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Thames Tunnel sewer costs rise up to £2bn

Thames Water said this week that the cost of the Thames Tunnel mega-sewer has risen from £2bn to between £3.6bn and £4.3bn.

Shorter route

Thames Water has confirmed its preferred option is now for a shorter tunnel route linking up with the Lee Tunnel. This is the cheapest option at £3.6bn.

The original plan was to take it all the way to Beckton Sewage Treatment Works.

The water company’s intention to cut the length of the tunnel by diverting it to connect with the Lee Tunnel at Abbey Mills Pumping Station was revealed by NCE last year (NCE 12 November 2009).

The plans have now been made public at the start of a 14 week public consultation into the scheme.

The original cost estimate for the tunnel has been revised following extensive studies, said head of London Tideway Tunnels Phil Stride.

“We’ve had hundreds of people working on it, which comes at a cost in itself”

Thames water spokesman

The original £2bn figure was reached in 2006 by a desktop study worked on by “a handful of people”, he said, but more detailed research, ground investigations and site surveys have led to the revised figure. “It’s much more detailed. We’ve had hundreds of people working on it, which comes at a cost in itself,” said a Thames Water spokesman.

Stride said the original study was limited by the amount that could be spent on it given that the project had not been approved by the government at that time. “The accuracy of any estimate is dependent on the time and effort that goes into it,” he said.

Stride also said he does not anticipate the project going over budget.”The £3.6bn figure is a robust estimate that we’re confident the scheme can be delivered for.”

The 32km long tunnel route from Hammersmith to Beckton that was originally expected to cost £2bn has now been revised to £4.3bn. Thames Water said it now prefers a 22km route that would cost £700M less at £3.6bn and create 17% less carbon emissions.

This route follows the River Thames from west London to Limehouse before running northeast beneath Tower Hamlets and Newham, to Abbey Mills Pumping Station near Stratford.

Here it would connect with the £635M Lee Tunnel, which is currently under construction.

Deepest section “omitted”

Stride said this route is not only more cost and carbon effective but also easier to construct, as it would omit the deepest section of the original route, up to 75m deep in chalk.

“This is the higher risk area of the tunnelling,” said Stride. The new preferred route would see Thames Water customers paying £65 a year more by 2018.

The originally preferred option follows the river’s course much more closely, passing below land at the Greenwich peninsula before continuing beneath the River Thames toward Beckton Sewage Treatment Works in the east. This route was recommended in a December 2006 report to the government.

A Rotherhithe route is a third option, passing below the Rotherhithe peninsula before following the same path to Beckton as the River Thames option. This route sits between the other two in price and length.

The project is intended to reduce the amount of untreated sewage that is released into the River Thames through combined sewer overflows (CSOs) during storms.

Thames Water said that although the three routes would capture different amounts of sewage from CSOs, all three options would be connected to the 34 CSOs deemed unsatisfactory by the Environment Agency.

All three would also deliver an overall improvement in river water quality sufficient to meet the Agency’s project objectives, it said.

Value drive

Environment secretary Caroline Spelman gave her support to the project last week, but said she will push for value for money (News last week).

“I will ensure that Defra and Ofwat continue to scrutinise the costs and options,” she said.

The scheme also has yet to win over local authorities on the route.

London Councils transport and environment committee chairman Catherine West said that local authorities do not have enough say in the project.

“It is wrong for the government to expect Londoners to foot the bill for this very expensive project and then refer the planning decision to a national commission,” she said.

The decision about whether to grant planning permission to the scheme will fall to whatever replaces the Infrastructure Planning Commission.

  • NCE is publishing a project London Tideway Tunnels report later this month.

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