On July 10, DSRL informed the Scottish Environment Protection Agency of elevated levels of radioactivity found in a manhole in a redundant offsite drainage system upstream of the site.
Initial samples of sludge were taken from the manhole which indicated elevated levels of alpha activity.
Further analysis of the samples has been completed and the results indicate that the alpha activity is from natural uranium, possibly concentrated through a chemical process used by the Shebster water treatment plant upstream of the manhole.
A now-disconnected pipeline from the water works enabled sludges from treatment at the works to be disposed into the Dounreay drainage system.
This is a phenomenon seen in other areas of the UK where similar material and concentrations of naturally occurring uranium have been found in abandoned pipelines.