World's largest storm reservoir begins filling up

THORNTON, Ill. (AP) - A nearly century-old limestone quarry south of Chicago is beginning its new life as a massive reservoir for capturing stormwater overflows.

The Thornton Reservoir began taking in water during a rainstorm in late November, trapping 400 million gallons of combined sewer overflow before pumping it to a treatment plant. And that's only a small fraction of its 7.9 billion gallon capacity.

The Metropolitan Water Reclamation District of Greater Chicago says the new stormwater reservoir is the largest in the world.

It serves as an escape hatch when Chicago's Deep Tunnel system fills to the brim, which happens during some heavy storms.

It will help stop stormwater tainted with sewage from running into Lake Michigan and other area waterways, as well as flooding basements.