Government regulators sided with environmental advocates, in part, when they ruled recently that a U.S. Steel plant in the Mon Valley might be violating clean-air laws under a current permit that restricts its emissions.

The federal Environmental Protection Agency (EPA) delivered a split decision last month over petitions by four environmental groups, who claimed county permits for Clairton Coke Works don’t comply with some Clean Air Act requirements. The agency sided with the petitioners on some claims — such as inadequate emission testing and compliance schedules — and disagreed with others.

Allegheny County health officials now must revise the plant’s Title 5 permit to ensure that emissions are more closely regulated, among other changes, EPA officials said.

Allegheny County spokeswoman Amie Downs confirmed the health department received the EPA notice and is drafting a response.

“It would be inappropriate to comment before that response is complete,” Downs said.

U.S. Steel “will work with the Allegheny County Health Department to appropriately respond to the EPA order,” spokeswoman Amanda Malkowski added.

One petitioner — Clean Air Council, which has offices in Pittsburgh and Philadelphia — celebrated the decision Tuesday.

“Clear Air Council is grateful to the EPA for taking this important action to protect clean air in the area,” Legal Director Alex Bomstein said.

“What is absolutely clear, no matter how you slice it, is that the coke works is a massive polluter that has had a major impact on people’s health,” he added. “Any incremental change that can be made will improve people’s lives.”

In April, PennEnvironment Research & Policy Center’s “Toxic Ten” report called the Clairton plant the worst air polluter in Allegheny County. The group said 10 area facilities emitted more than 1.4 million pounds of toxic pollutants in 2021 — including substances linked to cancer, birth defects, reproductive problems and other ailments.

U.S. Steel first obtained its Title V permit for the Clairton plant from county officials in 2012, EPA officials said. The Allegheny County Health Department announced a new draft permit in January 2022, then issued a final renewal permit after a public-comment period in November 2022.

All major, stationary sources of air pollution must apply for Title V permits every five years, EPA officials said. These permits are issued locally, and limit emissions to ensure businesses follow clean-air laws. The permit doesn’t impose air-quality controls, but does require adequate monitoring, record-keeping and reporting.

The EPA’s ruling doesn’t “prevent the source from continuing to operate while the Allegheny County Health Department works on revisions to the permit,” spokesman David Sternberg said Tuesday.

The Clairton plant, built in 1901 and operated by U.S. Steel since 1904, is the largest by-products coke plant in the U.S., the EPA said in its ruling. The facility produces 13,000 tons of coke daily by distilling more than 18,000 tons of coal.

The facility is a major source of particulate matter, a form of air pollution; carbon monoxide, which can produce flu-like symptoms ; sulfur dioxide, which is a main component of acid rain; and volatile organic compounds, some of which cause cancer, among several other pollutants.

More than 30,000 people live within five kilometers (about 3.1 miles) of the facility, EPA officials said. Roughly one-third of them are deemed low income.

Those living near the massive plant, on the banks of the Monongahela River south of Glassport, have claimed for years the facility’s emissions have worsened their health.

A study published in 2020 showed 22.4% of children in Clairton have asthma and are getting sick at a rate that is three times higher than the national average.

Last December, the Environmental Integrity Project said it found concentrations of benzene in homes near U.S. Steel operations that indicated residents there might face an increased risk of noncancerous health effects, such as weakened immune systems.

The executive director of one of the petitioners — Group Against Smog and Pollution (GASP) — objected to a settlement U.S. Steel struck with county officials in 2019, after emissions flared due to a Christmas Eve 2018 fire.

“The facility is actually in worse compliance now,” said Patrick Campbell, who has led the Regent Square-based group for two years.

“It’s encouraging to see the EPA is taking these petitions seriously,” Campbell said. “They realized the scope and the scale of this facility and how much pollution it puts out in the region.”

Others among the four groups that petitioned the EPA — GASP, Clean Air Council, Environmental Integrity Project (EIP), and PennFuture — echoed that.

“Air quality issues are an ongoing public health problem in Allegheny County and ensuring that industry polluters are operating within their permit limits is critical to protecting our health and environment,” said Angela Kilbert, senior attorney for PennFuture.

EIP called it “a long-overdue win for local residents, who can see that environmental groups and now EPA are stepping up to stop polluters like U.S. Steel from being able to continue operating with lax permits.”