St. John’s Harbour Clean-Up
June 1, 2011
By CH2M HILL & NDAL
St. John's, the provincial capital of Newfoundland and Labrador, is the oldest city in North America. For over 500 years raw sewage has been flowing into the harbour that lies at the heart of the historic city.
St. John’s, the provincial capital of Newfoundland and Labrador, is the oldest city in North America. For over 500 years raw sewage has been flowing into the harbour that lies at the heart of the historic city.
It is estimated that before new treatment facilities were recently built, 120 million litres of raw sewage and stormwater flowed into the harbour every day. During wet weather storms the flow might be up to five times as much. The harbour was so polluted that at times unsightly material floated on the surface.
Plans to help the situation began in the 1970s, but it wasn’t until 1997 that the comprehensive St. John’s Harbour Clean-up Project was begun.
Phase I provided immediate relief to the harbour’s western end by collecting and screening the raw wastewater. Then in 2001, the city contracted Newfoundland Design Associates Limited (NDAL) in association with CH2M HILL to do the conceptual and detailed design for phase 2, known as the Riverhead Wastewater Treatment Project. The project included building a new Harbour Interceptor Sewer, which is a 1600-mm diameter pipe that stretches two kilometres around the harbourfront to collect the sewage.
As well, phase 2 involved building a new wastewater treatment plant to treat the sewage before it is discharged into the harbour and ocean.
Finding a site for the Riverhead Wastewater Treatment plant fairly close to the harbour was difficult, but eventually Southside Hills on the southwest of the town harbour was selected. The site had to be literally carved out of the rock — over 800,000 cubic metres of rock were excavated at a cost of about $20 million.
Because the plant is highly visible across the harbour from the centre of St. John’s, care was taken over the architectural design. It was decided that a “contextualized” approach was best i.e. one in which the buildings are recognizable for what they are, but at the same time they are visually interesting and not obtrusive. They are designed for a long service life.
The wastewater treatment plant provides conventional primary treatment, but it has provision for upgrading to either enhanced primary treatment or full secondary treatment. Other more compact treatment approaches were considered, but the traditional approach was selected because it offers opportunities for upgrading, has a better lifecycle cost, and is easier to operate and maintain.
After entering the plant the sewage passes through aerated grit tanks and primary clarifiers. Then, after chlorination, the treated wastewater is discharged through the existing diffused outfall at the west end of the harbour.
As well, the outfall was extended with new diffusers to provide improved dispersion of the effluent.
Completed in 2009 at a cost of approximately $137 million, the project will, over time, help to heal the environment in the harbour. cce
Newfoundland Design Associates Limited (NDAL) (William Noseworthy, P.Eng.) in association with CH2M HILL (Robert Hook, P.Eng.)