Inflow and Infiltration

Inflow is a direct connection of “clear” water (rain/storm water) into the wastewater (sanitary sewer) collection system. Infiltration is an indirect connection of “clear” water to the wastewater (sanitary sewer) system. Inflow is by far the larger problem of the two and occurs in direct proportion to rainfall. Inflow is most often the result of improperly installed sump pumps (used by many homeowners to keep groundwater out of basements), roof downspouts, and foundation drains illegally connected to the City’s sanitary sewer system. Sump pumps are also sometimes illegally connected to the sanitary sewer system via a hose leading from the sump to a laundry tub or floor drain. Infiltration occurs when groundwater seeps into sewer pipes through cracks, leaky joints or deteriorated manholes.

The City’s sanitary sewer master plan, finalized in 2009, identified five sewersheds, or areas of the community which are the sources of high sanitary sewer flows during rainfall events. These high flows caused sanitary sewer back-ups into basements, overflows into creeks and wetlands, and increased operational costs at the Water & Resource Recovery Center. These five areas include approximately 7,000 properties. As part of a five-year I&I program to reduce and eliminate I&I, the City conducted private property inspections and smoke testing to identify improper private property connections. Meanwhile, smoke testing, manhole inspections, and sanitary sewer grading were used to identify I&I in the public infrastructure.

For more questions or more information related to I&I, contact City Engineering at 563-589-4270.