Ottawa’s Municipal Sewers And Sewage Treatment Infrastructure

As part of our home inspection services, we perform sewer data research. It is not something that is normally included in a home inspection, but it is something we personally feel may be beneficial for our clients to know about, and therefore we put in a little extra work to identify what your house is connected to. After all, if your home is connected to an old combined sewer that is prone to backups, it may be beneficial to know about it since you could qualify for a free backwater valve installation from your municipality! In this article we discuss the main types of sewer systems utilized in the City of Ottawa, the advantages and disadvantages of each type of sewer system, the key dates and developments in the city of Ottawa’s development of its sewer infrastructure, the city of Ottawa’s sewage treatment facilities (ROPEC, the Robert O. Pickard Environmental Centre), Ottawa’s efforts to reduce stormwater pollution and combined sewer overflows into the Ottawa River, and some information on the regulation of industrial sewage and wastewater.

A separated sewer system is a modern type of wastewater collection system which has two distinct systems, and thus two distinct sets of pipes:

1. Sanitary Sewers – These pipes carry sanitary sewage from homes, businesses, and industries to a sewage treatment plant. This wastewater includes sewage from toilets, sinks, showers, basement floor drains, as well as industrial processes (to a certain extent).
2. Stormwater Sewers – These pipes collect stormwater and runoff from melting snow and ice from streets, roofs, and other surfaces and discharge it directly into nearby water bodies, particularly the Ottawa and Rideau rivers. If you own a relatively modern home which is directly connected to both sewers (double lateral configuration), the stormwater sewer also collects the stormwater from your home’s foundation footing drain, also known as a weeping tile.

The benefits of a separated sewer system include:

• Reduced Overflow – Unlike a combined sewer system, separated systems prevent raw sewage from overflowing into the Ottawa and Rideau rivers during periods of heavy rain.
• Improved Water Quality – Since stormwater and sewage are handled separately, untreated sewage is less likely to contaminate natural water bodies.
• Lower Treatment Costs – Wastewater treatment plants only process sanitary sewage, reducing the load and costs compared to combined sewer systems.

The challenges of a separated sewer system include:

• Stormwater Pollution – Runoff can carry pollutants (oil, chemicals, trash, etc.) directly into the Ottawa and Rideau rivers.
• High Infrastructure Costs – Constructing and maintaining two separate sewer systems can be expensive.
• Maintenance Issues – If stormwater gets into sanitary sewers (infiltration), it can overwhelm treatment plants, and if sewage leaks into storm drains, it can contaminate local water bodies.

A combined sewer system (CSS) is an older type of wastewater collection system which uses a single pipe to carry both stormwater and sanitary sewage. These systems were commonly used in cities built before modern stormwater management systems were developed. The city of Ottawa continues to operate combined sewer systems, some dating back to the end of the nineteenth century! Areas where combined sewers remain in use are the Golden Triangle, Chinatown, Little Italy, Hintonburg, Mechanicsville, The Glebe, Old Ottawa East and old Ottawa South, Manor Park and some parts of Rockcliffe Park.

The benefits of a combined sewer system include:

• Cost-effective in early development – Combined sewer systems are often cheaper to install during initial urban development because they require only one set of pipes to handle both sanitary sewage and stormwater.
• Simpler urban development – Residential, commercial, and industrial buildings only require a single sewer connection, known as a “sewer lateral”, since both the sanitary sewage from the indoor plumbing, as well as the stormwater from the foundation footing drain (weeping tile) connects to a single sewer (single lateral configuration). CSSs are also simpler since the sewer pipes all lead to a wastewater treatment centre, direct discharge points to nearby water bodies are not required.
• Integrated management – Having a single system for both stormwater and sewage can simplify the management and maintenance of the system, as it reduces the number of different types of infrastructure that need to be maintained.
• Historical relevance – Many older cities have CSSs in place, so modernizing and maintaining these systems can be more economical than replacing them entirely.

