One of the incidents on the Dee occurred last July, when extensive foaming was spotted downstream of Welsh Water's Queensferry sewage works. Effluent samples taken by the Environment Agency showed that the discharge contained ammonia and BOD levels above consent limits.
The company appeared before Mold magistrates on 13 June to plead guilty to two charges of causing sewage effluent to be discharged outside the terms of its consent, contrary to section 85(6) of the Water Resources Act 1991.
The court heard that the breaches occurred while repairs were being carried out on the works' aeration lanes. Three of the four lanes had been closed, causing an overload. The firm was fined £10,000 on each charge, with costs of £475.
Welsh Water's second conviction occurred at Northwich magistrates court on 17 June after it pleaded guilty to breaching the discharge consent for its Chester sewage works, contrary to section 85(6) of the 1991 Act.
Agency staff discovered the breach last September while the works was undergoing repairs. Samples of effluent contained 40 times the permitted level of suspended solids. Welsh Water was fined £4,000 and ordered to pay costs of £240.
The company pleaded guilty to causing polluting matter to enter the Herrings Stream, contrary to section 85(1) of the 1991 Act. The court heard that a member of the public warned the Agency after spotting dead fish in the stream at Hickstead. An inspector traced the pollution to Southern Water's Hurstpierpoint pumping station.
The pumping station is unstaffed and operated from an office in Brighton. Control room staff maintained that they had been alerted to a problem with the plant at 10.30am and arrived on site by 12.00am, but this was inconsistent with the scale and timing of the damage.
Dead fish were spotted three kilometres downstream of the works more than two hours before the company said the problem arose. A four-kilometre stretch of the stream was affected, and ammonia concentrations downstream of the pumping station were four times those lethal to fish. Southern Water was fined £5,000 with costs of £580.
Appearing before Flax Bourton magistrates, Wessex pleaded guilty to a charge of polluting controlled waters under section 85(1) of the 1991 Act. It was fined £2,500, with £250 costs.