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How to Address Inflow and Infiltration in Wastewater Systems
One common challenge for all wastewater systems is inflow and infiltration (I/I). By understanding how I/I impacts system performance and capacity during wet and dry weather conditions and how to efficiently address I/I, utility owners can safeguard the service life of wastewater assets and ensure sustainable and reliable services for the community. Let's start by unpacking the differences between infiltration and inflow.
What Is Inflow and Infiltration?
Infiltration occurs when groundwater seeps into the collection system through cracks, pipe defects, faulty joints, and other openings.
In contrast, inflow occurs when water directly enters the system from inappropriate or illegal connections such as open cleanouts, improper or missing manhole covers, sump pumps, or drain spouts. Excessive surface run-off during heavy rainfall can also contribute to inflow.
Inflow and infiltration strain wastewater systems by increasing flow levels. This overwhelms collection systems and treatment facilities, which leads to sewer overflows and back-ups. In other words, I/I robs a system of capacity. The impacts of I/I can be significant and far-reaching, including increased operational and treatment costs, damage to private property, compromised water quality, environmental concerns, and regulatory violations.
Identifying and Assessing Inflow and Infiltration
There are numerous tactics and approaches to identifying sources of I/I which can be tailored to each system, including:
Flow monitoring — establishes a baseline for the system flows and pinpoints areas with recurring, excessive flows during wet-weather events
Manhole inspection — identifies structural defects and improperly installed covers that allow I/I to enter the system
Smoke testing — simulates rainfall, where clean water can enter the system, forced smoke will escape showing where pipe defects or improper connections will contribute to I/I
Dye testing — injects non-toxic dye into the flow at suspected storm and private property connections to trace and quantify I/I contributions to the system
Sewer televising — inspects pipe interiors using robotic devices with cameras to record the condition of pipes, including deterioration and buildup of sediment and fats, oil, and grease (FOG)
Acoustic testing — locates blockages like roots and FOG to direct preventative cleaning programs
The National Association of Sewer Service Companies (NASSCO) standards and certification programs are the industry norm for manhole inspection protocols and grading manhole, lateral, and pipe conditions. Implementing the NASSCO Manhole/Pipeline/Lateral Assessment and Certification Program (MACP/LACP/PACP) standards for I/I assessments produces a reliable and consistent approach to evaluating risks and planning maintenance and capital improvement programs.
Mitigation Strategies for Infiltration and Inflow
Managing infiltration and inflow is essential for wastewater systems' long-term sustainability and efficiency. Strategies to mitigate I/I include:
Preventative maintenance — including televising, cleaning and lining programs, root management, and FOG initiatives stop I/I before it enters the system. Consistent, planned system maintenance is a way of fixing minor issues before they become overflows and backups.
System Improvements — such as pipe rehabilitation, sealant applications, and root intrusion prevention help address structural issues that diminish system capacities. Regular inspections and a robust asset management program are essential to know which areas require pressing maintenance.
Public education — increases awareness and supports mitigation strategies that reduce I/I by increasing wastewater flow capacities and decreasing treatment costs.
At RJN, we provide comprehensive solutions to address a wide range of system challenges — including infiltration and inflow — our proactive approach is designed to minimize risk while extending the service life of system infrastructure.