The challenges of a combined sewer system include:

• Overflow risks – One of the biggest drawbacks is that when it rains heavily, the combined sewer system may become overwhelmed. This can lead to combined sewer overflows (CSOs), where untreated sanitary sewage and stormwater are discharged directly into local water bodies, such as the Ottawa and Rideau rivers, which can severely impact water quality and public health.
• Capacity limitations – As urban areas grow, combined systems can become overburdened and fail to handle the increased volume of wastewater and stormwater, which might require costly upgrades or additional infrastructure.
• Environmental impact – The discharge of untreated wastewater and stormwater into rivers, lakes, or oceans during a CSO event can harm aquatic ecosystems, increase the risk of flooding, and degrade water quality.
• Maintenance complexity – Over time, combined sewer systems require more maintenance, as the risk of blockages, corrosion, and sediment buildup increases due to the mixing of stormwater and sewage.
• Cost of upgrades – Retrofitting existing CSSs to prevent overflows (for example, by building storage tanks or upgrading treatment facilities) can be very expensive.

Cities facing issues with CSSs often consider separating the sewage and stormwater into distinct systems (a process known as sewer separation) or implement green infrastructure solutions like permeable surfaces and green roofs to manage stormwater. Overall, while combined sewer systems were a practical solution in the past, the challenges posed by population growth, urbanization, and climate change have made them less viable in the long term without significant investment in upgrades and mitigation strategies.

In the city of Ottawa, there are mainly only these two main types of sewer systems, combined sewers and separated sewers. However, there are other types of systems in use in other cities. These include:

• Effluent Sewer (Septic Tank Effluent Gravity, or STEP System)
  • A hybrid system where households have septic tanks that partially treat sewage.
  • The liquid effluent is then piped to a centralized treatment plant.
  • Common in rural or semi-urban areas where full sewer systems are costly.
  • The Township of Alfred and Plantagenet operate a STEP sewer system within the municipality of Wendover. If you live along Principale Street or some private roads in the village of Wendover, your home may be serviced by a STEP system. As a home inspector who often inspects homes in this area, I’ve personally come across STEP systems on several occasions.
  • Maxime Myre from TheReview.ca published an article about Wendover’s STEP system: Alfred-Plantagenet township asks some Wendover residents to verify their septic systems
  • The Clark Regional Wastewater District has also published a helpful guide which describes the STEP system in more detail.
• Vacuum Sewer System
  • Uses vacuum pressure to move wastewater through pipes instead of gravity.
  • Used in areas with flat land or high water tables where traditional gravity sewers are inefficient.
  • This type of system is not utilized in the Ottawa or Gatineau regions.
• Pressurized Sewer System (Low-Pressure Sewer System)
  • Uses pumps (often in each home or neighborhood) to push wastewater through smaller-diameter pipes.
  • Useful in hilly or rocky areas where gravity sewers would be difficult to install.
  • This type of system is also not utilized in the Ottawa or Gatineau regions.

Separated sewers were introduced in Ottawa in the early 20th century as part of the city’s efforts to modernize its wastewater management systems. Prior to that, the city primarily relied on combined sewers, where both stormwater and wastewater were carried in the same pipes.

1. Early 1900s: Ottawa’s sewer system began to shift from a combined sewer system to a separated sewer system around this time. The separated system was introduced to address growing concerns about public health and environmental pollution. This shift was part of a larger trend in cities across North America and Europe, which realized that separating stormwater from wastewater would improve both the efficiency of treatment and reduce the likelihood of water pollution during heavy rains.
2. 1920s–1940s: During this period, the separation of sewers continued to be implemented in new areas as Ottawa expanded. As the city grew, it became more common for residential and industrial developments to be served by separate stormwater and sanitary sewer systems.
3. Post-WWII Expansion: After World War II, Ottawa continued to invest in separate sewer infrastructure, particularly in newly developed suburban areas and expanding neighborhoods. This was in response to population growth and the increasing need to address sanitary sewer and stormwater management more effectively.
4. Ongoing Upgrades and Projects: While the city’s sewer system has been mostly separated by the mid-20th century, there are still areas with combined sewers, particularly in older parts of Ottawa. The city has been actively working to upgrade these older systems to reduce the occurrence of combined sewer overflows (CSOs), where untreated sewage and stormwater are discharged into rivers during heavy rain.

