Equivalent of 400 Olympic-sized swimming pools of sewage spilled into Thames on each of two days

Image above: Raw sewage in the River Thames at Strand on the Green

Our bit of Thames was mentioned in a parliamentary select committee report, and not in a good way. The Environmental Audit Committee has just published the Fourth report of Session 2021-22 on water quality in rivers. It revealed a staggering fact about the amount of raw sewage released into the Thames.

The committee heard from Peter Hammond, retired Professor of Computational Biology of University College, London that on each of two days in October 2020 Mogden wastewater treatment works in Isleworth “spilled 1 billion litres plus, which is the equivalent of 400 Olympic-sized swimming pools of sewage each day.”

Sarah Bentley, chief executive of Thames Water, sought to set the events at Mogden in context. She explained that the works had been ‘inundated’: 3 and 4 October 2020 “were the wettest days on record and we struggled to treat both the permitted amount, but also just struggled to treat the sewage. On that day there was enough rainfall to fill Loch Ness.

“In order to deal with that at Mogden, we have eight storm tanks at the moment that currently hold about 40 Olympic-sized swimming pools of storm water contaminated with sewage. We would have needed either another treatment works the same size as Mogden treating another 1 billion litres or we would have needed 150 more storm tanks” she said.

Sewage regularly discharged into rivers

The sewerage networks operated by water companies frequently discharge untreated and partially-treated sewage into streams and rivers. Without these overflows, when the system is overloaded, when for instance there is heavy rain, the alternative could be sewage backing up into domestic and commercial properties.

Overflows are supposed to be used infrequently, in exceptional circumstances, but the report says: ‘their use nevertheless appears to be increasingly routine.’

The number of sewage spills from overflows officially recorded by water companies and reported to the Environment Agency went up by nearly 30% in just one year, (27% between 2019 and 2020) and citizen science analysis of water company data suggests that the true number of sewer overflow discharges may be considerably higher than those reported by the water companies.

The systems are not keeping pace with the number of people they serve.

‘Chemical cocktail’ of sewage, slurry and plastic

The public has recently become much more aware of the issue as groups such as Surfers Against Sewage have done their level best to bring it to their attention and the passage of the Environmental bill through parliament has highlighted the extent of the problem.

READ ALSO: Chiswick’s two MPs both voted against dumping untreated sewage in rivers

Despite the recent publicity, the revelation of the volume of sewage discharged into the Thames made in the report is staggering.

The report describes a ‘chemical cocktail’ of sewage, slurry and plastic polluting English rivers, putting public health and nature at risk. They conclude the problem is a result of chronic underinvestment and multiple failures in monitoring, government and enforcement.

The government has said it welcomes this report and will be reviewing its recommendations carefully before responding later this year.

Read more stories on The Chiswick Calendar

See also: Chiswick’s Tidefest organiser Martin Salter instrumental in forcing Government’s U turn on environment bill

See also: Raw sewage in the Thames is “unacceptable”

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