This one involves the Illinois Prairie Path along the DuPage River. The path will be closed for the season from Warrenville Road to Ferry Road as workers remove thorium, a radioactive substance, from the West Branch of the river.
The homepage for the 62-mile-long Illinois Prairie Path calls it “North America’s first successful rails-to-trails conversion. Founded 1963.”
Take a look at the Daily Herald report on the closure. Evidently, the trail is closed to recreational users because project workers will be traveling by ATV.
UPDATE: The League of Illinois Bicyclists suggests this unsigned detour around the affected section of trail.