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Sanitary Sewer Overflows

Frequently Asked Questions – Sanitary Sewer Overflows (SSOs)

What is a SSO?

A simple definition of a SSO would be a discharge from the sanitary sewer system prior to treatment at a publically owned treatment works (POTW).

What causes SSOs?

The United States Environmental Protection Agency grouped SSO causes into the following categories:

  • Blockages: generally from root intrusion, grease, or other items in a sanitary sewer
  • Wet weather and Infiltration and Inflow (I&I): stormwater and/or groundwater that enters the sanitary sewer system through holes, breaks, joint failures, connection failures, illegal private connections, and improper cross connections with the storm sewer system.
  • Power and mechanical failures at pumping stations
  • Sewer collapses or breaks
  • Miscellaneous (e.g., vandalism, contractor error): The Erie County Sewer Districts have retrieved items ranging from bowling balls to folding chairs to car parts from the sewer system.  All these items block sewers/flows and cause backups or overflows.
Why do the Erie County Sewer Districts have SSOs?

Unintentional discharges from municipal sanitary sewers unfortunately occur in almost every system. Pipe breaks or collapses, mechanical failures, and blockages may occur despite the best operation and maintenance efforts of the sewer service provider. Additionally, I&I from both private and public sources may cause the capacity of the sewer systems to be exceeded during certain wet weather events. As sewer systems age, oftentimes I&I becomes more of an issue. Older systems are also often more susceptible to private property I&I.

In the 2000's, the Erie County Sewer Districts took over the sanitary sewer systems of several local municipalities. Through these mergers / consolidations, the County obtained sewer systems that had preexisting and recurring SSO locations. The vast majority of SSO occurrences in the Erie County Sewer Districts are in these merger areas.

What are the Erie County Sewer Districts doing to prevent SSOs?

The Erie County Sewer Districts have a multifaceted approach to mitigating SSOs. The strategies include:

  • Blockages: the Erie County Sewer Districts have a proactive sewer maintenance program that includes flushing, vactoring, bucketing, root cutting, and chemical root treatment to remove sediment, debris, and root obstructions from sewers.  The County also has a "Fats, Oils, and Grease" (FOG) program to address this common cause of sewer blockages (see "Fats, Oils, and Grease" (FOG) for additional information).
  • Wet weather and I&I: the Erie County Sewer Districts have invested vast resources towards the identification and removal of extraneous flows into the system.  See Infiltration and Inflow (I&I) Program for additional information. The County has also implemented improvements to increase the conveyance capacity of sewer system components, such as relief sewers, overflow retention facilities, etc.
  • Power and mechanical failures at pumping stations: the Erie County Sewer Districts employ an asset management approach to best serve its ratepayers.  This includes the use of a centralized maintenance management system (CMMS) to schedule and track preventative and corrective maintenance activities.  In addition, redundancy - such as backup generators, portable pumps, installed spare equipment, etc. - has been built into the systems to maintain service during a failure.  Finally, capital improvements are implemented to promote reliable operation of these facilities.
  • Sewer collapses or breaks: the Erie County Sewer Districts utilize closed circuit televising (CCTV) equipment to view, analyze, and assess sewers in an attempt to identify sewer problems before a collapse or break.  The County uses its Capital Improvement Planning program to prioritize the rehabilitation/replacement of sewers.  In addition, the Erie County Sewer Districts collectively budget over $3.5 million annually towards sanitary sewer rehabilitation methods such as cured in place pipe (CIPP) lining (a trenchless technology that can renew sewers at a fraction of the cost of a traditional open cut excavation method).  The County’s "PipePatch" system also allows the sewer districts to perform smaller trenchless repairs. 
What have the Erie County Sewer Districts already done to prevent SSOs?

Everything listed above are ongoing programs that have already limited the occurrence of overflows. Over the years the Erie County Sewer Districts have implemented numerous large-scale SSO mitigation projects. The following two (2) items are examples of recent initiatives:

What can you do to help prevent SSOs?

There are many things you can do to assist in the prevention of SSOs:

  • Do not dump fats, oil and grease down drains or toilets (see
  • Do not flush diapers, baby wipes, paper towels, and personal hygiene products down the toilet.  These items do not ‘breakdown’ in the sewer system and block sewers/flows or clog pumps. (See Flyer)
  • Eliminate private property I&I.  Significant portions of the extraneous flows in a sewer system come from private property (some studies have estimated up to 80% of the total!).  Sources of private property I&I include footer/foundation drains, sump pumps, roof leaders, low lying vents, and leaky lateral sewers. 
  • Support infrastructure investment.  Sewer systems are critical to the protection of public health and the environment and these systems require continual maintenance, rehabilitation, and improvement to provide proper service levels.