A once-dormant power plant is humming with activity outside Pittsburgh as thousands of miners work 24 hours a day.
The miners at this site aren’t people, but supercomputers running complex math equations. The first to solve the equation is rewarded with the digital financial token known as bitcoin.
But the large amount of power needed to run these computers has re-ignited a debate in Pennsylvania and around the country about the potential climate consequences of cryptocurrency.
Bitcoin is a type of digital money not regulated by any company or government. It can be exchanged online between people anywhere in the world without going through a bank. While coins like quarters or pennies are physically minted -- bitcoin is minted as a virtual token by computers, through a process called “mining.”
Some investors see bitcoin as the currency of the future. The value of one bitcoin has skyrocketed from around $10,000 two years ago to more than $33,000 as of this publishing.
Jeff Campbell, who oversees the bitcoin mining operation at the Scrubgrass Power Plant in Kennerdell, Pennsylvania, said each of their computers generates an average of $30 a day mining bitcoin.
“These are computers that are just designed to do one thing. They're designed to run as fast as possible 24 hours a day,” he told ABC News Live.
The computers in a bitcoin mining operation need a lot of power both to run and to operate fans that stop them from overheating. By one estimate from the Cambridge Center for Alternative Finance, annual global bitcoin mining uses more electricity than the entire nation of The Netherlands.
Climate activists question whether the growth of cryptocurrency mining operations could generate more carbon emissions and create a new market for fossil fuels at a time when the world is trying to reduce energy use and cut carbon emissions as fast as possible.
Under fire for their emissions and reliance on fuels like coal and natural gas, some bitcoin mining companies in the U.S. are transitioning to more renewable types of power like solar or wind.
Stronghold Digital Mining, which owns the Scrubgrass plant, has found its power source in the form of coal waste, which is abundant at this 221-acre pit just outside of Pittsburgh. Coal waste is a combination of rock, coal, and other materials that were deemed unsuitable for burning and left abandoned since the 1970s when coal mines in the area were closed.
There are 220 million cubic yards of waste coal pits like the one in Russellton across 9,000 acres in Pennsylvania, according to testimony from Pennsylvania Department of Environmental Protection Director Patrick McDonnell. The agency says the pits cause environmental problems like leaching acid into nearby rivers and streams. There are also 40 continual fires in waste coal pits across the state that can release carbon dioxide and other pollutants as they burn, according to a document from a waste coal industry group.
The entrepreneur behind Stronghold, Bill Spence, said that while burning waste coal isn’t the cheapest form of energy, the bitcoin operation keeps the plant viable through its constant demand for power. This helps achieve his goal of reducing the toxic waste piles across the state, Spence said.
“What cryptocurrency and bitcoin has done for us is, it's enabled us to sustain the work that this power plant does as an environmental plant cleaning up the waste coal, the remnants of the mining industry here in the state of Pennsylvania,” he told ABC.
The Pennsylvania Department of Environmental Protection says the state has benefited from waste coal power plants because the state has limited funding to clean up the piles and address the environmental problems.
“Waste coal-fired units burn waste coal to generate electricity thereby reducing the size, number and impacts of these piles otherwise abandoned and allowed to mobilize and negatively impact air and water quality in Pennsylvania,” Press Secretary Jamar Thrasher said in an emailed statement.
Pennsylvania provides up to $20 million a year in subsidies to waste coal power plants and Thrasher said the state includes their CO2 emissions in the state’s carbon budget in an effort to help them compete with cheaper forms of energy like natural gas.
Waste coal is burned using a different process than traditional coal but still releases carbon dioxide that contributes to warming the atmosphere. The EPA says the type of waste coal found in Pennsylvania also releases more acid gas and sulfur dioxide than other types of coal.
Stronghold says they have put technology in place to capture pollutants like sulfur dioxide or methane emissions from their plant, but according to publicly available data they still released about 365,000 metric tons of carbon dioxide in 2019 -- the equivalent of about 80,000 cars on the road for a year, according to an EPA emissions calculator. The facility also released more than 1,000 metric tons of methane, a potent greenhouse gas, and nitrogen oxides, or NOx, that contribute to air pollution
Rob Altenburg, director of the environmental nonprofit Penn Future, said bitcoin is “wasteful by design” and that there are better alternatives for generating that power than burning waste coal.
“They're not removing pollution. They're moving pollution. They're moving pollution from the land and they're moving it to the air,” Altenburg told ABC News.
And because waste coal contains less coal than what would typically be used to generate energy, more of it needs to be burned to create the same amount of power which could generate more CO2 emissions and air pollution.
“The dirtiest source of power we have in the state should be your last choice for you for generating that electricity,” he said.
Altenburg said that instead of burning waste coal, the state and federal government should provide more funding to move the material to lined landfills where it can no longer contaminate the soil or water.
The federal infrastructure bill has allocated $11 billion toward abandoned mine cleanups, some of which could be used to clean up waste coal in Pennsylvania.
Spence acknowledges that Stronghold’s operation generates carbon dioxide and that their operation isn’t perfect, but they’re trying to improve further by testing technology to capture the carbon they emit. And he said the bitcoin operation is helping fund his efforts to use up the waste coal which otherwise won’t go anywhere on its own.
“I don't think we should stop what we're doing in order to get the perfect,” Spence told ABC.
“Let's evolve into perfect.”
ABC News' Seiji Yamashita contributed to this report.