The plan involves construction of a 30 kilometre-long tunnel under the river Thames from Hammersmith in the west to Beckton in the east. The seven-metre diameter tunnel will collect sewage overflows from at least 36 discharge points and transport them to Beckton sewage works for treatment. An additional tunnel will link the largest overflow, at Abbey Mills near Stratford, to Beckton.
Approval for a single-tunnel scheme is a victory for the Environment Agency, which considered it the only option which would meet UK obligations under the urban wastewater treatment Directive. A cheaper alternative, with two shorter tunnels in east and west London, has been ruled out.
"The tunnel is the right solution for London and for the environment," Mr Pearson said.
London Mayor Ken Livingstone added: "I am delighted that industry and government are taking the right decision. It will be the biggest investment in London’s sewerage system since Joseph Bazalgette built the system in the 1860s."
The tunnel will prevent the discharge of much of the 52 million cubic metres of untreated sewage that escape from the capital’s overloaded Victorian sewerage network each year. The discharge kills thousands of fish, litters the river with sewage debris and increases health risks to river users.
The scheme has been given the go-ahead in outline only and many details have yet to be decided. The estimated completion date is 2019 or 2020, but the Abbey Mills link will be built first. The Abbey Mills discharge into the Lea is close to the planned Olympic site and fears that overflows in 2012 could affect the Games were a consideration.
The impact on Thames Water customers’ bills will be an average increase of £37, Ofwat said, but it warned that the costs might well rise.