites have been added to PitWatch.Org. View snapshots of the maps below, click on an image to view a larger version, or use the links at the bottom of the page to download printable .pdf versions of the maps.

This map shows the locations of groundwater monitoring points for the alluvial aquifer in the East Camp area of the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.
This map shows the locations of groundwater monitoring points for the alluvial aquifer in the East Camp area of the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.

 

This map shows the locations of groundwater monitoring points for the bedrock aquifer in the East Camp area of the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.
This map shows the locations of groundwater monitoring points for the bedrock aquifer in the East Camp area of the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.

 

This map shows the locations of groundwater monitoring points for the West and Outer Camp areas of the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.
This map shows the locations of groundwater monitoring points for the West and Outer Camp areas of the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.

 

This map shows the locations of groundwater monitoring points for the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.
This map shows the locations of all groundwater monitoring points for the Butte Mine Flooding Operable Unit of the greater Butte Superfund site.
The area of the slough that occurred in Feb. 2013 can be seen in approximately the center of this photo of the Berkeley Pit, taken in July 2013 by Fritz Daily.

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.
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.

The Berkeley Pit and connected tunnels act as a sink that collects groundwater in the area due to the fact that the basin of the Berkeley Pit lake is the lowest point in the groundwater system. Image from Google Earth.

Do Butte residents need flood insurance?

No. Butte residents don’t need to worry about flood insurance in regard to the Berkeley Pit and connected underground mine workings. The Berkeley Pit and connected tunnels act as a sink that collects groundwater in the area. Water levels in the Berkeley Pit and associated mine shafts are currently 175 to 200 feet below the rim of the Pit.

Elevations above sea level for Berkeley Pit water and surrouding Butte, Montana landmarks. Map image from Google Earth, graphic by Justin Ringsak.
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.

The lowest point on the Pit rim, on the east side near the Montana Resources concentrator, is 5,509 feet above sea level. As of June 2013, the Berkeley Pit water level was 5,310 feet, and the highest water level in the system, in the Pilot Butte shaft, was 5,335 feet.

Under the management plan for the Berkeley Pit, these water elevations will always be maintained at levels 100 feet or more below the rim. This will be accomplished by pumping and treating Berkeley Pit water. Pumping and treating will start when the water level at any one of the monitoring compliance points reaches the critical level of 5,410 feet. The Montana Bureau of Mines & Geology (MBMG) monitors water levels at all compliance points, as well as at several other monitoring sites, on a monthly basis. Based on the rate the Pit is filling now, that should happen around 2023.

Berkeley Pit groundwater monitoring locations and water levels, including wells and abandoned mine shafts, June 2013. Graphic by Justin Ringsak.
Berkeley Pit groundwater monitoring locations and water levels, including wells and abandoned mine shafts, June 2013.

The elevation of the Metro Storm Drain near the Pit at Texas Avenue and Continental Drive is 5,470 feet, about 60 feet above the highest water level allowed for the Berkeley Pit system.

For further comparison, a monitoring well at Greeley School has an elevation of 5,503 feet, about 93 feet higher than the critical level. The current water level in this well is 5,462 feet, about 52 feet higher than the critical level. This difference in water levels tells us that groundwater is flowing toward the Pit, and will continue to do so after the waters in the Berkeley Pit and connected mines reach their highest allowed levels.

In other words, water is flowing into the Berkeley Pit, and the Pit will be managed so that water is always flowing into it. Butte residents can rest easy knowing that the Berkeley Pit is not going to overflow, and that there is no need for flood insurance due to the Pit or underground mines.

This image illustrates how the Berkeley Pit, with the lowest water levels in the area, acts as a sink that collects groundwater. Water levels indicated for each monitoring point are from June 2013.
This image illustrates how the Berkeley Pit, with the lowest water levels in the area, acts as a sink that collects groundwater. Water levels indicated for each monitoring point are from June 2013. Click on the image to view a larger version.
Monitoring compliance points in the Berkeley Pit groundwater system

What is being done to manage the Berkeley Pit now?

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.

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.

Berkeley Pit groundwater monitoring locations and water levels, including wells and abandoned mine shafts, June 2013. Graphic by Justin Ringsak.
Berkeley Pit groundwater monitoring locations and water levels, including wells and abandoned mine shafts, June 2013. Click on the image to view a larger version.
Monitoring compliance points in the Berkeley Pit groundwater system
Monitoring compliance points in the Berkeley Pit groundwater system. The water level a each point is monitored monthly by the Montana Bureau of Mines & Geology. When the water at any compliance point reaches the Critical Level (5,410 feet above sea level), pumping and treating of Berkeley Pit water will begin to prevent contaminated water in the Pit and groundwater system from spreading outward. Click on the image to view a larger version.

 

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.