The city of Ottawa operates two sewage treatment plants to manage the city’s wastewater and ensure it is properly treated before being released into the environment. ROPEC, the main plant handles the sewage for over 90% of Ottawa’s population. The Pinecrest Creek Treatent Plant, a smaller facitlity, processes wastewater from the western parts of Ottawa, and helps to divert load from ROPEC during peak times.

• Location: Situated on the Ottawa River in the east end of the city, off of Shefford Road. This used to be called the Green’s Creek Sewage Treatment Plant, due to its proximity to Green’s Creek, which happens to run near my backyard!
• Function: ROPEC is the primary sewage treatment plant in Ottawa. It handles both the regular sewage and the combined sewer overflow (CSO) during heavy rains.
• Capacity: The plant is designed to treat up to 1.02 million cubic meters of wastewater per day, with provisions for expansion to accommodate growing city populations.
• Treatment Process: ROPEC uses a multi-stage treatment process:
  • Preliminary treatment: Removal of large debris and grit.
  • Primary treatment: Sedimentation to remove suspended solids.
  • Secondary treatment: Biological treatment to remove organic material using bacteria.
  • Tertiary treatment: Advanced filtration and disinfection to further improve water quality before discharge.
• Combined Sewer Overflow Management: ROPEC also helps manage the overflow from combined sewers by capturing excess water in storage tanks and releasing it only when it’s safe, to reduce pollution.
• More information: Please refer to the following brochure from the city of Ottawa, which explains in more detail the functions of ROPEC: https://documents.ottawa.ca/sites/default/files/wastewater_treatment_en.pdf

• Location: In the west end of Ottawa, near the Pinecrest Creek.
• Function: This smaller treatment facility processes wastewater from the western parts of the city, helping to divert load from ROPEC during peak times.

• Challenges: Ottawa also faces challenges with stormwater runoff, especially in areas with combined sewer systems. Efforts have been made to reduce the frequency of CSOs by upgrading infrastructure, including building storage tunnels and other systems to handle excess rainwater without overloading the sewage treatment plants.
• Efforts for Improvement: Ottawa has been involved in long-term planning to improve its sewage and stormwater management systems. A key part of this includes reducing CSOs and improving water quality in the Ottawa River, a vital water resource for the city.

Ottawa’s sewage treatment plants play a crucial role in maintaining public health and protecting the environment, especially given the city’s proximity to water bodies like the Ottawa River, a protected waterway.

ROPEC has been steadily upgrading its facilities as needs arise. Improvements towards pollution reduction and energy efficiency have been at the forefront of its development. For example, the excess sludge and scum collected during the treatment process are treated in six sealed tanks called anaerobic digesters. Naturally-occurring bacteria digests these solids, converting about half of the sludge into methane gas and carbon dioxide. The methane gas produced is then burned in engines and boilers, producing heat and electricity to help operate the facility. This reduces the electrical consumption of the treatment facility, as well as reduces the consumption of natural gas during the winter season. The remaining half of the biosolids is spun in large centrifuges, removing any remaining water. The resulting material consists of a nutrient-rich soil-like material called biosolids, which is then sold to local farmers as a valuable fertilizer.

• Environmental Goals: The city is committed to ensuring the wastewater treatment process is as environmentally friendly as possible, utilizing energy-efficient technologies, reducing chemicals, and increasing the use of renewable resources in the treatment process.
• Long-Term Investments: Ottawa has also been working on projects to replace or repair aging infrastructure, upgrade treatment facilities, and invest in green infrastructure to further minimize environmental impacts from sewage.

As discussed throughout this article, the primary disadvantage of the older Combined Sewer system is the possibility of overloading local treatment centres during periods of heavy rainfall and/or heavy thaw. Under extreme situations, local treatment plants are forced to dump raw sewage into the Ottawa river when the incoming wastewater overwhelms their collection capacity. The city of Ottawa has been steadily investing in ways of reducing this risk. One of the biggest developments is Ottawa’s Combined Sewage Storage Tunnel (CSST).

