A combined sewer is a sewage collection system of pipes and tunnels designed to also collect surface runoff. Combined sewers can cause serious water pollution problems during combined sewer overflow (CSO) events when wet weather flows exceed the sewage treatment plant capacity. This type of sewer design is no longer used in building new communities (because current design separates sanitary sewers from runoff), but many older cities continue to operate combined sewers.
A sanitary sewer or "foul sewer" is an underground carriage system specifically for transporting sewage from houses and commercial buildings through pipes to treatment or disposal. Sanitary sewers are part of an overall system called sewerage or sewage system.
Sewage may be treated to control water pollution before discharge to surface waters. Sanitary sewers serving industrial areas also carry industrial wastewater.
Separate sanitary sewer systems are designed to transport sewage alone. In municipalities served by sanitary sewers, separate storm drains may be constructed to convey surface runoff directly to surface waters. Sanitary sewers are distinguished from combined sewers, which combine sewage with stormwater runoff in the same pipe. Sanitary sewer systems are considered beneficial because they avoid combined sewer overflows.
A storm drain or drain system is designed to drain excess rain and ground water from impervious surfaces such as paved streets, car parks, parking lots, footpaths, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems. They are fed by street gutters on most motorways, freeways and other busy roads, as well as towns in areas which experience heavy rainfall, flooding and coastal towns which experience regular storms. Even the gutters from houses and buildings can be connected to the Storm drain. Many storm drainage systems are designed to drain the storm water, untreated, into rivers or streams. As a result, it is not okay to pour certain types of chemicals into the drains.
Some storm drains lead to a mixing of stormwater (rainwater) with sewage, either intentionally – in the case of combined sewers – or unintentionally.
Chattanooga Wastewater Collection & Treatment System
The Waste Resources Division is responsible for the operation and maintenance of the interceptor sewer system of Chattanooga, as well as the regional wastewater treatment plant known as the Moccasin Bend Wastewater Treatment Plant.
The interceptor sewer system encompasses approximately 1,250 miles of sewer lines, 7 large custom-built pumping stations, 8 custom-built storm stations, 53 underground, wetwell mounted, submersible pumping stations, approximately 130 residential/grinder stations, 8 combined sewer overflow (CSO) facilities and one major regional wastewater treatment plant (Moccasin Bend).
The City's Interceptor Sewer System serves the City and a surrounding metropolitan area which together have a population of approximately 400,000, encompassing about 200 miles. In addition to the City, the system serves the following areas: City of Collegedale, Tennessee; part of Hixson Utility District service area in Hamilton County, Tennessee; City of Red Bank, Tennessee; City of East Ridge, Tennessee; City of Soddy Daisy, Tennessee; City of Rossville, Georgia; City of Fort Oglethorpe, Georgia; Town of Lookout Mountain, Tennessee; Lookout Mountain, Georgia and portions of Walker County and Catoosa County, Georgia.
Sanitary Sewer Overflow (SSO) Observation Report
Sanitary Sewer Overflow (SSO) refers to any overflows caused by line stoppages, heavy rains, pump station failures, vandalism, building backups due to main line problems and any other causes.