What to Do with 264 Billion Pounds of Coal Ash
UNC-Charlotte engineers are developing novel techniques to manage coal ash, but time is running short.
By Gabe Rivin
John Daniels claimed he could make water stand on a block of coal ash.
“Have I ever given you my little show-and-tell trick?” he asked, as he rushed to his cabinet. He returned with a chalky gray cylinder and a bottle of water. “Making stuff water repellent, to me, is just neat.”
Daniels laid two drops of water on the flat face of the cylinder. One droplet began to sink. Soon all that remained was a dark-gray spot.
But on the other side of the cylinder’s face, the water droplet remained globular and inert, repelled by a seal of water-resistant chemicals.
“If it’s water repellent, water’s not getting in,” Daniels said. “Water’s not getting in, water’s not getting out.”
Daniels is one of several engineers at UNC-Charlotte helping to answer a multi-billion-dollar question: What should Duke Energy do with its bounty of coal ash in North Carolina?
The ash, created when coal is burnt to produce electricity, has proven vexing for Duke, environmentalists and state lawmakers, all of whom are jockeying over its fate.
On one hand, the science seems clear. North Carolina’s coal ash is stored in large basins that are dug into the ground. These were constructed without liners, and so toxic metals in the ash, such as arsenic and chromium, can leach out of the basins.
The metals can find their way into subsurface water, or groundwater. This migration has the potential to contaminate drinking water for nearby residents who draw their water from wells drilled into the ground.
After a new round of tests near coal ash ponds, the N.C. Department of Environment and Natural Resources in April raised the possibility that coal ash is contaminating residents’ drinking water.
How to eliminate this threat though has been passionately contested, with some calling on Duke to move its ash to lined landfills and others saying that Duke can safely keep much of the ash where it is, provided that it’s dried out and covered up.
For either method, Duke faces an enormous engineering challenge. Duke’s surfeit of ash, a total of some 264 billion pounds, is also spread across 32 basins in the state, some of which are filled with water.
Duke also faces several tight timelines to close its sites.
All of which helps explain the urgency behind UNCC’s research.
Although North Carolina’s legislators prescribed much of Duke’s cleanup plan, there’s still a lot to learn about coal ash, the researchers say. And there are plenty of soon-to-be-proven methods to transform the ash, whether that means turning it into waterproof construction material or using it to build barriers that keep the rest of the ash dry.
In the lab
Milind Khire pointed at what looked like a metal drum, inside of which was a pair of metal arms.
“This is a geo-centrifuge,” he said. “We can actually create a prototype of a dam or a levy system here.”
Khire, another engineering researcher at UNCC, is planning to use the centrifuge with coal ash. By spinning wet ash at high speeds, he’ll be able to measure some of its fundamental physical properties. These include the behavior of water when ash is stacked in 200-foot piles, as may be the case at Duke’s landfills.
Khire said that much of this research is new.
“Very little strength and hydraulic property measurement has been done by anybody for coal ash,” he said.
And that’s a problem, he said, given some of the rushed deadlines for Duke’s ash basins. For three of its sites, Duke has until 2019 to dig up its coal ash and transport it to landfills.
But Khire said Duke should be given more time as engineers work to better understand ash and develop novel techniques to manage it in place, rather than shipping it to other communities.
Daniels, who has advised Duke on ash management, also criticized a one-size-fits-all approach to coal ash, such as environmentalists’ demand that Duke excavate and landfill all of its ash.
“The notion of excavating every site and putting it on a bunch of trucks – or even rail – and hauling it hundreds of kilometers or miles to some other far-flung site and entombing it is not necessarily the best approach,” he said. “Jumping from, ‘Every site has an impact, therefore excavate,’ to me is understandable, but it’s irresponsible from an engineering perspective.”
Daniels said novel engineering techniques could protect people’s health, at a fraction of the cost.
Those techniques may include deploying organosilanes, a chemical class that can render coal ash waterproof. Since 2007, Daniels has run small-scale tests using the compounds. He’s found organosilanes could efficiently transform large quantities of coal ash, allowing it to serve as a cover for ash ponds.
Khire is experimenting with a similar technique. By mixing coal ash with North Carolina’s soils, it’s possible to create a spongy material that keeps water out of an ash basin, he said. This too could serve as a cover for Duke’s ash.
Elsewhere in his lab, Khire is developing a technique that could improve Duke’s ability to pump water from its ponds. The technique uses charged electrodes to attract water while leaving behind the coal ash.
This technique would help Duke to dry out the ash so it doesn’t leach metals into groundwater. Combined with a waterproof cover, the ash would be protected from rain. Such a combination, the researchers believe, could protect the public’s health while saving enormous costs.
The problem with water tables
“The role of research and development in this entire process is really key,” Erin Culbert, a spokeswoman for Duke, said.
Culbert said researchers have extensively studied ash recycling; coal ash can be used to make concrete and wallboard, among other products. But closing ash basins “in a somewhat urgent timeline is really a place where we feel like there could be a lot of additional assistance and reconnaissance,” she said.
While Khire said Duke’s deadlines are needlessly rushed, environmental groups aren’t so patient.
D.J. Gerken, an attorney with the Southern Environmental Law Center, said that Duke and state regulators have known about these problems for years.
“When you start the clock from the time that Duke Energy and the state discovered that these ash pits were failing and contaminating nearby rivers, we are by no means on an aggressive timeline,” he said
He also argued that a system of dewatering and covering the ash, as Khire envisions, would not work. Many of Duke’s ponds were dug below the water table, the highest vertical level of groundwater, he said. And that means groundwater can flow into and out of ash basins, toxic compounds in tow.
Khire admitted this is possible. But he said Duke could still dewater and seal its ponds and continuously pump out any groundwater. He admitted this would be expensive though.
Gerken was skeptical of this plan.
“It is an engineering Band-Aid that must be continuously operated by Duke Energy forever if we’re going to protect groundwater and rivers,” he said.
Regardless of the method, Duke’s priority is to protect groundwater, the company’s spokeswoman Culbert said. When evaluating the options for a site, she said, Duke wouldn’t choose to cap an ash basin if doing so would allow for contamination.
Who will take it?
For now, state regulators have paused their work to determine the fate of Duke’s ash in response to a court fight between Gov. Pat McCrory and the General Assembly.
Nonetheless, Duke has plowed ahead. The company is beginning to excavate – or plans to excavate – 20 ash basins across the state. Duke says it will recycle the ash or transfer it to lined landfills. This meets the strictest requirements under the 2014 coal ash law.
But that hasn’t appeased some environmentalists. Several groups have protested Duke’s proposal to place ash in two abandoned clay mines, even though the ash will be blocked off with liners.
Gerken takes a different view. He said that while there’s no perfect solution for coal ash, “Having it in a modern, properly lined facility anywhere is better than having it in an unlined pit.”
And there’s still 264 billion pounds of waste – the byproduct made from powering refrigerators and air conditioners, North Carolina’s hospitals and homes for several generations – that remains to be disposed of safely.
And it has to go somewhere.