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Casualties of Copper: The Berkeley Pit, Montana

Walter Hinick, AP

Tales of gold rushes and silver booms are often recounted from a nostalgic perspective, driven by tall tales of adventures into the lawless Wild West. Perhaps less sentimental is the story of copper, a metal with less value but more significance to the growth of infrastructure. Copper was a major component of industrialization and essential for everything from electrifying the world to fortifying nations during war.

Few mining operations could match the lifetime output of the Anaconda Copper Mine in Butte, Montana. For nearly a century, mining in Butte Valley sacrificed the earth to build and defend America. Today the legacy of Anaconda’s enterprise is the Berkeley Pit, a large open pit mine collecting billions of gallons of toxic groundwater.


Anaconda Mine, Butte MT
Anaconda Mine, Butte MT (courtesy miningartifacts.org)


Anaconda Mine (courtesy miningartifacts.org)

Butte sits in the southwest corner of Montana, just north of the Highland and Pioneer mountain ranges. The region experienced a boom in the late nineteenth century when mining activity in the 1870s uncovered rich deposits of valuable ore.

The camp quickly turned into a large city; by 1890 Butte was the largest city west of the Mississippi with an estimated population of 24,000.

Until this time, regional stakes to mining claims were spotty and unorganized. In 1881, and with the help of Hearst family money, Marcus Daly formed the Anaconda Copper Mining Company. He made an early bet on copper and acquired dozens of area claims for the Anaconda company.

The draw was the near abundant supply of precious metals. It’s prodigious yield in gold, silver, and copper earned Butte the nickname “The Richest Hill on Earth.”

Daly’s bet would pay off. From 1892 until 1903, the Anaconda Mine was the largest copper-producing mine in the world. Word of copper profitability spread, introducing new money. The European-based Rothschilds purchased a 25% stake in 1895, but sold to newly-formed trust Amalgamated Copper Mining Company just four years later.

(Click thumbnails to enlarge)

Anaconda-Mine-1100-ft Butte-Ore-Wagons Anaconda-Mine-1910

photos courtesy miningartifacts.org

After the turn of the century the electricity revolution swept the United States. Demand increased and so too did the demand for copper, a key conductor. Butte Valley was rich in the ore; the mining companies couldn’t extract it fast enough.

As operations in the area expanded, the corresponding population would boom. By World War I Butte was the largest city in Montana with a population over 50,000.

Butte, Montana (circa 1922)
Butte, Montana circa 1922 (courtesy miningartifacts.org)


Berkeley Pit

Underground mining had been a staple of Butte for nearly 70 years. Generations of miners spent lifetimes tunneling thousands of miles through the Butte hills. Over time, mining technology improved and more efficient methods of extraction were developed.

In 1955, the area was introduced to open-pit mining when the Berkeley Pit opened. The new mine would take advantage of the existing tunnels and drainage systems from earlier mining operations to help control groundwater levels beneath Butte. The pit was profitable from the start, producing 17,000 tons of copper per day by the end of the first year.

Over the decades the pit grew in size, swallowing several communities of Butte along the way. The towns of East Butte, McQueen, and Meaderville were absorbed by the mine during the 1950s and 60s. When underground mining finally ended in 1975, the Anaconda mine operation in Butte included nearly 50 miles of vertical shafts and over 10,000 miles of various work-way tunnels.

Kris Taelema
courtesy Kris Taelema

In 1977 the mine was sold to the Atlantic Richfield Company (ARCO), however the acquisition was doomed from the start. ARCO had little prior experience in hard rock mining, and to make things worse, copper prices collapsed soon after.

In addition to declining ore values, operational costs had risen. By 1982 the lack of profitability forced ARCO to scuttle the main operation at the Anaconda mine in Butte. In the 27 years the Berkeley Pit was mined, a billion tons of various ores were extracted. Copper was the principal metal, although others such as silver and gold were also extracted in smaller quantities.

Today the Berkeley Pit is one mile long by a half mile wide. It reaches a depth of over 1780 feet and occupies a total area of 675 acres. During the life of the operation, approximately 320 million tons of copper ore and 700 million tons of waste rock were mined from the earth.


