Chicago Deep Tunnel Design and Construction

The Tunnel and Reservoir Plan (TARP) is the Chicago area's plan for cost-effectively complying with Federal and State water quality standards. TARP's main goals are to protect Lake Michigan - the region's drinking water supply - from raw sewage pollution; improve water quality of area rivers and streams; and provide an outlet for floodwaters to reduce street and basement sewage backup flooding. Phase I of TARP (operational since 1980 and completed in 2006) captures and stores combined sewer overflows (CSOs) that previously discharged at hundreds of outfall locations. After storms fill the tunnels with the first flush from combined sewers, the captured CSO is pumped to water reclamation plants for full secondary treatment. Phase I includes 109.4 miles of 8' to 33' diameter rock tunnels, 150' to 350' below the ground, providing 2.3 billion gallons (BG) of CSO storage. Phase II of TARP consists of three large reservoirs that will increase the TARP system storage volume to 17.5 BG. The 350 million gallon (MG) Majewski Reservoir has been in operation since 1998. The dual purpose Thornton Composite Reservoir is scheduled to be completed in 2015 and will provide 3.1 BG of flood water storage and 4.8 BG of CSO storage. The 10 BG McCook Reservoir is being constructed in two stages, with 2017 and 2029 completion dates. At both reservoirs, there is a mining agreement with a local quarry operator to provide the reservoir hole, and several construction contracts to turn the hole into a functioning reservoir. The mining, design, and construction activities are currently underway. Close coordination with several different stakeholders is required to bring these projects to completion Since its inception, TARP has abated flooding and pollution in the Chicagoland area and preserved the integrity of Lake Michigan. Area waterways are once again abundant with many species of aquatic life and have been reclaimed for recreation. The full benefits of TARP will be reached when the McCook and Thornton Composite Reservoirs are completed.