Thornton Transitional Reservoir

A portion of an enormous, active dolomite quarry in Thornton, Illinois, just south of Chicago, is now a 3.1 billion gallon stormwater reservoir, thanks to design work recently completed by CTE for the Metropolitan Water Reclamation District of Greater Chicago.  Larger than all the other reservoirs in the watershed combined, it provides flood control along Thorn Creek and the Little Calumet River for an average benefit of $4.2 million per year.  Floodwaters from Thorn Creek flow through a diversion inlet structure, drop 230 feet down a 24-foot diameter shaft, and flow through an 8,000-foot long, 22-foot diameter tunnel into the reservoir.  After the storm passes, the reservoir is drained through an 8-foot diameter tunnel and the water pumped to the Calumet Water Reclamation Plant for treatment and eventual discharge to a local waterway.