The Thornton Composite Reservoir, known to Chicago residents as the “Grand Canyon of the South Suburbs,” will help alleviate flooding concerns for residents in South Holland and other south suburbs through improved storm water protection and water quality.

U.S. Sen. Dick Durbin, the U.S. Environmental Protection Agency, the U.S. Army Corps of Engineers and other stakeholders joined the Metropolitan Water Reclamation District of Greater Chicago (MWRD) to cut the ribbon in September for the nearly $450 million facility, which will officially come online by the end of the year.

The Thornton Reservoir is a key component of the MWRD’s Tunnel and Reservoir Plan known as TARP. It is one of the largest water infrastructure projects in the world. TARP is designed to protect Lake Michigan, the region’s primary source of drinking water. It will also protect against combined sewer overflows (CSOs) as well as overland and basement flooding.

The firm of Black & Veatch performed heavy infrastructure tunneling and engineering at Thornton reservoir. The company contributed innovations in grouting practices in the design and construction of the reservoir.

TARP has significantly improved the quality of life for people living and working in the area. Previously, sewage-laced floodwater often inundated residential properties after heavy rains. Additionally, moving that water to the reservoir will lessen the need to release sewage into Lake Michigan when rains overwhelm the area’s storm sewers. Thornton Reservoir will provide an additional 7.9 billion gallons of storage for capture and treatment of CSOs and floodwaters.

“In past years, that polluted, untreated water would enter our waterways or worse, our basements,” said MWRD President Mariyana Spyropoulos. “Because of TARP, combined sewer overflows have been drastically reduced, and the addition of Thornton reservoir will again lead to more water quality improvements upstream.”

“Other cities beset by chronic combined sewer overflows and flooding will look to this system as a model,” said Mike Orth, Executive Managing Director for the Americas in Black & Veatch’s water business. “We are proud to take part in helping the MWRD provide this vital water quality and flood protection to and for the people in and around Chicago.”

On the evening of November 26, the Thornton Composite Reservoir began to fill for the first time. It reached a depth of 17 feet and contained 400 million gallons of combined sewer overflow prior to being transported by tunnel for treatment at the Calumet Water Reclamation Plant. This amount is only 5 percent of the reservoir’s full capacity.

Video footage of the Thornton Composite Reservoir filling for the first time. In this time-lapse footage, combined sewage and stormwater can be seen entering the reservoir from the 30-foot diameter Thornton Connecting Tunnel: