"We have found a way to get better protections, lower emissions and lower costs as well," said the Environmental Protection Agency's top air pollution official, Gina McCarthy. In a conference call with reporters, McCarthy said the agency had found the "sweet spot" since issuing the final rule under a court-ordered deadline in March.
That "spot is affordable, practical regulations that provide the vital and long overdue health benefits that Americans demand and deserve," she said.
The changes would require pollution controls at the 5,500 largest and most polluting boilers nationwide, such as those at refineries and chemical plants. Another 195,000 smaller boilers would be able to meet the rule through routine tune-ups.
The bulk of boilers nationwide - about 1.3 million - would not be covered by the rule, since they are too small and emit too little pollution to warrant controls.
The tweaks are the latest for a rule that has undergone numerous revisions, and has been among the most criticized by industry and lawmakers for its cost and its scope. Sen. Lamar Alexander, R-Tenn., has said the boiler rule has "come from another planet", even as he has defended the agency in the face of other Republican rollbacks.
The agency had already found ways to cut the cost of compliance in half, by about $1.8 billion, when it announced the final rule in March, promising future revisions.
On Friday, industry groups still were not satisfied.
Jay Timmons, president and CEO of the National Association of Manufacturers, said in a statement that the boiler rules would still do significant harm to job growth.
"We will continue to urge the EPA to extend the compliance time frame and consider a more reasonable approach to setting the emission standards to ensure additional jobs are not put at risk," he said.
The American Chemistry Council, which represents chemical companies, pressed for legislation to delay the rules while acknowledging improvements had been made.
The Republican-controlled House passed a bill in October seeking to delay the boiler regulation and lower the threshold that boiler operators would have to meet from "maximum achievable" pollution control to the "least burdensome." A bipartisan bill pending in the Senate would give the EPA additional time to rewrite the rule and for industry to comply.
Industrial boilers burn coal and other fuels to generate steam and hot water for heat and electricity. They're the nation's second-largest source of mercury emissions, a potent neurotoxin, after coal-fired power plants. But boilers are among a handful of pollution sources that still have no standards for toxic emissions.