TRAVERSE CITY, MI (AP) — A massive flood is raising fears of setbacks in a hazardous waste cleanup along a central Michigan river. Floodwaters overwhelmed two dams this week, chasing 11,000 people from their homes in or near Midland. The Tittabawassee River flows past Dow Chemical Co.’s headquarters plant, which for years produced dioxins. The highly toxic compounds were dumped into the river, where they became embedded in sediments and floodplains. Dow has been cleaning up the area since 2007 and has made considerable progress. The company says its projects survived a flood three years ago. But some scientists and activists fear this week’s flood could sweep the toxins downstream.