TBM excavation for Lake Ontario outfall 6 Aug 2014

Construction of a 6.25km wastewater outfall tunnel into Lake Ontario, Canada, is awarded to low bidder Strabag for a contract sum of just under Can$79 million.

The 2.6m i.d. tunnel will extend from Mid Halton Wastewater Treatment Plant, for a distance of 4.1km under the town of Oakville, before reaching out a further 2.15km under the bed of Lake Ontario.

Project scope also includes excavation of a 60m deep x 12m diameter permanent shaft at the location of the treatment works site, which will also serve as a TBM launch site. An intermediate permanent access shaft measuring 50m deep x 6m diameter, and sited on the shoreline at Coronation Park, is also included.

In a closely run contest, seven contractors submitted bids to the project owner, the Regional Municipality of Halton (Table 1), with a bid spread between highest and lowest of approximately $30 million.

6.25km outfall tunnel includes two permanent shafts

Brenda Kingsmill, Project Manager for the owner, told TunnelTalk from Ontario: “The tunnel is of a concrete lined design, with an o.d. of 3.6m and a finished inside diameter of 2.6m. We have not approved any changes to the design parameters yet, but I understand that Strabag is looking at some value engineering change proposals though nothing is approved as yet.” She added that the project is due for completion by the end of August 2017.

A TBM of 3.6m diameter will be procured to execute the tunnel drive, which will be mostly through the Georgian Bay Formation at an average depth of 50m. Engineering design for the owner is by Hatch Mott MacDonald.

The Mid-Halton Wastewater Treatment Plant, located in Oakville, Ontario, is part of the densely populated and rapidly growing Greater Toronto Area. In order to meet increased demand and continue to protect the water of Lake Ontario, it became necessary to increase the plant’s capacity from 75 million liters/day to 125 million liters/day.