Bordering on Illinois, Indiana, Michigan, and Wisconsin, Lake Michigan is the only Great Lake to be located entirely within the United States. It is the second largest Great Lake by volume, with a capacity of 1,180 cubic miles of water, and the third largest by area.

The City of Chicago utilises Lake Michigan as its source of drinking water. Water is treated via two plants – the Jardine Water Purification Plant serves the northern areas of the City and suburbs, while the South Water Purification Plant serves the southern areas of the City and suburbs.

Water is distributed throughout Chicago via century-old pipes that require ongoing maintenance. The City of Chicago commonly uses trenchless techniques such as sliplining and CIPP, together with CCTV inspection and condition assessment to inspect and maintain the system. In addition, the City has implemented the Tunnel and Reservoir Plan (TARP), also known as the Chicago Deep Tunnel, which aims to reduce flooding of the city and prevent raw sewerage from entering Lake Michigan by diverting the flow to holding reservoirs.

In the pipeline – a short sewer history

The Chicago Sewers Collection has collated a history of the development of the wastewater network.

From the establishment of Fort Dearborn in 1803 along the Chicago River to the present day, water and sanitation have always been crucial to Chicago. Chicago’s low-lying location combined with the livestock and waste of the settlers resulted in a serious waste disposal problem. The Collection states that by 1845, Chicago was facing an environmental crisis and then experienced two cholera epidemics.

In 1855, the Chicago City Council employed Boston engineer Ellis S Chesbrough to design the first comprehensive system of underground sewers in the United States. The Board of Sewerage Commissioners adopted Mr Chesbrough’s plan to drain sewage into the Chicago River, in order to limit the cost and extent of the proposed sewer system. The level of Chicago’s streets was raised from six to ten feet to accommodate sewer pipes, gas and water mains. Owners lifted buildings to meet the new street level; in some cases whole blocks were raised at a time.

By 1930 Chicago’s sewer system was the most extensive in the world. Today the Chicago Department of Water Management continues to employ new technologies in inspection, materials and maintenance.

Planning for future

Despite the reversal of the Chicago River and the construction of the largest water treatment plant in the world, polluted combined sewer overflows (CSOs) persisted in Chicago throughout the first half of the 20th century.

In 1972, in order to improve the Chicago Area Waterway System (CAWS), the TARP was adopted by the Metropolitan Water Reclamation District of Greater Chicago (MWRD).

MWRD explained that construction of Phase 1, primarily for pollution control, began in 1975 and was completed in 2006. The total length is 176 kilometres (109.4 miles) of deep, large diameter, rock tunnels providing 2.3 billion gallons of volume to capture CSOs. The tunnels were bored using tunnel boring machines (TBMs), with pipe diameters ranging from 9–33 feet. MWRD says that the TARP tunnelling work led to major improvements to the TBMs, and pushed them beyond their then-proven capabilities. For example the Mainstream tunnel was mined three times faster than the 0.6 metres per hour that had been estimated in 1975.

Mining records were set on many of the TARP contracts. On the last tunnel leg completed on the Calumet system (Little Calumet), the TBM crew broke several world records for a machine of its size.

In addition to contributing to an increase the speed of mining, the TARP project has led to improvements in accuracy. The TBM used on the Little Calumet leg used a laser target system to permit continuous steering control and monitoring of line and grade – a huge improvement from the machines used on the first tunnels of the TARP, which had to be adjusted at the end of each push. Phase 2 of the TARP is in construction and is expected to be completed by 2019.

In late 2009, Governor of Illinois Pat Quinn and Illinois Environmental Protection Agency (EPA) Director Doug Scott announced grants and loans for environmental projects to improve wastewater quality in Illinois, using funds from the American Recovery and Reinvestment Act of 2009 (ARRA). The recovery program was authorised in 2009 by the United States Congress and President Barack Obama. Illinois EPA receives approximately $US180 million for wastewater projects and $US80 million for drinking water projects through ARRA.

The same year the Department of Water Management completed a city-wide computer model of its large auxiliary sewers (42 inches in diameter and larger) and CSOs. This dynamic flow model represents the best available information on the hydrologic and hydraulic characteristics of the sewer system. The model will be used as a planning tool to regulate development and investigate the need for future sewer projects.

Chicago’s main sewers convey flow to interceptor sewers. These interceptor sewers are owned and operated by the MWRD. The interceptor sewers convey dry weather flow to MWRD’s treatment plants for treatment and release to local waterways. During storm events, flows in excess of the capacity of the interceptor sewers discharge into the MWRD’s TARP system for storage.

Dr A S Paintal, a sewer engineer with MWRD spoke with Trenchless International about maintaining Chicago’s sewer network. MWRD is responsible for approximately 550 miles of the sewer network. Pipe diameters range from approximately 18 inches up to 24 feet, with the majority between 5 and 7 feet in diameter. Dr Paintal explains that, as the sewer network was built in the early part of the 20th century, the engineering department needs to use trenchless techniques such as slip lining and CIPP to maintain the network.

Mayor of Chicago Richard Daley says “We are proud of our efforts to renew Chicago’s infrastructure with the installation of new water and sewer mains.”