Marathon Petroleum, a major contributor to pollution in the state's most polluted ZIP code, said it has installed new equipment to control toxic air emissions at its Detroit refinery, and plans to do more.

Besides changing the way it flares gases -- the process of burning waste gases in a tall smokestack, which releases toxins -- the company will spend $2.2 million by Sept. 30, 2013, to improve its sludge handling and further cut emissions in Detroit.

The sludge project will remove 15 tons of toxic volatile organic compounds and at least 1 ton of benzene from the air each year.

Those pollutants can cause cancer, lung diseases such as asthma, and blood diseases such as leukemia.

The actions are part of a national settlement with the Environmental Protection Agency over violations of the Clean Air Act at six refineries, including the one in Detroit. The company faces a fine of $460,000 for those violations.

The company and the agency have been negotiating a settlement since 2008, and the changes in how it flares will reduce air toxins by at least 91%, the EPA said.

"That doesn't give me comfort," said Theresa Landrum, who lives in the area near the Marathon refinery. "They're still putting out pollution that's detrimental."

She said she's concerned that even with a reduction in pollution compared to the past, the plant is undergoing a $2.2-billion expansion in order to process heavy oil from Canadian tar sands, which will mean more pollution in the future.

Detroit's 48217 ZIP code, where the refinery is located, was found to be the most polluted in Michigan by researchers at the University of Michigan in 2010, based on the amount of air emissions from several plants in the area and their health risks.

Besides Marathon, there are major steelmakers, cement and asphalt manufacturers, metal plating plants and oil recyclers that all emit toxic substances in the area.

Neighbors in the ZIP code have pushed for tighter pollution controls for years, complaining that falling dust and gases in the air are endangering their health.

Last year, Marathon agreed to voluntarily buy as many as 350 homes to create a buffer between the expanding refinery and its neighbors.

The EPA said the changes in flaring would reduce harmful air pollutants by more than 5,000 tons per year at all six refineries. A flare is a tall stack used to combust waste gases to get rid of them. If the burning is inefficient, the toxins are released into the air.

Despite the violations, the EPA praised the company, which the agency said had been willing to work with officials to find new methods to measure its emissions and control them. The company will do that with new equipment that can help burn waste gas more efficiently.

Marathon has already spent $45 million on the new emission controls and plans to spend at least an additional $6 million, the EPA said.

In addition, Marathon has installed air monitors at the fence lines of four of its refineries, including Detroit, to monitor emissions and share that data with neighborhood residents.

Contact Tina Lam: 313-222-6421 or tlam@freepress.com