The project's treatment plant will be one of the biggest of its kind in the world

The tunnel is part of Lot 3 of the Riachuelo Environmental Restoration project, a sustainable development financed by the World Bank to clean up Argentina’s Matanza-Riachuelo river basin, one of the most polluted in the world.

The 60km-long Matanza-Riachuelo originates in the Buenos Aires Province and empties into the Ríver Plate near the Tandanor shipyard.

Thousands of small industrial units line the banks of the Matanza-Riachuelo and discharge high levels of industrial effluent into the river.

The new 4.3 metre-diameter tunnel runs for 10.5 kilometres and is buried 40 metres below the bed of the River Plate. It will receive wastewater that has been taken from the Matanza-Riachuelo and treated at a new plant and will diffuse this into the River Plate at a rate of 27m³ per second.

The treated water will be pumped into the river through 34 one-metre diameter steel risers installed at intervals along the ceiling of the tunnel.

The treatment plant and associated pumping stations are being built by Webuild subsidiary Fisia Italimpianti and Spanish contractor Acciona, which has a 35% stake in the project.

According to Webuild, the treatment plant will be one of the biggest of its kind in the world.

Once the entire project is completed, an estimated up to 2.3 million cubic metres of wastewater from the Matanza-Riachuelo will be treated every day, improving the lives of more than four million people who live in the heavily industrialised area.