Problems at a Southern Water sewage treatment works in 2006 led to the company being fined £22,000 and ordered to pay £8,900 costs on 2 January by Sevenoaks magistrates court.
The company pleaded guilty to three offences of failing to meet the standards prescribed in its discharge consent for ammonia and biochemical oxygen demand, contrary to section 85(6) of the Water Resources Act 1991. It also pleaded guilty to causing sewage to enter controlled waters, contrary to section 85 (1) of the Act.
The court heard that on 18 June 2006, the Environment Agency received a report that dead fish were in the river Grom, at Groombridge, near Tunbridge Wells, and that the water was cloudy.
Southern Water later informed the Agency that its Tunbridge Wells South sewage treatment works had discharged poorly treated effluent the day before. A breakdown of the site’s aeration equipment had caused the incident. The company could not account for why it had failed to inform the Agency immediately.
The effluent had a major impact on the river’s ecology for two kilometres to the point where it flowed into the river Medway. About 500 fish were killed, alongside more pollution-tolerant river life. Water quality was affected for 14km.
It was not until five days after the initial discharge that Southern managed to restore the plant to full operation. This led to further breaches of its discharge consent on 19 and 20 June.
The plant is permitted to discharge effluent with a biochemical oxygen demand (BOD) of 20 milligrams per litre and ammonia levels up to 10mg/l.
A sample on 19 June revealed an ammonia level of 34.4mg/l and BOD of 92.5mg/l, almost five times the consented amount. A sample taken the next day recorded ammonia at 28mg/l and a BOD of 34mg/l.
A further sample taken by Southern Water on 31 July narrowly exceeded the permitted level.
The court said Southern had failed to inform the Agency of the incident and deal with it promptly. The site also lacked back-up systems.
The company was fined £16,000 for the 17 June incident and £3,000 for each of its failures on 19 and 20 June. No separate penalty was imposed for the 31 July offence.
After the case, Agency officer Ben Tragett said: "Southern Water should have put systems in place to ensure the incident was resolved immediately and that any temporary equipment did not also fail. Had the Environment Agency been told of the aeration equipment failure, systems could have been put into place so that a totally preventable long-term pollution of the river would not have taken place."
Southern Water told the court that it had pleaded guilty as soon as possible and had spent more than £2.3 million in dealing with the incident and improving the Tunbridge Wells South plant. Failing to inform the Agency was an oversight and not deliberate, it added.