A sanitary sewer overflow (SSO) is a wastewater overflow from a sanitary sewer system, causing significant environmental, health and safety risks. SSO prevention is important to ensure the safe and unimpeded transport of raw wastewater to the City's wastewater treatment plants.

What causes an SSO?

SSOs can be caused by anything capable of obstructing the flow of wastewater in a sewer, including a build-up of solids and fats, oils and greases (FOG) in the wastewater collection system, which is a major concern (View our Grease Trap Maintenance Presentation in English or en EspaƱol Adobe PDF). When an obstruction blocks wastewater flow within a pipe, the wastewater may back up and overflow through a manhole, cleanout, or drain. This overflowing wastewater may make its way into the environment, a house or a business.

What is the Pretreatment Program Doing to Prevent SSOs?

What can you do to prevent SSOs?

  • Collect waste cooking oil in a can. When cool, place this receptacle in a trash bag, seal tightly, and discard in the trash. Waste oil from restaurants can be collected and sold to rendering facilities;
  • Scrape food from plates into a compost or trash bin;
  • Before washing, wipe oily pans thoroughly with a used paper napkin or paper towel;
  • Minimize or avoid using your garbage disposals. A lot of food waste contains fats, oils and grease and could clog your own pipes and/or the city's sanitary sewers;
  • Install and maintain baskets, screens and or strainers over all sink and floor drains;
  • For restaurants, an appropriate cleaning schedule must be followed in order for the grease trap to function properly. Restaurants must adhere to our policy regarding the prohibited use of certain enzymes, bacteria and other agents in grease traps.
  • Spread the word to your friends and neighbors about what they can do to help prevent SSOs.
  • Remember the 3 "R's": Reduce, Reuse, and Recycle.