Metro Vancouver uses a range of methods to monitor and address odours from sewers and wastewater treatment plants.
Why the sewer smells
Sewer odours are created when human waste and waste from some industrial and commercial operations breaks down in the sewer system. This is a biological process that happens in all sewer systems.
What’s in an odour
Odours typically contain hydrogen sulphide, mercaptans and other volatile organic compounds normally found in wastewater. Hydrogen sulphide is what gives off that rotten egg smell that we typically associate with sewer odours.
At the low levels typically found in residential areas, sewer gas is not a health hazard. In our region, sewer odours dissipate quickly into the surrounding air with little to no impact on the environment.
Detecting and monitoring odour
Metro Vancouver uses instruments in various locations in the sewer system to measure odour. Wastewater treatment plants use a combination of methods that include portable instruments to monitor odour at various plant locations, along with individuals who are specially trained to gauge the intensity of an odour.
Metro Vancouver regulates odour from businesses on a case-by-case basis. Municipal and Metro Vancouver utilities are self-regulated and have varying emission guidelines to minimize odour impacts. Odour is regulated according to the intensity of the odour and is measured in “odour units”. The amount of acceptable odour units coming from a facility depends on where the facility is located and whether it is existing or new.
The intensity of an odour is often measured in “odour units”:
- One to five units - One odour unit represents the lower limit that an average person can detect. Odour units up to five are considered weak.
- Up to ten units - These are more noticeable odours and may generate complaints.
- Above ten units - Odours above ten odour units are considered to be in the nuisance range and those measuring 20 odour units and above are considered intolerable.
What Metro Vancouver is doing to address odour
Depending on the type of odour, Metro Vancouver manages odours using filtration, chemical and biological treatment systems. This can involve:
- Using passive activated carbon systems to address less intense, localized odours in sewers
- Installing air management facilities in areas with chronically high concentrations of odours
- Using sophisticated odour controls systems at wastewater treatment plants to minimize odour outside of the plant footprint
Cost to address odour issues
The cost of managing odours varies depending on the source and amount of the odour, and how close it is to people. It can be very expensive – sometimes millions of dollars – to address odours at wastewater treatment plants and in parts of the sewer system that have ongoing high concentrations of odours.