The U.S. Attorney's Office is suing a division of Questar Corp. for alleged violations of the federal Clean Air Act at five of its natural gas compressor stations in northeastern Utah.

In a 49-page complaint filed in U.S. District Court in Salt Lake City on Feb. 29, federal prosecutors claim that Questar Gas Management Co. has failed to control toxic air emissions at its Coyote Wash, Chapita, Island, Wonsits Valley and River Bend compressor stations in the Uinta Basin.

All five plants lie within the historic boundaries of the Uintah-Ouray Indian Reservation, which gives the EPA, not the state, regulatory control over the compressor stations.

"What we're seeing out (in the Uinta Basin) is unprecedented oil and gas development by not just Questar but many companies, and we're concerned about the cumulative impact on the air quality in the region," said Jim Eppers, an attorney with the U.S. Environmental Protection Agency's Legal Enforcement Program in Denver.

In the complaint, prosecutors claim that the five compressor stations emit benzene, toluene, ethyl benzene, xylenes and hexane, all toxic air pollutants typically contained in emissions from oil and natural gas production facilities. The compressor engines at these facilities also produce formaldehyde as a byproduct, the complaint states.

All six of these chemicals are known to cause cancer and birth defects.

In addition to claiming that Questar allowed airborne toxins to be released from the five compressor stations, prosecutors allege that the company made repeated equipment upgrades to the facilities without going through the proper notification and inspection process.

"We consider this to be serious noncompliance," Eppers said. "We'd like to assure, through federal enforcement, that those companies which do comply with the law aren't placed at a competitive disadvantage by those that don't."

Eppers declined to comment on any possible settlement negotiations with Questar, citing the confidentiality of such talks. However, he did say that the EPA "has been involved with Questar Gas Management for several years on this."

"It is unusual to file a complaint (alone) in federal district court," Eppers said, noting that typically a complaint is filed in conjunction with a mutually approved settlement between the EPA and a company that violates federal environmental regulations. "Usually things get worked out. The filing of the complaint does not preclude that we will continue negotiating; in fact, I will expect that we will."

Questar Communications Director Chad Jones said Thursday the company will not comment on the government's claims while the lawsuit is pending. However, in a filing Wednesday with the U.S. Securities Exchange Commission, Questar told investors that it has the resources on-hand to pay any fines that could be levied against the company if it were to lose the case.