The incident occurred in February 1991 as the company, a subsidiary of the Austrian firm Fritz Egger, was constructing a sump to prevent contaminated surface water from entering the river Tyne from its site at Hexham.
A visiting National Rivers Authority (NRA) officer noticed a brown patch in the river 100 metres in length. Investigations revealed that the sump had filled with run-off from the construction site and the company's staff had pumped this into the river. Formal samples taken by the NRA showed that the discharge had a significant biochemical oxygen demand (BOD).
The plant is said to have a poor environmental reputation locally due to emissions and fires. This may have been a factor behind its decision to avoid the local magistrates court and take the case to the Crown Court in Newcastle.
Egger pleaded not guilty to a charge brought under section 85 of the Water Resources Act 1991. Its defence was that the discharge had had no appreciable effect on the river, and was not polluting matter in the sense of the Act. The NRA argued that the BOD of the discharge would have reduced oxygen levels in the river and could have had a harmful effect, even though no fish kill of other apparent damage had resulted.
The company also maintained that its consent for cooling and surface water permitted the discharge, although it did not specifically mention BOD. In contrast, the NRA argued that the discharge was illegal in the absence of a specific BOD limit.
The company was found guilty and fined £20,000, although the judge acknowledged that the company had not deliberately flouted the law and had a good record. Egger was also ordered to pay costs of £9,500.
In summing up, the judge said it was of the "very greatest importance to preserve, so far as is possible, the standards of purity of all rivers and especially rivers such as the Tyne". The river at Hexham is class 1A and noted for its salmon fishery.