Construction of the CSO will help reduce the amount of untreated waters entering Lake Washington Ship Canal during heavy rains.
During a heavy storm, the new tunnel will capture and temporarily store untreated stormwater and sewage until the treatment plant is ready for it. The 4.2km tunnel is expected to keep an annual average of more than 276 million litres of polluted stormwater and sewage out of the canal, as well as Salmon Bay and Lake Union.
Salini Impregilo has said that it is ready to expand further in the United States, its biggest market by revenue, following the appointment of Mark Schiller as president and chief executive of Lane.
The order backlog at the end of June was more than US$4bn and the company has new orders totalling more than US$800m, including contracts that are new or in the process of being finalised. The group is aimed to increase its market share with new projects in the transport, water and tunnelling sectors.
In March, Lane won a US$524m contract to build a basin storage reservoir in Florida to reduce harmful discharges into an estuary. Other projects include the Three Rivers Protection & Overflow Reduction Tunnel in Indiana; the Dugway Storage Tunnel in Ohio; and the Anacostia River Tunnel, which is part of the Clean Rivers Project in Washington, DC.
Work on the new Seattle CSO project is expected to start this month and be completed in 2022.