Investigations

This section contains summaries of reports on drinking water
quality incidents and investigations.

Report on drinking water quality incident at:
Lochenkit Water Treatment Works in November 2007

Scottish Water Executive Summary

Lochenkit Water Treatment Works is a small works in Dumfries and Galloway serving Corsock and Kirkpatrick Durham areas. On 15 November, a burst on the inlet main to one of the service reservoirs caused an increase in demand for treated water that caused the clear water tank at the works to drain down. A filter backwash fault at the works, together with several communication and information technology issues amongst operational staff, including some missed water quality alarms, meant that the flow through the treatment works was not restored before the clear water tank had been allowed to drain completely. As service water and backwash water for the works was derived from the clear water tank, it was not possible to restore works operation immediately. Through tankering water and re-zoning the supply to reduce demand, it was possible to re-start filter washing and chemical dosing. Due to the interruption in the treatment process, water quality leaving the works did not meet regulatory quality standards initially, with elevated turbidity and aluminium levels. Scottish Water scoured the system at a number of points in the distribution system in order to remove the non-compliant water as quickly as possible. Scottish Water has proposed a number of actions in response to this incident, including measures to improve awareness and communications amongst operational staff involved with networks and treatment. The possibility of providing a larger service water tank at the works has been considered and discounted, and Scottish Water is now investigating ways of reducing the demand for service water placed on the tank.

DWQR Assessment on the incident

DWQR's assessment of this incident from the comprehensive report provided by Scottish Water is that it involved an unfortunate combination of circumstances, any one of which would probably not have caused an incident in isolation. The poor communications between networks and treatment is of concern, as is the uncertainty surrounding the passing on and receipt of water quality telemetry alarms. The actions proposed by Scottish Water to resolve these issues are to be welcomed, and DWQR has since received confirmation that they are now complete. Scottish Water's actions following the deterioration in treated water quality were appropriate, except that operational staff did not inform the Public Health Team of the event as per procedure. This meant that external stakeholders such as NHS Board and Local Authority were not informed as they should have been. Scottish Water realise that they were deficient in this respect, and this omission is not typical of this operational region. DWQR accepts the findings of the report and the subsequent actions undertaken by Scottish Water.