Thames Water has been fined £4m after untreated sewage escaped from sewers below London into a park and a river.
The court heard how dozens of high-priority alarms would have told staff about the incident but were either missed or ignored, leading to pollution of a popular park, a woodland and the Hogsmill River.
The sewage treatment works at Surbiton could not handle the amount of sewage produced by Storm Imogen in winter 2016, resulting in the incident. The pumps failed, allowing raw effluent to back up along the sewer network and burst out of a manhole, covering an area the size of three football pitches.
An engineer from Thames Water described finding an “avalanche of foul waste” and said the sewage travelled with force across the park and into the river, leaving thick sludge, toilet paper and wet wipes covering the riverbank, grass, shrubs and a wooded area. Enough toilet paper to fill 2,500 refuse bags was recovered from the scene.
An investigation by the Environment Agency discovered that problems at the works began just after midnight on 8 February 2016. The park was closed for a month during clean-up, but toilet paper was still visible in the woods months later.
A power failure triggered alarms after pumps used in sewage treatment stopped working. The malfunction should have been answered remotely by Thames Water staff and an engineer sent immediately to the works, which is unmanned at night. As untreated sewage built up below ground, almost 50 warning alarms were set off during the next five hours – but each was left unchecked.
It was only after several hours that a Thames Water engineer arrived at the treatments and found problems with sewage flow and the power supply. With many pumps out of action, effluent rushed through the network and out above ground, flooding the surrounding area.
Thames Water took 15 hours to report the incident to the Agency – a legal requirement – and it was another 12 hours before the company had a sizeable presence at the scene.
At Aylesbury Crown Court on 26 May, the judge noted Thames Water’s new commitment to improving compliance, but issued a warning that it will be held to this commitment in future cases.
Around 79m litres of sludge escaped across an area of about 6,500 square metres, and it took 30 people per day almost a month to clean up sludge that was ankle-deep in places.
Thames Water pleaded guilty to depositing sewage waste at the ground in February 2016. The court also took into consideration the breach of a permit regarding this incident and discharge incidents into the Hogsmill River in January and October 2018, as well as an incident in September 2019 where sewage sludge was released from Hogsmill Sewage Treatment Works in error.
The Agency charged Thames Water under the Environmental Protection Act 1990 and the Environmental Permitting (England and Wales) Regulations 2016. It was fined £4m and ordered to pay the Agency’s costs of £84,669. This latest conviction brings the total amount of fines given to Thames Water since 2017 to £28.4m for 10 cases of water pollution.
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