The Environmental Protection Agency (EPA) says it will seek to revise 2015 guidelines mandating increased treatment for wastewater from steam electric power-generating plants.

EPA Administrator Scott Pruitt first moved in April to delay implementation of the new guidelines. The wastewater from coal-fired plants that enters rivers and lakes often contains traces of heavy metals such as lead, arsenic, mercury and selenium.

“After carefully considering your petitions, I have decided that it is appropriate and in the public interest to conduct a rulemaking to potentially revise (the regulations),” Pruitt wrote in the letter addressed to the pro-industry Utility Water Act Group and the U.S. Small Business Administration.

Pruitt’s letter, dated August 10, was filed with the Fifth Circuit U.S. Court of Appeals in New Orleans, which is hearing legal challenges of the wastewater rule. With Pruitt now moving to rewrite the standards, the EPA has asked the court to freeze the legal fight.

While that process moves ahead, the EPA’s existing guidelines from 1982 remain in effect, according to news reports.

The EPA estimates that the 2015 rule, if implemented, would reduce power-plant pollution by about 1.4 billion pounds a year. An estimated 12 percent of the nation’s steam electric power plants would have to make new investments to meet the higher standards, according to the agency.

According to Obama-era estimates, utilities would need to spend about $480 million on new wastewater treatment systems, resulting in about $500 million in estimated public benefits, such as fewer incidents of cancer and childhood developmental defects.