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Coal ash is spilling into North Carolina’s river. Here’s why it’s so hard to regulate.

When power plants burn coal, they leave behind plenty of waste. Each year, coal plants across the United States produce more than 100 million tons of "coal ash," which can contain toxic elements and is either recycled or stored in landfills and ponds. And, now and again, these storage sites can leak or spill.

That's what happened in North Carolina this past Sunday: Duke Energy said that up to 82,000 tons of wet coal ash had spilled out of one of its retired coal-plant sites into the Dan River. The cause? A broken storm pipe. So far, municipal officials say they've been able to filter contaminants from the water supply, but the ash turned the river into a gray sludge, threatening wildlife.

This isn't the first time coal ash has wreaked havoc: Famously, in 2008, a giant storage unit at the Tennessee Valley Authority's Kingston Fossil Plant ruptured, releasing 1.1 billion gallons of coal ash slurry that damaged three homes and poured into the Emory River. On a smaller scale, environmental groups have found at least 207 sites around the United States where coal ash has contaminated the air or water.

Yet regulation has been a topic of sharp debate for decades. Ever since the 1980s, lawmakers have disagreed on whether to treat coal ash as a "hazardous waste," which would trigger specific, complex regulations. In 2010, the Environmental Protection Agency proposed the first-ever rules to regulate the stuff. But coal mining and utility companies argued that overly strict rules would impose unreasonable costs and fought hard against them. Ever since, the Obama administration has been sitting on the proposal — though the EPA has now agreed to reach a decision by Dec. 19, 2014

It's a contentious issue. So below is a basic primer on what coal ash is and why it's proven so difficult to regulate:

What is coal ash? When pulverized coal is burned to produce electricity, it leaves behind inorganic matter, including fly ash, bottom ash, and boiler slag. This residue is loosely referred to as "coal ash." Nowadays, most of the ash gets trapped by filters and scrubbers rather than being released into the air.

There's a staggering amount of coal ash being produced each year: In 2012, the nation's coal plants generated some 110 million tons of it. Roughly 45 percent of that ash gets recycled to help make concrete, pavement, and other materials.

The rest is stored in landfills, quarries, and ponds as either dry ash or as a wet slurry. Companies typically accumulate hundreds of thousands or even millions of tons of the material over the course of decades. Currently, there are more than 2,000 storage sites around the country, including over 400 dry landfills and 676 wet ash ponds:

The amount of coal ash at power plants is also likely to increase in the coming years as the EPA requires power plants to scrub mercury and other pollutants out of their exhaust.

Why are people worried about coal ash storage? One big concern is a sudden, catastrophic spill like the one in Tennessee. But there's also the risk that ash could contaminate the water or air on a smaller scale, too. Coal ash often contains a variety of toxic elements like selenium, mercury, and lead — although the precise amounts vary widely. In some cases, those heavy metals can pose health risks to humans and wildlife.

The big spills are somewhat rarer, with the 2008 Kingston disaster in Tennessee being the largest to date. But they're not impossible: The EPA has identified 45 wet ash ponds around the country that are "high hazard" — that is, if the encasing broke, it could lead to a loss of human life. (It would be as if a massive dam broke.) Two of those high-hazard ponds are located at Duke Energy's Dan River site in North Carolina.

The risk of smaller-scale contamination is also worth noting. In its 2010 proposed rule, the EPA identified a variety of potential health risks: If the coal ash was deposited in an unlined landfill or sand pit or quarry, some of those toxic elements could leach into the groundwater or migrate off-site. Or liquid waste could leak into surface water during a flood. Or dust from dry ash could become airborne.

The environmental group Earthjustice has found 207 sites in 37 states where coal ash has already contaminated the water or air in violation of federal health standards. For example: Out in Prince George's County Maryland, millions of tons of coal ash from a landfill leaked into a nearby creek after two recent hurricanes. Out in Nevada, the Moapa River Reservation has alleged that dry coal ash was frequently blowing into their communities from uncovered dumps, leading to a rash of illnesses.

Why is there such a fierce debate about regulation?  Currently, there are no federal standards on how coal ash is disposed or where and how it can be recycled. It's all handled by the states, where the rules can vary from state to state.

That debate was upended in 2010, when the EPA proposed two main options for regulating the ash. The first option would regulate coal ash as a "solid waste." The more comprehensive option would essentially regulate coal ash as a hazardous waste.* That wording tweak turns out to make a fairly big difference:

1) The "solid waste" option would require more frequent inspections for wet ash ponds, impose controls on the dust at dry ash sites, and close dumps that were structurally unsound. It would allow companies to maintain wet ash ponds, but they'd have to install liners and other safeguards. (Utilities wouldn't, however, be required to go back and look at older inactive dumps, ponds, or landfills.)

But there wouldn't be any federal enforcement of these standards — this would all be left to either the states or citizen lawsuits. In all, the EPA estimates that this would cost some $587 million per year, or $8 billion total.

2) The more comprehensive "hazardous waste" option would involve an additional set of rules on top of the above. For starters, the federal government would have direct say over enforcement and monitoring, not the states. What's more, under this option, utilities couldn't build any new wet ash ponds and would have to phase out their existing ponds — moving everything over to specially designed landfills.

The EPA would also oversee every aspect of coal ash handling, from storage to transportation to disposal. And companies would have to show that they have the financial resources necessary to clean up after disasters. All  told, the EPA estimates that the "hazardous waste" option would cost companies $1.4 billion per year, or $20 billion in all. (Industry groups say the cost could be triple that.)

Environmental groups tend to favor the second option, with direct EPA enforcement. But mining and utility companies have long argued that the "hazardous waste" rule would be far too costly. They'd have to move coal ash off-site or set up expensive hazardous-waste landfills.  Opponents also tend to note that there's little evidence to suggest that states are doing a poor job of regulating coal ash themselves. Finally, they argue, recycling companies could be more reluctant to purchase coal ash if it was deemed "hazardous."

Strict coal-ash rules could also increase the cost of maintaining coal-fired power plants, the Government Accountability Office has found. Last year, the Tennessee Valley Authority closed eight coal plants in Alabama and Tennessee, with the prospect of costly coal-ash rules being just one factor among several.

So where does regulation stand now? So far, utility companies have lobbied strongly to fend off the rules. And the EPA hasn't moved forward on either proposal since 2010. So environmental groups, including Earthjustice, sued over the delay, and a judge ordered the EPA to come up with a timeline. Now the agency says it will release some sort of final rule by Dec. 19, 2014.

Environmental groups have accused the White House of punting on the rule until after the 2012 election, for fear of angering swing states that depend on coal. The EPA, for its part, said it was merely taking its time considering and responding to more than 450,000 comments on the rule.

In the meantime, Congress has tried at various points to pass its own legislation. In 2012, House Republicans passed two bills that would have prevented coal ash from being deemed "hazardous" and left regulation to the states. Democrats blocked those rules, calling them overly lax. That stalemate isn't expected to change anytime soon.

*Note: Technically, in the more stringent option, the EPA would classify coal ash as a "special waste," but it would basically be treated like hazardous waste for most purposes.

Further reading:

--The Congressional Research Service has a useful, if dense, overview (pdf) of the EPA's coal-ash regulations.