Berkshire-based Costain was under contract to Welsh Water to improve the sewerage system in the Llynfi Valley, near Bridgend. The company was installing a large storm water storage tank in September 1999 when a member of the public reported a fish kill in the river Llynfi.
An Environment Agency investigation found that all fish had been killed for at least 1.6 kilometres downstream of a discharge of cement slurry at Nantyffllon. The final death toll was 4,059 trout and 69 salmon.
Costain appeared before Bridgend magistrates on 16 November to plead guilty to causing polluting matter to enter controlled waters, contrary to section 85(1) of the Water Resources Act 1991, and causing water to be poisonous or injurious to fish, contrary to section 4 of the Salmon and Freshwater Fisheries Act 1975.
In mitigation, Costain said it had carried out a £30,000 emergency plan under Agency supervision to restore the river. The programme involved removing the top layer of the riverbed and landscaping the underlying material to recreate river features.
Costain was fined £13,000 for the offence under the 1991 Act and £3,000 under the 1975 Act. It was also ordered to pay costs of £4,930, bringing Costain's total bill to over £50,000.
The court heard that the incident occurred in October 1999 on a former abattoir site which the company had acquired for development. The site had numerous tanks and drums containing materials and was not secure. Oil escaped from one of the tanks and spread through a derelict building and entered the stream, causing damage which cost £30,000 to clean up.
Although the damage was probably caused by vandals - police caught youths playing on the site - the site owners were held to be liable. Beazer was fined and ordered to pay prosecution costs of £1,510.