Water & Sewer

Monitoring Wastewater Overflows and Bypasses

No Active Wastewater Treatment Plant Bypass

Wastewater Treatment Plants operating as expected.

Wastewater Treatment Plant Bypass Events

A wastewater treatment bypass event could occur when:

  • The volume of storm water (rain and melt water) and wastewater reaching the wastewater treatment plant exceeds the capacity of the plant.
  • When elevated lake levels cause lake water to back-feed into the wastewater collection system.
  • To facilitate vital maintenance repairs at the treatment plant

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

Although a bypass event will send partially treated wastewater into Hamilton Harbour, this does not have any impact on the quality of the City’s drinking water.

Wastewater Treatment Plants Bypass Log

Initiation Completion Wastewater Treatment Plant Bypass Location Duration
December 1, 2019
12:03 pm
December 1, 2019
11:56 pm
Woodward Secondary Bypass 11 hrs 53 mins

Why Wastewater Bypass 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 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.

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.

Additional Wastewater Treatment Plant Bypass 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.