Thames Water has been fined £250,000 and ordered to pay costs of nearly £7,000 at Reading Crown Court for polluting Chase Brook in Newbury, Berkshire.

The case was brought by the Environment Agency after untreated sewage polluted the whole length, 600m (1,950ft), of the brook in September 2012 which "severely impacted" aquatic wildlife within a 143 acre nature reserve.

The court was told that sewage had flowed from the Broad Layings Sewage Pumping Station emergency overflow pipe after pumps had become blocked.

On 3 September 2012, untreated sewage was seen entering the Chase Brook following a non emergency discharge from the Broad Layings Sewage Pumping Station Emergency Overflow pipe (PSEO). The discharge happened because the pumps at the pumping station had become blocked on 29 August 2012 and Thames Water had failed to act on their alarms system to attend and unblock them.

The failure led to the pumping stations wet well becoming full and caused Thames Water to discharge the sewage through the emergency outfall, rather than carried through the pumping station and sewage network to a treatment plant for proper processing.

Matthew Rice, Environment Agency Environment Officer, said:

"Our officers attended the site after a member of public reported a strong smell of sewage and discoloured water in the Chase Brook. It soon became apparent that the whole length of the Chase Brook (approximately 600 metres) was polluted with sewage."

"Water quality testing revealed that there were high levels of both ammonia and e-coli in the pond and Brook. This combined with low oxygen levels meant that recovery from the incident was a long process. Ammonia is toxic to aquatic organisms and low dissolved oxygen levels starve creatures of oxygen which is of course essential for life”.

Despite the fact that Thames Water had fixed the two pumps which were blocked and had organised a tanker to control flows, the raw sewage had already severely impacted aquatic life in over 600 metres of the Chase Brook.

Since the incident in 2012, Thames Water has made several changes at the Pumping Station - the firm has sealed up the PSEO outfall to the Chase Brook and created a bunded area around the SPS into which the contents of the well will overflow, instead of the Chase Brook. They have also replaced both of the pumps on site with a new type which can deal with blockages.

During sentencing Judge, Mrs Recorder Arbuthnot, said:

“The parties agree that the level of culpability is negligence and with which I agree. With regards to harm I find that this is a Category 3 offence but at the severe end.”

Judgement takes Thames Water £346.7m profit into account

Prosecutor for the Environment Agency, Rooma Horeesorun, said:

“The offence was sentenced following the New Environmental Offences Sentencing Guideline. In addition to the culpability and harm factors the Judge took into account the financial circumstances of the defendant."

The defendant’s profit for the year ending 31 March 2014 was £346.7 million. The message is clear and the level of fines ordered reflects proportionately with the financial circumstances of the defendant”.

Thames Water pleaded guilty and said changes had been made at the site which would prevent sewage flowing in to the brook again.