Water & Sewer

Monitoring Wastewater Overflows and Bypasses

Wastewater Treatment Plant Bypass or CSO Storage Tank Overflow Completed

A wastewater treatment bypass or CSO storage tank overflow has occurred within the last 48 hours.

Wastewater Treatment Plant Bypass and CSO Storage Tank Overflow Events

A wastewater treatment bypass or combined sewer overflow (CSO) storage tank overflow event could occur when:

  • The volume of storm water (rain and melt water) and wastewater exceeds the capacity of the sewer system, CSO storage tank or the wastewater treatment plants
  • When elevated lake levels cause lake water to back-feed into the wastewater collection system
  • To facilitate vital maintenance repairs at the treatment plant or at CSO tanks

Wastewater Treatment Plant Operations staff monitor incoming flows and system/plant levels and make operational adjustments to the treatment processes as required. Operations staff will initiate a bypass or CSO tank overflow event when the system is full to protect the system from infrastructure damage and to prevent basement and/or surface flooding.

Wastewater treatment plant bypass or CSO storage tank overflow events do not have an impact on the quality of the City’s drinking water.

Wastewater Treatment Plants Bypass Log

Initiation Completion Wastewater Treatment Plant Type of Bypass Duration Volume
January 24, 2020
8:53 pm
January 25, 2020
10:51 pm
Woodward Secondary Bypass 25.97 hrs 206.6 million litres
January 11, 2020
11:21 am
January 13, 2020
4:15  am
Woodward Secondary Bypass 40 hrs 54 mins 638 million litres
December 30, 2019
3:30 am
December 30, 2019
7:52 pm
Woodward Secondary Bypass 16 hrs 47 mins 127 million litres
December 14, 2019
10:36 am
December 14, 2019 11:35 pm Woodward Secondary Bypass 12 hrs 59 mins 106 million litres
December 1, 2019
12:03 pm
December 1, 2019
11:56 pm
Woodward Secondary Bypass 11 hrs 53 mins 78 Million Litres
Table data is not official record.

Combined Sewer Overflow (CSO) Tank Overflow Log

Initiation Completion CSO Tank Duration Volume
January 25, 2020
10:56 am
January 26, 2020
12:01 am
Eastwood 13.08  hrs Flow monitor out of service
January 25, 2020
2:45 am
January 25, 2020
11:35 pm
Main/King 20.83 hrs 51.1 million litres
January 25, 2020
2:16 am
January 26, 2020
10:50 am
Greenhill 30.56 hrs 180.4 million litres
January 13, 2020
1:05 pm
January 13, 2020
5:25 pm
Greenhill 4.33  hrs 7.4 million litres
January 12, 2020
4:45 am
January 12, 2020
5:41 am
McMaster 56 min 258 thousand litres
January 12, 2020
12:59 am
January 12, 2020
07:38 am
Red Hill CSO Pipe 7.65 hrs 10.7 million litres
January 11, 2020
5:21 pm
January 11, 2020
9:14 pm
Red Hill CSO Pipe 3.9 hrs 4.6 million litres
January 11, 2020
4:55 pm
January 14, 2020
5:18 am
Eastwood 60.383 hrs Flow monitor out of service
January 11, 2020
4:01 pm
January 13, 2020
8:37 am
Royal Stroud 40.6 hrs 298.8 million litres
January 11, 2020
3:22 pm
January 13, 2020
6:49 am
Greenhill 39.45 hrs 404.7 million litres
January 11, 2020
3:01 pm
January 13, 2020
11:37 pm
Main/King 56.6 hrs 127.1 million litres
Table data is not official record.

Combined Sewer Overflow & Plant Bypass Location Map

View the combined sewer system overflow outfall locations (both monitored and unmonitored) and the location of the Dundas and Woodward Wastewater Treatment Plants. CSO & Plant Bypass Location Map (PDF, 381 KB)

Why Wastewater Bypass and CSO Events Occur

The City of Hamilton has a large complex wastewater collection network consisting of both separated sewer and combined sewer systems. Modern areas of the City have separated sewer systems, which consist of sanitary sewers that carry wastewater from toilets and household drains in one sewer system, and storm sewers which carry surface water such as rainwater or snowmelt in another separated system. In older areas of the City a combined sewer system collects both storm water (rainwater or melt water), and wastewater in the same pipe. During periods of heavy rainfall or snowmelt, combined sewers are inundated with large volumes of storm water that can exceed the capacity of the pipes. 

