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Green light imminent for £1.6bn London sewer tunnel

ENVIRONMENT MINISTER Ian Pearson is likely to back scaled back plans to build a new £1.6bn London sewer tunnel running under the River Thames, sources close to the project said this week.

Two options for building the Thames Tideway tunnel, a vast sewer are being worked up by Thames Water to stop the 20Mm 3 of foul water that spews into the Thames each year.

The most expensive is to build a 7.2m diameter, 34km tunnel between Hammersmith, west London and Beckton to the east.

More likely is a phased approach which would see two larger diameter but shorter tunnels built. One would take storm water from Hammersmith, west London to Battersea, south London with treatment or storage in Battersea. The second would carry water from Abbey Mills in Stratford east London south to the river at Beckton.

Thames Water's sewage treatment works at Beckton is already being upgraded to provide extra capacity.

This approach will effectively deliver two thirds of the scheme and eliminate the worst of the storm water overflows.

A source close to the project said: 'Thames Water is getting strong signals from the minister that he wants [the project] and that it ought to start with the Abbey Mills-Beckton link.

This offers the opportunity to greatly improve water quality in the rivers Lea and Thames in time for the 2012 Olympic Games, the source added.

A Department for the Environment Food & Rural Affairs (DEFRA) spokeswoman said that plan to improve water quality in time for the Games was politically attractive.

She added that the UK could be prosecuted under European law if it fails to prevent foul water discharges.

'We face infraction proceedings from the European Union if we don't comply with the directives. There has to be a solution to the discharge problem, ' she said.

Another project insider added that there should be no significant planning obstacles to clear before starting work, although detailed design and procurement of tunnel boring machines (TBMs) for the job would take at least 12 months. 'If the minister wants the scheme in time for the Olympics a swift decision is needed, ' he said.

A Thames Water funded steering group submitted the case for the Tideway tunnel to DEFRA in July after four years of study. It was later asked to develop a phased approach.

The Abbey Mills-Beckton tunnel could be delivered ahead of the Hammersmith-Battersea tunnel, and would cost between £200M and £300M.

Thames Water is due to submit the options to Environment Secretary Ian Pearson on 31 December. He is expected to consult on the proposals for up to three months, and make an announcement in next spring.

To ensure gravity drainage, the tunnel would have to run at a gradient beneath the Thames, reaching a depth of 80m at Beckton.

'At 80m you're close to the limits of what's possible with TBMs and diaphragm walling, ' said the insider. 'The TBMs will be operating under 8bar of water pressure. It's likely tunnelling will have to be done with slurry machines and compressed air, ' he added.

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