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Wastewater collection and treatment

Wastewater is thoroughly treated at the Robert O. Pickard Environmental Centre to ensure it is safe for the public’s health and the environment.

Wastewater treatment

Wastewater is water that has been used and discharged by homes, businesses and industries. It is 99.9 percent water by weight, with a very small portion (0.1 percent) of dissolved and suspended solids.

Wastewater is thoroughly treated at the Robert O. Pickard Environmental Centre to ensure it is safe for the public’s health and the environment. For a detailed description of each treatment stage, download our wastewater treatment brochure: Let's Explore Wastewater Treatment.

Treatment process

1. Preliminary:

  • Coarse screening/pumping: Wastewater flows to the plant through enormous pipes buried deep in the ground. Once the wastewater arrives at the treatment plant, any object bigger than a shoe gets screened out.
  • Fine screening: Screens will catch smaller objects like sticks and rags.
  • Grit removal: Degrit tanks separate pebbles, grit and sand from the other solids that can be further treated.

2. Primary:

  • Removal of settled solids (sludge) and floatable material (scum).

3. Secondary:

  • Naturally occurring bacteria remove dissolved and suspended organic pollutants. Removal of phosphorus takes place by adding a solution of iron to the wastewater. Iron captures the phosphorus, creating a solid that can sink and be separated from the water. 

4. Disinfection:

  • Before it is finally returned to the Ottawa River, the treated water is first disinfected using sodium hypochlorite, year round.

Process control

Protecting the health of the Ottawa River is an important part of treating wastewater. Processing of wastewater or sewage is monitored 24/7. Sensors throughout the plant allow staff to monitor the treatment process and notify them of any problems. The monitoring and testing program ensures quality targets are met and potential process problems are identified early.

Generating electricity at the Robert O. Pickard Environmental Centre (ROPEC)

As wastewater is treated and processed, methane and carbon dioxide are produced. In 1998 a process was added to convert these gases into electricity and heat through a process called cogeneration. Cogeneration produces 5 megawatts of heat and electricity which provides 50% of ROPEC's energy needs on an annual basis. The cogeneration facility produces enough electricity for approximately 1,500 homes.


The Robert O. Pickard Environmental Center meets all provincial guidelines for wastewater effluent as defined by the Ontario Ministry of the Environment.

Actual volume of wastewater treated at the Robert O. Pickard Environmental Centre

  Capacity (millions of litres/day) Actual (2017)
Average 545 470
Peak 1,362.5 1,435

Ottawa’s wastewater treatment plant

About the Robert O. Pickard Environmental Centre (ROPEC)

  • Provides secondary level treatment (physical and biological) of domestic, commercial and industrial wastewater - returning treated water to the Ottawa River.
  • Situated on 67 hectares of land adjacent to the Canotek Business Park in Ottawa East. 28.4 hectares remains available for future growth.

An aerial view of the Robert O. Pickard Environmental Centre.


  • Originally built in 1962, providing primary level treatment, and called the Green’s Creek Pollution Control Centre.
  • Expansions in 1971 and 1975 to provide needed capacity for the growing City.
  • Major expansion and rehabilitation from 1988 to 1993 increasing treatment capacity, improving biosolids processing, and adding odour control. Level of treatment improved from primary treatment to include biological secondary treatment.
  • Renamed for Robert O. Pickard, retired Commissioner of Works in the former Regional Municipality of Ottawa-Carleton.
  • Mr. Pickard helped initiate an expansion and upgrade of the centre to provide Ottawa with improved wastewater treatment capacities.
  • Addition of dechlorination process in 2013 to remove chlorine prior to discharge of treated water to the Ottawa River.

Sewer collection system

Ottawa's sewer collection system gathers wastewater from homes, businesses and industrial sites, transporting the waste through a network of sewers, pumping stations and forcemains to trunk sewers. The wastewater then flows to the Robert O. Pickard Environmental Centre for treatment.

