A penstock gate which was jammed and a failed bypass which blocked a sewer has cost water supplier Thames Water £169,045 in costs after it polluted the River Crane and the Duke of Northumberland’s River in London. Isleworth crown court chose to fine the company £75,000 and ordered it to pay £94,045 in court costs. The case was brought to light by the Environment Agency after Thames Water breached its Environmental Permit by allowing sewage which was untreated to enter the River Crane at Cranford Bridge for two days in October 2011. The sewage came from the trunk foul sewer at Cranford Bridge, Hounslow.
Untreated sewage entered the River Crane through a storm overflow, which has been put in place to prevent properties flooding with sewage during a period of heavy rainfall. The sewer itself was blocked by a jammed penstock gate and a failed bypass.
Ruth Shaw, a senior environment officer said about the incident:
“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, untreated sewage discharged for over 20 hours over the course of two days and sadly all fish and invertebrate life in 15km of river downstream was killed.”
Isleworth Crown Court heard that the incident occurred when Thames Water commissioned contractors to carry out a survey of the Brent Valley Main Line Sewer. A penstock gate was closed at Cranford Bridge to reduce flows and enable the safe working of the survey crew in the downstream sewer. Once the work was complete, the team tried to raise the penstock gate but a ‘sharp crack’ was heard and it broke. The broken gate combined with the failure of the bypass channel resulted in discharges of untreated sewage via the storm overflow into the review.
From October 30, following the incident there were 44 public reports of dead fish in the River Crane. Surveys and fish carcass counts were carried out over the following weeks and it was estimated that more than 10,000 fish were killed, 17 species in total. The Environment Agency has recommended a fish restocking strategy to the Crane Valley partnership which will aim to restock the fish in the river over a number of years. In 2012, Thames Water funded the introduction 0f 50000 yearling fish and has also donated £400,000 to the Crane Valley Partnership for projects to enhance the river.