Managing Infiltration Inflow

Managing Infiltration and Inflow (I/I) 
Successful I/I reduction programs combine good operations and maintenance practices with data-driven decision making. While some utilities hire consulting engineers to conduct comprehensive studies, many communities can identify and correct a significant portion of their I/I problems using their own personnel and existing resources.

The most successful programs typically begin with utility staff identifying obvious problems and collecting system data. Consultants can then be used to investigate more complex issues, prioritize rehabilitation projects, or prepare capital improvement plans.

Utility-Led Approach 
Municipal personnel are often the first to recognize developing I/I problems because they operate and maintain the system on a daily basis. Before investing in a comprehensive engineering study, utilities should develop a systematic understanding of how their collection system performs.

Recommended activities include:

• Maintain accurate GIS mapping or other current maps of the collection system.
• Collect pump station run times, flow data, and treatment plant influent records.
• Monitor system performance during both wet-weather and dry-weather conditions.
• Document sanitary sewer overflows, customer backups, surcharging manholes, and recurring maintenance locations.
• Compare rainfall data with pump station and treatment plant flows.
• Walk priority sewer basins after significant rainfall events.
• Inspect manholes for signs of infiltration or inflow.
• Clean sewer mains, siphons, force mains, and manholes on a routine schedule.
• Use smoke testing, dye testing, CCTV inspection, or other investigative methods where appropriate.
• Repair obvious defects as they are identified and maintain records of completed repairs.

Many utilities find that relatively inexpensive repairs—such as sealing leaking manholes, replacing broken cleanout caps, eliminating illegal inflow connections, or repairing damaged service laterals—can substantially reduce wet-weather flows.

Consultant-Assisted Approach 
When I/I problems are widespread or difficult to isolate, municipalities may benefit from retaining a qualified consulting engineer to perform a Sanitary Sewer Evaluation Study (SSES) or similar system assessment.

Depending on the needs of the utility, an engineering study may include:

• Basin flow monitoring.
• Rainfall correlation analysis.
• Hydraulic modeling.
• Closed-circuit television (CCTV) inspection.
• Smoke and dye testing.
• Manhole condition assessments.
• Prioritized rehabilitation recommendations.
• Cost estimates and implementation schedules.
• Assistance with grant or loan applications.

Engineering studies are particularly valuable when utilities are considering major rehabilitation projects or treatment plant expansions because reducing I/I may eliminate or postpone the need for costly capital improvements.

Selecting the Appropriate Approach 
Every wastewater system is different. Utilities should first determine the nature and extent of their I/I problem before selecting an investigation strategy.

As a general guideline:

• Systems experiencing localized inflow problems or isolated maintenance issues can often make significant progress through utility-led investigations and routine maintenance.
• Systems with widespread groundwater infiltration, aging infrastructure, or recurring wet-weather capacity problems often benefit from a comprehensive engineering evaluation.

These approaches are not mutually exclusive. Information collected by utility personnel frequently becomes the foundation for a successful engineering study and allows consultants to focus their efforts where they will produce the greatest benefit.

A Continuous Improvement Process 
Reducing I/I is not a one-time project but an ongoing component of wastewater system management. Utilities should continuously monitor system performance, maintain accurate records, evaluate rehabilitation results, and update capital improvement plans based on observed conditions and available funding.

The most successful I/I programs combine proactive maintenance, targeted rehabilitation, careful data collection, and periodic engineering evaluations to improve system reliability while making the best use of limited financial resources.