Ottawa’s sewer system covers 2,796 square kilometres and extends from West-Carleton to Cumberland. It includes:

  • 2,853 km of sanitary sewers
  • 102 km of combined sewers
  • 61 wastewater pumping stations
  • More than 90,000 public maintenance holes
    • 1,656 combined
    • 42,617 sanitary
    • 46,451 storm
  • Approximately 234,000 service connections
  • Sewer pipes ranging in size from 20 cm to three metres in diameter

In the rural areas, a variety of collection methods are used:

  • Richmond, Munster Hamlet and Carp are connected to the municipal trunk system.
  • Elsewhere individual septic systems are used and the sludge from septic tanks is transported to the Robert O. Pickard Centre for treatment.

Stormwater collection system

Storm sewers carry rainfall and other surface runoff directly to the nearest creek, stream or river, frequently with limited or no treatment. Everyone plays a role in preventing pollutants from entering the storm sewer system and damaging the water ecosystem. Over time, stormwater collection has graduated from being concerned only with draining excess water away as quickly as possible, to flood and erosion prevention in waterways to restoring water quality before releasing to nearby waterways.

Various practices are used to manage stormwater runoff throughout its journey from rain to river. Stormwater management begins with lot-level controls where rain first drops. It then proceeds to conveyance controls which help transport stormwater. Finally, end-of-pipe measures treat stormwater before it is discharged into our local waterways.

The City of Ottawa maintains a network of culverts, storm sewers and municipal drains that transport stormwater to nearby creeks, lakes or rivers. In Ottawa, the stormwater system includes:

  • More than 2,700 km of storm sewers
  • More than 300 stormwater management facilities including 158 stormwater ponds, 12 stormwater pumping stations, underground storage, bioswales, and oil and grit separators
  • 1,200 km of municipal drains in rural areas

Lot-level controls

Lot-level controls are measures implemented at individual private and public lots that help reduce the volume of runoff coming from properties and the amount of pollutants carried by runoff. Effective and sustainable stormwater management starts at the source where rain falls. To help protect our water supply, visit how to reduce your stormwater impact.  

Typical lot level measures include:

  • Downspout redirection: Downspout redirection diverts flows from roof tops to areas such as grass, gravel, or infiltration trenches. This reduces the quantity of stormwater that must be treated by reducing the amount of stormwater flowing onto impervious surfaces such as driveways which drain directly to the storm sewer system.
  • Rain barrels and cisterns: Rain barrels and cisterns capture roof runoff and temporarily store it for reuse. This practice reduces runoff and pollutants, and can provide a benefit in terms of reduced water consumption.
  • Rain gardens and other absorbent landscaping: Rain gardens are designed to absorb and clean stormwater by capturing runoff in human-made depressions lined with water thirsty (hydrophilic) plants and soil that encourages infiltration. This lot-level measure decreases peak flows through additional on-site storage and reduces pollutants released into the stormwater system through plant/ground absorption.

Conveyance controls

Conveyance controls are used to treat, limit and/or control storm water before reaching the municipal storm sewer. Typical conveyance control measures include:

  • Catch Basins: Openings along curbs and parking lots where rainwater enters the storm sewer system designed to capture heavy debris and grit. Storm sewer catch basins are usually marked with a fish to remind people that stormwater eventually makes its way into nearby waterways.
  • Bioswales: Vegetated, shallow, open channels designed for conveyance and treatment of stormwater runoff, particularly from roadway drainage. Grass swales can sometimes reduce runoff volumes and pollutant loads by filtration through the vegetation. Plants are often selected due to their ability to filter sediments and nutrients.
  • Infiltration Trenches: Long, narrow, rock-filled trenches that receive stormwater runoff from roadways or landscaped areas. These trenches are effective in removing fine particles and associated pollutants.
  • Perforated Pipe Systems: Perforated pipes have tiny holes that allow water to filter into the surrounding soil. This measure reduces the quantity of stormwater runoff that is managed by the stormwater collection system.
  • Oil-Grit Separators (OGS): An oil-grit separator (OGS) uses separate chambers to remove coarse sediments (grit), oils and other buoyant pollutants (floatables).
  • Inlet Control Devices (ICDs):  Much like an hour glass, ICDs are engineered to only allow a certain amount of stormwater over time. ICDs are located throughout various storm water entry points and help manage stormwater quantity when storm sewer capacity is exceeded. ICDs prevent stormwater from discharging at critical points in the stormwater collection system and redirect it to parking lots, parks, or underground storage.
  • Street Cleaning: Streets are a significant contributor of pollutants to urban runoff. Street cleaning can reduce this impact. The City of Ottawa uses tandem street cleaning machines that use brooms and vacuums to prevent debris from entering our stormwater system.
  • Smart About Salt Program: During the winter, the City manages the use of rock salt on roads and parking lots. While this is a necessary tool to help combat Ottawa’s fluctuating winter climate, it is important to ensure we understand the impact of using too much salt. That is why the City has partnered with the Smart About Salt Council to become an active participant in the Smart About Salt Program.

