By Dylan Tussel
Parts of eastern Ohio and western Pennsylvania and West Virginia sit atop thousands of abandoned coal mines, spent of their bounty and flooded with polluted water.
But geologists and energy experts say there might be a clean future for mines remembered for their dirty past.
“We basically have an underground lake we live on. There’s enormous potential,” said Terry Ackman, president of M. T. Water Management Inc. in Pittsburgh and a former U.S. Department of Energy scientist.
Underground mines have been used successfully for geothermal heating and cooling in Europe and Canada, said Tim Leftwich, a geologist with the Ohio Department of Natural Resources.
U.S. scientists hope they can bring the technology home.
“Underground coal mines will probably be the next big thing,” Leftwich said.
Geothermal refers to using Earth’s natural heat. In conventional systems, wells are drilled deep into the ground, and water or other fluids are piped down and back up.
Using a heat exchanger, the systems pull the warmth from the ground to heat buildings on cold days and remove heat from the buildings and transfer it into the ground on warm ones.
Emerging research, however, suggests that flooded underground mines might be a much more efficient source of geothermal energy in some areas.
The temperature below ground remains constant year-round. In the summer, it’s lower than surface temperature, and in the winter, it’s higher.
The area experts are considering is called the Pittsburgh coal seam, which contains about 5,000 square miles of abandoned mines, said Ackman, who used to work at the National Energy Technology Laboratory.
Ohio has about 7,390 abandoned underground mines, many of which are located in the east, said Jim McDonald, with the Ohio Geological Survey. Those mines cover about 761 square miles.
Leftwich said many of the mines could heat and cool a large area.
“Instead of heating and cooling just one house, you can heat and cool a number of facilities, or a very large one,” he said.
The water’s temperature can be tapped in two ways.
The more common method is to use an open-loop system, said Mark Wolfe, with the Ohio Geological Survey. In this system, mine water would be piped into a heat exchanger at the surface and then injected back into the mine.
“They’re just circulating that water out,” Wolfe said. “It’s not wasting any supply.”
The other method uses a closed-loop system, similar to ground-source wells, in which contained water or other fluid is circulated through the mine water to a surface-level heat exchanger and back.
Flooded mines require minimal drilling compared with ground-source geothermal systems.
“You can drill four or five holes rather than hundreds,” Wolfe said.
And there is so much available water to draw from that a single mine potentially could do the work of hundreds of traditional geothermal wells, which cannot handle as much water.
“Mines can hold so much water down there,” Leftwich said. “With that volume of water, you can really pump without changing the water’s temperature.”
To figure out how well geothermal systems including those in mines could work across the country, the U.S. Department of Energy provided $21.9 million for a three-year, $22.1 million exploration project (the rest of the money came from the recipient states).
The project is in its second year, and Ohio researchers are still in the preliminary stages of measuring the geothermal potential of the mines here. Testing will start next year.
The process is working elsewhere. For example, the John Wesley AME Zion Church in Pittsburgh is heated and cooled with mine water. The heat exchanger in the building uses the water’s naturally constant 56.6-degree temperature to do both, said Darwin Burtner, president and owner of Western Pennsylvania Geothermal Heating and Cooling Inc., which worked on the project.
The water in the mine near the church flows to the surface, making the process simpler than drilling traditional geothermal wells.
“All we had to do was make the concrete vault (for the heat-exchanger) and run the water … into it,” he said. “We didn’t have to drill. The water came to us; we didn’t have to go to the water.”
Marywood University in Scranton, Pa., also uses a flooded mine below campus to cool its Center for Architectural Studies. Mine water is pumped into a heat exchanger in the building, where it cools the building’s water. That water is pumped through hollow metal ceiling beams to cool the building during warm months, said Wendy Yankelitis, assistant vice president of Buildings and Grounds at Marywood.
The mine water then goes back underground.
The open system, which required drilling two wells — one to extract water from the mine and another to pump it back in — pulls out about 300 gallons of water per minute.
“We don’t need any fans or anything,” Yankelitis said. “It’s just a natural system.”