What is Inflow and Infiltration?
Inflow and Infiltration ( I & I ) are terms used to describe the ways that groundwater and storm water enters into dedicated wastewater systems or sanitary sewer systems.

Inflow is storm water that enters into sanitary sewer systems at points of direct connection to the systems (i.e. foundation drains, roof drains, downspouts, etc.). Storm water should be entering the storm water sewer systems or be allowed to soak into the ground without entering the sanitary sewer system.

Infiltration is groundwater that enters sanitary sewer systems through cracks and/or leaks in the sanitary sewer adjustment ring sections or through cracks in the pipes. These cracks and leaks in the pipes, or manholes, are usually caused by age-related deterioration and installation/maintenance errors. Groundwater can enter these cracks or leaks wherever sanitary sewer systems lie beneath water tables or the soil above the sewer systems become water saturated.

I & I water is called "clear water" (although it may be dirty) to distinguish it from normal sanitary sewage water in the sewer system.

Why is Inflow and Infiltration a problem?
Sanitary sewer systems are designed to carry wastewater from toilets, dishwashers, sinks or showers in homes or businesses. I&I add "clear water" to sewer systems, increasing the load on the systems. "Clear water" belongs in storm water sewers or on the surface of the ground and NOT in the sanitary sewers. A storm water sewer is a system designed to carry rainwater away and is normally much larger than sanitary sewers because they are designed to carry much larger amounts of water.

When "clear water" enters sanitary sewer systems, it must be transported and treated like sanitary waste water. I&I costs water treatment facilities AND consumers large amounts of money in water treatment operating expenses. By reducing I&I, capital and operating costs can be lowered. Minimizing I&I can also increase the lifetime-capacity of a treatment facility and wastewater transport system.

Other costs include the city or agency failing to meet federal or state guidelines and causing the community to become ineligible for low interest loans from grant or revolving fund opportunities.

How can Inflow & Infiltration problems be solved?
The reduction and control of I&I in sanitary sewer systems should be maintained by a disciplined, long-term monitoring and maintenance program. A city or agency must first determine how significant the I&I problem is, evaluate the quantity of I&I, determine the sources and decide on a cost effective corrective action plan. At this point, many cities follow a rigid maintenance program involving the re-building of the adjustment ring sections of manholes and catch basins.