corner of a house with a storm drain

Inflow and Infiltration

What is inflow and infiltration (I&I)? It describes the introduction of water into the sanitary sewer system that does not require treatment, this is typically rainwater. Inflow refers to “direct” connections to the sanitary sewer system. Inflow connections can include downspouts, foundation/footing drains, storm drains, window well drains or any other connection that directly introduces water into the sanitary sewer system. Infiltration is the ingress of water into the sanitary sewer system through cracks or breaks in services lines, sanitary sewer mains and manholes.

Why should you be concerned? The introduction of rain/stormwater into the sanitary sewer system can lead to flooding of basements (possibly yours), sanitary sewer overflows and increased pumping costs. MMU estimates it spends approximately $250,000 annually to pump stormwater that enters the sanitary sewer system from I&I.

What is MMU doing to reduce I&I? MMU budgets funds annually to repair, replace and/or re-line areas of the sanitary sewer collection system. Another tool that is used to find sources of I&I is referred to as “smoke” testing. Smoke is introduced into the sanitary sewer system, typically at a manhole and blown into the system revealing sources of I&I.

Inflow and infiltration are a problem in all sanitary sewer systems, not just in Marshall. MMU is committed to reducing the impacts from I&I and will continue to budget funds for its reduction.