What are (SSOs) sanitary sewer overflows and (CSOs) combined sewer overflows?
(back to top) A separate sanitary sewer system is designed to carry only wastewater to a water quality treatment center; a separate stormwater system is designed to carry only stormwater that is transported to ditches and streams. In a combined sewer system, both wastewater and stormwater are carried in the same set of pipes to the treatment plant. During nearly every rain, stormwater gets into these sewer systems, which results in untreated sewage overflowing into area streams and the Ohio River. When these overflows occur in the combined sewer system, they are known as CSOs. Likewise, when such overflows occur in the separate sanitary sewer system, they are known as SSOs. These overflows are generally caused by aging sewers or illegal stormwater and groundwater connections to the sanitary sewers and can contribute to water quality problems in our streams.
