Killylour WTW - July 2009

The DWQR's assessment of this incident is that it was caused by the failure of the duty polymer dosing pump which is used to assist the coagulation process. It would appear that there is no provision for auto change over from the duty to the standby pump as this process had to wait for the operator to do this task manually when the problem was eventually investigated. This dosing pump failure resulted in elevated levels of turbidity and aluminium, together with a lower level of chlorine than would otherwise have been the case. Filtered water turbidity alarms were generated but as these had only been set as priority 3 when they were installed in early 2008, they were not passed on to the operator. A request to change the alarm priority from 3 to priority 2 was made in July 2008 but this was not carried out due to human error. As a result, there was a 7 hour delay between the first alarm and the Operations Management Centre passing this on to the operator.

Fortunately the regulatory limits on the quality of the water being supplied were not exceeded.

Since the incident, Scottish Water has changed the priorities on the turbidity alarms to what they should be and has also resolved other issues which were found at the same time with the analogue and digital alarms for aluminium. Scottish Water will also be fitting alarms to the polymer dosing pumps to provide an early warning of future problems with the running of these pumps.

DWQR notes the other actions which Scottish Water has listed in its report regarding the maintenance of telemetry alarms and the planned introduction of revised procedures to control any changes to alarm settings which should reduce the opportunity for human error.