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Peel’s east-west trunk sewer diversion another piece in region’s servicing puzzle

Dan O'Reilly
Peel’s east-west trunk sewer diversion another piece in region’s servicing puzzle

Planning and delivering wastewater treatment service in Peel Region almost seems like a massive jigsaw puzzle.

The next carefully thought-out big move will be the tunnel construction of the 11-kilometre $250-million, 2,400-mm East to West Diversion Trunk Sewer. Design by Jacobs Canada Inc. (formerly CH2M Hill) started in 2017 and will be completed later this year, says Ajay Puri, the region’s wastewater division project manager.

Construction will commence in April 2020 and it will require both a rock tunnel boring machine and earth-pressure balance TBM because of the different ground conditions along the route, he says.

“Prequalification of contractors will begin either later this year or early next year.”

Servicing Mississauga, Brampton, and parts of Caledon, the region’s wastewater system is comprised of two principal trunk systems. They include the west trunk system which delivers flows to the Clarkson Wastewater Treatment Plant and the east trunk which sends sewage to the G. E. Booth Wastewater Plant, which is often simply referred to as Lakeview.

To be built primarily along Derry Road from Pearson International Airport, the diversion trunk will ease pressure on Lakeview by redirecting it to the west trunk system and then to the Clarkson plant which has been the focus of a number of expansions during the past few years.

Once the diversion is completed it will enable the region to facilitate retrofits and expansions at either plant—although as Puri notes—“Lakeview has only so much land to grow.”

A master servicing plan which the region aims to update every five years or so pinpointed the need for the diversion to provide greater flexibility to support greenfield development in Brampton and intensification in Mississauga, he says.

The Derry Road corridor was chosen because it is shorter and less built up compared to a more southerly route that had also been under consideration, says Puri.

Last year the Region approved new wastewater standards to limit groundwater infiltration and inflow and that will have major impact on this project. The winning contractor or contractors will have to install concrete pipe which must pass a minimum 50 PSI water (pounds per square inch) pressure test.

“Peel Region is a leader in developing these standards and other municipalities are now considering them. This (water infiltration) is a real problem.”

At a sewer and watermain conference, which Puri attended, a consultant showed a CCTV image of a sewer into a new development which had water flowing through it even though the homes hadn’t even been connected to the sewer, he says.

Manufacturers are aware of the new standards and he doesn’t foresee any fabrication problems or supply delays. Pipes meeting the 50-PSI criteria have been installed in one previous Peel project, the East Brampton trunk sewer.

Similarly, he believes there will be minimal inconvenience to adjacent homes and businesses along the route. Most of the seven entry/exit shafts for the TBMs will be located in either industrial areas or parks and the region is currently negotiating with the small number of impacted owners, he says.

There may also be an opportunity to decommission a sewage pumping station in the community of Meadowvale which would eliminate the costs of operating that plant and “lessen the carbon footprint.”

However, a small portion of the route of the diversion trunk sewer will be on Creditview Road and that is where the Ministry of Transportation will be building a new bridge as part of a major widening of Highway 401 in the area.

“The bridge construction may impact the progress and scheduling of the tunnel.”

As the tunnel will cross under Hurontario Street, there will also have to be close co-ordination with Metrolinx and the City of Mississauga to ensure there will no interference or disruption to that city’s Hurontario Light Rapid Transit project, he says.

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