Inflow and Infiltration and Wastewater Overflows

Inflow and Infiltration (I&I) occurs when stormwater and groundwater enter sanitary sewer systems. In general, I&I issues are related to improperly cross-connected stormwater collection pipes, and the age of sewer systems, which deteriorate and allow groundwater intrusion into the sewer over time.

I&I becomes a problem in sewer systems by exceeding the capacity of the system to convey and/or treat the high volume of clean rain or groundwater that infiltrates the sewer during wet winter months and rain events. When this capacity is exceeded, the excess flow of mixed stormwater and wastewater overflows to the marine environment at various emergency discharge points. The system is designed to overflow under these conditions to prevent major damage to infrastructure.