Why do sewers overflow?

Sanitary sewer overflows (SSOs) occasionally occur in almost every sewer system, even though systems are intended to collect and contain all the sewage that flows into them. When SSOs happen frequently, it means something is wrong with the system.

Problems that can cause SSOs include:

• Inappropriate materials sent to the sewers that may create blockages, such as fats, oils, grease, and some household products like baby wipes and sanitary pads;
• Tree roots entering through defects or openings in a sewer line that may cause blockages;
• Leaky sewers that allow stormwater, groundwater, and snowmelt to enter the sanitary sewer through cracks and faults in the joints, which can overload a sanitary sewer;
• Poor connections of sources of water, such as sump pumps, roof leaders, foundation drains, and area drains that can overload a sanitary sewer;
• Inappropriate maintenance and cleaning of sewers;
• Ineffective pump maintenance and lack of backup power;
• Undersized sewers and/or pumps; and
• Equipment failures and breaks.