Posted by Tim Lester on Wednesday, May 21, 2025
If your sewer system experiences inflow or infiltration, it could cause a Sanitary Sewer Overflow (SSO), which is bad news for your community. SSOs can result in public health hazards, unsanitary conditions, and environmental hazards, like contamination of waterways and the spread of disease.
Inflow and infiltration (I&I) is extraneous water entering the sanitary sewer system. Inflow is from rainwater and runoff entering the sanitary sewer system via improper connections such as roof leaders, drains, and sump pumps, as well as leaky manhole covers and stormwater cross-connections. Infiltration is from groundwater entering the sanitary sewer system via defects in manholes and pipes such as cracks, leaks, and poor construction.
Reducing I&I is vital for your community. Here's why:
- Prevent hydraulic overloads.
I&I can lead to hydraulic overloads, sanitary sewer overflows, environmental and public health hazards, backups into homes, compliance issues, and overloads at downstream pump stations and wastewater treatment plants.
- Address problems proactively.
Rather than wait for hydraulic overloads and sanitary sewer overflows to happen at the most inconvenient times, rehabilitation and repair efforts can be made proactively, at your pace and schedule. Addressing small I&I issues now can prevent bigger issues later. No one likes doing emergency work on busy days, in the rain, at night, or on weekends!
- Efficiently use public funds.
Planned work can be budgeted and financed, and is less costly than emergency work. Also, when I&I is removed, costly upgrades to the sewer system may be avoided.
- Restore capacity in your system.
Eliminating extraneous flow can help reduce overloads and compliance issues in your sewer system. If enough I&I is removed, you may be able to add customers to the sewer system again. This means additional revenue in terms of user rates and tapping fees.
- Be aware of what’s happening in your system.
A vital part of an I&I program is investigation. Whether it is a flow study, manhole inspections, or sewer main televising, if done properly, these all result in awareness of where, what, why, and how big the problems are.
Left unchecked, I&I can cause some serious issues for you and your community, and while some I&I is inevitable, it is possible to keep it tamed. Keeping I&I at bay is essential for keeping your sewer system not only working properly for your community, but also reducing surprises or emergencies.
If you need more information, have questions on how to get started, or what to do next, please don’t hesitate to contact me.
Tim Lester, PE
project manager
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Categories: Municipal Infrastructure
Tagged: Wastewater | Stormwater | Health & Safety