Michigan State and Ford company officials have determined a Ford plant as the source of benzene vapor in sewers that forced almost a dozen homes and a school in a Detroit suburb to evacuate. Ford executive Bob Holycross, who serves as vice president of sustainability, environment, and safety engineering, issued a warning Wednesday that the company had discovered "what originally looked to be a relatively small leak in a pipe that carries gasoline used to fuel vehicles built at the plant." 

The leak of benzene, a flammable chemical found in crude oil and gasoline, prompted Gov. Gretchen Whitmer on Thursday to declare a state of emergency for Wayne and Monroe counties. By Friday, Ford determined the leak was "much larger," and that "Ford is likely the source of the problem … for which we apologize." 

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The Michigan Department of Environment, Great Lakes and Energy (EGLE) said in an email Friday that an estimated 1,000 to 3,000 gallons of unleaded gasoline spilled into the sewers. 

"HAZMAT technicians will begin mitigating flammable vapors in the municipal sanitary system by injecting fire suppressant foam," the department said. "These activities will take place at various locations where levels of benzene have been detected in a 4-square-mile perimeter of Flat Rock."

EGLE spokeswoman Jill Greenberg explained that Ford had inserted plugs into the on-site sewer system. Flat Rock started using firefighting foam to suppress the vapors, the Detroit Free Press reported. 

"The emulsifying foam solution, which does not contain the contaminant PFAS (per- and polyfluoroalkyl substances), is designed to bond with hydrocarbons like gasoline to help break down the organic compounds," Greenberg said. "It will be applied inside impacted sanitary sewers to lower combustibility."

Holycross announced that the Ford plant is on a planned closure through the Labor Day weekend, and personnel are "urgently" addressing the fuel spill.