United Utilities (UU) and a contractor have been prosecuted for killing up to 900 fish in a pollution incident in Bolton.

UU and KMI+ pleaded guilty to the offence at Bolton Crown Court on Friday, 24 June.

UU was fined £600,000 with over £19,000 in costs, while KMI + was fined £333,000 with £26,172 in costs.

The court heard how KMI+ was contracted by UU to carry out improvement works at Wayoh water treatment works at Turton Bottoms in December 2013.

As part of the scheme, the contractor emptied and removed a tank which had been used to store sodium hypochlorite in 10% solution. The chemical is used in the water purification process and is also the principle ingredient of household bleach. It is very corrosive and is highly toxic to aquatic organisms.

The court heard that by 04 December 2013, the majority of the tanks contents had been removed but up to 300 litres of the chemical was left in the bottom and needed to be emptied.

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Instead of pumping or siphoning the remaining liquid out, a hosepipe was placed into the tank to dilute the sodium hypochlorite with water, letting it overflow into a bunded area and leaving the hosepipe running unattended overnight for 15 hours. This was carried out without any risk assessment or method statement and the companies were not in agreement on what they understood had been agreed prior to the removal taking place.

In addition, neither company had surveyed the drainage adequately and did not realise there were faults in the drainage system, which allowed the diluted toxic chemical to enter the surface water drainage system and discharge to Bradshaw Brook, a trout spawning ground.

The Environment Agency (EA) was alerted two days later by a member of the public who discovered dead fish floating in a 1.7km stretch of water. The pollution was so bad nearly all aquatic organisms, including fish, shrimp and earthworms were killed. Up to 900 dead fish were recovered.

By the end of June 2014, the brook recovered enough for restocking to take place, which UU paid for.

Gordon Whitaker, Environment Manager of the EA, said: "This was a serious and avoidable pollution incident caused by the negligence of both parties. It took several months for Bradshaw Brook to return to a healthy state and even then it was necessary to assist this process by restocking fish in the affected stretch. This case should bring home the message to all company directors and shareholders that environmental offences are taken seriously both by the regulators and the courts."

(LM/CD)