Burncrooks WTW - January 2009

This incident involved two periods when water leaving Burncrooks Treatment Works exceeded the PCV for Aluminium. Although the exceedences were separated by approximately 12 hours, they were both caused by a blockage in the lime dosing plant, which meant that the pH of the water fell below the optimum range for the coagulation process to be effective. Consequently, aluminium levels rose above the PCV, peaking at 334 microgrammes per litre in the first period, and 500 microgrammes per litre in the second.

The incident was exacerbated by the failure of the operator to respond appropriately to the initial exceedence. The lime dosing was operating on a temporary system due to construction works. This was compounded by the aluminium alarm being set at the PCV value of 200 mg/l giving no time to respond before failure occurred, and fact that the alarm was not connected to Scottish Water’s WMS central telemetry system. These issues have been rectified and the operators’ actions have been discussed with him. DWQR accepts Scottish Water’s response to this incident as being appropriate.