Bypass and CSO events are a necessary operating condition to prevent rainwater and wastewater from backing up and causing basement flooding, surface flooding of our roads and potential damage to the Wastewater Treatment Plants. Flooding from large volumes of storm water at the treatment plants can cause significant damage to mechanical and electrical equipment as well as ‘wash out’ the microscopic organisms needed for secondary wastewater treatment, which can affect the wastewater treatment plant’s ability to function for several days or weeks.

Wastewater Treatment Plant Bypasses
The Wastewater Treatment Plant (WWTP) operations staff can bypass the WWTP at four locations, a total plant bypass, headworks bypass, primary bypass, and secondary bypass.

Plant Bypass
A plant bypass sends untreated sewage from the main pumping station (MPS) wet-well directly to the natural environment. This type of bypass would only be initiated if there was danger of flooding the MPS, or if there was significant maintenance or other works taking place for downstream WWTP processes.

Headworks Bypass
A headworks bypass sends partially treated sewage to the natural environment, bypassing the majority of the WWTP processes.  In the event of a headworks bypass, large solids and heavy grit have been removed from the sewage, and chemicals have been added for phosphorous removal. This type of bypass would be initiated if the maximum primary and secondary bypass capacity was reached and flows continue to increase.

Primary Bypass
A primary bypass sends partially treated sewage to the natural environment, bypassing the majority of the WWTP processes. In the event of a primary bypass, large solids and heavy grit have been removed from the sewage, and chemicals have been added for phosphorous removal. Between May 15th and October 15th each year, primary bypasses will also be disinfected with chlorine, and then the chlorine will be removed. This type of bypass would only be initiated if there was danger of flooding or damage to the primary treatment processes, or if there was significant maintenance or other works taking place for downstream WWTP processes.

Secondary Bypass
A secondary bypass is the most common type of bypass event at a WWTP. A secondary bypass sends partially treated sewage to the natural environment, bypassing the WWTP’s secondary treatment processes (biological treatment and final clarification). In the event of a secondary bypass, large solids and heavy grit have been removed from the sewage, chemicals have been added for phosphorous removal, and the majority of settleable solids and floatable materials have also been removed. Between May 15th and October 15th each year, secondary bypasses will also be disinfected with chlorine, and then the chlorine will be removed. This type of bypass is initiated when WWTP flows exceed the WWTP capacity risking non-compliance of the Environmental Compliance Approval (ECA) for the WWTP and ‘wash-out’ of the WWTP’s biological treatment processes (which would result in partially treated sewage being discharged from the WWTP continuously for days or weeks until the biological processes can be restored), or if there was significant maintenance or other works taking place for downstream WWTP processes.

Combined Sewer Overflow (CSO) Tank Events
Hamilton has nine CSO tanks that were built from the 1980’s through 2010 to help add capacity to the combined sewer system The nine large storage tanks hold more than 314,000 cubic metres of diluted wastewater. During rain events the combined sewer overflow tanks will fill and store the excess water. If the storm continues the combined sewer system - now being full and at capacity, will then overflow into the environment.

When the storm stops, and the sewer system and treatment plant have capacity for the volume of wastewater inside the combined sewer overflow tanks, the water is then put back into the sewer system to head to the treatment plant for cleaning.

If the combined sewer system didn’t have the designed overflow option to release wastewater to the harbour, large areas of Hamilton would experience flooding -  which would impact homes, business, roadways, public spaces and public health.

Additional Wastewater Treatment Plant Bypass/CSO Information

Public Health services monitors beaches in accordance with the Ministry of Health and Long-Term Care’s Operational Approaches for Recreational Water Guideline 2018 and the Recreational Water Protocol 2018 under the Ontario Public Health Standards. As outlined in the above protocols, beach samples are collected and tested for E. coli bacteria at least once per week during the swimming season.

Beach sampling results cannot be guaranteed accurate as conditions can change quickly depending on the weather. You should not swim at the beach during and after storms, floods or heavy rainfall. Cloudy water may indicate high levels of bacteria.

For more information on ways to stay safe at the beach, visit the Canadian Red Cross’s website

The Government of Ontario provides fish consumption advisories for Ontario’s lakes and rivers which are available in the Guide to Eating Ontario Fish. You can use this guide and the interactive map to help you identify the types and amounts of fish that are safe to eat from more than 2,400 fishing locations.

There are 2 Wastewater Treatment Plants in Hamilton:

Woodward Wastewater Treatment Plant
700 Woodward Ave. Hamilton

Dundas Wastewater Treatment Plant
135 King St. E. Dundas

All bypasses are promptly reported to the Ministry of Environment, Conservation and Parks (MECP) Spills Action Centre and to Public Health Services as required by the WWTP’s ECA.