What are Infiltration and Inflow (I/I)?
Infiltration is groundwater or stormwater which enters the sanitary sewer through cracks, holes, and open pipe joints. During rainfalls, the water table may rise above the elevation of the sanitary sewer, allowing the water to surround the pipe and find its way in. This is especially common in low-lying areas, areas near wetlands, and areas which use flood irrigation. Also, granular-backfilled pipe trenches can fill up with water, acting like a perched water table. Inflow is storm water which enters the sanitary sewer system directly from cross-connection with the storm sewer, from storm water collectors such as roof drains or catch basins, or from ponding over manhole covers. Inflow enters the sanitary sewer very soon after rain begins and stops soon after the rain stops. Infiltration enters the sanitary sewer after the stormwater has seeped through the ground to the level of the sewer. It continues until the groundwater table falls below the level of the sewer line. How do sewers dev
