The City of Evanston has three sewer systems. The Combined Sewer System is the City's original sewage collection system. Most of this system was installed in the early 1900s and is present throughout the City. It is designed to carry both sanitary sewage and surface runoff from rain events, though the small size of the combined sewer mains limits their ability to convey runoff during heavy rain events.
The Relief Sewer System is designed to carry storm water as well as overflows from the combined sewer system. It was installed in strategic areas across the community to reduce the number of basement backups experienced during wet weather. During dry weather there is generally no flow in the relief sewers, as sewer services are not directly connected to the Relief Sewer System.
The Storm Sewer System was installed in the southwest part of the City in the late 1970s and early 1980s. Additional storm sewers were installed in select locations near the North Shore Channel and Lake Michigan as part of the Long Range Sewer Project beginning in the 1990s. Storm sewers are only utilized during rain events to convey storm water from the street to the channel or the lake.
Below are links to view maps of the combined, relief, and storm sewer basins, showing pipe sizes and discharge points to waterways and MWRD interceptor sewers.