Turning coal ground pollution into air pollution

Proof of problems: Bitcoin mining’s pollution toll on U.S. communities

‘Miners are setting up operations without telling anyone’

Rob Altenburg, director, PennFuture Energy Center

VENANGO COUNTY, Pa. – Coal is the environmental problem that keeps finding ways to harm communities across this state, with proof of work bitcoin mining creating another way to pollute as crypto companies look to waste coal to power their operations.

With two bitcoin mining operations in the Keystone State, Stronghold Digital Mining has a sleek website with a glossy video boasting that its energy intensive operations are actually an “environmentally beneficial” way to “remediate the impacts of 19th and 20th century coal mining in some of the most environmentally neglected regions of the United States.” 

The company talks a good game, claiming to be more of a coal refuse reclamation company than a bitcoin miner. Stronghold’s co-chairman and CEO boasts that his company is saving communities living near coal refuse from further environmental harm in addition to cleaning up dangerous coal refuse piles. He says this burning produces no nitrogen oxide emissions. 

Bill Spence, co-chairman and CEO of Stronghold Digital Mining, shows off the Scrubgrass Power Plant, where large shipping containers house thousands of bitcoin mining machines.

Bill Spence, co-chairman of Stronghold Digital Mining, shows off the Scrubgrass Power Plant, where large shipping containers house thousands of bitcoin mining machines

Photo credit: Associated Press/Andrew Rush, Pittsburgh Post-Gazette

Stronghold mixes waste coal with limestone and then sends it to a circulating fluidized bed combustor that produces steam to generate electricity. 

A byproduct of the process is coal combustion waste, or coal ash, which can be reused in small amounts in products like wallboard and fertilizer, but which also has a notorious history. In 2008, a coal ash storage pond in Tennessee collapsed, sending more than 5 million cubic yards of the waste into the Emory River. A similar coal ash spill in North Carolina, in 2014, sent unburned carbon and various metals, including arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium, and zinc into the Dan River, threatening drinking water, wildlife, and agriculture.

Stronghold, a publicly traded company, has two waste coal-fueled generating facilities: the 85 MW Scrubgrass Plant, in Venango County, Pa., and the 80 MW Panther Creek Plant, in Carbon County, Pa. Before the company bought these coal plants, in 2021, they were all but closed, with electricity generation and coal consumption dropping 95 percent between 2014 and 2020.

Stronghold claims to be saving Pennsylvania communities by taking piles of waste coal stored out in the open and burning it for bitcoin mining. But the process still ends up producing more coal ash. During 2022, the company combusted about 1 million tons of waste coal and returned nearly 700,000 tons of coal ash to waste coal sites.

The waste coal the company burns to mine bitcoin is low-quality coal discarded by previous coal-mining operations. That’s because its low energy content and high contamination levels rendered the coal unfit for commercial sale. So burning waste coal is not only more inefficient but also more pollution-intensive than burning even commercially marketed coal.

Stronghold takes the ash leftover from burning coal refuse and spreads the ash back over land areas in what is termed “beneficial use” as fertilizer by the state.  Coal ash is known to contain all the heavy metals and a wide variety of other toxic substances found in coal that are concentrated when the coal is combusted. When coal ash is spread over the ground, every time it rains these toxic pollutants like arsenic, cadmium, and many others, are washed into nearby streams and rivers, polluting groundwater throughout the watershed. 

Not only does burning coal waste create carbon emissions that contribute to the climate crisis, but it also increases emissions of heavy metals, acid gasses and air toxics. These pollutants can hurt communities living closest to the facilities that are powering crypto mining, including some areas that have been historically disproportionately affected by pollution.

Despite environmentally friendly claims, under Stronghold’s ownership the plant has burned 830 percent more waste coal, compared to 2020, and in 2022 waste coal consumption was up by about 1,800 percent over 2020 – the most since 2014.

After more than six years of steadily declining emissions at the waste coal plants, Environmental Protection Agency monitoring data show the company’s bitcoin mining activity increased emissions of sulfur dioxide by 351 percent in 2022, to 1,965 tons, and nitrogen oxides by 1,224 percent, to 645 tons, compared to 2020 levels. The company’s waste-coal-fueled crypto mines also released over 1.4 million tons of carbon dioxide in 2022. 

“They’re turning the ground pollution into air pollution and really not paying attention to the downwind impacts,” says PennFuture Energy Center Director Rob Altenburg.

Other bitcoin miners in the state are cropping up at natural gas well pads almost overnight, with some detected only by accident, says Altenburg. “Miners are setting up operations without telling anyone,” he adds, often with huge shipping containers stacked with mining hardware.

That makes the fight against proof of work bitcoin operations almost like a game of environmental whac-a-mole, with communities often surprised by the arrival of so-called data centers, which turn out to be bitcoin mines that promise jobs and other boosts to the local economy that often fail to materialize. But it doesn’t mean the fight is impossible.

Indeed, PennFuture and other environmental advocates are leading the charge against bitcoin operations because of their reliance on coal and other dirty fossil fuel power sources, particularly those that are reviving once-shuttered fossil fuel power plants.

“Fossil-based crypto mining operations pose the same environmental and public health threats as their underlying methods of energy generation,” wrote Altenburg and representatives from Clean Air Council and Earthjustice in a January 17, 2023, letter to state regulators. The advocates were opposing the use of a gas well pad in Elk County, Pa., that had the goal of powering proof of work mining.

Not only does burning coal waste create carbon emissions that contribute to the climate crisis, but it also increases emissions of heavy metals, acid gasses and air toxics.

It doesn’t have to be this way. Proof of work is a ridiculously energy-guzzling approach to crypto mining that bitcoin remains wedded to, despite the existence of alternative consensus mechanisms. Ethereum, the world’s second-largest cryptocurrency, last year “merged” to using a process known as proof of stake, which uses 99 percent less electricity than proof of work. It obviates the need to harness dirty fossil fuel power, as the energy demands of proof of work no longer exist.

“From my perspective as an environmental advocate, if you are going to do crypto blockchain . . . do it with proof of stake and don’t waste energy – change the code,” says Altenburg. “There’s no unique thing that bitcoin brings to the table, aside from name recognition and a highly inflated market cap, that other coins don’t do and probably do better.”

But communities have few options to force bitcoin miners to change their ways, and fights over planned or existing crypto mines remain largely case-by-case, he notes.