A major multi-phased redevelopment of a large quadrant of northwest Whitby is the driver of a $40-million sewer project which comes with its fair share of challenges and obstacles.
Not only did Highway 401 have to be traversed, thick bedrock and two provincially significant wetlands are along the route of the Jeffery Street Sewage Pumping Station and West Whitby Sanitary Trunk Sewer project.
“We wanted to minimize any impacts to the wetlands,” says Durham Region project manager Jeff MacDonald, in explaining why a 100 per cent tunneling operation was chosen.
Bolton-based Dibco Construction Ltd. was the tunneling contractor for the 2.4-kilometre-long, (1.5-mile) 20-metre-deep, (65-foot) 900-mm to 1,200-mm sewer which extends from the existing Jeffery Street pumping station south of Highway 401 in a northwest direction under the GO Transit/CN Railway Line and the highway to Dundas Street.
The tunnel sections were connected by five shafts which were spaced periodically to accommodate tunnel drive lengths and changes in horizontal alignment, he says.
Construction started in late 2016 and is targeted for completion this July. At this stage the actual tunneling has been completed and concrete pressure pipe installation and manhole construction are now underway, says MacDonald.
For the most part, the tunneling was a straight-forward five-day-a-week process with only one tunnel boring machine. However, the shifts had to be modified periodically to meet the contract schedule, he says.
Overseen by general contractor Kenaidan Contracting Ltd., the project also includes the building of a new more technologically advanced Jeffrey Street sanitary sewage pumping station. Its output will vary and increase as the development of the West Whitby lands progresses.
“The 3,800 homes it will service translates to an approximate average flow of 154 litres per second.”
Design started in 2014, with Aecom completing the design of the pumping station, while WSP was the consultant for the sanitary sewer, says MacDonald.
Although the old station will be demolished, the feedermain and some of the below ground infrastructure components will be retained, says MacDonald.
And that demolition will commence as soon as the now-underway commissioning of the new structure is completed, says Kenaidan project manager Christopher Stewart.
Asked to highlight some of the project challenges, he points out that both the tunnel and the founding elevation of the pump station are in shale bedrock and that required extensive monitoring and ventilation of methane gas.
The remote nature of the tunneling shafts also meant that several access roads had to be built and maintained regularly, especially throughout the winter, to ensure they remained passable at all times.
As well, the tight delivery timetable also necessitated significant winter concrete pouring and the precautions that entails.
“It is the regular challenges of working with concrete in the winter,” says Stewart, stressing the need for heaters and concrete blankets.
About 30 workers were on site at the peak of the project which occurred about January 2018, says Stewart.
The sewer is needed to ultimately service approximately 500 hectares of developable land in the West Whitby Secondary Plan Area which is bounded by Lyndebrook Road to the north, the town’s existing built boundary to the east, Highway 401 to the south and Lakeridge Road to the west.
Approximately 7,600 housing units and mix of industrial and commercial buildings will ultimately developed there. Servicing for some of the Phase 1 subdivisions has started and, in some areas, completed, says Alex Lam, manager of development engineering and environment services with the Town of Whitby’s public works department.