End-of-pipe measures

End-of-pipe measures treat and/or control stormwater before it flows back into natural waterways. End of pipe measures used in Ottawa include:

  • Biofilter: A biofilter uses grass or other dense plants to filter out sediment and nutrient material before re-entering local waterways. As stormwater passes through the plants, pollutants are removed. Biofilters provide treatment for pollution but do not control the amount of stormwater passing through them. 
    photo of biofilter
  • Underground Storage Tanks: The use of underground storage tanks help control the flow of stormwater and aid in preventing flooding, erosion and combined sewer overflows. Stored water is released back into the storm sewer system at a reduced rate, decreasing the stresses placed on downstream stormwater infrastructure.  
  • Stormwater Ponds: Stormwater ponds receive stormwater runoff and hold the water back for a period to allow pollutants to settle before they are discharged into a watercourse. The controlled release rate also helps prevent flooding and erosion.

Get to know your local stormwater pond Ottawaphoto of a stormwater pond

There are three main types of stormwater ponds in Ottawa:

  1. Dry Ponds: Designed to be dry most of the time and temporarily detain water to prevent overloading the storm sewer system during large storms. The stored water is released back into the storm sewer system at a reduced rate, preventing downstream flooding. These facilities are often incorporated as depressions in parks or adjacent to roadways.
  2. Infiltration Ponds: Collected stormwater filters into the ground, improving water quality as it slowly passes through the soil. These ponds are also capable of recharging or replenishing the groundwater table. Suitable sandy soils are required for these special facilities and are not common in the Ottawa area.
  3. Wet Ponds: Water levels in wet ponds rise and fall with each storm, but they always hold a certain volume of the water and may include man-made wetland features. Wet ponds are intended to mimic natural lakes and often have healthy aquatic ecosystems including fish, bird and waterfowl populations. Never consume any fish caught from a stormwater pond.

Always remember:

  • Stay out of stormwater ponds. Recreational activities such as swimming, wading, and fishing are prohibited for your own health and safety. These ponds contain surface pollutants such as oil, metals, and feces
  • Stay off the ice in the winter as water levels and flows change rapidly making skating or other activities extremely dangerous
  • Protect your pet’s health and safety by keeping them out of stormwater ponds 

Reducing your impact on stormwater

We all play a part in reducing the impact of stormwater in our community. Help keep stormwater clean by following these tips:

  • Vacuum, sweep, and use rags or dry absorbents on your driveway - don’t hose it down
  • Select native and adapted plants that require less fertilizer to minimize runoff
  • Apply lawn and garden chemicals sparingly and according to directions. Ontario's province-wide pesticide regulation prohibits the sale and use of most pesticides for cosmetic purposes on lawns, gardens, park and schoolyards.
  • Deposit yard waste in your green bin to prevent catch basin blockages
  • Wash vehicles at a car wash so that cleaning products do not flow directly into the storm sewers or ditches
  • Check underneath your car to ensure engine fluids are not leaking
  • Dispose of chlorinated and salt water pool wastewater using the City’s pool maintenance tips.
  • Keep litter, pet waste and debris out of street gutters, storm catch basins and ditches so they are not washed directly into streams, rivers, lakes and wetlands
  • Always pick up after your pets. Stormwater will carry feces into local waterways increasing the total E. Coli and bacteria levels
  • Dispose of used oil, antifreeze, paints and other household chemicals at a household hazardous waste depot or Take it Back! retailer, not into catch basins or ditches
  • If you’re unsure of how to dispose of any chemicals or household hazardous materials, consult the City’s Waste Explorer
  • Take part in cleanup initiatives such as the great Canadian Shoreline Cleanup or Ottawa’s very own bi-annual GLAD Cleaning the Capital!
  • If you spot someone pouring harmful material into a catch basin, call 3-1-1
  • Ensure cigarette butts are disposed of safely in a designated spot. More than 85,000 cigarette butts were gathered as part of Ontario’s Great Canadian Shoreline Cleanup in 2014.
  • Don’t feed geese and other wildlife. One bird’s dropping can contaminate up to one acre of water

