Reduced sewer conveyance and treatment capacity caused by inflow and infiltration can increase wastewater operation and maintenance costs, restrict urban development, and increase potential for environmental spills and overflows. 

Various studies have shown that I&I generated from private property can represent over 60% of the total I&I in a wastewater system. This number can be significantly higher in older systems, and presents unique challenges for municipalities, ranging from legal and policy issues to funding and implementation.

As a result, it’s often difficult for municipalities to significantly reduce I&I coming from private properties. But it’s a different story in Ontario, Canada, where Civica Infrastructure Inc., in partnership with several municipalities in Ontario and the Greater Toronto Area, has successfully reduced the amount of private-side I&I through a public-private partnership. 

The specific partnership framework allows municipalities to pass most — if not all — of the liability, cost and risk of the investigations, remediations and verifications to the private partner (i.e. land developer), while ensuring proper communication, coordination and warranties are in place. In return, the private partner receives a portion of the sanitary servicing capacity created through the sewer flow reduction. This process produces a net reduction in flow in the public sewer system by only allocating a portion of the reduction.

Benefits of the P3 program

The benefits of reducing significant I&I gives obvious advantages over adding more conveyance and treatment capacity in a system. Additional direct benefits of a P3:

1. No program costs to municipalities: The burden of program costs is shifted to the private partner (developer), relieving municipalities of financial obligations.
2. Liability mitigation: The identification and remediation of I&I defects on private properties become the responsibility of the private partner, reducing liabilities for municipalities.
3. Improved storm drainage handling: Through the retrofit of Low Impact Development techniques, storm drainage capabilities can be enhanced, and in some cases, stormwater treatment can be improved.
4. Reduced operation and maintenance costs: Compared to constructing additional sewers, pumping stations and treatment facilities, I&I reduction leads to decreased long-term operation and maintenance expenses for municipalities.
5. Lower costs for developers: The elimination of new sewer construction, pumping stations, and treatment system design and construction reduces overall costs for private developers.
6. Faster timeline for increased sewer capacity: By focusing on I&I reduction, the program achieves increased sewer capacity more quickly than traditional infrastructure expansion.
7. Residual capacity for future growth: By understanding the available residual capacity, municipalities can defer planned new infrastructure, leading to potential savings.
8. Enhanced system resilience: The program contributes to the sanitary sewer system’s resilience and sustainability, helping address climate change risks and system aging.

In York Region alone, a significant increase in sewer capacity has been realized through I&I reduction, allowing more service areas and populations to be served by the same sewer system. More specifically, capacity has been created for over 12,000 people in new development and 24,000 in total.

The successful transfer of improvement costs and liabilities to the private partner has been a key advantage of the P3 program. The private partner takes on the responsibility for intrusive investigations, remediation works and construction, while the municipality holds a security for a warranty period to ensure the quality and longevity of the work.

A customer-centric approach based on transparent and friendly communication has contributed to the program’s success. Each private property project is assigned a dedicated project coordinator who facilitates agreements with homeowners and oversees construction works. The financial and physical facilitation of the program has played a vital role in achieving near-perfect success rates for stormwater disconnection from sanitary sewers. This success surpasses other programs relying on homeowner-led initiatives or enforcement-based approaches.

Status of completion

The program commenced in 2010 and is at different stages of implementation throughout the Greater Toronto Area. To date, over 25,000 private lots have undergone investigations using various techniques, including specialty testing.

Overall, testing has resulted in the identification and remediation of over 250 stormwater defects, including over 200 residential downspouts, 25 commercial flat-roof drains, five catch basins (approximately 250,000 cubic feet) disconnected from the sanitary system, four reverse sloped driveway drains, the entire roof area of a hotel, and other open storm access hatches draining to sanitary sewers.

Across the GTA, the program has completed each stage, from preliminary design to post-remediation warranty, with all necessary improvements made. The last stage of the program is the warranty period. The warranty mechanism has worked well, with little to no follow-up repairs required and ensuring all storm connections remain disconnected and properly connected to the storm drainage system. 

Ongoing investigations and remediation work is taking place in multiple GTA municipalities. Based on the established framework’s demonstrable successes, the program is expected to expand to include other areas in Ontario facing similar growth and capacity pressures. The completed projects have already created sewer capacity equivalent to serving a population of nearly 50,000.

Net benefits

The success of P3 projects can be attributed to the specialized processes followed by private consultants/contractors and the collaborative efforts of all involved parties. Municipalities have achieved significant I&I reductions, resulting in increased sewer capacities that offer flood protection and enable land developers to expedite sewage connections using sustainable practices.

The primary focus of the program has been to create net benefits by reducing I&I and allowing new development flows. The program has achieved tangible and quantifiable fixes that ensure stormwater remains disconnected from sanitary sewers. The P3 program provides an effective mechanism to accelerate improvement and address challenging fixes on private properties that may be subject to ownership and legal constraints. This flexible framework can be applied in other jurisdictions facing growth and infrastructure challenges.

The P3 program’s successful reduction of private-side I&I has provided municipalities in the Greater Toronto Area with increased wastewater system capacity. The program’s benefits extend to cost savings, liability mitigation, improved storm drainage and enhanced system resilience. With ongoing expansion and the potential to replicate the program in other regions, the P3 approach holds promise for addressing I&I challenges and supporting sustainable growth in wastewater systems.