Civica Infrastructure Inc. is a leading provider of wastewater management and monitoring services. With expertise in inflow and infiltration (I/I) reduction, we are a frequent collaborator of municipalities like the City of Toronto.
Civica’s investigations of Toronto’s Wirral Court Pumping Station and Basement Flooding Area 9 pilot areas uncovered a need for private property-involved efforts to mitigate excess water entering the sewer system. These insights prompted the City to innovate a robust program aimed at minimizing sewer overloads before severe weather events occur. The envisioned program was expected to diminish environmental harm, prevent basement flooding, and expand sewer capacity for Toronto’s growth.
This case study will provide a detailed account of the I/I reduction pilot projects.
I/I and Wet-weather Flow (WWF) Impact on Current Level of Service
Wet-weather flow (WWF) is excess flow into combined sewer systems during rainfall or snowmelt events. It consists of wastewater, groundwater infiltration, and stormwater runoff.
Assessing I/I in sewers is crucial to address service quality and safeguard properties and infrastructure. In the case of these projects, both public and private property sources were contributing to I/I to the wastewater system. High I/I levels often exceed design capacity, leading to basement flooding, environmental issues, and sewer congestion. Public I/I sources, like maintenance holes and city pipes, are typically handled by the City’s municipal wastewater management programs, whereas private contributions, from residential and business properties alike, also require significant focus to maintain system efficiency.
Overview of Pilot Areas
Inflow and Infiltration Reduction Pilot Project (Phase 1) on Wirral Court Sewage Pumping Station Sewershed
The Wirral Court sanitary pumping station, situated in Scarborough’s south-central region, spans 113.8 hectares, with significant portions being non-serviced lands. The serviced 94.98-hectare area utilizes a separate sewer system.
Extensive flow monitoring over the years showed that rainfall significantly affected sanitary sewer flows, surpassing city design standards. Notably, 2016 data revealed an average I/I rate of 0.64 L/s/ha, with peak rates reaching 0.94 L/s/ha—nearly four times the stipulated norm. The area also experienced 90 basement flooding incidents during a major storm in July 2012, highlighting infrastructural challenges.
Basement Flooding Study Area 9 Inflow and Infiltration Reduction Study
Study Area 9, located in Etobicoke Central (former City of Etobicoke), includes 557 mid-20th-century properties across 45 hectares with 1,505 residents. The area’s drainage utilizes separate storm and sanitary systems, with stormwater flowing to Lake Ontario via Elmcrest and Etobicoke Creeks.
High I/I rates were detected, exceeding the city’s standard during 2015 water flow monitoring. Notably, the May 2000 and July 2013 storms caused significant local basement flooding, highlighting the area’s vulnerability to extreme weather events.
Wet Weather Flow Reduction in the Scott Street Sewage Pumping Station Service Area
The historic Scott Street Sewage Pumping Station (SPS) in downtown Toronto, serving key urban areas, was scheduled to undergo an assessment starting in Fall 2017. Despite a capacity increase to 660 liters per second after a 2013 upgrade, the station still faced challenges, with extraneous flow issues identified since 2009.
Strict rezoning conditions were suspected to impact extensive planned development over the next two decades. Consequently, an I/I reduction project was underway to address extraneous water flow challenges in this rapidly developing region.
On-Going Inflow and Infiltration and Wet Weather Flow Reduction Initiatives
State of Good Repair Program
The State of Good Repair (SOGR) program applies thorough procedures to evaluate the health of wastewater systems, rating sewer infrastructure using the City’s inspection standards. Inspections utilize technologies like CCTV to determine the condition of sewers and manholes. Data gathered helps prioritize fixes for I/I issues within public systems but excludes private property.
Mandatory Downspout Disconnection Program
In 2007, the City mandated property owners to disconnect downspouts from sewer systems, granting exemptions only where hazards or infeasibility arise. Aimed at improving the Wet Weather Flow Master Plan, the goal is an 80% citywide disconnection rate.
At the time, Area 9 exceeded expectations with 87%, while Wirral Court lagged at 75%. Investigations indicated that 10% to 20% of downspouts in those areas still fed into the sanitary system. Estimations showed over 9,000 downspouts citywide remained improperly connected, necessitating further disconnections to alleviate pressure on waste and stormwater systems.
The City was advised to reassess exempted downspouts for potentially viable alternatives to support system efficiency improvements.
Basement Flooding Protection Program
Launched in 2006 to tackle frequent flooding, the Basement Flooding Protection Program (BFPP) encompasses 41 areas across the City. Its comprehensive strategy involves an integrated approach promoting surface flood prevention and minimizing stormwater in sewers. Key measures of the program include sewer inspections, obligatory downspout detachment, and engineering analyses of both overland and underground drainage systems.
Additionally, a subsidy aids residents in adopting flood prevention measures, yet it’s noted that these incentives may not fully motivate homeowner participation. While the City of Toronto covers 80% of costs up to a maximum amount, the actual expenses can be significantly higher.