The Combined Sewage Storage Tunnel (CSST) connects to high-volume combined sewage overflow (CSO) sites, storing runoff and wastewater until treatment at the Robert O. Pickard Environmental Centre before returning it to the Ottawa River. The tunnel functions as an underground, linear storage facility, intercepting surface runoff and wastewater from combined sewers until ROPEC has available capacity to collect and process the waste. The planning and construction of the CSST has spanned for over a decade, and the tunnel is now in operation. Among the many benefits, the CSST will:

• Significantly reduce the frequency of CSOs (untreated sewage release) into the Ottawa river, up to 43,000 cubic metres per event, or approximately eighteen Olympic-sized swimming pools!
• Reduce basement flooding risks for residential properties in areas such as The Glebe and Centretown.
• Provide a redundant twin to a critical downtown sanitary sewer, known as the Interceptor Outfall Sewer, or IOS, allowing flow to be diverted for inspections and maintenance to the city’s aging infrastructure.

The CSST runs East to West from Stanley Park to LeBreton Flats, and North to South from the Ottawa River to Chamberlain Street. For a map of the CSST, please visit the following site: The Combined Sewage Storage Tunnel (CSST)

In Ottawa, stormwater sewers do not typically go through settling ponds before being discharged into rivers. The stormwater collected from the city’s streets, parking lots, foundation footing drains, and other impermeable surfaces is generally directed directly into rivers and streams with minimal treatment. This is because stormwater is usually not as contaminated as wastewater, but it can still carry pollutants like oil, litter, debris, and sediments.

The city of Ottawa has been steadily investing in ways of reducing the environmental impact of stormwater pollution. Through the use of traditional methods such as settling and retention ponds, as well as more modern methods such as the implementation of green infrastructure, Ottawa has been reducing the infiltration of pollutants into the Ottawa and Rideau rivers.

• Settling Ponds and Retention Ponds: While most stormwater is directed straight into rivers, there are some areas in Ottawa where stormwater management facilities are in place, such as settling ponds, detention ponds, or swales. These are designed to slow down the flow of stormwater, allowing sediment and debris to settle before the water is released into the environment.
• Rain Gardens & Green Infrastructure: Ottawa has also been increasingly incorporating green infrastructure, such as rain gardens, vegetated swales, and bioswales, to naturally filter stormwater before it enters the river. These systems help capture pollutants like heavy metals, oils, and nutrients, reducing their impact on the water quality.

• Pollutants: While stormwater runoff is not as contaminated as wastewater, it can still carry pollutants, especially after rainfall or snowmelt events when debris, chemicals, and oils from streets are washed into the system. These pollutants can degrade water quality in rivers, lakes, and other water bodies.
• Pollution Reduction: Ottawa has been working on implementing measures to reduce the amount of pollution in stormwater through the use of best management practices (BMPs), which include the stormwater facilities mentioned above.

• As discussed in this article, Ottawa still has some combined sewer systems (where stormwater and wastewater share the same pipe network), particularly in older parts of the city. During heavy rainstorms or snowmelt events, these systems can become overwhelmed, resulting in combined sewer overflows (CSOs), where untreated water (including both sewage and stormwater) may be discharged directly into the river.
• To mitigate CSOs, Ottawa is investing in infrastructure upgrades and storage solutions to capture excess water during heavy rain and reduce the frequency of these overflows, such as the construction of the CSST.
• Despite ongoing investments and improvements, CSOs continue to occur. The practice of releasing untreated sewage in local rivers when combined sewers are overflowing remains acceptable by the Ministry of the Environment, Conservation and Parks (MECP). In Ottawa, these events are monitored and reported to the MECP and downstream municipalities and water purification plants. In Ottawa, there are 13 combined sewer overflow sites.

