Chicago Deep Tunnel Project

Chicago Deep Tunnel Project
Name	Chicago Deep Tunnel Project
Caption	Tunnels beneath the Chicago River and Calumet River watersheds
Location	Chicago, Cook County, Illinois
Coordinates	41.8781°N 87.6298°W
Status	Operational / phased completion
Began	1975
Owner	Metropolitan Water Reclamation District of Greater Chicago
Length	~109 miles (planned)
Depth	up to 350 feet
Capacity	hundreds of millions of gallons

Chicago Deep Tunnel Project

The Chicago Deep Tunnel Project is a large-scale underground infrastructure program to capture and store stormwater and wastewater beneath Chicago and portions of Cook County, Illinois, protecting the Chicago River, Lake Michigan, Calumet River, and surrounding communities. It is administered by the Metropolitan Water Reclamation District of Greater Chicago and connects to historic waterways and facilities including the Chicago Sanitary and Ship Canal, Stickney Water Reclamation Plant, and the O'Brien Water Reclamation Plant. The project integrates with regional plans by agencies such as the U.S. Army Corps of Engineers and the Illinois Environmental Protection Agency.

Overview

The system consists of deep, large-diameter tunnels, reservoirs, and diversion structures designed to prevent combined sewer overflows into the Chicago River, Calumet River, and Lake Michigan during heavy precipitation events. It interfaces with surface conveyances like the North Shore Channel and infrastructure such as the Chicago Water Tower, Wacker Drive flood control measures, and the Chicago Transit Authority rights-of-way. The project complements flood mitigation efforts connected to the historic Chicago Portage and regional hydraulic engineering advances begun with projects like the reversal of the Chicago River in the 19th century.

History and Planning

Planning for deep underground storage followed recurring flooding and pollution problems documented in the 19th and 20th centuries, echoing earlier interventions by figures and institutions such as William B. Ogden, the Izaak Walton League, and the Board of Public Works (Chicago). The modern tunnel program was initiated in the 1970s under leaders at the Metropolitan Water Reclamation District of Greater Chicago and was influenced by federal policy shifts involving the Clean Water Act and funding programs administered by the Environmental Protection Agency. Major planners consulted engineering firms with precedents from projects like the Thames Tideway Tunnel planning studies and municipal programs in New York City, Boston, and Los Angeles. Political support involved officials from the Governor of Illinois office, the Cook County Board, and congressional delegations including members from Illinois's 5th congressional district.

Engineering and Design

Engineers adapted tunneling methods including tunnel boring machines used on projects like the Channel Tunnel and Boston's Big Dig while accounting for Chicago’s geology, notably glacial till and bedrock near the Chicago Lake Plain. Design criteria incorporated hydrology models from the National Weather Service and storm frequency analyses used by the United States Geological Survey. Key components include large-diameter circular tunnels, control gates, pumping stations similar in concept to facilities at the New Orleans Sewerage and Water Board, and connections to major plants including Stickney, O'Brien, and Calumet. Structural design referenced standards from the American Society of Civil Engineers and corrosion protection practices employed by the American Water Works Association.

Construction and Components

Construction used methods seen in projects managed by contractors and firms associated with the Army Corps of Engineers and private firms that worked on the Hoover Dam and the San Francisco Bay Area Rapid Transit tunnels. Major components include the Mainstream Tunnels beneath the Chicago Loop, linking to reservoir sites such as the Thornton Composite Reservoir near Thornton, Illinois and the McCook Reservoir near McCook, Illinois. The program also built shaft structures, drop shafts, and connection tunnels to existing interceptors like those serving the Calumet and North Side service areas. Construction milestones involved collaborations with unions like the International Union of Operating Engineers and contractors headquartered in cities such as Chicago, Peoria, and Cleveland.

Operations and Flood Control

Operational protocols coordinate storage, conveyance, and treatment to reduce flows to treatment plants during storms and to prevent backups into neighborhoods and assets like the Merchandise Mart and Willis Tower basements. Operational oversight involves agencies including the Metropolitan Water Reclamation District of Greater Chicago, coordination with the City of Chicago Department of Streets and Sanitation, and incident response with the Chicago Fire Department when urban flooding events occur. The system reduced emergency closures on corridors such as Lake Shore Drive and transit disruptions affecting the Chicago Transit Authority network during extreme weather events tied to storms tracked by the National Oceanic and Atmospheric Administration.

Environmental and Public Health Impact

By capturing combined sewer overflows, the tunnels have improved water quality in the Chicago River and Lake Michigan', benefiting users served by utilities like the Chicago Department of Water Management and recreational areas managed by the Chicago Park District. The project influenced fish and wildlife habitat restoration efforts with partners including the Shedd Aquarium and conservation NGOs such as the Audubon Society and the Nature Conservancy. Public health outcomes relate to reduced pathogen loads regulated by the Centers for Disease Control and Prevention and water quality standards enforced by the Illinois Environmental Protection Agency. Studies by academic institutions including University of Illinois Chicago, Northwestern University, and University of Chicago have assessed ecological and human health effects.

Costs, Funding, and Controversies

Funding combined local revenue from MWRD bonds, state allocations from the State of Illinois, and federal grants linked to programs administered by the Environmental Protection Agency and discretionary appropriations from members of Congress representing Illinois's 7th congressional district and other districts. Costs and scheduling prompted debate involving elected officials such as mayors of Chicago and county commissioners from Cook County, contractors, and community groups in neighborhoods like Englewood and Pilsen. Controversies have included cost overruns, debates over reservoir siting near communities such as Thornton, litigation involving environmental groups and agencies like the U.S. Environmental Protection Agency, and comparisons to other megaproject disputes like those surrounding the Big Dig. Fiscal oversight involved audits by entities such as the Government Accountability Office and state-level review by the Illinois Auditor General.

Category:Water infrastructure in Illinois