A federal appeals court in Denver ruled that the Environmental Protection Agency illegally allowed the state to exclude some greenhouse gas emissions when deciding if a source is subject to stringent Clean Air Act regulations.

In a decision issued Sept. 18, for a lawsuit brought by the Center for Biological Diversity against the EPA, the court struck down a provision of Colorado law that exempts “temporary emissions” from consideration when classifying a major pollution source as part of Colorado’s State Implementation Program for ozone management the EPA approved in May 2022.

“As we understand the ruling, the court sent Colorado’s plan back to EPA to review,” said Kate Malloy, spokesperson for the Colorado Air Pollution Control Division in a statement. “Regardless of what happens, the division is prepared to work with the EPA to ensure that Colorado’s plan moves the state forward on its path to achieving federal ground-level ozone pollution standards.”

“Colorado exempts temporary emissions from its air permitting program, and the largest source of pollution that they classify as temporary emissions is drilling and fracking oil and gas wells,” Center attorney Robert Ukeiley said in an interview with The Denver Gazette.

In their complaint the Center claimed that temporary emissions cannot be excluded, and that the state has been ignoring the issue for a very long time.

“In the past they’ve just pretended like those emissions don’t exist, but the court said they can’t do that anymore,” Ukeiley said. “They have to consider those emissions in determining whether a source of pollution is classified as major.”

Colorado statutes differ from federal law by defining both temporary and secondary emissions. The federal statute only defines and excludes secondary emissions, which are “emissions which would occur as a result of the construction or operation of a major stationary source … but do not come from the major stationary source … itself.”

While the EPA argued that temporary emissions fall within the definition of secondary emissions, the judge disagreed, saying that while some temporary emissions may come from exempt construction or vehicles, it is possible that some such emissions may not, and that the federal statute did not expressly include temporary emissions in the exemption statute.

“The court did not vacate the Colorado SIP, but rather vacated EPA’s approval of the state’s temporary emissions exclusion in the existing Nonattainment New Source Review permit program,” said Richard Mylott, spokesperson for the EPA in a statement to The Denver Gazette. “The temporary emissions exclusion in the permit program is only part of the Colorado SIP. All other existing approved Colorado SIP requirements remain in effect.”

Mylott said Colorado can revise the portion of the State Implementation Program that the court held EPA erroneously approved.

“If Colorado submits a SIP revision to address the provisions that EPA approved and that the court vacated, EPA will follow its usual process for acting on SIP submissions, which includes taking public comment on a proposed action before taking final action,” Mylott said.

Once the state submits a program revision, the Clean Air Act requires EPA to take final action on it within 18 months, Mylott said.

Ukeiley said the decision is not going to apply retroactively — it’s only going to apply to new sources starting construction after the court decision.