Heavy machinery excavates and carrie coal ash from a drained coal ash pond at Possum Point Power Station in Dumfries, Va., in 2015. Dominion Resources is moving all existing coal ash to the only lined coal ash pond, which will be capped in a three-year process. (Kate Patterson for The Washington Post)

The Environmental Protection Agency plans to reconsider parts of an Obama-era effort to regulate potentially toxic waste known as coal ash, again siding with energy-industry efforts to slow or reverse standards put in place in recent years.

Federal regulators have struggled for several decades with how to address coal ash, the substance that remains when coal is burned in power plants to generate electricity. A toxic mix of mercury, cadmium, arsenic and other heavy metals, coal ash can pollute waterways, poison wildlife and cause respiratory illness among those living near the massive storage pits plant operators use to contain it.

A rule finalized in 2015 by the Obama administration imposed new standards on coal ash disposal sites by ramping up inspection and monitoring levels and requiring measures such as liners in new waste pits to prevent leaking that could threaten adjacent drinking water supplies.

In May, however, industry officials petitioned the EPA to ask that the new administration revisit the rule. The existing regulation, they wrote, “affects both the utility and coal industries and also affects the large and small businesses that support and rely upon those industries. It is causing significant adverse impacts on coal-fired generation in this country due to the excessive costs of compliance — even EPA acknowledges the costs of the rule outweigh its benefits.”

Their pleas found a sympathetic ear in EPA Administrator Scott Pruitt, who in a letter dated Wednesday replied that it was “appropriate and in the public interest” for the agency to rethink the regulation.

“It is important that we give the existing rule a hard look and consider improvements that may help states tailor their permit programs to the needs of their states, in a way that provides greater regulatory certainty, while also ensuring that human health and the environment remain protected,” Pruitt said in a statement Thursday.

The agency stressed that it had not committed to changes or that it necessarily agrees with the merits of the industry’s petition. If the EPA ultimately decides to roll back the coal ash standards, it will go through the usual rulemaking procedure, which could take years.

Environmental groups were quick to criticize Pruitt’s latest decision as another nod to special interests.

“Donald Trump and Scott Pruitt are continuing their capitulation to the coal industry at the expense of the health of our families,” Mary Anne Hitt, director of Sierra Club’s Beyond Coal campaign, said in a statement. “This is another example of Pruitt not caring about science, working families, or clean water, and instead bending over backwards for polluters eager to avoid accountability to the laws that keep our communities and families healthy.”

Ken Kopocis, the former top official in EPA’s water office under President Barack Obama, said the original rule had taken industry concerns into account and that rolling it back would endanger public health.

“We bent over backwards for industry both in terms of the substance of the rule and in terms of the timing,” Kopocis said. He noted the dangers that coal ash pits pose, particularly in light of the severe storms the country has experienced in recent weeks. “These things are ticking time bombs.”

Calls to strengthen safeguards for coal ash waste intensified after a massive December 2008 spill. A dike failed at the Tennessee Valley Authority’s Kingston Fossil Plant, allowing 5.4 million cubic yards of ash to flow into nearby rivers. Another accident at a Duke Energy facility in North Carolina in February 2014 resulted in thousands of tons of coal ash pouring into the Dan River.

Utility operators produce more than 110 million tons of coal ash annually, according to the EPA, and a rule the agency finalized in December 2014 established stricter guidelines for constructing and maintaining coal ash storage pits. The regulations said new pits had to be lined — to prevent the waste from seeping out — and that companies must conduct local water quality tests as well as disclose more information about their operations on a publicly available website.

The regulation did not classify coal ash as hazardous waste, as environmentalists have sought unsuccessfully for more than 35 years. More than 40 percent of coal ash is recycled to help make concrete, gypsum wallboard and pavement, and a broad industry coalition has said identifying it as hazardous would raise the cost of handling the material.

Then-EPA Administrator Gina McCarthy described the Obama administration’s standards as “a pragmatic step forward,” and key industry players said they viewed them as acceptable.

Read more:

Trump administration halts Obama-era rule aimed at curbing toxic wastewater from coal plants

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