Residents of a northern Michigan town are getting briefed today on a threat to their drinking water. For decades, fire crews trained at Wurtsmith Air Force Base not far from Lake Huron. But while the base closed more than 20 years ago, the chemicals used to extinguish the flames continue to seep into nearby wells and streams. The plumes of perfluorinated chemicals (PFCs) have been migrating from the former air force base into surrounding neighborhoods and the Au Sable River. PFCs have also been