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Why Do Our Sewers Overflow?
Cincinnati’s first sewers were built in the 1800s to carry rainwater away from homes, businesses and streets. In those horse-and-buggy days, our city didn’t have sewage treatment or even indoor plumbing.
Later, when indoor plumbing came, home and business owners hooked their sewage lines to the existing storm sewers, combining storm water and raw sewage into one pipe. The pipes emptied directly into the nearest river, stream or ditch, which carried the untreated sewage to the Ohio River.
Our first wastewater treatment plants began operating in the post-war boom of the 1950s. The combined sewer system remained in place, and overflow pipes were installed to relieve the system when it gets overloaded — or full of too much water — during wet weather.
During dry weather, this “combined” sewer system works much like a sanitary (or sewage-only) sewer — carrying all waste to the treatment plant for treatment and disinfection. However, when it rains, these sewers can be overloaded with incoming storm water. When this happens, the sewers are designed to overflow into nearby streams and rivers to prevent sewage from backing up into homes and businesses.
Today, we build separate sewers for storm water and sewage. However, even sanitary sewers can develop cracks and breaks, or become clogged by tree roots or grease. Sometimes an area’s population grows beyond the capacity of the sewer system. These problems can cause the sanitary sewers to overflow into waterways or even backup into basements.
Combined Sewer
Carries both waste and storm water to treatment plant from:
- Toilets
- Sinks
- Showers
- Streets
- Storm drains
Problems:
- Can be overloaded and overflow into our streams during wet weather
Sanitary Sewer
Carries waste to treatment plant from:
- Toilets
- Sinks
- Showers
- Washing machines
- Anything that sends water down a drain
Problems:
- Too much wastewater or cracks and clogs in the sewer can cause backups
- Pipes age and must be repaired
