Thames Tideway Tunnel

The Thames Tideway Tunnel, often dubbed London’s “Super Sewer,” is a major infrastructure project designed to modernize the capital’s aging sewer system and drastically reduce pollution in the River Thames.

London’s Victorian-era sewer system, built for 4 million people, now serves over 9 million. Even light rainfall could overwhelm it, causing raw sewage to spill into the Thames.

The Thames Tideway Tunnel is designed to intercept and store storm sewage before it can overflow into the river, reducing spills by around 95%.

Running for 25 km from Acton in West London to Abbey Mills in the east, the 7.2 m diameter tunnel is between 30m and 70m underground.

WJ’s involvement with the project began at the site investigation stage, as the very deep and complex structures at Kirtling Street were essential to enable the tunnelling to get underway, and extensive groundwater pumping tests would be needed for construction confidence, environmental compliance and ensuring that nearby Thames Water abstraction wells were not impacted. WJ subsequently carried out fully instrumented tests at over 10 locations and designed, operated and maintained dewatering system for 9 out of the 10 sites where connection shafts or pumping stations were sunk.

WJ also secured an environmental monitoring contract and have collected and tested over 10,000 water samples from monitoring wells in the Wandsworth and Westminster areas and will continue to until the Environment Agency is satisfied that the new tunnel has not adversely impacted the important chalk aquifer in the area.

The project was officially opened on 7 May 2025 by King Charles III.