GRAND RAPIDS, Mich. (WOOD) — Two Grand Rapids trucking companies and their owners have been sentenced after federal investigators say they deliberately removed the emissions control systems from semi-trucks in violation of the Clean Air Act.

Accurate Truck Service and Griffin Transportation were each ordered to pay $500,000. The companies will also be on probation for a year, the U.S. Attorney’s Office said in a Tuesday release.

The companies and four defendants all pleaded guilty to conspiring to violate the Clean Air Act.

Craig Scholten and Ryan Bos were each sentenced to four months of home detention, a year of probation and a $6,000 fine. Douglas Larsen received two months of house arrest, a year of probation and a $7,500 fine. Bos, Larsen and Scholten jointly own Accurate Truck Service and Bos and Scholten own Griffin.

Scott DeKock, who previously owned a shipping company involved in the case, was sentenced to a year of probation and a $10,000 fine.

Federal prosecutors filed charges in April. They say Accurate Truck Service would remove the emissions controlling hardware from diesel engine trucks and another company, Gaylord-based Diesel Freak, would reprogram the engine computers so they could keep running despite the alteration. Feds say Diesel Freak did it at least 362 times and Accurate at least 83 times.

Investigators say Griffin and DeKock’s company sent their trucks to Accurate and Diesel Freak to have the emissions controls removed — Griffin at least 12 times and DeKock’s company at least four.

Getting rid of the emissions controls can improve trucks’ fuel economy, but federal investigators pointed out that it also allows more harmful exhaust into the air.

Diesel Freak, owner Ryan Lalone and employee Wade Lalone are scheduled to be sentenced Dec. 11. The company has already agreed to pay a $750,000 fine.