In wastewater systems, which condition is caused by infiltration and inflow on lines?

• A. Backflow
• B. Hydraulic overload
• C. Inflow
• D. Surcharge

Answer: (B)

When extra water enters the sewer system from infiltration (groundwater seeping in through cracks and joints) and inflow (stormwater or surface water entering through manholes and connections), the volume of wastewater pushed through the pipes increases beyond what the system was designed to handle. That mismatch between the actual flow and the system’s capacity is called hydraulic overload. The pipes and pumps can’t convey the surge, so flows rise, leading to overflows or backups and sometimes surface flooding.

Backflow describes water moving in the reverse direction due to downstream pressure, which isn’t specifically caused by the added water from infiltration/inflow. Inflow refers to the water entering the system, not the resulting condition. Surcharge is a potential outcome of hydraulic overload—water in the sewer rises above the sewer grade and may back up into streets or basements—but the direct condition caused by the infiltration/inflow itself is hydraulic overload.