Over the years, residents of Bonnie Doon and the surrounding communities have reported smell of sewer
odour to the City. The City, together with the University of Alberta and other industrial partners, is
undertaking studies and developing plans to find a long-term solution to addressing this issue.
What causes the odour?
The odorous compounds (predominantly hydrogen sulphide) are formed as a result of the natural
decomposition of organic matter in the wastewater. These odours cause problems when the air in the
sewers escapes to the surface.
The sewer system in this area is a combined system - meaning wastewater from homes and businesses
and storm water enter the same pipes. Lateral local sewers (small-to-medium shallow pipes that run on the
streets) collect the water and transport it to bigger deep trunk sewers, which then carry the water to the
wastewater treatment plant. A number of lateral sewers run throughout this area and are connected to the
trunk sewers through structures called drop shafts. As the water descends through the drop shafts to the
trunk sewers below, it can become turbulent and cause odorous compounds formed in the wastewater to
escape as gases. Under certain conditions, the gases can vent through manholes, catch basins and other
openings to the surrounding areas.
What is being done?
Previous attempts over the years to prevent the release of odours in the area included:
● installing one-way flaps in selected catch basin leads;
● sealing manhole openings; and
● regular flushing of the lateral sewers to remove sediment and stagnant water.
This approach has had limited success, as the City continues to receive odour reports. The City and its
partners are therefore conducting a thorough study to find long-term solutions.
This approach is looking at reducing the formation of the odorous compounds at the source, and mitigating
any releases into the community.
● Extensive field data (gas pressures and hydrogen sulphide concentrations) is being collected in
the sewer trunks from Bonnie Doon all the way to the Blue Quill/Twin Brooks areas to better
understand how the sewer gases are formed and also how they escape into the communities.
● Inspection and cleaning of selected deep trunks in and leading to the area to remove sediment
and organic materials built-up over the years are being investigated. This approach is expected to
reduce the formation of the odour compounds. This project will start all the way from the
Steinhauer/Duggan to this area. Logistics to get a contractor (who has the right equipment to
access these deep trunks) on board is currently being explored. The execution of this plan will
start in 2017.
● Laboratory testing at the University of Alberta to fully understand the effectiveness of some of the
engineering solutions that the City plans to implement is currently ongoing. These solutions
include making changes to some of the drop shafts in the area and treating odorous compounds
at some strategic locations including pump stations. The implementation of these major system
changes will start in 2019 and beyond.
For more information, please contact:
Stephen Edwini-Bonsu, PhD., P.Eng.