Soak it up and slow it down:

  • Maximize infiltration of rain into the soil to recharge groundwater and protect aquifers for the future.
  • Reduce peak stormwater flows through rainwater-harvesting and natural landscaping. Feed your garden not the storm drain!
  • Redirect your downspout to drain away from hard surfaces such as asphalt or patio stones onto grass, gardens, or an infiltration trench
  • Install a rain barrel to use rainwater at a later date
  • Plant trees, shrubs and ground cover to reduce soil erosion
  • Keep stormwater on your property through smart stormwater landscaping such as building a rain garden or infiltration pit
  • Reduce the amount of impermeable surfaces on your property such as patio stone or asphalt and replace with permeable options such as interlock, gravel, or grass

For other ways on how you can do your part, please see the resources below:

Stormwater: Frequently asked questions

What is stormwater runoff?

Stormwater runoff is rain or melting snow that collects on the surface or flows into sewer pipes instead of seeping into the ground.

Runoff will either:

  • Soak into the ground
  • Get absorbed by plants
  • Evaporate
  • Flow along the surface to the nearest sewer or waterway

In urban areas, we have a greater amount of runoff since we have decreased our natural ability to soak up water. When fields and forests are replaced with roads, parking lots and buildings, less rainfall can soak back into the ground and more water collects on hard surfaces. This increased runoff quickly drains via paved surfaces and storm sewers to local streams and rivers. For a brief video explanation, visit the Eastern Subwatersheds Stormwater Management Retrofit Study.

Why should I care about stormwater?

When we replace plants with pavement, we decrease the city’s natural ability to soak up stormwater.  This means that when it rains, less water soaks into the ground and more water collects on the surface.  A small storm can cause a surge in the levels and flows of rivers and streams which can lead to flooding and erosion.   

In addition to increased volume and speed, the runoff picks up pollutants like dirt, oil, and animal waste as it flows over the surface and decreases the quality of our local waterways.  Eventually, all stormwater reaches the Ottawa River which is the drinking water source for Ottawa and many downstream communities. With extreme weather events becoming more frequent, managing stormwater is even more important to reduce flooding and protect water quality.

How does stormwater become polluted?

Rain or melted snow falls on roofs, driveways, parking lots and roads and travels as runoff to reach a waterway. This runoff collects various pollutants (dirt, phosphorous, metals, nitrogen, animal waste) and debris (grass-clippings, garbage, cigarette butts) as it flows over these surfaces, resulting in polluted water.

What is the difference between a storm, sanitary, and combined sewer?

In Ottawa, we have three types of sewers:

  1. Storm sewers carry rainfall and runoff directly to either a stormwater pond or the nearest creek, stream or river, generally without treatment.
  2. Sanitary sewers gather wastewater from homes, businesses and industrial sites, and transport the waste through a network of sewers to the Robert O. Pickard Environmental Centre for treatment.
  3. Combined sewers carry both wastewater and runoff to the Robert O. Pickard Environmental Centre for treatment. These sewers are located in the downtown core and can overflow into local waterways if stormwater exceeds their capacity.

What does the fish symbol on a sewer grate mean?

Storm sewers are often marked with a fish symbol to remind that it drains to local rivers and streams. The fish symbol is there to remind the public that what goes down the drain can harm our rivers and streams. Remember: Only rain goes down the drain.

How does the City manage and treat stormwater?

Stormwater management has been applied to new urban developments in Ottawa since the 1980s. Over the last few decades it has evolved to include improving water quality and reducing the total amount of runoff by designing sites to allow more rainfall to soak back into the ground. Stormwater facilities such as man-made ponds, culverts and catch basins are built to temporarily hold water.

Ponds also provide water quality treatment via filtration to remove pollutants or and debris. The “cleaned” water is then slowly released back to the natural waterway, mimicking the natural runoff rate and quality. This helps prevent flooding and stream bank erosion.

