Samples of sludge were taken from the manhole during site characterisation work which indicated elevated levels of alpha activity .
We have agreed with SEPA that we will obtain further samples and subject them to detailed analysis to confirm the level and source of the radioactivity. The results are expected mid-August.
Until the result of the analysis is received, DSRL does not wish to speculate on what the activity is and where it came from, although we are investigating the possibility that the activity in the manhole may have come from sludges produced at the Shebster water treatment plant upstream of the manhole.
There was a pipeline from the water works that enabled sludges from treatment at the works to be disposed into the Dounreay drainage system, which was disconnected in 2011.
DSRL is keeping SEPA informed, and will report on the findings once all the analysis has been complete.