The first phase of construction, 85 percent complete in 1999, is designed to minimize water pollution by reducing the discharge of untreated sewage into the area's streams and Lake Michigan, the source of the region's drinking water. Phase 2, begun in 1990, will reduce sewer backup into homes and businesses if adequate flood storage capacity can be constructed or acquired. The entire project is expected to be completed after 2015.
Because of the region's aging infrastructure and high runoff characteristics, frequent large storms can cause commingling of sanitary and storm sewer flows that exceed the system's ability to handle the load. The Deep Tunnel is designed to reduce and nearly eliminate the release of untreated water to streams, Lake Michigan, and people's basements.
American Society of Civil Engineers. “The Tunnel That Cleaned Up Chicago.” Civil Engineering, July 1986.
The Electronic Encyclopedia of Chicago © 2005 Chicago Historical Society.
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