Oxford County’s Wastewater Treatment Plants (WWTP) operate according to provincial and federal regulatory requirements as stipulated in each plant’s Environmental Compliance Approval.

A by-pass occurs when wastewater is diverted around one or more treatment processes within the WWTP. The bypassed wastewater will still go through screening, grit removal, primary treatment and final disinfection prior to discharge.

This can be necessary due to several reasons, one of note is because of more common extreme weather events experienced due to climate change. An increased volume of sewage (due to inflow/infiltration of rainwater) can be fully treated for a period of time at the WWTP. However, if heavy rain continues, the volume of sewage reaching a WWTP may be more than can be treated and processed in a short period of time. In this case, some of the wastewater may be diverted around the biological process (secondary treatment process) to protect the WWTP.

Bypasses are necessary because they help to:

  • Prevent wastewater in the sewers from backing up and potentially causing basement and/or surface flooding;
  • Prevent flooding of the WWTP and protect the WWTP’s ability to continue treating wastewater;
  • Protect the core biological plant process (secondary treatment) from damage – too much flow can “wash out” the microscopic organisms needed for secondary treatment, affecting the WWTP’s ability to function for several days or weeks; and,
  • Prevent the WWTP from flooding, which can cause significant damage to mechanical and electrical equipment.

Incidents in the following Table are being posted here for public notification. This covers all of Oxford County’s WWTP and Sewage Pumping Stations (where the volume exceeds 10 cubic metres).


Bypass/Overflow- Location, Frequency & Duration

SiteDateDuration (Hours)Volume (m3)Reason
Tavistock William St SPS Jan 24, 2022 0.6 35 Backup float switch failed to start pump
Norwich Lagoon April 1 to 5, 2023 95 hours 2,150 Heavy precipitation (increased inflow/infiltration)
Tillsonburg John Pound Rd SPS July 29, 2023 3.8 hours 2,000 Heavy precipitation (increased inflow/infiltration)
Mount Elgin Wastewater Treatment Plant SPS Jan. 26, 2024 1.5 15 Heavy precipitation (increased inflow/filtration)
Mount Elgin Peggy Avenue SPS Jan. 26, 2024 0.45 17 Heavy precipitation and snow melt
Norwich Sutton Street SPS Jan. 26, 2024 2.95 15 Loss of prime on second pump and heavy precipitation and snow melt
Woodstock Wastewater Collection System (Near Woodstock WWTP) Jan. 26, 2024 12 2193 Rainfall and Snow Melt Event