Concern After Shutdown

Underground mining requires constant monitoring of groundwater levels to prevent possible cross-contamination of the water table and flooding of the mines. As the tunnels reached lower depths, more groundwater had to be pumped out of the mines. For decades the Anaconda mine utilized a system of subterranean pumps to keep the levels manageable – and they work when they’re turned on.

When ARCO shut off the lights on the Anaconda mine operation in 1982, they also shut off the pumps. Before long, groundwater began to slowly fill the mines – and eventually filling the Berkeley Pit – at a rate of about one foot per month.  If the water in the pit breaches the ground water table, the danger is a contamination to the ground water for all in Butte.

The continuous inflows of acidic water to the pit haven’t stopped accumulating Since ARCO shut off the pumps 31 years ago. If ignored, the flooding of the pit would cause it to eventually overflow and spill its poison into the Clark Fork River.

Cross section of Berkeley Pit
Cross section of Berkeley Pit courtesy Montana Bureau of Mines and Geology (MBMG)

Plans to address the growing environmental issue started to develop in the 1990s. One attempt to stave off advancing pit water levels was to divert water to slow the rise of the overall water level. While this helped, it only slowed the bleeding; something more needed to be done.

In 1994 an EPA directive called for the Butte Mine Flooding Operable Unit to utilize cleanup alternatives as a Superfund site. At the time of EPA’s record of decision, estimates had the Berkeley Pit containing 26 billion gallons of acidic water – with 5,000 gallons per minute of inflows totaling 7.2 million gallons per day.


Snow Geese Incident

snow_gooseThe environmental community was aware of the issues surrounding the Berkeley Pit, but it wasn’t until November of 1995 the mine started receiving serious attention outside of ecological circles.

That winter, a flock of migrating snow geese landed in the Berkeley Pit. Several days of inclement weather and an accompanying dense fog prevented the birds from leaving.

When the weather finally cleared, 342 of the geese were found dead. The event received national attention, and before long the EPA and State of Montana investigated the matter.

The state determined toxic water of the pit had corroded the birds’ esophagi – something ARCO denied, citing Colorado State University’s necropsy findings of an infection caused by a grain fungus.

Montana disputed this with evidence of their own. The state’s necropsy exam revealed the birds had suffered burns and festering sores from exposure to high concentrations of copper, cadmium, and arsenic.

In the years since, steps have been taken to prevent a repeat of the incident. Various methods–from structured firecracker arrays to loudspeakers playing sounds of animals in distress–have tried to discourage birds from landing in the water.


Horseshoe Bend

In the late spring of 1996, ARCO and Montana Resources Group (MRG) had completed the Horseshoe Bend drainage water diversion facility. It was able to divert up to 3,000 gallons per minute from Berkeley Pit, slowing the rising water level. For four years Horseshoe Bend diverted the incoming water while MRG continued operations in the area.

Horseshoe-Bend-WTP2By July of 2000, high energy costs had forced Montana Resources to suspend operations. The drainage water diversion facility was closed, allowing the Berkeley Pit fill rate to increase once again.

Disputes between the various operators over responsibility for site clean up would delay action, but by March of 2002 the Montana Department of Environmental Quality and the EPA had entered into a consent decree with ARCO and the MRG.

Ultimately a settlement, ARCO and MRG agreed to cover specific past and future costs associated with the site as outlined in the decree.

The plan called for construction of a $18 million dollar water treatment plant, with all costs borne by the defendants of the settlement. The new Horseshoe Bend Water Treatment Plant would treat up to 5,000 gallons per minute using lime (calcium oxide) to raise the pH levels and reduce the acidity of the water.

As the pH rises, metals are removed from the water and form a sludge. The water and sludge are then separated; some goes back to the pit while the rest is re-incorporated into the mining process.

The plant is visible next to the waterfall on the northeastern rim of the pit (see on map). It sits on four acres near the former McQueen neighborhood of Butte, absorbed by the Anaconda company decades prior.

(Click thumbnails to enlarge)

 Horseshoe-Bend-clarifier Horseshoe-Bend-WTP3 Yankee-Doodle-Tailings-Pond

Operational costs were initially estimated to be $2 million per year, with certain scenarios possibly raising the number to $4.5 million. Under terms of the 2002 decree, ARCO and MRG are liable to cover expenses in perpetuity, with the next review of the operation scheduled for November 2017.

