How Combined Sewers Function
Our first sewers were designed over 100 years ago to carry both stormwater and sewage from homes and businesses. During dry weather, sewage flows safely through our sewers to the Greater Peoria Sanitary District wastewater treatment plant. However, between 20 to 30 times a year, the sewers are overwhelmed by incoming rainwater or melting snow. This causes untreated sewage to overflow into the Illinois River.
During wet weather… Between 20 and 30 times a year, stormwater from rain or melting snow overloads these sewers. They don’t have enough capacity to carry wastewater to the Greater Peoria Sanitary District's (GPSD) treatment plant. So untreated sewage flows over the internal dam into the Illinois River.
During Dry Weather… Peoria’s combined stormwater/sanitary sewers work much like a modern sanitary sewer. All sewage from homes and businesses is sent to the treatment plant by a “regulator,” or small dam, in the sewer.