Since a spill polluted the Dan River early last year, coal ash has become an environmental head ache for Duke Energy. But while Duke, state regulators, and environmental groups struggle with how to safely store or bury more than 100 million tons of the waste, other industries don’t look at coal ash as waste—it’s a commodity, and they want more.
In a conference room lined with models of cement trucks, the president of Concrete Supply Company, Henry Batten leans back in his chair and says he’d like more coal ash.
“Absolutely I want it. Our whole industry wants it,” Batten says.
Batten bought 250,000 tons of the same waste Duke Energy is trying to get rid of.
It’s used outside at the cement mixing plant—an industrial swirl of beige metal pipes, sheets, and catwalks. Batten points to three silos at the top. Each holds an ingredient for concrete.
“One of those is ash, and it discharges into a pipe, and goes into a scale, so we weigh it up, and then it discharges into the mixer,” says Batten.
The ash makes concrete stronger, more durable, and cheaper. Many buyers require it. Its use also has support from environmental groups. Scott Slesinger is the legislative director for the Natural Resources Defense Council.
“The most important issue with coal ash is erosion from water,” Slesinger says. “You don’t want water to hit coal ash to allow the toxic chemicals, the arsenic and the mercury that’s contained in it, to be leached.”
The concern in North Carolina, and many states, has centered on the ash leaching into groundwater from earthen ponds where it’s stored. Concrete, though, binds it—no leaching. But, with many coal plants closing nationwide, there’s less ash to be had, so the construction industry has complained of shortages.
While that may seem an opportunity for Duke Energy, a company with five years to move all ash from four coal plants and possibly more to follow, Batten says his company mostly has to import from out of state.
“Duke is still our smallest source, when we can get it,” says Batten. “There were several times this year when we couldn’t get any.”
There are two obstacles. Duke burns a type of high-carbon coal, and the ash needs to be processed to make good concrete; the company says it’s been less expensive to store it in the ponds. That calculus may have changed since a state law requiring the company has to close those ponds, but Duke spokeswoman Catherine Butler says that law has led to the second obstacle.
“It’s a scope and scale issue,” says Butler.
With 15 million tons of ash to move now, Butler says the company couldn’t reprocess and sell enough to make it worthwhile.
“We’re looking at faster options that reuse a large amount, so that’s where the structural fill can often be a more beneficial opportunity,” Butler says.
Structural fill means using the ash to flatten or grade uneven land before construction. Environmental groups have generally approved this use, as well, provided the ash gets wrapped in clay and plastic liners so it won’t leach. Duke supplies fill to Asheville Regional Airport at no cost, and has another in the works to refill old mines in Chatham County—although over the objection of residents.
Still, Butler says transporting ash more than 100 miles rarely makes financial sense, either for the utility or ratepayers, who pay fuel costs.
So, Duke only recycled about a third of what it produced last year. Compare that to South Carolina power company Santee Cooper, which has reused as much as 90 percent.
“Your preferred choice ought to be reusing it,” says UNC Charlotte engineering professor John Daniels. “The way I look at ash is number one as a construction material. And the extent to which the market can’t use that construction material, then you’re left with disposal.”
Daniels sits on a Duke-sponsored advisory panel and s looking for other ways to reuse ash. He holds a gray, cylindrical brick made mostly of coal ash and wastewater they’ve made at the university.
“The objective here is to develop a material that if you have to dispose of it you don’t have to worry about it impacting groundwater, or perhaps you can go on and use this in other product,” says Daniels.
Daniels suggests coal ash bricks. A recent report from the state’s Coal Ash Management Commission floats the use of coal ash in roofing shingles or even bowling balls. But Daniels and that report also say for now, the most obvious, underutilized reuse is still concrete.
Duke says it will hire a consultant to do its own study in the next few weeks, but has no plans to sell any of the ash in its storage ponds to cement companies.
At Concrete Supply in Charlotte, Henry Batten says he doesn’t understand that.
“Taking a waste product, selling it, and getting the value of that sale is less expensive than putting it in a truck, taking it to a landfill, putting it in a landfill, and maintaining that landfill in perpetuity,” Batten says. “It just doesn’t make sense to me.”