Description of Business Need – Existing Conditions in Pilot Areas
Wirral Court Sewage Pumping Station Service Area
Civica’s 2016 investigation pinpointed key sources contributing to water inflow and potential spots for higher infiltration. The breakdown of these sources was:
- 29 residential downspouts
- 4 commercial roof leaders
- 1 reverse slope driveway drain
- 245 private lateral segments
- 140 mainline defects
- 160 maintenance holes at risk of flooding
- 214 public lateral segments
- 1 sanitary cleanout
Inflow and infiltration inspection analysis showed that private sources added roughly 90% of the rain-related inflow, significantly more than that from public sources. This data corresponded to a July 2016 storm event, mirroring a 10-year storm scenario.
Basement Flooding Study Area 9
In 2015 and 2016, studies pinpointed 451 properties with foundation drains improperly linked to sanitary systems as key sources of excess flow during heavy rainfall, particularly during the benchmark event in May 2000. A cost-effective solution was adopted to curtail this issue, aiming to disconnect 80% of these drains, alongside other measures such as downspout disconnections, manhole sealings, and specific drain repairs. This approach not only met the City’s criteria to prevent basement flooding by preserving a significant safety margin but also served as a more affordable alternative to extensive system upgrades for similar urban areas.
Scott Street Sewage Pumping Station Service Area
The exact scope of the I/I issue in the study area was not clear, but to meet the 30% reduction target in peak WWF, a mix of public and private repair efforts was anticipated. Potential remediation activities included:
- Constructing local sewer separation systems
- Laying new sewers
- Modifying catch basin and stormwater drain infrastructure
- Updating manhole covers
- Fixing or replacing faulty pipes and connections
- Rerouting house drains and sump pumps
- Sealing sewers
- Sealing or capping openings
- Repairing sewer lateral damage
- Detaching roof downspouts from sewers
- Tweaking combined sewer overflow controls
- Pumping station upgrades
Some of these measures were expected to occur on private properties, requiring coordination with homeowners and the possible creation of new right-of-way agreements.
Problem/Opportunity Statement – Additional Effort Required
Prioritized Requirements
The initial two I/I reduction initiatives in Wirral Court and Area 9 had revealed a predominant contribution of I/I from private property sources (80% to 90%). This summary underscores the necessary work identified in these pilot areas.
Summary of Work Required in the Wirral Court Sewage Pumping Station Service Area
To significantly reduce peak flow rates to the pumping station during extreme wet-weather events by an estimated 56%, the following interventions were recommended:
- Disconnecting one driveway drain with a reverse slope
- Disconnecting four commercial building downspouts
- Detaching 29 residential downspouts
- Repairing one sanitary sewer cleanout and securing it with a cap
- Replacing 160 manhole covers with integrated frames and covers for improved sealing
Summary of Work Required in the Basement Flooding Protection Program Study Area 9
Civica’s cost-effective mitigation strategy was expected to reduce flood risk in 111 homes to zero. By disconnecting 80% of foundation drains connected to the sanitary system and 12 downspouts, while also sealing 60 manholes, one basement walkout drain, and one sanitary cleanout, Civica would meet City protection standards at an estimated cost of $6.65 million. The approach would cut peak intrusion rates, ensuring a safer community.
Summary of Desired Outcomes
Proposed Inflow and Infiltration Reduction Program
Given the success of past I/I reduction strategy efforts in Etobicoke and Scarborough, the City was advised to establish a dedicated I/I Reduction Program to complement existing initiatives like by-law enforcement, repair, and basement flooding protection.
Contact Civica for Expert Inflow and Infiltration Reduction Services
Initial pilot projects in Wirral Court and Area 9 found that up to 90% of I/I originated from private sources, prompting a proposal by Civica to disconnect many of these property-linked I/I contributors. While the City’s existing programs addressed stormwater in the wastewater system, none focused on disconnecting I/I sources on private properties. Therefore, Civica recommended a new, targeted I/I reduction program for better stormwater management as part of Toronto’s wastewater network.
Watch this space for part two of the case study, which delves deeper into analysis, management and capacity, and recommendations.
Since 2012, Civica has sought to provide solutions to clients’ most complex water management issues, from rainfall management to sewage water management. For more information on their I/I reduction services, including wastewater and sewer flow monitoring, please contact Civica today.
Learn more at:
Case Study: Inflow and Infiltration Reduction of Pilot Areas (Part 2)
Inflow and Infiltration and Wet Weather Flow Reduction of Pilot Areas (Part 3)
Basement Flooding Area 9 Inflow and Infiltration Reduction Project
New Subdivision Inflow and Infiltration (I/I) Prevention in York Region
Inflow and Infiltration Inspection Case Studies
Shining Hills (Bazil) Inflow & Infiltration Reduction Project
Find Inflow and Infiltration (I&I) with Wet Weather Inspections – Part 1
Wet Weather Inspections to Find Inflow and Infiltration (I&I) – Part 2
