Eastside Combined Sewer
- Location: East of Ridge Road.
- History: First version was installed in 1890s.
Combined Sewer Specs:
- 47 miles of sewer lines.
- Clay and reinforced concrete pipe, 8- to 96-inches in diameter.
- Flows into MWRD system.
- MWRD treats the combined waste at the Northside Water Reclamation Plant.
- The treated water flows into the Chicago River.
Combined Sewer Issues:
- Infiltration/inflow due to aging pipes and other issues.
- Outmoded design mixes stormwater with raw sewage.
- Prone to combined sewer overflows (CSOs).
Sequence for combined sewer overflows (CSOs):
- If the MWRD system is full, sewage overflows into an MWRD deep tunnel.
- If the tunnel is full, sewage overflows into the North Shore Channel.
- If the channel is full, the locks open, dumping sewage in Lake Michigan.
Recent Combined Sewer Projects:
- Televising, dye water testing, repairing, and relining pipes.
- Storm Water Runoff Control Program (1990s-2000s):
Street berms, basins, and flow restrictors were built to store runoff on streets. Wilmette added a relief sewer to prevent flooding, sewage backups, and CSOs.
- Annual maintenance includes inspection of 20 percent of the drains, restrictors and sewers to comply with the Combined Sewer Overflow (CSO) permit, as required by the Illinois EPA.
Combined Sewer Map (Still searching for this…)
Find out about regulations and restrictions for combined sewers:
- Street Storage System for Control of Combined Sewer Surcharge, which describes the street berms, basins, and flow restrictors built in Wilmette and Skokie to store runoff, mitigate flooding, and reduce the frequency of CSOs.
- Learn about the Nine Minimum Controls for combined sewer systems.
- Get details on the National Pollutant Discharge Elimination System (NPDES) permit program, authorized by the Clean Water Act.
History of Combined Sewer Upgrades:
As explained in the Village of Wilmette, Public Works Dept., 2014 Annual Report (p71):
In the mid-1990’s, the Village constructed various relief sewers, upsized existing sewers and installed storm water berms throughout the combined sewer area. Through the use of restrictors on the sewer inlets and street berms, the streets and parkways serve as detention areas. Rather than inundate the sewer system with surface water, the on-street detention holds the water until the sewer system can accept it. When the existing combined sewers reach capacity they overflow to the relief sewers strategically installed in the system. The relief system only functions during large storm events and drains to the MWRDGC Tunnel and Reservoir Project (TARP) commonly referred to as “The Deep Tunnel”. When the TARP system reaches capacity and is closed by the MWRDGC, the Village relief sewer system overflows into the North Shore Channel outfall located near the TARP connection. This occurrence is known as a Combined Sewer Overflow (CSO).
After the large trunk sewers were installed in the 1990’s the Village ceased construction in 1999. In August, 2001 and again in August, 2002, the Village experienced intense storm events. The 2001 storm measured 4.11” at the Water Plant; the 2002 storm measured 5.53”. They were categorized as 100-year and 50-year storm events, respectively. Data on sewer back-ups was gathered after these rain events and compared to similar rain events in the late 1980’s. The results conclude that the construction of relief sewers and on-street detention have dramatically reduced the frequency and severity of basement back-ups in the combination system. In 2004, the Village Board supported the continuation of the relief sewer program. Rather than approve one large, multi-million dollar project, the relief sewers are being installed in conjunction with our road program over several years. It is anticipated that the relief sewer project will be completed in 2018.
- For an overview of the combined sewer, see Village of Wilmette Public Works Dept., 2014 Annual Report (2014), p 71.
- For detailed specs for the combined and relief sewers, see Village of Wilmette, Combined Sewer Overflow Operational and Maintenance Plan Summary (April 2014), pp 3-5.