The NRA's Northumbrian region began the investigation last November after swans began to sink on the river Tweed. An unknown pollutant washed the natural oils from their plumage. Solvents were the prime suspects.
Although it appears unrelated to the swan problem, solvent contamination was subsequently discovered by the NRA in the local Fell sandstone aquifer. The water, which was being abstracted by a company from its own borehole, contained up to 35µg/l of tetrachloroethylene, well over the statutory limit of 10µg/l in drinking water.
The aquifer is also used for drinking water supplies but the NRA believes these are not currently at risk of contamination. The aquifer is fragmented and drinking water boreholes are several kilometres away from the polluted zone and up the gradient of groundwater flow.
The NRA is considering prosecution of a local company over the incident. Although it declines to name the firm, its investigations are known to have focussed on Pringles of Scotland, which has been using the solvent for 18 years at its knitwear finishing plant about one kilometre from the contaminated borehole.
The company has been asked to improve its solvent management arrangements. Some months ago, a large spill of tetrachloroethylene occurred at the site, but this alone could not account for the observed contamination.
The firm whose borehole was contaminated has not been named. It was able to switch to an alternative supply, but is likely to press for compensation if the NRA's case succeeds.