To the list of environmental threats facing modern America, add coal ash. Seen largely as a necessary evil turned good by industrial recycling, the leftovers of coal-burning steam generators gained greater villain status on Christmas Eve 2008, when the containment dam at a coal-slurry disposal site in Tennessee gave way — and spilled more than a billion gallons of sludge on the town of Kingston.

The destruction of a dozen homes and the 300-acre swath of ruined land were only part of the disaster: What's in coal ash was the real worry — mercury, lead and other heavy metals; arsenic, cadmium, selenium, thorium and chromium are left in the ash.

About half of what's left from coal combustion is reused — in asphalt road-base, in cement and in drywall, with no noticeable health effects once the stuff is set and sealed.

But what about the other half? There is no federal agency overseeing its disposal, so by now there's an estimated yearly buildup of at least 65 million tons of ash and sludge. It goes to landfills, storage ponds and slag piles; sometimes back into mines as fill.

Most states have few, if any, requirements for monitoring, for slurry-pond liners or for dust controls that would help protect against the ash's toxins seeping into aquifers.

The Environmental Protection Agency is proposing to regulate the disposal of that ash — and since New Mexico power plants generate the 10th-greatest amount of the stuff, our state's, and region's, environmental community took great interest in the EPA hearings Thursday in Denver. So did farmers and ranchers, some already threatened by slag heaps and slurry ponds.

There's more than mere regulation at issue: Should coal ash be considered hazardous waste, which would call for federal monitoring and for adequate linings beneath it? Or a non-hazardous waste, leaving it up to state regulators — and, likely, concerned-citizen lawsuits — to keep the coal-burners in line?

Power-company lobbyists argued for the latter choice — noting, in their trendy new veiled-threat approach to the environment, that federal oversight would mean more-expensive electricity generation, thus higher rates; and, of course, they raised today's handy-dandy bugaboo, the chance of lost jobs.

New Mexico sheep rancher R.G. Hunt, Jr., of Waterflow, wasn't buying into the non-hazardous argument. He says the nearby Four Corners power plant is poisoning his water with coal ash; that the stuff has killed 1,400 of his animals, and that it's seriously harming his family's health.

Trust the utilities people to come up with their own studies saying there's no health danger to coal ash — and in Denver, they contended that there'd be enough environmental protection under the non-hazardous category.

But a leading objection to calling the ash hazardous is a public-relations one: The utility companies have made great strides in recycling the ash. Would their customers in the drywall, roofing, concrete, and asphalt business steer clear of it if they had to acknowledge that their contents include hazardous materials?

It could still be beneficially used if EPA judges it hazardous — and we're confident that the utilities' formidable public-relations and advertising people can overcome any stigma to the stuff. In fact, they could tout themselves as environmental do-gooders for being part of such a creative solution in this ongoing era of coal-fired power.

EPA already has issued reports pointing to a need for calling coal ash what it is: hazardous waste; perhaps "special" hazardous material, as some in the agency suggest — setting it apart from the worst of the hazmat categories, yet recognizing it as material that's got to be monitored.

The Denver hearings were only one of several to be held around the country during the next few weeks. They're long overdue — and, since groundwater contamination isn't something easily remedied once it starts, the EPA should pay special attention to the plaints of the power plants' farming and ranching neighbors.