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Untreated sewage discharge costs Thames Water nearly £170K

A jammed penstock gate and failed bypass that blocked a sewer has cost Thames Water £169,045 for polluting the River Crane and the Duke of Northumberland's River in west London. Isleworth Crown Court fined the company £75,000 and ordered it to pay £94,045 in costs.

Around 10,000 coarse fish were killed as a result of the incidentAround 10,000 coarse fish were killed as a result of the incident

The Environment Agency (EA) brought the case after Thames Water breached its Environmental Permit by allowing untreated sewage to enter the River Crane at Cranford Bridge in October 2011.Three discharges of untreated sewage occurred between October 29 and 31, 2011 from the 2m diameter trunk foul sewer at Cranford Bridge in Hounslow.

The discharge resulted from a jammed penstock gate and failed bypass that blocked the sewer. Untreated sewage entered the River Crane through a storm overflow, which is there to prevent properties flooding with sewage during heavy rainfall.

EA senior environment officer Ruth Shaw said: “Our officers attended the site after it became apparent that the incident was very serious. Thames Water’s attempts to raise the penstock and minimise the environmental impact had failed. Raw sewage discharged for 20 hours over the course of two days and sadly all fish and invertebrate life in 15km of river downstream was killed.” 

The Court heard Thames Water had commissioned contractors to carry out a survey of the Brent Valley Main Line Sewer. A five-tonne penstock gate was closed at Cranford Bridge to reduce flows and enable the safe working of the survey crew in the downstream trunk sewer. 

When the survey work was complete, Thames Water’s trunk sewer team tried to raise the penstock but a “sharp crack” was heard and it could not be raised. The lifting mechanism (drive shaft) of the penstock broke when it was being reopened at 4am on October 29, causing it to become jammed in the closed position. This combined with the failure of the bypass channel resulted in discharges of untreated sewage via the storm overflow into the River Crane.

From October 30, there were 44 public reports of dead fish in the River Crane and Duke of Northumberland’s River downstream of Cranford Bridge. Invertebrate surveys and fish carcass counts over the following days and weeks indicated a total loss of all species. It was estimated that more than 10,000 coarse fish were killed, 17 species in total including eel, barbell, pike, dace, chub and roach.

Sewage also backed-up several kilometres in the Bath Road Sewer upstream of Cranford Bridge, causing the basement of the Sheraton Heathrow Hotel to flood with sewage, and up to the Central Terminal Area pumping station at Heathrow Airport. 

Since the incident, the Environment Agency has recommended a fish restocking strategy to the Crane Valley Partnership (CVP) that aims to reintroduce fish over a number of years. Thames Water funded the introduction of 5,000 yearling fish in December 2012 and has also given £400,000 to the Crane Valley Partnership for projects to enhance the River Crane. 

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