Part 1 of this case study provided an overview of inflow and infiltration (I/I) reduction projects completed by Civica for the City of Toronto in pilot areas Wirral Court and Area 9. Part 2 will delve deeper into strategic analyses, including technical, financial, and SWOT.
Technical Analysis Performed for I/I and WWF Reduction
Design Guidelines and Criteria
The City, along with the provincial government, aims to reduce stormwater entering sanitary and combined sewers. The goal is to align with the City’s sanitary sewer design guidelines by managing inflow and infiltration levels. Sanitary sewers are designed to handle regular waste flow and an allowance of 0.26 liters per second for every hectare (L/s/ha). Meanwhile, combined sewers can manage waste and additional water from a 2- or 5-year storm.
To combat excess stormwater, the City has introduced programs for residents to disconnect downspouts and foundation drains from sewers, with the latter supported by subsidies. Elevated protection criteria are in place for areas prone to basement flooding, ensuring sewers can cope with heavy rainfall without compromising home interiors.
The Ministry of Environment and Climate Change’s (MOECC) Procedure F-5-5 supports minimizing overflows during dry weather and reducing the environmental impacts of combined sewer overflows (CSOs). It requires implementing controls to treat wet weather flow (WWF), especially when public interaction with water bodies is at risk.
Current Level of Service – Wirral Court
The Wirral Court area’s separate sanitary and stormwater sewer systems were overwhelmed during a storm on July 27, 2016. Despite being designed to handle 52.1 L/s, the flow peaked at 102.5 L/s, nearly double the expected maximum, according to flow monitoring measurements.
Current Level of Service – Area 9
Area 9’s system manages sanitary and stormwater separately, aiming for standard peak flow plus an I/I rate of 0.26 L/s/ha. Despite an allowed peak flow of 23.5 L/s, recorded flows spiked to 199.3 L/s during a May 12, 2000, rain event, far surpassing expectations.
Best Practices & Available Implementation Strategies
Cities in North America are addressing stormwater overwhelming sewer systems by implementing a mix of techniques and incentives to reduce water influx from private properties.
Key remediation strategies include:
- Incentive Programs: Homeowners receive rebates or funds as motivation to address private-side I/I problems. Some cities also offer deferred payment plans featuring low- or no-interest loans to facilitate repairs.
- Regulatory Enforcement: Cities enforce compliance through fines or cutting off utility services to ensure that property owners fix I/I issues.
- Direct Action by Agencies: City agencies themselves may take on the responsibility of locating and fixing I/I problems or incentivizing property developers to address these issues, usually within a broader municipal development plan.
City Design-Bid-Build
Implementing an I/I management program can greatly improve urban water systems. The program involves three key phases:
- Identification and Evaluation: Trained professionals perform field inflow and infiltration inspections to identify potential I/I sources. Upon confirmation, an evaluation determines if remediation is required.
- Remediation: If cost-benefit analyses and risk assessments satisfy set criteria, City-approved contractors carry out the necessary repairs swiftly to mitigate I/I issues.
- Verification: After remediation, the effectiveness is verified by measuring the reduction in I/I, ensuring the integrity of the water system.
Benefits include:
- Enhanced efficiency and control, leading to cost and time savings
- Simplified tracking of I/I metrics post-remediation
- Greater participation from homeowners since the City covers costs and shares contractor liability
- Substantial cost reductions due to the expected high participation in the program
This approach, echoing the City’s Scott Street SPS drainage area project, focuses on streamlining management and maximizing water infrastructure performance.
By-Law Enforcement
The City uses officers to enforce by-laws on illegal drainage connections, requiring disconnection. Non-compliant owners face fines under Chapter 681, City of Toronto Municipal Code. The lack of an inventory system in past initiatives hindered tracking disconnection status accurately.
Subsidy Programs
The City incentivizes property owners to enhance their infrastructure through its Basement Flooding Protection Program, with subsidies for:
- Backwater valve installation: Get 80% covered up to $1,250.
- Sump pump installation: Up to $1,750 in rebates (80% covered).
- Foundation drain disconnection: Covering 80%, maximum rebate $400.
Note that some private-side repairs like downspout and driveway drain disconnections are not included in this program.
Public-Private Partnerships
Innovative city-developer collaborations can enhance sewer systems by incentivizing projects that reduce overflow and peak flows. Developers must demonstrate pre-construction that flow reduction efforts are effective. This approach benefits cities cost-neutrally, with developers covering all expenses.
