Work has begun on the final phases of the London super sewer to join it to the wider network.
Connections are being made from the existing sewer network to the new Thames Tideway tunnel, with walls are being broken down between the two.
Major construction work was completed on the £4.5 billion project last month when the deepest shaft at Abbey Mills pumping station in east London was covered.
Now, the teams are working to connect the 6.9km Lee Tunnel, which has been operating since 2016 to the main Tideway tunnel.
This will involve breaking down and removing a 1.5 metre thick wall made of concrete and steel between the two tunnels, which sit 66 metres underground.
Connecting the two tunnels will enable flows from the main Tideway tunnel to be transported to Thames Water’s sewage treatment plant at Beckton, once the tunnel is in operation. A new weir wall is being constructed at the treatment works.
The Lee tunnel will be out of commission for two weeks to allow the work to go ahead safely.
Once these two parts have been connected, Tideway will work towards commissioning the sewer. Combined sewage overflows (CSOs) along the River Thames will be connected as part of the measures to protect the river from pollution.
The commissioning will take several months and include testing the sewer in assorted weather conditions both at half and full capacity.
Work began in 2018 for the 25km tunnel that runs from east to west London and is up to 70 metres deep under the capital.
Tideway, the company delivering the tunnel, is financed by Bazalgette Tunnel Limited, which in turn is owned by a consortium of investors. The project is being funded from water bills under the regulatory asset base model that is also being introduced for new nuclear projects.
Full operation is due to commence from 2025 on the scheme.
Ofwat modified Tideway’s licence to change the planned system acceptance date, the point at which the Tideway Tunnel is handed over to Thames Water to operate, from 28 February 2027 to 31 August 2027. This was to reflect delays incurred during the pandemic when work had to vastly alter to adhere to social distancing requirements.