Digging into Peel’s $350M east to west sewer diversion project

It’s an immense, complicated and expensive project that took four years to design.

It’s also only at about the mid-point of six years of construction under two contracts by two tunnel boring contractors using different machines due to the varying ground conditions.

Designed by Jacobs Canada Inc., the approximately $350 million east to west diversion sanitary sewer in Peel Region, however, will give the region more flexibility in the timing and optimization of its wastewater treatment plants on the shores of Lake Ontario.

The contractors are McNally Construction Inc. for contract one and Technicore Underground for the second contract.

Wastewater servicing in Peel, and that includes the cities of Mississauga, Brampton and parts of the Town of Caledon, is a complex undertaking requiring two principal trunk systems.

A west trunk system delivers flows to the Clarkson Wastewater Treatment Plant and an east trunk sends sewage to the G.E. Booth Wastewater Plant, or Lakeview, as it’s known locally.

As its name implies, the 2.4-metre-diamater diversion sewer will allow the region to reroute sewage flows to either of those trunks to allow planned expansion/retrofits at one or the other plants, says the region’s wastewater division project manager Ajay Puri.

To be installed completely by tunnel along Derry Road West, Old Derry Road, Old Creditview Road and Creditview Road in Mississauga, the diversion trunk will connect with those trunks.

The project has been lengthy both in terms of design and the even-longer construction phasing. Some of the challenges included relocating the numerous utilities, meeting the complex provincial standards for archeological investigations and obtaining the various approvals including encroachment permits from the Ministry of Transportation for going underneath highways 410 and 401, he says.

Preceded by years of planning, design by Jacobs Canada started in 2016 and it wasn’t until near the end of 2020 that the first phase contract by McNally Construction Inc. got underway. The contractor has faced a number of worker shortages created by COVID and a large logistical hurdle long before construction began, says Puri.

A Chinese-manufactured and imported rock tunnel boring machine “got stuck” in the Port of Vancouver. In the heavy rains and landslides that hit the region in the spring of 202l, rail and road connections with the port were severed. The TBM had to be rerouted to Seattle Washington and trucked through the United States to the construction site, says Puri.

Now in use for more than two years, the TBM has been excavating hard rock on a two-shift basis from a compound base of operations at Highway 410 and Derry Road.

After completing a westerly section towards Mavis Road last December, McNally pulled out the machine from a shaft, returned to the compound and is now excavating in an easterly direction to Dixie Road, the limits of its scope of work. The excavation will be completed by July or August.

“The rock is self-supporting,” says Puri, explaining the 2,400 millimetre concrete pressure pipe does not have to be installed simultaneously, as is the procedure in some tunnelling operations.

Another McNally crew is now installing the pipe in the first excavated section and by the beginning of 2025 the contractor will have completed its phase of work.

“There are two shifts, from about 7 a.m. to 12 midnight,” says Puri, when asked if the tunnelling is conducted on a 24/7 basis. The overnight hours are used for maintenance work.

As for Technicore Underground, it will be excavating and installing the sewer in a north and northeast direction towards Mavis Road, and a small stretch along Derry Road from Dixie Road to Bramalea Road.

It began mobilizing onsite last November and is currently excavating a shaft in the Argentina Road/Creditview Road area. Expected to be completed by July or August, the shaft will be used to lower an earth pressure balance TBM. That type of machine is necessary because of the soft soil conditions in the area, especially under and near the Credit River, says Puri.

By the end of 2026 the entire project should be completed, he adds.