Government considers Thames sewage tunnel options

The Government is considering whether or not to build the Thames Tideway tunnel to protect the river from wet weather discharges of sewerage overflows.

The River Thames suffers considerably from untreated sewage overflowing from its ageing underground networks. Between 50 and 60 incidences occur annually amounting to an estimated 20 million cubic metres of untreated sewage entering the river.

This was brought into sharp focus last summer when 600,000 tonnes of sewage was forced into the water in a single day killing thousands of fish (see related story).

For many years, the Environment Agency and others have argued that the situation could be resolved by building the Thames Tideway – an interceptor tunnel 35km long which would run beneath the river from Hammersmith in west London, capture the effluent from the combined sewer overflows, and convey the discharges to the Crossness sewage works in east London.

Ofwat excluded the tunnel from its final price determinations meaning that Thames Water could not afford to build it despite being allowed to raise prices by 24% over the investment period (see related story).

Now, a new report by the Thames Tideway Strategic Study has been delivered to Government recommending building the tunnel as the best solution out of the options considered.

Given that the tunnel is likely to take at least 15 years to build, the report also considers extending the range of smaller scale interim measures to provide short-term alleviation much sooner.

Environment Minister Elliot Morley said the issue of overflows had long been of concern to the Government.

“I am aware that the outcome of our deliberations is anticipated eagerly, particularly given recent speculation about the impact of intermittent sewage discharges on the site of the London 2012 Olympics,” he said. “We are committed to action. The only issue is what course of action will be the most effective.”

The latest report from the Strategic Steering Group finds that the tunnel had the highest net benefits in their cost benefit analysis of the available options.

The group calculated the cost of building at £1.5 billion with an annual operating cost of £3.2 million. This translates into an average annual sewerage bill rise of between £40 and £45 over the level it would otherwise reach were the Tideway project not to be implemented. The majority of the increase would take effect over the expected construction period.

It would take the average annual bill in the area to just over £300.

By David Hopkins

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