Blasting, Construction Continues at Illinois' Thornton Reservoir

In 1998, the Metropolitan Water Reclamation District of Greater Chicago (MWRD) executed an agreement with the owner of the Thornton quarry to mine the north lobe of the quarry for use as an important component of the MWRD’s Tunnel and Reservoir Plan (TARP). Since that time, 152 billion lb of 400 million year old dolomite limestone has been removed from the Thornton Composite Reservoir, and while blasting and construction continues, this project is due for completion in less than three years.

Located along Interstate 80 in southern Cook County, Thornton Reservoir, which is designed to reduce pollution and flooding, will have almost 8 billion gal of combined sewage and storm water storage capacity. Communities throughout the Southside of Chicago and south suburbs of Cook County will experience tremendous benefits once the reservoir is complete.

The construction of three reservoirs is the second phase of TARP. Phase I was completed in 2006 and consists of 109.4 miles of deep, large diameter tunnels in rock with a total storage capacity of 2.3 billion gal. Phase II consists of three reservoirs which will provide more than 18 billion gal of storage capacity.

Besides the Thornton Reservoir, the McCook Reservoir is also under construction.  Stage 1 of McCook 1 is scheduled for completion by Dec. 31 2017 and will add 3.5 billion gal of storage capacity. The McCook Stage 2 Reservoir is scheduled for completion in 2029 and will add 6.5 billion gal of storage capacity. The Gloria Alitto Majewski Reservoir was completed in 1998 and provides 350 million gal of storage.

TARP’s large tunnels and reservoirs are designed to reduce the amount of combined sewer overflows (CSOs) and hold the polluted water until it can be fully treated at MWRD water reclamation plants. Since the TARP tunnels went online, the average number of days with CSOs in a year has reduced to 50 from 100.

TARP was the first system of its kind to address pollution and flooding and is emulated by cities around the world, including London, Singapore and Vienna. While these projects are large and costly, TARP has provided solid evidence that such a system is effective and valuable infrastructure.

The Thornton Reservoir is set to come online at the same time as disinfection facilities at the MWRD’s Calumet Water Reclamation Plant in Chicago, which also serves the southern area of the county. Working in tandem, the combination will maximize water quality while minimizing flooding.

Source: Metropolitan Water Reclamation District of Greater Chicago