Which method is used to mitigate inflow and infiltration in the collection system?

• A. Flow equalization basins
• B. Chlorination in the collection system
• C. Chemical precipitation
• D. Removal or rehabilitation of pipes in the collection system

Answer: (D)

Mitigating inflow and infiltration means reducing the extra water that enters the sanitary sewer, especially during rain, by addressing the source in the collection system. The most direct and effective approach is to remove or rehabilitate pipes in the collection system—replacing damaged sections, relining cracked or aging pipes, and sealing joints or repairing manholes. This directly cuts down on where groundwater or stormwater can enter the sewer, lowering peak flows and helping avoid overflows downstream.

Flow equalization basins can smooth out flow fluctuations, but they don’t prevent the water from entering the system in the first place, so they don’t address the root cause of I&I. Chlorination in the collection system isn’t a method for reducing I&I and isn’t appropriate for that purpose; it targets disinfection rather than inflow. Chemical precipitation is a treatment process step to remove contaminants, not a method to mitigate infiltration or inflow.