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.
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.
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’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.
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 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.
After several highly publicized incidences of bird deaths at the Berkeley Pit, a popular myth arose: migratory waterfowl are instantly killed if they land on water in the Berkeley Pit. In fact, hundreds of waterfowl land on the surface of the Berkeley Pit every month during migration seasons, and they typically fly off unharmed within a few hours, either on their own or through Montana Resource’s hazing activities, also known as the waterfowl mitigation program.
The 2002 Consent Decree recognizes that “birds exposed to Berkeley Pit water for less than 4-6 hours should not be at substantial risk.” If a bird is observed suffering from the effects of water toxicity, it is netted and brought on board the houseboat used to patrol the Pit lake. The bird is placed in a 5-gallon bucket of fresh water and brought to shore. It is then transported to a veterinarian or released into fresh water at the north end of the Yankee Doodle Tailings Pond; tailings particles settle out on the south portion of the pond, leaving clear, alkaline (or non-acidic) water in the north end which mixes with snowmelt runoff from upper drainages, resulting in very low concentrations of dissolved metals.
In November 1995, a flock of snow geese landed on the Pit lake. After several days of stormy weather and fog, 342 birds were found dead. In response to this incident, the two responsible parties for the Pit under federal Superfund law, Montana Resources and British Petroleum-Atlantic Richfield, also known as BP-ARCO, implemented a waterfowl mitigation plan, which was approved by the EPA and other agencies in May 1998. This program is aimed at locating waterfowl in the area and then inciting the birds to fly away. An observation station was set up overlooking the Pit area. This station is an enclosed building equipped with spotting scopes and spotlights for night viewing to locate, count and identify species of waterfowl on the Pit lake.
Montana Resources’ personnel make hourly observations for birds during the spring and fall migrations, while the pit is not frozen, and cut back to 5-6 observations per day during non-migratory seasons. A variety of devices are used to chase birds off the water and out of the Pit. From the observation station near the southeast rim of the Berkeley Pit, Montana Resources’ personnel use rifles and shotguns to scare birds into the air.
In addition, three Phoenix Wailers – high-tech devices that emit predator and electronic sounds – are located near the surface of the Pit lake to discourage birds from landing. A 22-foot houseboat, docked near the pump barge, is used for periodic excursions on the water to haze waterfowl that ignore other warnings. Not all types of birds react to hazing. Typically, most ducks, geese and swans will react immediately to the noises. Diver birds such as grebes and loons tend to go underwater as a natural defense mechanism when they are alarmed.
Normally, if birds are not hazed or disturbed, they leave the Pit area at nightfall. If a dead bird is found on the water or near the Pit, then the US Fish and Wildlife Service is contacted. They decide if an autopsy is necessary.
From 1995 through 2004, 75 birds were found dead. The advances made to deter migrating waterfowl from landing on the water or staying on the Pit appear to be working. Thousands of birds land and are hazed off of the Pit each year.
Though many local authorities decided that the 1995 incident was isolated and not likely to happen again with the safeguards that are in place, in October 2007, 37 birds, including ducks, geese, and one swan, were found dead at the Pit after a weekend of fog. It is unclear why mitigation activities failed to haze these birds away from the site, although the weather was almost certainly a factor. As the mitigation program continues, all involved continue to work to keep such incidents to a minimum.
The chart below, from the 2011 EPA Five Year Review Report on the site, shows Pit-related bird deaths from 2006-2009.
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.
The community has many common misconceptions about the Berkeley Pit. This section addresses a few of those most often heard false statements.
Migratory waterfowl are instantly killed if they land on water in the Berkeley Pit.
Hundreds of waterfowl land on the surface of the Berkeley Pit every month during the migration season, and they fly off within a few hours, either on their own or through MR’s hazing activities. The Consent Decree recognizes that “birds exposed to Berkeley Pit water for less than 4-6 hours should not be at substantial risk.”
If a bird is observed suffering from the effects of water toxicity it is netted and brought on board the houseboat used to patrol the Berkeley Pit. The bird is placed in a 5-gallon bucket of fresh water and brought to shore. It is then transported to a veterinarian or released into fresh water at the north end of Yankee Doodle Tailings Pond.
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.