Implementing proactive I/I certification programs ensures low inflow rates from new developments. Such strategic measures relieve pressure on municipal sewer systems, creating a win-win for the private and public sectors.
Summary of Implementation Strategies and Municipality Feedback
Southern Ontario municipalities have adopted effective strategies to reduce inflow and infiltration (I/I) in public and private properties. Below is a condensed overview of the outcomes achieved in three different regions:
In York Region:
- Achievements from developer-funded pilot projects
- Successful public-private partnerships
- Remarkable outcomes:
- Reduction of about 0.31 million liters per day
- No costs incurred by the Region, covered entirely by developers
- Over 99% success in homeowner remediations
In the Region of Halton:
- Programs focusing on basement flooding prevention and downspout disconnections
- Subsidy initiatives paired with strategic program implementation
- Major gains:
- Approximately 2,000 successful downspout disconnections
- A budget allocation of around $2 million
- Recorded reduction contributing to a more resilient sanitary system
In the City of London:
- Implemented grant programs and weeping tile disconnections to mitigate basement flooding risks
- Subsidy and strategic program deployment
- Key results:
- Participation from half of the targeted homes for weeping tile disconnection
- Expenditure stood at $500,000
- Positive initial flow monitoring results, with no flooding post-completion
Financial Analysis Performed for I/I and WWF Reduction
Cost Estimate Analysis Criteria
Civica employed a multicriteria method that weighs economic, environmental, and social considerations to analyze the proposed works in Wirral Court and Area 9. The anticipated costs included:
- Designing the project
- Construction expenses
- Risk management, including stakeholder coordination
- Securing the necessary permits
- Ongoing operations and maintenance after the cleanup
Included were the initial investigation and assessment costs for each study area.
Substantial associated benefits included:
- Savings on water conveyance and treatment
- Prevention against future water damage in basements
- Restored capacity for new construction developments
Risk Mitigation Costs
Performing a risk assessment is vital for planning how to reduce potential issues, particularly when it comes to managing water intrusion sources like residential downspouts. Assessing risk involves gauging the likelihood of a problem and the potential impact it could have. This helps prioritize mitigation measures, ensuring the remediation process runs smoothly.
Below is a guide to managing these risks:
- Avoidance: Choose different options that bypass the risk entirely.
- Acceptance: Recognize the risk but proceed without changes.
- Transfer: Share or move the responsibility to another party, such as insurance companies or involved stakeholders.
- Mitigation: Find alternatives or act to limit the risk, while still achieving remediation goals.
When it comes to cost, sometimes the expense to prevent risk is higher than the cost to fix the issue if it occurs. It is essential, therefore, to set acceptable risk levels backed by clear criteria as part of an overall risk management plan.
Remediation tasks with minimal risk are typically those that are routine with established methods and do not require invasive actions—for example, disconnecting downspouts or sealing manholes.
The two main factors that hike up risk mitigation costs are:
- Economies of Scale: Mitigating risk becomes more cost-efficient as the size of the area needing remediation grows.
- Coordination Challenges: For any work that involves private property, cities will need the buy-in from homeowners, which requires significant engagement and coordination effort.
Cost-Benefit Analysis
Civica conducted the cost-benefit analysis based on present costs in 2017, stacking them against a standard 50-year life cycle’s benefits. Some remediation types, like those involving downspouts and driveway drains, were expected to permanently disconnect from the sanitary system, with ongoing maintenance costs included to prevent issues like local flooding.
By comparing immediate costs with 50-year lifecycle benefits and applying a 2% annual inflation rate, Civica computed the net present value (NPV) to determine the overall financial gain of remediation. The valuation used several metrics, such as:
- Conveyance and Treatment Costs: Calculated by assigning an annual wastewater volume to each I/I source (6% and 3% of total rainfall for Area 9 and Wirral Court, respectively) and multiplying it by the cost of wastewater treatment over 50 years.
- Future Basement Flooding: Assessed by relating each I/I source’s impact on peak flow rates to the financial toll of basement flooding in the city for similar past events.
- Capacity for Future Developments: Estimated the economic opportunity of additional development space gained by reducing I/I, based on how much peak flow each source contributes.
This concise assessment underscores Civica’s effort to invest wisely in remediation that not only saves money but also improves the City’s infrastructure resilience and facilitates future urban growth.
Value for Money
Considering the disconnection labour required on private property in Area 9 and Wirral Court, the best values for money (highest NPVs) were:
- Foundation Drains – $38,495,000
- Residential Downspouts – $13,776,000
- Commercial Roof Leaders – $3,061,000
- Reverse Slope Driveway Drains – $1,273,000
The “Do Nothing” Option
Choosing inaction leads to unmet service levels in the sewer system due to insufficient drainage, resulting in hidden costs and missed benefits. The cumulative cost for areas like Area 9 and Wirral Court could reach $56 million. Inaction is impractical and costly.