Source data obtained from City of Ottawa: Combined sewer overflows (CSOs)

Thanks to ongoing investments and upgrades by the City of Ottawa, the number of combined sewer overflow events has steadily decreased over the past 20 years. Two abnormalities in trends between CSO events and total volume discharged are present in 2017 and 2019, likely due to abnormaly large storm surges and/or equipment failures, but the steady decrease in CSO events demonstrates Ottawa’s ongoing improvements to reduce sewage discharge into the Ottawa river.

With the opening of the CSST in 2020, the chart shows CSO events dropping to single digit numbers. Raw data shows an average of only 6 events per year from 2021 to 2024. Compared to 384 events in 2009, this should make a tremendous impact towards the reduction of pollution in the Ottawa River.

• Ottawa has been focusing on improving stormwater management through long-term strategies aimed at reducing the environmental impacts of runoff. This includes efforts to replace older infrastructure, incorporate more green solutions, and ensure stormwater is managed sustainably to protect rivers and water quality.

While much of Ottawa’s stormwater is directly discharged into rivers, the city is investing in strategies to reduce its pollution, including settling ponds and green infrastructure. Additionally, combined sewer overflows remain a concern during heavy rains, but improvements such as the CSST are being made to reduce these events.

When I perform home inspections, I like to encourage my clients to follow me around and ask questions. As a teacher at heart, I love sharing knowledge, and as a proud Ottawa-born local, nothing pleases me more than educating fellow Ottawa residents on our city’s infrastructure. When explaining the home’s sewer connections to my clients, the conversation sometimes skews into our city’s sewer infrastructure and sewage treatment procedures. A question that is sometimes asked is, what is sent to our sewage treatment plants, are industrial wastes released into our sewer infrastructure and if so, does it negatively impact our local environment? In short, the answer is no, industries cannot dump their waste directly into sanitary sewers.

There are strict regulations and guidelines in place to ensure that only appropriate wastewater is discharged into the sanitary sewer system. The discharge of industrial waste into sewers is regulated to protect public health, the environment, and the proper functioning of sewage treatment plants.

Here’s why and how industries are controlled:

• Municipal Guidelines: Municipalities, including Ottawa, have specific rules for industrial wastewater discharges. These guidelines typically prohibit the direct discharge of harmful chemicals, solids, and toxic materials into sanitary sewers.
• Federal and Provincial Laws: In Canada, industries must comply with regulations set by bodies such as the Environmental Protection Act and Water Pollution Control Regulations, which regulate wastewater disposal and pollution. Provinces may have additional laws, such as Ontario’s Environmental Bill of Rights and Ontario Water Resources Act, which govern wastewater handling.
• Permits for Discharge: Many industries must apply for special permits for wastewater discharge. These permits set limits on the type and amount of waste that can be discharged into the sewer system. Industries may need to install pretreatment systems to ensure their wastewater is within acceptable limits before it enters the public sewer system.

• Chemical and Toxicity Concerns: Industrial waste can contain hazardous substances (e.g., heavy metals, solvents, acids, oils, and other toxic chemicals) that can damage the sewer infrastructure, pollute water bodies, and harm aquatic life.
• Sewage Treatment Disruption: Many industrial wastes are not treatable by conventional sewage treatment processes. Discharging untreated industrial waste could overwhelm or interfere with the functioning of sewage treatment plants, potentially leading to inadequate treatment of residential and commercial sewage, or even sewage overflows.
• Public Health Risks: The presence of harmful chemicals or pathogens in sewage can pose serious health risks to communities, including those involved in the treatment process.

• Industrial Pretreatment Systems: Before discharging waste into the sanitary sewer system, industries are typically required to treat their wastewater onsite to reduce harmful substances to acceptable levels. Pretreatment systems can include physical, chemical, or biological processes to remove pollutants.
• Monitoring and Reporting: Industries are often subject to regular monitoring and must report their wastewater quality to local authorities. Failure to comply with regulations can result in fines, penalties, or the revocation of discharge permits.

