Thames Water notified the National Rivers Authority (NRA) on 3 November last year of a serious leak of sewage sludge from the digester at its Brentwood sewage works. Some of the sludge entered the river Ingrebourne and prompted complaints from the public as dead fish floated downstream.
The NRA brought a charge of polluting controlled waters under section 85(3)(a) of the Water Resources Act 1991. The company pleaded guilty before a stipendiary magistrate in Romford on 11 April, and was fined £7,500 with costs of £440.
Thames Water blamed the fault on contractors who had used a coupling which was unsuitable for use in pressurised applications such as a digester. However, an NRA spokesman said roadside ditches on the site drained into the river and had contributed to the incident.
The conviction was the firm's second this year. In January, it was fined £5,000, with costs of £450, after a telemetry failure at its Beehive pumping station, Welwyn Garden City, allowed sewage to overflow into the Hatfield Hyde brook.