The Chicago Metro Water Reclamation District (MWRD) Thornton Composite Reservoir project was recently named a 2016 Public Works Project of the Year by the American Public Works Association (APWA). The project is being honored with APWA’s Project of the Year award in the Environment category at a cost greater than $75 million. For 2016, the team of winners includes the Metropolitan Water Reclamation District of Greater Chicago as the managing agency; F.H. Paschen/Cabo Construction Corporation, Joint Venture; Walsh/ll in One, Joint Venture as the primary contractors; and Black & Veatch Corporation Inc. and MWH Americas Inc., as the primary consultants, who will all be presented with the award during APWA’s 2016 PWX, or Public Works Expo, Awards Ceremony in Minneapolis, MN during August 28-31, 2016.

The APWA Public Works Projects of the Year awards are presented annually to promote excellence in the management and administration of public works projects, recognizing the alliance between the managing agency, contractor, consultant and their cooperative achievements. This year, APWA selected projects in five categories including: Disaster/Emergency Construction/Repair, Environment, Historical Restoration/Preservation, Structures, and Transportation.

Chicago MWRD’s Tunnel and Reservoir Plan (TARP) was adopted in 1972 as the cost-effective plan to comply with federal and state water quality standards for the region’s combined sewer area of the city and 51 suburban municipalities. The plan’s main goals were to protect Lake Michigan’s drinking water supply from raw sewage, improve the water quality of area waterways and provide an outlet for area floodwaters to reduce street sewage backup. The Thornton Composite Reservoir, part of Phase II, was a major step toward achieving these goals.

Phase I of TARP included 110 miles of 8-foot to 33-foot diameter rock tunnels, 150-foot to 350-foot below the ground, providing 2.3 billion gallons (BG) of combined sewer overflow (CSO) storage. The Phase I captures and stores CSOs that previously discharged to waterways. After the tunnels receive the first flush from combined sewers during significant storm events, the captured flow is pumped to water reclamation plants for full secondary treatment of the combined sewage.

Phase II of TARP consists of three large reservoirs that connect to the Phase I deep tunnel system and ultimately increase the TARP system storage volume to 20.5 BG, and one of the three reservoirs is the Thornton Composite Reservoir. Completed in 2015, the reservoir has a storage capacity of 7.9 BG - the largest CSO facility in the world. The reservoir, with a surface area of about 83 acres, serves a 90-square-mile area in Cook County. The reservoir provides an estimated $40 million per year in flood control benefits to 556,000 people in 14 communities, including the South Side of Chicago and 13 suburban communities.

The reservoir measures 2,480 feet long, 1,580 feet wide and 300 feet deep. The reservoir was also designed to provide 3.1 BG storage for overbank floodwaters from Thorn Creek. The design approach for the reservoir focused on four major elements: sealing the perimeter of the reservoir to protect adjacent groundwater from possible pollutant seepage; sealing the reservoir to protect ongoing mining operations in the adjacent quarry; connecting the reservoir to the existing MWRD Calumet TARP deep tunnel system; and connecting the reservoir to the Thorn Creek overflow structure and diversion tunnel.

American Public Works Association (APWA)

During construction of the drop shafts and tunnels to the reservoir, the contractor was vigilant in monitoring gas levels in the tunnels. If levels exceeded the allowable limit, contractors and engineers were required to evacuate the work areas for designated periods of time.

For more information on the APWA 2016 Projects of the Year or for a complimentary press pass to the APWA PWX conference in Minneapolis during August 28-31, 2016, please contact APWA Media Relations and Communications Manager, Laura Bynum, at, or call 202.218.6736.

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