In older areas of the city, stormwater runoff drains directly to creeks and rivers with no treatment or control of any kind. The continued discharge of uncontrolled stormwater runoff to the Ottawa River and its tributaries has been recognized as an important issue for the City to address. The City launched the Ottawa River Action Plan (ORAP) in 2010 to improve and protect the health of the Ottawa River and its tributaries.

What happens to stormwater in rural areas?

In rural areas, stormwater runoff infiltrates through a greater amount of impermeable surfaces. However, runoff can be subject to agricultural by-products such as excess fertilizer, pesticides and manure. The runoff from agricultural operations can have an impact on surface water sources such as groundwater, streams, lakes, and rivers. The Ottawa Rural Clean Water Program provides funding to improve surface water and groundwater quality. 

Sewer cleaning

The City of Ottawa conducts routine cleaning of sewers to ensure that wastewater from homes and businesses is efficiently transported to the Robert O. Pickard Environmental Centre (ROPEC), the City’s treatment facility.

Learn More

Sewer odours

Who do I call if there is a strong sewer smell coming from outside my home?

Call 3-1-1.

What to do if there is a strong sewer smell coming from the basement?

To prevent smells from the sewer entering your home, the plumbing in your basement has a ‘trap’ installed that creates a barrier when filled with water. The trap is under the floor in the basement and is the first place to look if you have odours in your home.

  • Sometimes in older homes the water in the trap leaks or evaporates and the barrier is broken. To reintroduce the barrier, pour a few cups of water in the basement floor drain.
  • In newer homes, the trap in your home is kept full through a discharge from the trap seal primer valve. If this odour occurs in newer homes, check to see if the primer valve is operating properly or call a plumber.

If the smell persists after a few hours or if the smell is from a sewer back-up, please contact 3-1-1.

What to do if there is an offensive odour coming from one of my sinks?

Often residents may experience an offensive odour while near a sink or after filling a glass.  If you think the odour is from the glass of water, take the glass to another room.  If you no longer detect the odour from the glass, it may be the sink that is the source of the odour.  Often a little commercial drain cleaner will remove any material collected in the trap of the sink that is creating the odour.

Combined sewer overflows (CSOs)

Overflow activity: Information and estimated volumes for the current year’s overflow activity.

What is a combined sewer overflow (CSO)?

The City of Ottawa has three types of sewers: wastewater, stormwater, and combined. 

  • Wastewater sewers: Collect wastewater from homes, businesses and industries, and transport the wastewater through a network of sewers, pumping stations and forcemains to main or trunk sewers, and direct it to the Robert O. Pickard Environmental Centre for treatment. 
  • Stormwater sewers: Carry rainfall and other surface water run-off directly to the nearest creek, stream or river, generally without treatment.
  • Combined sewers: Collect and transport both sanitary wastewater and stormwater runoff in a single pipe. This type of collection system was typically installed from 1880 to 1960 and is still in operation in older areas of most Canadian cities.

During dry weather, wastewater is collected and carried from a combined sewer to the City's wastewater treatment plant. During heavy rainstorms or snowmelts, the combined sewer may not be able to handle the high volume of stormwater runoff entering the system. Most of the wastewater is transported to treatment plants via the wastewater pipe, but to prevent flooding and sewer backups, some of the rain and wastewater mixture is diverted as overflow into the river.

The practice of discharging overflows during the normal operation of combined sewer systems is accepted by the Ministry of the Environment, Conservation and Parks (MECP). In Ottawa, these events are monitored and reported to the MECP and downstream users such as water purification plants and special interest groups.

What is the City doing to prevent overflows?

The City of Ottawa has implemented the following plan to mitigate the impact of combined sewer overflows into the Ottawa River:

  • Real time controls to ensure maximum capture of overflows before they occur
    • Real time controls permit the remote activation and control of overflow equipment combined with continuous monitoring of pipe flow data to maximize the capture and treatment of wastewater flow from combined sewer systems
  • Construction of storage facilities to hold the additional wastewater volume from combined sewer systems generated during wet weather events
  • Ongoing sewer separation projects
  • Review of the effectiveness of the current sewer separation program, in comparison to other projects
  • Development and implementation of a Wet Weather Infrastructure Management Plan
  • Installation of devices to remove floatable material from wastewater and prevent it from reaching the river in the event an overflow occurs

The City has been working for many years to separate remaining combined sewers. The value of the work completed to date is estimated at $750 million. With the current funding framework, it is expected the planned separation work will be completed in approximately 25 years.

