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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.

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.

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.

Consent Decree Announced


Berkeley Pit, 2006.
Berkeley Pit, 2006. Click on the image to view a larger version.

Pitwatch Issue Volume 7, Number 1

In March 2002, the Atlantic Richfield Company (ARCO) and Montana Resources (MR) agreed to sign a Consent Decree, a legally binding document that will be entered in federal court. The Consent Decree requires these companies to reimburse EPA and DEQ for past costs, and pay now for future oversight costs. It also guarantees that these companies will perform a number of tasks and provide financial assurances to pay all costs to complete the required work.

Most importantly, the Consent Decree sets a firm schedule for Arco and MR to build a water treatment facility, and confirms their obligations to operate and maintain the facility – including sludge disposal – in perpetuity. Also included in the Consent Decree are commitments to enhance the waterfowl protection program at the Berkeley Pit, to establish a groundwater control area surrounding the Berkeley, to fund the Montana Bureau of Mines and Geology (through the EPA and DEQ) to continue the mine flooding monitoring program, and to fund public education activities (e.g., PITWATCH).

As part of the process, ten changes were made to the Record of Decision (1994). For example, changes were made to recognize new stream and discharge standards for the treated water, to allow Continental Pit water treatment in the Horseshoe Bend plant, and to allow sludge disposal in the Berkeley Pit. Another change eliminates the requirement to reevaluate treatment technologies when the water level in the Pit reaches the 5,260′ level, since the treatment plant will already be built. The Consent Decree also clarifies which cleanup tasks will be done under the Superfund program and which will be done under the State’s active mine permit reclamation program.

The Consent Decree was released on March 26, 2002 for public comment until May 4, and is expected to be finalized thereafter. Contact the Committee with any questions.

Record of Decision (ROD) for the Berkeley Pit

The Record of Decision (ROD) is a public document that explains which cleanup alternatives will be used to clean up a Superfund site. The ROD for sites listed on the NPL (NPL Site Listing Process) is created from information generated during the Remedial Investigation/Feasibilty Study (RI/FS). The ROD for the Butte Mine Flooding Operable Unit, which includes the Berkeley Pit, was published in 1994 and can be downloaded below.

1994 Record of Decision Download

A ROD contains site history, site description, site characteristics, community participation, enforcement activities, past and present activities, contaminated media, the contaminants present, scope and role of response action and the remedy selected for cleanup.

  • You can search for RODs in EPA’s Record of Decision System. It contains full-text Records of Decision (RODs), ROD Abstracts, ROD Amendments (AMDs) and Explanations of Significant Differences (ESDs).
  • Examples of well written RODs are available on the EPA ROD of the Year Contest Web page. The purpose of the ROD-of-the-Year Contest is to foster increased awareness of decision document quality.

Records of Decision for other Butte/Silver Bow Creek area Superfund Operable Units are available from the EPA Superfund Information Systems.

The Montana Bureau of Mines & Geology also offers a summary of the ROD on their website.

The site is also managed through a Consent Decree (2002) that resulted from a lawsuit filed by the State of Montana against the Potentially Responsible Parties (PRPs) for the site.