Storage Options
- Wirral Court: During the Scarborough Flood Protection Study, a combined approach of source control and on-site storage was proposed to prevent basement flooding. The cost-effective solution involves targeting private property Inflow/Infiltration (I/I) directly, significantly reducing rates by $606,000.
- Area 9: XCG Consultants Ltd.’s initial $28.8 million cost estimate for an Environmental Assessment project was significantly reduced to $12.87 million by Civica’s revised hydraulic model. The more affordable solution of $6.5 million involves disconnecting residential downspouts and foundation drains to achieve the desired Hydraulic Grade Line.
End-of-Pipe Options
- Wirral Court: The upgrade of Wirral Court’s pumping station and the enhancement of Ashbridges Bay’s wastewater treatment were dismissed because they failed to meet City standards or reduce basement flooding risks. Despite impending necessity within five years, physical limitations at the site could render these upgrades impractical.
- Area 9: Area 9’s wastewater is channeled through the Elmcrest Creek system towards the nearby Peel Region’s G.E. (Lakeview) Treatment Facility. Peel’s strategic planning spotlights the urgent need to reduce wet weather surges during peak times—a whopping 20% of which originates from Toronto. Minimizing these inflows could postpone or scale down Peel’s expensive expansion plans for its facilities.
SWOT Analysis
A SWOT analysis is a strategic planning tool used to assess the strengths, weaknesses, opportunities, and threats involved in a project or a business venture.
Strengths
Assets and resources within the municipality that provide an advantage for the I/I reduction program, including the following:
- Restoration of initial design capacity of combined/sanitary system
- Reduced capital expenditures by offsetting conveyance and treatment costs
- Alleviates system from surcharging and basement flooding
- Allows for new capacity allocation
- Increased system resilience
- Increased customer satisfaction with the level of service provided
- Positive environmental impact with less overflows to natural water bodies
Weaknesses
Limitations that could impede the program’s success, necessitating improvement or mitigation, such as:
- Requires work on private property subject to property owner approval
- Intensive monitoring and evaluation pre- and post-remediation
- Requires effective coordination with other City programs—permitting, development engineering, and review—new subdivision inspection before assumption, by-law enforcement
- Non-traditional approval is required for implementation
- Requires additional City program (no existing precedent in the City)
Opportunities
Favourable external factors that the City can utilize to address program challenges include:
- Synergy with other ongoing programs (Basement Flooding Protection Program, State of Good Repair Program, Mandatory Downspout Disconnection Program, etc.)
- Potential for revenue increase by adding new users/connections to the sewer system
- Increased customer satisfaction with the level of service provided
- Lower cost and higher budget for other system works that are needed
- Programs offered in other municipalities that can be leveraged for program design and administration
Threats
External challenges that could obstruct the program’s implementation or the City’s service sustainability, such as:
- Overwhelming the sewer systems (due to capacity overload)
- Low customer satisfaction due to poor level of service
- Limited capacity available for new allocation/users
- Increased capital for pipe, pumping station, and treatment plant upgrades
- Increased operation and maintenance costs
- Increased basement flooding work (i.e. distribution of capital to other programs)
This analysis is crucial for supporting decision-making processes, ensuring that internal and external factors are carefully considered for the successful execution of the City of Toronto’s initiatives.
Why Choose Civica?
This post detailed the range of analyses that supported the business rationale behind the I/I and WWF reduction projects. Stay tuned for part three of the case study, which will cover management capacity and recommendations.
Civica Infrastructure Inc. is a leader in municipal wastewater management solutions. We often partner with cities seeking to optimize their existing drainage system capacity through I/I reduction and prevention. Some of our services include sewer flow monitoring, water flow monitoring, and wastewater monitoring.
For more information on sewage water management solutions, please contact Civica today.
Learn more at:
Case Study: Inflow and Infiltration Reduction of Pilot Areas (Part 1)
Inflow and Infiltration and Wet Weather Flow Reduction of Pilot Areas (Part 3)
New Subdivision Inflow and Infiltration (I/I) Prevention in York Region
Inflow and Infiltration Inspection Case Studies
Find Inflow and Infiltration (I&I) with Wet Weather Inspections – Part 1
Wet Weather Inspections to Find Inflow and Infiltration (I&I) – Part 2
