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Sanitary Sewer Overflow (SSO)

Sanitary Sewer Overflows (SSOs) are discharges of raw sewage from separate sanitary and stormwater sewer systems (SSSs). SSOs can release untreated sewage into basements or out of manholes and onto city streets, playgrounds or into streams, depending on where the problem in the system occurs. SSOs are often caused by the following problems:

  • Infiltration and inflow (high levels of infiltration of groundwater and inflow from storm drains)
  • Undersized systems (the amount of wastewater received from the community exceeds the system's capacity)
  • Pipe/equipment failures
  • Unauthorized sewer connections
  • Deteriorating sewer systems
  • Fat, oil, and grease blockages

A few types of SSOs are unavoidable and may occur due to the following causes:

  • Vandalism
  • Certain types of blockages (e.g., root intrusion, leaves and trash)
  • Extreme rainstorms
  • Acts of nature such as earthquakes or floods

SSOs contain raw sewage and can expose people to bacteria that may cause illness through contaminated water sources or public access areas. Shellfish that are harvested for human consumption can also be contaminated with raw sewage.

What's being done about SSOs?

SSOs are prohibited discharges and are required to be stopped and fixed. DEC has developed a SSO permitting and compliance approach for municipal State Pollutant Discharge Elimination System (SPDES) wastewater treatment facilities with SSOs. If a SSO occurs, facilities are required to evaluate the cause and implement corrective actions to prevent the SSO from happening again. DEC's approach includes an evaluation of the cause of the SSO, whether it could have been prevented and if a compliance schedule to abate the SSO is needed. This could include expansion or construction of wastewater infrastructure and sewer maintenance to ensure that the facility remains in compliance and future SSOs do not occur.

A puddle of sewage water
Sanitary sewer overflows (SSOs) may be caused
by blockages, equipment problems, inflow from
stormwater, or inflitration of groundwater.

SSOs can be reduced or eliminated with the following methods:

  • Reducing Inflow & Infiltration through system rehabilitation and repairing broken or leaking service lines
  • Enlarging or upgrading sewer, pump station, or sewage treatment plant capacity
  • Sewer system cleaning and maintenance

Over time, the approach will lead to the abatement of existing SSOs and a reduction in the number of discharges of untreated sewage, resulting in a greater protection of the public health and the environment.

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