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Conveyance – The Sewer System

Conveyance of wastewater is achieved through a system of local sewers, combined sewers, intercommunity relief sewers, interceptor sewers, automated regulators and pump stations. Proper operation and maintenance of the conveyance system ensures that wastewater is safely and efficiently transported to treatment plants.


Smaller local sewers (combined sewers, and separate sanitary and storm sewers) are owned and maintained by the local municipalities. Local sewers transport wastewater to NEORSD’s interceptors, which lead directly to the wastewater treatment plants. Each kind of local sewer functions differently:

Combined sewers:

Combined sewers are most common in older parts of the service area, primarily Cleveland and the inner-ring suburbs. Combined sewers carry sanitary sewage and stormwater in the same pipe. This was a common design in the early 1900s and was very functional in capturing and conveying large amounts of wastewater away from populated areas and toward a water body or treatment. Now, combined sewers can contribute to environmental problems and major programs are making gains to address them.

Separate sanitary and storm sewers:

Beginning in the 1920s, developing suburbs began building separate sewer systems. Separate sanitary and storm sewer areas are comprised of two sets of pipes that transport wastewater and storm water separately and are not connected (Storm water is directed to the creeks, rivers and Lake Erie during rain events, while sanitary wastewater flows to the treatment plants). While separate sewer systems are generally preferred, combined sewers do have the advantage of providing treatment for a portion of storm water runoff that can also carry a high pollutant load.

Issues with storm water still may arise. Even with separate sewers, storm water can still flow into sanitary sewers, a process called infiltration and inflow (I/I). This may lead to pipe overflow, which may in turn cause residential sewer backups.


While local municipalities hare responsible for the maintenance and ownership of local sewers, NEORSD constructs and maintains intercommunity relief sewers, interceptors, and wastewater treatment plants.The Cuyahoga County Sanitary Engineer has full or partial responsibility for sewer maintenance in most Cleveland suburbs. In the City of Cleveland and remaining suburbs, the local Sewer Maintenance Department or Engineering Office of that city handles sewer maintenance.