In modern construction, separate sewers are used for sanitation and storm waters. However, Bloomington’s older sewers handle both waste and storm water in the same piping and send the mixture to the west-side sewer treatment plant. These are called combined sewers. While they may sound efficient – one line instead of two – combined sewers are viewed as a problem.
Combination sewers can cause a number of problems, but the big issue involves capacity of combined sewer lines during periods of heavy rainfall. In wet times, the pipes cannot handle all the liquid. Water has to go somewhere, and the ultimate goal of the City is to keep it out of people’s basements.
The old solution was to create Combined Sewer Overflows. An overflow pipe attached to the sewer system will, by design, channel the mix of rainwater and sewer water directly into streams.
Eliminating Combined Sewers
Under the U.S. Clean Water Act, the City is required to make progress toward eliminating these Combine Sewer Overflows (CSOs). It has done so. Since 1995, four of seven CSOs have been plugged. Eventually all will be eliminated.
The process usually involves sewer separation. A new, parallel sewer line is built solely for sanitation. All users are hooked to it. The old sewer connections on the old line are blocked, and the old line becomes a storm-only sewer. It is an expensive endeavor. Separate sewers enable the channeling of storm water to a creek and wastewater to a treatment plant.
Click on the two-minute video below to learn more about combined sewers and the City's efforts to eliminate them.