In a statement, EPA Administrator Andrew Wheeler said the Obama-era rules “placed heavy burdens on electricity producers across the country.”

“These proposed revisions support the Trump administration’s commitment to responsible, reasonable regulations,” Wheeler said, “by taking a common-sense approach that will provide more certainty to U.S. industry while also protecting public health and the environment.”

Under the new proposal, companies will have to stop placing coal ash into unlined storage ponds near waterways by Aug. 31, 2020, and either retrofit these sites to make them more secure or begin to close them. Unlike the Obama-era rules, the EPA will allow greater leeway and more time for operators to request extensions ranging from 90 days to three years, until Oct. 15, 2023, if they can convince regulators that they need more time to properly dispose of the waste.

Moreover, if a company can demonstrate it is shutting down a coal boiler, it can petition to keep its storage ponds open for as long as eight years, depending on their size. Slurry ponds smaller than 40 acres could get approval to stay in place until Oct. 15, 2023, officials said, while larger ones could remain open until Oct. 15, 2028.

In a phone interview Sunday, American Public Power Association general counsel Delia Patterson said the proposed rules reflect the fact that it can take time to design, permit and construct new facilities that can pass muster.

“I think the EPA is actually acknowledging the reality of the situation. It’s just really not in anyone’s interest to rush this,” said Patterson, whose group represents publicly owned utilities that provide 15 percent of the nation’s electricity.

Environmentalists have sharply criticized the proposals, arguing that these containment sites pose serious risks to the public at a time when more frequent and intense flooding, fueled in part by climate change, could destabilize them and contaminate drinking water supplies that serve millions of people. The rules will be subject to public comment for 60 days.

During the past decade, Tennessee and North Carolina have experienced major coal ash spills that have destroyed homes and contaminated rivers, resulting in sickened cleanup workers and extensive lawsuits.

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The question of how to handle coal waste, which is stored in roughly 450 sites across the country, has vexed regulators for decades. The Obama administration negotiated for years with environmental groups, electric utilities and other affected industries about how to address the waste, which can poison wildlife and poses health risks to people living near storage sites.

Lisa Evans, an attorney specializing in hazardous waste litigation for the environmental group Earthjustice, said allowing the electric industry to extend the life of coal ash pits represents a particular threat to low-income and minority Americans, who often live near such installations.

“Allowing plants to continue to dump toxic waste into leaking coal ash ponds for another 10 years will cause irreversible damage to drinking water sources, human health and the nation’s waters,” Evans said in an email. It was not surprising, she added, that the coal industry had lobbied against closing these storage sites. “Operating ponds is cheap. Closing them costs the utilities money,” she said.

It is also likely to add to consumers’ costs. Last year, for example, a member of the Virginia State Corporation Commission estimated it could cost ratepayers as much as $3.30 a month over 20 years — between $2.4 billion and $5.6 billion — to clean up Virginia-based Dominion Energy’s 11 coal ash ponds and six coal ash landfills in the state.

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The EPA’s proposals will retain several of the monitoring and public disclosure standards put in place in 2015, officials said, requiring companies to monitor nearby groundwater, publicly report the data and address any leaks that pollute area waterways. The “vast majority” of slurry ponds “are on the road to closure” under the new rule, an EPA official said.

Using monitoring data disclosed for the first time under the 2015 rule, a report published jointly earlier this year by the Environmental Integrity Project and Earthjustice found 91 percent of the nation’s coal-fired power plants reported elevated levels of contaminants such as arsenic, lithium, chromium and other pollutants in nearby groundwater.

The vast majority of ponds and landfills holding coal waste at hundreds of power plants across the country have leaked toxic chemicals into nearby groundwater at facilities from Texas to Pennsylvania to Maryland, according to that analysis. The report acknowledged, however, that the groundwater data alone does not prove drinking-water supplies near the coal waste facilities have been contaminated. Power companies are not routinely required to test nearby drinking water wells. “So the scope of the threat is largely undefined,” the report stated.

The EPA on Monday will also revise requirements for how power plants discharge wastewater, which contains some of the same kind of contaminants. Under the Obama administration, EPA staff had concluded it was feasible to prohibit any releases of such toxic materials by having the units continually recycle their water. The agency has now concluded this is much more costly than originally anticipated, and technological advances have made it cheaper to filter and capture the waste through a membrane system, officials said.

Under the new rule, plants would be allowed to discharge 10 percent of their water each day, on a 30-day rolling average. The administration projects the regulation would prevent 105 million pounds of pollutants from being released compared with the old standards because 18 affected plants would voluntarily adopt a more advanced filtration system. The administration also estimated it would save the industry $175 million each year in compliance costs and yield an additional $15 million to $69 million in annual public health and environmental benefits.

However, even if the 18 plants voluntarily adopted more advanced filtration techniques, they represent a minority of the nation’s total plants.

Elizabeth “Betsy” Southerland, former director of science and technology at the EPA’s Office of Water, said the proposed rule “relaxes the 2015 treatment requirements allowing increased selenium discharges and [the] release of contaminated water from coal ash handling. Even worse, it exempts a large number of plants from these relaxed requirements, allowing them to discharge more pollutants and continue disposing of ash in leaking ponds.”

Patterson said although it may be “just hard to understand” why companies need more time and flexibility, plant operators have no interest in contaminating nearby waterways. “They live in and around these communities,” she said.

Evans said environmentalists are likely to challenge the new rule on coal ash storage, and the federal government could again reverse course if a Democrat wins the presidency next year. She noted that, because 95 percent of coal ash ponds remain unlined, two-thirds lie within five feet of groundwater and 92 percent leak more than federal health standards allow, they could pose a risk to the public even as litigation winds its way through the federal courts.

“We have to hope that no wells are poisoned and no toxic waste is spilled in the interim,” she said. “Crossing your fingers is not a legal or sane way to regulate toxic waste.”