The City has made the following improvement to existing systems:

  • Water level, flow monitoring and alarm devices installed in major combined sewer overflows and monitored daily to alert staff if an overflow occurs
  • Strengthened protocols to provide prompt notification to the MECP Spills Action Centre and Council in the event of an overflow
  • Construction upgrades are in process for the overflow sites that were the major contributors to the total volume of sewage released during combined sewer overflows
  • Improved regulator inspection and maintenance are improved and now scheduled monthly, weekly after each rain and within 24 hours of receiving an alarm

Sewer overflow sites

There are 13 locations in Ottawa where sewer overflows may enter the river:

Map of Ottawa combined sewer overflow outfall locations

  1. Ladouceur CSO Outfall
  2. Merton CSO Outfall
  3. Booth Regulator Overflow and Brickhill CSO Outfall
  4. Kent Regulator Overflow
  5. Rideau Regulator Overflow
  6. Keefer Regulator Overflow
  7. Dufferin CSO Outfall
  8. Hemlock CSO Outfall
  9. Sandridge Storage Tank Overflow
  10. Alvin Heights CSO Outfall and RCAF CSO Outfall
  11. RCAF West CSO Outfall
  12. Springhurst CSO Outfall
  13. Clegg Street CSO Outfall

Combined sewer overflows are generally diverted to flow into the Ottawa River.

The three combined sewer overflow sites that contribute the largest volumes of CSOs are:

  • Rideau Regulator Overflow
  • Booth Regulator Overflow
  • Keefer Regulator Overflow

Overflow activity (January 1, 2018 to date)

PLEASE NOTE: The volume indicated in the chart below (CSO) denotes the volume of combined overflow mixture which is comprised of storm water and wastewater. The majority of overflows occur during heavy rain and snowfall/melting periods. The chart below indicates the date, cause, and volume of each overflow event.

  • CSO: Combined Sewer Overflow
  • SSO: Sanitary Sewer Overflow
Date Event Cause Volume (m3)
01-11-2018 CSO Rain 36,450 m3
02-28-2018 SSO Maintenance Activities 0.08 m3
03-21-2018 SSO Forcemain Commissioning 10 m3
04-28-2018 CSO Rain 210 m3
05-20-2018 CSO Rain 7,530 m3
06-03/04-2018 CSO Rain 68,530 m3
06-14-2018 CSO Rain 3,860 m3
06-18-2018 CSO Rain 52 m3
07-17-2018 CSO Rain 2,180 m3
07-23-2018 CSO Rain 22,420 m3
07-25-2018 CSO Rain 326,730 m3
07-25-2018 SSO Rain 274 m3
07-27-2018 CSO Rain 2,370 m3
08-01-2018 CSO Rain 40 m3
08-06-2018 CSO Rain 21,530 m3
08-21-2018 CSO Rain 32,070 m3
09-05-2018 CSO Rain 410 m3
09-21-2018 CSO Rain 23,490 m3
09-26-2018 CSO Rain 1,930 m3
10-04-2018 CSO Rain 710 m3
11-26-2018 CSO Rain 980 m3

Historical overflow activity (CSOs only)

CSO activity during the Annual Reporting Period (April 15 to November 15) 

Year Number of Events Volume Precipitation (mm)
2017 79 1,611,000 m3 923 mm
2016 85 413,000 m3 495 mm
2015 80 180,000 m3 332 mm
2014 101 552,000 m3 640 mm
2013 179 213,000 m3 581 mm
2012 142 237,000 m3 523 mm
2011 161 230,000 m3 533 mm
2010 322 673,000 m3 646 mm
2009 384 851,000 m3 649 mm
2008 325 877,000 m3 600 mm
2007 253 730,000 m3 555 mm
2006 271 1,090,000 m3 796 mm


The City of Ottawa is dedicated to being amongst Canada’s leaders in municipal biosolids management. Ottawa continually monitors research and new technology, follows the most stringent and proactive best management practices and works to share information and build understanding.

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