By the fall of 2003, Montana Resources Group had resumed operations and the water treatment plant was online. The plant is expected to pump and treat the pit water until at least 2023.

Horseshoe-Bend-WTPHorseshoe Bend Treatment Facility pictures courtesy PitWatch.org


Environmental Effects

water level for powerpointThe oxygen saturation of Berkeley Pit water allows the ore and minerals along the walls of the rock to decay. The dissolved oxygen exposure to pyrite and sulfide minerals creates a reaction that releases acid.

When a liquid solution with a transition metal (such as copper) is exposed to liquid sulfides, the reaction produces a solid with low water solubility. Through this chemical precipitation, the Anaconda Copper Mining Company was able to “mine” copper directly from the water.

Since 1901, the mine operators drained the ground water encountered in the mines to a common level for pumping to the surface – but the surface level was rising.

The “critical water level” of the Berkeley Pit is 5,410 feet above sea level. At the end of 1982, the pit’s water level had risen more than 1,300 feet. By the end of 2006 the water level had grown by another 3,100 feet. In 2009 the water had reached 5,285 feet. And most recently, in September of 2013 the water level reached 5,311.89 feet. (above left)

The rate of rise has slowed in recent years, but if the critical level is breached the ground water for over 30,000 residents in Butte would be in danger of further contamination. Historic mining operations have already taken their toll, forcing area residents have to pump in drinking water from highland reservoirs and the Big Hole River.

Berkeley Pit (photo courtesy Montana State Travel site)

These and other concerns earned the Berkeley Pit a spot on the EPA’s Superfund site list. A program was established to monitor the site and to ensure the Berkeley Pit remains the terminal pit for bedrock ground water which has penetrated the old mines.

The program also called for water samples to be collected semi-annually and it included a closed system to preclude waste water discharge to nearby aquifers.



Berkeley-Pit-Entry-MattVolz_APThe Berkeley Pit is not hospitable to local flora and fauna; there aren’t insects, plants, nor fish in the area. Metals leach from the rock, saturating the pit water with toxic chemicals.

The surface water is rich in iron and manganese, thus reddish in color. Below the surface, the higher concentration of copper turns the water into a lime green.

Water quality varies with depth; an estimated 1,000 feet are filled with sulfuric acid and toxic heavy metal concentrations of copper, iron, arsenic, cadmium, and zinc.

It is estimated the pit today holds 40 billion gallons of acidic water – nearly 13 million gallons of which are pumped to nearby scrap iron holding ponds. The resulting sludge yields up to 400,000 pounds of copper per month.

The Berkeley Pit is open to visitors between March and November. Pit admission is only $2 for access to the viewing platform – and don’t forget to visit the gift shop.


Copper Lining

Despite its ecological transgressions, the site has offered something of value back to mankind. In 1995, an analytic chemist found a clump of green slime floating on the pit water. The slime made its way to nearby Montana Tech, where biologists and biochemists studied the sample and determined it was an algae – one that was alive and well in the noxious pit water.

Scientists realized life had adapted to the harsh environment of the pit. Fungi and bacteria evolved; they were able to ingest metals and produce toxic compounds to survive. These extremophiles will thrive in severe environments detrimental to most other life on earth and naturally develop an immunity to toxins.

Experts believe the evidence of the organisms’ ability to adapt to the extreme toxic environment may be a salient discovery in the fight against cancer. Piquing the interest of cancer researchers is the uncommon ability of certain extremophiles to repair their own damaged DNA.

Berkeley Pit
This image shows the terraced levels & access roadways of the open mine pits. To the north of the Berkeley Pit is a large gray tailings pile of waste rock. (courtesy NASA)

The Berkeley Pit is a microcosm of the improper ecological considerations paid by mining companies over the last 150 years. Fortunately the increased attention and funding to cleanup efforts over the last decade suggest a more pro-active approach.

Reduced operations, advancements in technology, and cleaner initiatives have done their part to reduce the worsening ecological footprint of the site, but the damage has already been done. Today, the risk to the people of Butte is manageable – but it will never be absent.


The good folks at PitWatch.org put together this time lapse video demonstrating the worsening issue:


Pit Watch gallery of the Berkeley Pit over time