Infiltration is defined as groundwater that enters the wastewater collection system through physical defects such as cracked pipes/manholes or deteriorated joints. Typically, many sewer pipes are below the surrounding groundwater table, therefore leakage of clean groundwater into the sewer (infiltration) is a widespread problem. Where sewer pipes run through Zone II areas or other land areas contributing flow to water supply withdrawal points, infiltration into those pipes can significantly reduce the yield of the affected water supply.
Inflow is extraneous flow entering the collection system through point sources such as drainage pipes connected to sewer lines. Inflow may be directly related to stormwater runoff from sources such as roof leaders, yard and area drains, sump pumps, manhole covers, or cross-connections from storm drains or catch basins. Inflow may also be contributed from non-storm related point sources, such as leaking tide gates, cooling-water discharges, or drains from springs and swampy areas. I/I removal plays an important role in balancing the water budget by minimizing the amount of groundwater and stormwater lost into wastewater systems.
20.a Wastewater utilities should implement the seven overall goals approved by the I/I Task Force.