Certainty at last on London’s sewer overflows

Environment Minister Ian Pearson has given the go-ahead for a £2 billion scheme to tackle sewage overflows from London’s sewers. The government has approved the larger ‘single tunnel’ option, but it is unlikely to be completed in time to prevent overflows near the Olympic site during the games in 2012.

The announcement gave the Environment Agency everything it had asked for: a scheme that will ensure compliance with water quality objectives in the Thames tideway and river Lea, prevent sewage litter in central London and reduce health risks to river users.

The plan also alleviates the threat of prosecution from the European Commission over failure to meet the urban wastewater treatment Directive’s requirements (ENDS Report 375, p 5 ).

The scheme involves building a 30-kilometre tunnel under the Thames from Hammersmith in the west to Beckton in the east. Seven metres wide and sloping to a depth of 80 metres at its eastern end, the tunnel will collect sewage overflows from at least 36 discharge points and transport them to the Beckton sewage works. Another tunnel will link the largest overflow, at Abbey Mills near Stratford, to Beckton.

The announcement was received enthusiastically by Agency chief executive Barbara Young and the Mayor of London Ken Livingstone.

"Our world-class city needs a sewerage system that takes it out of the 19th century, brings it up to the standards of other EU and UK cities, and stops raw sewage discharges into the river virtually every week," Barbara Young said. "This option offers the best value for money and the environment. It gives us the greatest flexibility wherever rain falls across London. It will cope with future development and climate change."

The tunnel will prevent the discharge of much of the 52 million cubic metres of raw sewage escaping from the capital’s overloaded Victorian sewerage network each year. The discharges increase pathogen levels, litter the tideway with 10,000 tonnes of sewage debris, and kill an estimated 10,000 adult fish and 100,000 fry.

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 completed earlier.

It is conceivable this link could be finished in time for the London Olympic Games in 2012. The discharge point is close to the Olympic park site and there are fears that sewage releases during the games could prove an embarrassing international exposé of the poor state of London’s sewers.

Ministers said at the press launch that the scheme is required for London and the needs of the Olympics are a lesser consideration.

Ofwat stressed it was "most unlikely" the Abbey Mills link could be in place by 2012. Nevertheless, there may still be hope that this part of the scheme could be finished in time. It falls within the London Borough of Newham where Thames Water already owns the necessary land, suggesting minimal planning delays.

Abbey Mills also accounts for 50% of the total sewage overflows to the river, so there are environmental reasons for the scheme to be prioritised.

Ofwat’s "preliminary estimates" suggest the sewer will cost Thames Water customers an extra £37 per year on average. But a recent report by the water company suggests the increase is likely to be £45.1 Ofwat warned that any extra costs associated with the games should not fall on customers.

The decision to build a single tunnel, rather than an alternative two-tunnel scheme developed by Jacobs Babtie and Ofwat (ENDS Report 379, pp 20-21 ), is a victory for the Agency. The two-tunnel scheme was always a second-best option and the cost savings came at the expense of failing to address key problems.

Thames Water’s latest research into the proposals, sent to the Environment Department (DEFRA) last December, emphasised the single tunnel’s superiority.

The two-tunnel scheme would be £400 million cheaper but tackle only 50% of unsatisfactory storm overflows and reduce discharge volumes by 72%. As a result it would satisfy just 63% of aesthetic and hygiene objectives. The approved scheme will address all unsatisfactory overflows, reduce discharges by 94% and satisfy all aesthetic and hygiene objectives.

Perhaps the two-tunnel scheme’s inability to guarantee to meet short-term dissolved oxygen targets clinched the argument. Slumps in dissolved oxygen levels during summer months are a notorious killer of fish in many estuaries and the effect will worsen as climate change raises water temperatures.

Thames Water predicted the two-tunnel scheme could only guarantee to meet dissolved oxygen targets for 2006. By 2020, when the scheme is likely to be completed, dissolved oxygen levels would already be likely to exceed the target - meaning a continued reliance on oxygen addition and bubbler barges on the tideway.

But neither scheme will guarantee compliance by 2080, when higher temperatures are likely to mean improved treatment standards at sewage works will be needed to protect the river.

The announcement means planning and land acquisition for the tunnel can go ahead. A public inquiry may be needed and the scheme will involve a major expansion of Beckton sewage works. The area is earmarked for regeneration and development as part of the Thames Gateway.