Combined sewers are designed to collect both sanitary sewage and stormwater runoff in a single-pipe system. These systems were designed to convey sewage and wastewater to a treatment plant during dry weather. Under wet weather conditions, these combined sewer systems would overflow during wet weather conditions when large amounts of stormwater would enter the system. State and local authorities generally have not allowed the construction of new combined sewers since the first half of the 20th century.
During periods of heavy rainfall or snow melt, some wastewater systems are designed to occasionally overflow and discharge excess untreated sewage directly to nearby streams, rivers or other water bodies. These discharges are known as combined sewer overflows and are common in many cities nationwide.
The Illinois Environmental Protection Agency (IEPA) under the authority granted by the United States Environmental Protection Agency (U.S EPA) issued a National Pollutant Discharge Elimination System (NPDES) permit to the Village of La Grange Park for the operation of its combined sewer system overflow (CSO) structure. The condition of the permit require the Village to develop and maintain a plan for public notification, education and comment concerning combined sewer system operations and the operation of the overflow structure.
In accordance with the Village’s Municipal Code:
Sewer §50.40 Generally: No person shall discharge or caused to be discharged any storm water, ground water, roof runoff, subsurface drainage, uncontaminated cooling water or unpolluted industrial process waters to any sanitary sewer.