Placing the extended outfall.
The Eastern Wastewater Treatment Facility is the cornerstone for the Saint John Harbour Clean-up, which is a major initiative by the City of Saint John, the Province of New Brunswick and the Government of Canada to intercept and treat raw sewage from outfalls that discharge directly to the Bay of Fundy. Located adjacent to Red Head Marsh in East Saint John, the EWWTF is a conventional activated sludge wastewater treatment facility that is the largest secondary wastewater treatment facility in Atlantic Canada.
Designed to treat an average daily wastewater flow of 35,000 cubic metres, with a peak daily flow of 80,000 cubic metres, the EWWTF provides significant benefits to the local community. Treated effluent from the plant is now directed more than 1 kilometre offshore into a mixing zone, as opposed to the previous situation where effluent was directly discharged onto Red Head beach. As a result local residents can now safely enjoy recreation activities in the area.
The treatment plant provides preliminary treatment, screening, grit collection, sludge dewatering, primary clarification, secondary treatment, and disinfection via ultraviolet light.
The new outfall is a 1370-mm diameter high density polyethylene pipe that extends 1.4 kilometres from the plant into the harbour. There it disperses treated effluent through a diffuser. The diffuser has 19 duck-billed check valves to release treated effluent over a 100 metre section. The valves are ideal for marine environments as they prevent salt water intrusion as well as sediment infiltration and deposition in the outfall during low flow periods. The diffusers have the capability to self clean and reduce marine fouling.
CBCL helped to select the most viable treatment process and provided civil, environmental, architectural, structural, mechanical, electrical, and instrumentation design for the $48.5-million project, which was completed in 30 months, with commissioning and SCADA integration completed by the fall of 2011.
The design and construction faced challenges posed by the dynamic marine environment with its varying tide levels. Each day approximately 100 billion tonnes of seawater move in and out of the Bay of Fundy during tide cycles. This statistic is greater than the combined flow of the world’s fresh water rivers. The tide cycle can vary in water depth as much as 8 metres every six hours.
As part of the design, CBCL developed a 3D hydrodynamic model of Saint John Harbour to predict the “near field” and “far field” effects of treated effluent on the receiving water body during a rising and falling tide.
During the actual construction, the team had to cope with extreme low and high tides and quickly changing weather conditions. Also it was of paramount importance to coordinate the work with the local Port Authority, Transport Canada, cruise lines, and shipping lines, when working near navigation channels. As Canada’s first incorporated city, Saint John is a major port of call for the cruise ship industry and is becoming a vibrant tourism destination.
Another fundamental challenge was that the new plant is located on the site of the existing Hazen Creek Wastewater Treatment Plant and adjacent to pristine environmental features. The solution chosen was to design and construct the new facility around the existing plant, which continued operating until the new plant was completed. The Hazen Creek plant was then demolished.
The site is also adjacent to Red Head Marsh, a provincial environmentally significant wetland that serves as prime habitat for migratory birds including the at-risk species known as the Least Bittern. To avoid disturbing the wildlife, non-traditional rock removal methods were used, including fracturing and cleavage with air pressure rather than traditional blasting.
The team used the value engineering approach to optimize the design and provide maximum cost benefits to the city. The approach reduced the capital costs and improved the plant’s performance and operational flexibility. It also ensured that the client and team were fully engaged in the design. The EWWTF was the largest single project that the City of Saint John had ever undertaken.
Improvements to the wastewater collection and treatment system that convey untreated sanitary sewer flows to the EWWTF are ongoing. Dry weather raw sewage outfalls are being eliminated, and high bacterial loads have been eliminated in Courtenay Bay and over the Red Head Mudflats.
By these means, the Harbour Cleanup project is implementing the infrastructure required to effectively collect and treat wastewater in Saint John for many years to come.cce
Name of project: Eastern Wastewater
Treatment Facility, Saint John, N.B.
Award-winning firm: CBCL Consulting Engineers (John Flewelling, P.Eng.,
Kevin Murphy, P.Eng., Jody Blakely, P.Eng., Tim McCluskey, P.Eng.)
Owner/client: City of Saint John
Other key players: Conquest Engineering (geotechnical), Murdoch and Boyd
Architects (building code review),
Pomerleau (general contractor).
We liked this project because the consultant successfully designed the facility on an existing plant and adjacent to pristine environmental features. The outfall was efficiently constructed despite the challenging marine environment. Local residents can now safely enjoy recreational activities in the area.