Part 1 of this series on tackling inflow and infiltration (I&I) challenges covered methods to identify I&I root causes and reduce their impact on wastewater systems. Part 2 explored field investigation strategies, including sewer camera inspections and flow monitoring to locate specific I&I sources.
Part 3 will focus on quantifying I&I contributions and exploring practical mitigation measures. Using Civica Infrastructure Inc.’s Micro Drainage modelling and evaluating reduction strategies, this blog provides actionable insights for civil engineers, municipalities, and land developers tackling I&I challenges.
This piece is for readers striving to enhance wastewater system modelling, reduce I&I risks, or improve overall flood analysis efforts.
About Inflow and Infiltration Quantification
To effectively mitigate I&I contributions, it is first necessary to quantify the extent of the problem. This involves analyzing existing wastewater systems and leveraging advanced tools to measure the flow entering the sanitary sewer network from inflow sources (such as direct connections or surface runoff) and infiltration sources (like groundwater seeping through cracks).
By quantifying the volume, distribution, and timing of I&I flow during storm events, municipalities can prioritize remediation efforts and minimize costly disruptions.
Modelling Methodology for Accurate Quantification
Civica employs a robust combined hydrologic and hydraulic modelling approach, ensuring a comprehensive representation of I&I dynamics within the sanitary sewer system. Using the InfoWorks CS platform and Civica’s proprietary Micro Drainage Modelling methodology, this approach achieves two critical goals:
- Isolating individual I&I flow components for enhanced clarity.
- Establishing benchmarks for sewer system performance under real-world and design storm conditions.
The result? An accurate, actionable understanding of where and how I&I negatively impacts wastewater systems.
What Is the Micro Drainage Approach?
The Micro Drainage modelling methodology is a cutting-edge technique that models how overland runoff enters the sanitary sewer system through specific inlets, culverts, and defects. Unlike traditional methods, this micro-level analysis provides greater accuracy and precision when addressing I&I.
Components of the Micro Drainage Approach
Key components of the Micro Drainage Approach include:
1. Minor System
The minor system encompasses traditional sewer infrastructure like pipes and sanitary maintenance holes. Through detailed modelling of lateral service connections and structural conditions, inflow sources like roof drains, manhole openings, and groundwater infiltration are identified and quantified.
2. Major System
The major system includes surface elements such as roads, ditches, and channels. When the capacity of the minor system is exceeded during heavy storms, overflow travels along these pathways. The Micro Drainage approach models the geometry, slope, and roughness of these overland channels to evaluate their impact on I&I levels.
3. Connecting Systems (Catch Basins and Gullies)
Major and minor systems are linked via inlets such as catch basins and manhole openings. Civica integrates field-tested capture curves and laboratory data to precisely model how surface water enters the underground sewer network.
The ability to simulate “micro” interactions between surface and sewer flows is what sets this methodology apart, ensuring greater accuracy in diagnosing and mitigating I&I issues.
Evaluation of Inflow and Infiltration Mitigation Measures
To effectively address I&I, engineers must define clear reduction targets, such as meeting city guidelines for basement flood prevention. For example, many municipalities set targets to keep hydraulic grade lines (HGLs) below basement elevations during significant storm events.
Available Mitigation Measures
Several measures can be employed to reduce I&I contributions systematically. Below are the most widely used techniques:
- Downspout Disconnection: Redirect roof drainage systems away from the sewer network using extensions and splash pads to reduce water entering the system.
- Downspout Relocation: Move downspout discharge points at least 2 meters from the foundation wall to minimize moisture infiltration into basement drains.
- Sanitary Maintenance Hole Sealing: Retrofit maintenance holes with protective inserts and seal joints to prevent direct inflow during heavy rainfall.
- Foundation Drain Disconnection or Interceptor Drain Installation:
- Option 1: Direct foundation drainage water to overland outlets rather than sewer laterals.
- Option 2: Install an interceptor drain to capture and divert water before it reaches the foundation.
- Basement Walkout Drain Disconnections: Reconfigure floor drains to prevent sewer backups while ensuring adequate drainage away from structures.
How to Select Preferred Mitigation Measures
Selecting preferred mitigation measures involves a thorough evaluation of costs, effectiveness, and alignment with project objectives.
- Preliminary Cost Estimate of Mitigation Measures: Develop a detailed cost analysis for each mitigation measure alongside scenarios designed to optimize cost-effectiveness.
- Analysis of Mitigation Measures: Create and model various scenarios to determine the scope of work required to achieve I&I reduction targets.
- Selection of Mitigation Measures: Choose an approach based on implementation feasibility, long-term benefits, and compliance with municipal standards.
Implementation of Inflow and Infiltration (I&I) Mitigation Measures
Effective implementation of mitigation measures begins with a thorough inflow and infiltration inspection to identify problem areas and prioritize targeted interventions.
Stage 1 – Simple Disconnections
Begin with straightforward measures to address low-hanging fruit:
- Disconnect downspouts.
- Seal maintenance holes to reduce inflow.
Stage 2 – Foundation Drain Disconnection or Interception
Transition to more complex options, necessitating sewer lateral monitoring to assess the success of the disconnection strategy. For example, assess the efficacy of foundation drains in redirecting groundwater away from the sewer system.
Stage 3 – Ongoing Asset Management Strategy
Monitor, evaluate, and refine your mitigation plan over time. Adopting a robust asset management strategy ensures that I&I reduction efforts remain effective as the condition of infrastructure evolves.
Inspiration from Similar Successes
Many municipalities, such as Toronto through its Basement Flooding Protection Program, have successfully implemented staged I&I reduction plans to minimize urban flooding risks.
By learning from these experiences, other cities can harness proven practices to replicate success and sustain long-term wastewater management improvements.
Contact Us to Quantify and Mitigate Inflow and Infiltration (I&I) Risks
Inflow and infiltration reduction is fundamental to maintaining a resilient and efficient wastewater system. Whether you are a civil engineer, city planner, or land developer, Civica provides expert consultation and cutting-edge solutions to tackle I&I challenges at every stage.
Do not wait for the next storm—get proactive today. Contact Civica for a personalized wastewater system assessment and tailored I&I reduction strategy.
Learn more at:
Basement Flooding Area 9 Inflow and Infiltration Reduction Project
New Subdivision Inflow and Infiltration (I/I) Prevention in York Region
Methodology of Sanitary Maintenance Hole Inflow and Infiltration
City of Toronto’s Sewer Infrastructure and Sewer Capacity Assessment Guidelines
5 Key Takeaways from the CLI-ECA Stormwater Regulations
Role of Flow Monitoring in Inflow and Infiltration (I&I) (Part 1)
Flow Monitoring and Its Role in Inflow and Infiltration (I&I) (Part 2)