Suncor Energy’s Commerce City oil refinery is under investigation again for releasing too much pollution into the air. The U.S. Environmental Protection Agency and the Colorado Department of Public Health and Environment served a notice of violation last week to the refinery. The notice is the first step in an enforcement action after both agencies discovered violations during recent inspections, according to an EPA news release. The agencies accused Suncor of violating the federal Clean Air Act by releasing too much benzene and other hazardous pollutants.