• In some cases, industries may be required to manage their waste through alternative disposal methods, such as:
  • Onsite waste treatment: Treating or processing waste on the industry’s premises.
  • Hazardous waste disposal: For certain dangerous waste, the industry must arrange for hazardous waste disposal in accordance with the law.

In Ottawa, industrial waste treatment and environmental regulations for local industries are primarily regulated and enforced by the following organizations:

• Provincial Level: The MECP plays a central role in regulating environmental standards, including industrial waste management, air quality, water quality, and pollution prevention in Ontario. It enforces various provincial laws that impact industries in Ottawa, such as the Environmental Protection Act (EPA) and the Ontario Water Resources Act.
• The MECP is responsible for issuing environmental permits for industrial operations, ensuring compliance with waste disposal and treatment standards, and monitoring the environmental impact of industrial activities.
• MECP Inspectors: Inspectors from the Ontario Ministry of the Environment conduct regular and surprise inspections of industrial facilities to ensure they are following environmental regulations. These inspections cover waste management, pollution control, emissions, wastewater discharge, and compliance with the Environmental Protection Act (EPA).

• Local Health Agency: Ottawa Public Health works in coordination with the MECP to ensure public health and safety concerning industrial waste, especially as it relates to air quality and wastewater management. OPH can provide inspections and enforce regulations relating to industrial waste that may affect local communities.
• OPH may also be involved when industrial waste poses a direct threat to public health, such as hazardous waste spills or improper disposal practices.

• Local Municipality: The City of Ottawa is involved in enforcing certain local environmental regulations related to industrial waste management. It provides waste management services, including waste treatment, sewage, and stormwater systems, that industries must adhere to.
• The City of Ottawa may require permits for industrial waste discharges, including ensuring industries meet local standards for wastewater treatment and disposal.
• The city also oversees and enforces specific bylaws and regulations related to environmental management, such as the Waste Diversion Program and Stormwater Management.
• The city collaborates with the MECP for enforcement and to ensure compliance with the province’s regulations on pollution control.
• Ottawa By-Law Services: In some cases, the city’s By-law and Regulatory Services department can be involved in enforcing local bylaws that pertain to environmental violations, including issues related to industrial waste.

• Environmental Protection Act (EPA): This provincial law regulates waste management, pollution control, and environmental assessments, and governs how industries must treat and dispose of waste.
• Ontario Water Resources Act (OWRA): Regulates wastewater treatment and discharges into water bodies.
• Municipal Bylaws: The City of Ottawa has bylaws addressing waste management, including industrial waste, and stormwater treatment that industrial operations must adhere to.

Industrial discharges into sanitary sewers are highly regulated, and industries must follow legal processes, including pretreatment, to ensure their wastewater is safe for discharge. Direct dumping of untreated industrial waste into sewers is illegal and can result in significant penalties. The city of Ottawa has strict regulations in place to ensure that environmental regulations are followed and adhered to by our local industries.

• Environmental Violations: If an industrial facility is found in violation of regulations, such as improper waste treatment or disposal, they may face fines, penalties, or orders to make necessary changes to their operations to comply with environmental standards.

External References

• R.V. Anderson Associates Limited: Robert O. Pickard Environmental Centre
• Township of Alfred and Plantagenet: Water and Sewer Services
• TheReview.ca: Alfred-Plantagenet township asks some Wendover residents to verify their septic systems
• Clark Regional Wastewater District: A Homeowner’s Guite to Septic Tank Effluent Pumping (STEP) Systems
• Wikipedia: Robert O. Pickard Environmental Centre
• City of Ottawa: The Wastewater Treatment Process
• City of Ottawa: The Combined Sewage Storage Tunnel
• City of Ottawa: Stormwater collection and facilities
• City of Ottawa: Combined sewer overflows (CSOs)
• City of Ottawa YouTube Channel: Stormwater Management Pond Clean-Out
• Ontario Ministry of the Environment, Conservation and Parks (MECP)
• Ottawa Public Health
• City of Ottawa: Public Works
• City of Ottawa: By-Laws
• Ontario.ca: Environmental Protection Act
• Ontario.ca: Ontario Water Resources Act