Most I and I problems in sanitary sewers are due to what?

• A. Main Sewer
• B. Storm Drain
• C. Service Laterals
• D. Interceptor

Answer: (C)

Inflow and infiltration come from water entering the sanitary sewer, either as groundwater seeping in through cracks (infiltration) or water from storm drains, roof leaders, or yard drains entering through connections (inflow). The largest share of I&I typically comes from the service laterals—the pipes between the public sewer and each property. There are many of these laterals, and they are often old, cracked, or poorly connected, with more opportunities for water to get in than in the larger mains. Illicit or improper connections from stormwater systems to the sanitary line can also dump significant water into these laterals during rain, boosting I&I well beyond normal levels. The main sewer and interceptor collect from many laterals, but they usually have fewer weak points per mile and are designed to handle larger flows, so their contribution to I&I is generally smaller in comparison. Focusing on repairing service laterals and removing improper connections is typically where the biggest reductions in I&I come from.