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A local environmental group has made good on its threat to sue the TV personalities known as the Diesel Brothers.

Utah Physicians for a Healthy Environment is claiming in a federal lawsuit filed Tuesday that the four men made illegal modifications to the pollution-control systems on diesel vehicles at their Utah businesses.

Those changes, the suit asserts, caused the vehicles to produce as much as 30 times more pollution than is allowable under federal emissions limits. And because at least some of the modified vehicles were registered and operated in Utah, the lawsuit says, those increased emissions contributed to concentrations of ozone and fine particulate pollution on the Wasatch Front.

Consequently, the suit claims, the Diesel Brother's actions "pose a significant risk to the health and well-being" of the more than 2,000 members of Utah Physicians.

Under the Clean Air Act, private citizen may sue those who are believed to have violated federal air standards when the alleged violations harm them.

The suit targets David "Heavy D" Sparks, David "Diesel Dave" Kiley, Joshua "Redbeard" Stuart and Keaton "The Muscle" Hoskins as individuals, as well as their Utah businesses: LLC, Diesel Power Gear LLC, 4X4 Anything LLC, and Sparks Motors LLC.

The Discovery Channel, which will begin airing the reality show's second season next week, is not named in the suit.

The Diesel Brothers declined to comment. Attempts to reach the Discovery Channel for comment were unsuccessful.

Reed Zars, an attorney representing Utah Physicians, said he is not entirely certain how many vehicles were modified and sold. But based on the online ads Utah Physicians says it collected, there appear to have been "quite a few," Zars said.

According to the complaint, the Diesel Brothers advertised vehicles with modified emissions systems online on eBay and other sites.

Denni Cawley, the Utah Physicians' executive director, said modified diesel vehicles are of concern to the group because of the Environmental Protection Agency's recent proposal to classify parts of the Wasatch Front as "serious" nonattainment areas that fail to meet federal air quality standards.

Diesel vehicles produce more small particulate pollution — the stuff that builds up beneath Utah's winter inversions — than gasoline-powered cars and trucks. Cawley said their emissions contain numerous other pollutants that are associated with cancer, birth defects and neurological effects. Their emissions also contribute to the formation of ozone, which is created in the atmosphere when certain pollutants interact with sunlight. Various parts of the Wasatch Front exceed the EPA's new limit for ozone.

Zars said Utah Physicians attempted to negotiate with the Diesel Brothers to stop the ongoing production of modified diesel vehicles, but, he added, "It never really went anywhere."

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