Civica Infrastructure Inc. collaborated with the City of Toronto on inflow and infiltration (I/I) reduction projects involving two pilot areas: Area 9 in Etobicoke and Wirral Court in Scarborough.
When excess water enters the sewer system due to heavy rainfall or damaged pipes, the water levels can become too high for the system to handle, leading to water backup into homes and buildings. It’s important for municipalities to take preventative actions to mitigate these issues and create safer and more sustainable communities for all.
Project Objectives
The objective of each pilot project was to identify how excess rainwater and groundwater enters the sanitary sewers, quantify the problem, and then evaluate possible solutions that could reduce basement flooding.
Project Summary
The two I/I reduction projects aimed to identify the sources of I/I in the pilot areas and implement action plans to remediate and reduce I/I flows in the sanitary systems. Using the information gathered, Civica would develop I/I reduction strategy standards to be launched across the City of Toronto.
Area 9 is a primarily residential area of 45 hectares located in Etobicoke. Flow monitoring in this area revealed high I/I in sanitary sewers that resulted in multiple basement flooding events, including:
- 12 reports in May 2000 for a 5- to 10-year storm event
- 72 reports in July 2013 for a 100-year storm event
Wirral Court in Scarborough comprises an area of approximately 95 hectares that is mostly residential with some industrial and commercial operations. Flow monitoring also showed high I/I in sanitary sewers, with 90 reports of basement flooding in 2012 during a 25-year storm event.
Problems Associated with Inflow and Infiltration (I/I)
I/I pose a multitude of problems, with basement flooding being one of the most frustrating and common issues. Not only does it cause immense damage to personal property, but it can also increase the risk of health hazards associated with mould and bacteria growth.
In addition to basement flooding, inflow and infiltration can lead to costly infrastructure upgrades, environmental spills, and increased treatment and conveyance costs.
Common Sources of Inflow and Infiltration (I/I)
Both private and public property connections to sanitary sewers can contribute to I/I. Common private property sources are roof drains from commercial buildings and groundwater discharging from deep building foundations.
Common public property sources include leaky maintenance hole covers; catch basins; and cracks, holes, and open joints in sanitary sewers.
Inflow and Infiltration (I/I) Inspection Performed by Civica
For the Area 9 study, a desktop review of all available foundation drain records in the area indicated that the majority of residential foundation drains, also known as weeping tiles, were connected to the sanitary sewer system. In one subarea, dubbed 9-SAN-1, homes had a separate service lateral that directs water from foundation drains to the municipal storm sewer.
An extensive field I/I inspection, including wastewater monitoring and sewer flow monitoring, smoke and dye testing, and visual sewer inspections during rainfall, was conducted to validate the desktop results and rule out other sources of I/I.
The flow monitoring program, which had eight flow monitors distributed over the 45-hectare area, measured chronic levels of I/I in all but one subarea. As expected, subarea 9-SAN-1 showed significantly less I/I in all rainfall events.
To further validate these results, additional CCTV sewer inspections were commissioned to visually capture the foundation drains’ inaction during wet weather. Findings indicated that the sewer pipes were in good condition under wet weather conditions, with no significant contributions noted from pipe defects. However, significant amounts of clear water were observed coming in from the sanitary service laterals.
Dye testing was also completed during a sizable rainfall event to reflect the saturated soil conditions that would exist during a storm causing basement flooding. It only took 10 minutes for the water to get from the ground surface into the foundation drain, through the sanitary lateral, and into the sanitary sewer.
Using the findings of the field inspection program, a sophisticated numerical model was created using the InfoWorksÒ ICM software to determine the possible benefits of disconnecting the foundation drains.
Results showed that in addition to removing all I/I contributions from downspouts and maintenance hole pick holes, an 80% reduction of I/I flow generated by foundation drains in the study area would also be necessary to achieve the targeted level of protection. This would require disconnecting the foundation drains of 361 Area 9 homes from the sanitary sewer system.
Area 9 and Wirral Court Results
Private I/I sources contributed up to 90% of the identified I/I in the pilot areas.
In Area 9 of Etobicoke, private I&I sources identified included:
- 361 foundation drains
- 12 roof downspouts
In Scarborough’s Wirral Court, private I/I sources were:
- 29 roof downspouts
- 4 commercial roof drains
- 1 driveway drain
- 1 cleanout
Cost-Benefit Analysis
Costs to remediate I/I sources included:
- Design
- Construction
- Permitting
- Risk mitigation
- Operation and maintenance
Benefits of remediating I/I sources included:
- Reductions in conveyance/treatment costs
- Reductions in basement flooding
- Reduced overflows to the environment
- Additional sewer capacity for new development
Other Municipalities with I/I Programs
Other southern Ontario municipalities have developed programs to address I/I issues.
York Region:
- Publicly funded I/I programs
- Developer-funded I/I programs
Halton Region:
- Publicly funded downspout disconnection program
- Enhanced basement flooding prevention subsidy program
City of London:
- Publicly funded weeping-tile disconnection program
- Basement flooding grant subsidy program
Civica’s Approach to I/I Reduction Program
Civica planned to implement a “find and fix” program consisting of concurrent I/I source identification and remediation. Completely voluntary, it comes at no cost to property owners and benefits from positive perception and increased buy-in.
It also features a robust communication plan, which is an essential aspect of any I/I program. Key performance indicators (KPIs) such as flow reductions, stakeholder satisfaction, and costs will be used to monitor the success of I/I reduction programs.
A Successful Inflow and Infiltration (I/I) Reduction Program
The City of Toronto-led reduction program is expected to lead to capital and operational savings, including zero pipe upgrades and reduced conveyance and treatment costs. In addition to reduced basement flooding, there will also be fewer spills to the environment from sanitary sewer overflows. Furthermore, the higher sanitary sewer capacity allows for future development in the City.
Civica is a leading provider of stormwater and sewage water management solutions across southern Ontario. With expertise in inflow and infiltration reduction, they provide guidance to municipalities on how best to address any failures in collection and drainage systems.
Contact us today for more information.
Learn More At:
Real-Time Monitoring for Quantifying Combined Sewer Overflow and Water Quality
New Subdivision Inflow and Infiltration (I/I) Prevention in York Region
Creating Wastewater System Capacity to Support Housing – GTA Project
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)
Methodology of Sanitary Maintenance Hole Inflow and Infiltration
Inflow and Infiltration Inspection Case Studies
New Subdivision Flow Monitoring to Assess Performance of I/I Prevention
