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.
The Montana Bureau of Mines & Geology (MBMG) measures the water levels at the Pit and in connected mine shafts and wells each month. To monitor water quality, water samples are collected from the Pit semi-annually at multiple depths as safe access allows.
23 wells and 14 mine shafts supply information about the deep bedrock aquifer. 36 wells provide similar data about the alluvial aquifer, which is much closer to the surface. Each month, scientists manually check and record the water levels in these wells. Twice a year, they collect samples to analyze the water’s chemistry. All of this information helps scientists understand where the water is coming from and how it is moving underground.
Complete MBMG monitoring reports and data can be downloaded from our Monitoring Reports page.
The Horseshoe Bend Water Treatment Plant can be seen on the northeast edge of the Pit. The plant was constructed in 2002-2003 to fulfill the EPA Record of Decision, which requires that surface water flowing into the Berkeley Pit be captured and either used in the mining process or treated.
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.
The plant was designed to treat up to 7 million gallons of water per day using lime (calcium oxide) to raise the pH (reduce the acidity of the water) and remove metals. As pH rises, metals come out of the water and form sludge. The sludge is separated from the water and returned to the Pit at a current rate of about 491,000 gallons per day. Montana Resources incorporates the treated water into their mining process.download full movie The Discovery
In 2012 the plant treated about 5 million gallons of water per day. This water comes from the Horseshoe Bend drainage north of the Pit. The plant has been working continuously since it came online in November 2003. No water or waste leaves the Pit or mine site.
The Horeseshoe Bend Water Treatment Plant, seen here in 2009, was constructed in 2002-2003 to fulfill the EPA Record of Decision, which requires that surface water flowing into the Berkeley Pit be captured and either used in the mining process or treated. Currently the plant is used to capture and treat surface water that would otherwise flow into the Pit. Treated water is then used in Montana Resources mining operations.
Yes, after a treatment technology review and upgrades to the plant are completed.
The 1994 EPA Record of Decision and 2002 Consent Decree require a review of treatment technologies when the Critical Water Level (5,410 feet) is about four years away. The review will consider the plant’s ability to treat both Pit water and water coming from the Horseshoe Bend drainage to the north. Based on the review, the Treatment Plant will then be upgraded to best treat the water.
Upgrades must be completed two years before the critical level is reached. Projections show water levels at one of the compliance points connected to the Pit will near the critical level around 2023, so a treatment review would take place in 2019, with any needed upgrades completed by 2021, as indicated by the timeline below.
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.
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.
Soon 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.
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.
Over the active lifespan of the Berkeley, approximately 320 million tons of ore and over 700 million tons of waste rock were mined from the Pit. Put another way, “The Richest Hill on Earth” produced enough copper to pave a four-lane highway four inches thick from Butte to Salt Lake City and 30 miles beyond.
In 1955, mining in Butte saw the light, literally. Excavation on what would become the Berkeley Pit, named from one of several nearby historic underground mines that the Pit would later engulf, began that year in a transition from underground to open pit mining.
The Pit would, in the next decade, swallow Butte neighborhoods like Meaderville, Dublin Gulch, and McQueen. The transition to open pit mining, a highly industrialized form of mining, also meant fewer jobs for the city’s miners. But mining had always been the lifeblood of Butte, and so the community embraced the new mine, and there was little objection to the sacrifice of some of the city’s neighborhoods.
The Anaconda Company’s decision to begin open pit mining in Butte was not without its reasons. In 1955, copper prices were the highest they had been since the end of World War I in 1918. And the following year, 1956, would mark the highest copper price seen until 2006 (with the exception of the lone year 1974, when copper briefly spiked due to an end to price controls and the ongoing demands of the Vietnam War).
Those high prices gave the Company a big incentive to rethink its Butte operations. The most accessible parts of the Butte hill had already been mined out. Legend has it that Marcus Daly’s original ore vein was 30% copper. That is extraordinarily rich ore, and the veins of that quality could not last- as a point of comparison, when it opened, the ore mined at the Berkeley was about 0.75% copper, and the ore being mined at Montana Resources nearby Continental Pit operation today is approximately 0.25% copper. In order to economically extract copper from lower grade ore, the Pit was born.