The next few posts will describe Chicago’s major underground networks. We will start with most important and least appreciated—sewers and water.
Deep Tunnel: Planned 193 miles in Cook County.
300-350 feet down in limestone bedrock, up to 53 feet in diameter. Built late 20th century.
Although largely unseen, the Deep Tunnel is one of Chicago’s largest public works projects. It funnels storm runoff into huge tunnels 300 feet underground. The runoff is stored there until it can be treated. It generally follows the course of the rivers.
The Deep Tunnel is officially named the Tunnel and Reservoir Project, abbreviated TARP.
For more information see the Deep Tunnel booklist.
Intercepting sewers: 550 miles in Cook County.
About 10-15 in diameter, but up to 27 feet in diameter and about 15 feet down, these generally follow each bank of the rivers and lakes. Built early in the 20th century, hey convey municipal sewage to the Metropolitan Water Reclamation District’s sewage treatment plants and have vertical drop shafts to the Deep Tunnel system.
Chicago Sewer System:
4,400 miles. Varying sizes, mostly small. Generally shallow. Built 1850s to date. They convey sewage from buildings and streets to the intercepting sewers. Prior to 1900 these just flowed to the nearest body of water. Sewers on private property are not considered part of the network, so the actual length is much longer.
Chicago water tunnels:
60 miles. 5 to 30 feet in diameter. Built 1860s to early 1900s. Connection between the water intakes, the filtration plants and pumping stations. Lake Tunnels are about 60 feet down. Land tunnels are usually 300 feet deep in the bedrock. The city may lease space to utilities wishing to run wires.
Chicago water mains:
4,300 miles. 6 inches to 5 feet in diameter. From pumping stations to individual buildings. Less durable than other underground structures, these are being constantly replaced.