Overview: Michigan regulators approve air quality permit for Marathon Petroleum's Southwest Detroit refinery. Michigan regulators approved air quality permits Thursday for Marathon Petroleum and MPLX Terminals in Southwest Detroit, less than a month after a flaring event at the oil refinery. Sheffield said the Detroit Fire Department’s hazmat unit tested the air near the refinery and found no health risk. The new state permit adds missing language from an existing Environmental Protection Agency consent decree with Marathon, according to EGLE. Details on Marathon refinery permitThe air permit requests filed by Marathon Petroleum Company and MPLX Terminals LLC for the “Feedstock & Fuels Flexibility Project” were approved as a single stationary pollution source.