What is Inflow and Infiltration?

Inflow and Infiltration (I&I) are terms used to describe the ways that groundwater and stormwater enter a sanitary sewer system.

• Inflow is storm and surface water that enters the sewer system at points of direct connection. These include footing/foundation drains, roof drains/leaders, downspouts, drains from window wells, outdoor basement stairwells, drains from driveways and groundwater/basement sump pumps. Ideally, inflow water should enter the stormwater system or be absorbed into the ground.
• Infiltration is rain and ground water that enters into the sewer system through cracks in sewer pipes, joints or manholes. These leaks may be caused by age-related deterioration, loose joints, poor design, root damage or maintenance issues. Sewer pipes are designed to last about 20-50 years. Often, sewer system pipes go much longer without maintenance and are likely to be damaged.

Flow Monitoring

Flow Monitoring equipment is used to determine if there is excessive I&I. Many types of flow monitoring instruments are available and pricing varies. To measure wastewater flows throughout the sewer system, it is important to select the appropriate Flow Meter.

A probe measures water velocity and depth. Long-term flow calculations can be made using simple water level recorders. More sophisticated flow meters can output, display and record flow information directly, but they represent a larger investment.

Benefits of Low Infiltration & Inflow 

• Efficient operation of wastewater treatment facilities
• Lower overall capital and operation costs
• Fewer/smaller expansions of hydraulically-sized system components (i.e. sewer lines, pumping stations, etc.)
• Decrease in the energy required to operate pumps
• Increased Compliance/Elimination of Violations with EPA requirements

Darcy Sullivan Industry flow meter, flow monitoring, infilitration, inflow, Level Sensing, probe, sewer system