Appearing before Newcastle-under-Lyme magistrates on 7 May, Johnson Matthey pleaded guilty to causing polluting matter to enter the River Blithe, contrary to section 85(1) of the Water Resources Act 1991. It was fined £7,500 and ordered to pay £2,583 costs.
The incident came to light last October when the Environment Agency received a report of dead fish on a tributary of the river. An officer took a water sample and found high levels of alkalinity.
The next day, Agency officers traced the pollution to the Meir Brook, and found 3,977 dead fish. No live fish were found along a three-kilometre stretch of the brook.
The pollution was traced back to a surface drain serving the former caustic soda storage area at Johnson Matthey's factory on the Meir Park industrial estate.
The factory was part of the company's colours and coatings division. It was closed in April 2003 as part of a rationalisation programme.
Agency investigations revealed that the site was being decommissioned at the time of the pollution. The caustic soda storage tank was emptied in June and its contents taken away for disposal. In October, it contained only caustic soda washings from the pipework leading to it.
The tank was subsequently sold and removed from the site on 21 October after the washings were transferred to a leak-proof bund. Later that day, though, a Johnson Matthey employee opened a valve on the bund to drain the water, allowing it to pass into a surface sewer and then into the Blithe.
In mitigation, Johnson Matthey said that the pollution was an accident, and as soon as it was alerted to the problem it had purified the sewage system with 5,000 litres of clean water.