Tunnel and reservoir plan solution to Chicago's combined sewer overflow, basement flooding, and pollution

Abstract

In 1890, the Metropolitan Sanitary District of Greater Chicago was formed to permanently protect the region's drinking water supply from devastating contamination by sewage. The solution was to excavate a massive canal across the continental divide and to thus reverse the flow of the Chicago River, causing it to flow into the tributaries of the Mississippi River and away from Lake Michigan. Later, sewage treatment works were constructed to treat dry weather flows.Each time rainfall exceeds 8.4 mm, the combined sewers' capacities are exceeded, and they discharge directly to the canal system on the average of 100 times per year without benefit of treatment. When the sewers and canal system are overtaxed, raw sewage backs up the sewers in Chicago and 51 suburbs, flooding streets, businesses, and home basements.In order to solve these problems on a regional basis, the Sanitary District in 1972 adopted the tunnel and reservoir plan (TARP). TARP is a second river system which is being constructed by boring tunnels up to 11 m in diameter in rock as much as 100 m under the city. When the surface sewers' capacities are exceeded, the excess flows will drop into TARP. Huge reservoirs totalling 157 000 000 m3 capacity will store the sewage until it can be gradually pumped back to the treatment works. Key words: sewage, combined sewers, overflows, water pollution, water quality, stream pollution, flood control, tunneling.