Strabag has been awarded a CAD$79M (£43M) contract to build the Mid-Halton outfall tunnel from a water treatment plant in Oakville, Canada.
The project centres on the excavation of two 60m deep shafts and a 6.3km rock-bored tunnel to discharge waste water into Lake Ontario.
The section on the mainland will have a length of 4.1km. The 2.2km of offshore tunnel will terminate in an underwater diffusion structure.
A tunnel boring machine with a diameter of 3.6m will be used to drive the bore through the shale and limestone geology.
Work will begin this month and is expected to last until October 2017.