Many of western Pennsylvania’s biggest polluters are operating with expired air quality permits. And an environmental group says that makes it harder for the public to understand what kind of emissions are coming from power plants, oil and gas storage terminals and manufacturers.

The Group Against Smog and Pollution (GASP) says about one third of facilities considered “major sources” of air pollution within a 10-county area around Pittsburgh are operating with expired Title V permits. These are comprehensive legal documents required under the Clean Air Act that determine how much and what kind of air pollution a facility can emit.

LISTEN: Who’s To Blame for All These Expired Air Permits?

According to GASP attorney John Baillie, in every case the companies had re-applied for the permits, but they were never acted on by state and local regulators. Baillie says that doesn’t necessarily mean the companies are polluting any more than they would have with a current permit. Under state law, if the Department of Environmental Protection (DEP) or local air agency fails to issue or deny a permit renewal, the conditions of the old permit remain in effect.

But Baillie says in these cases, the public has less information about these facilities than they should. The Title V permit is a single document containing details—accessible to the public—about what each facility is supposed to do to comply with the law. That includes new conditions that may be imposed because of updates to clean air regulations.

“Without the permit, you have to determine on your own what obligations this source is subject to,” Baillie says. “It makes it harder to determine whether or not they’re complying with the law.”

The Allegheny County Health Department’s Melissa Wade says, in some cases, permit requests can get delayed when the agency requires more testing.

“The lack of a permit, or an expired permit, does not alleviate in any way the obligations of a source to comply with all county, state and federal regulations or other requirements,” Wade said in an emailed statement.

The Pennsylvania DEP, which issues permits for facilities outside of Allegheny County, says it’s performing its “compliance inspection and oversight duties” of these facilities in accordance with federal law. The DEP did not respond to questions about why the air permit applications had not been acted on—in some cases—for years.