Blairnamarrow WTW Overdosing of Treatment Chemical Oct 2009 | |
Summary of Incident
On Monday 19 October, the sodium carbonate dosing equipment at Blairnamarrow WTW began to malfunction and overdose the chemical, which is used to correct the pH of the water. As a consequence, the pH of the water began to rise, but this did not trigger a treated water pH alarm as this alarm signal had been suppressed some months previously. The changing water quality did affect the chlorine residual, and an operator attended site some four hours after the overdosing began, but he simply adjusted the chlorine dose and failed to spot the root cause of the problem. Further alarms from the site were not acted upon.
On 20 October, during a routine visit to the site, the operator discovered the problem with the sodium carbonate dosing and put measures in place to get this fixed later in the day. No action was taken regarding the high pH water already in supply. By this stage, consumers were beginning to telephone Scottish Water with concerns about an unusual taste and feel. Early that afternoon, an electrician attended the site to repair the sodium carbonate dosing. He left site thinking the repair had been successful, but actually the fault was intermittent and the pump began overdosing again that evening, resulting in a number of calls to Scottish Water from worried consumers in Tomintoul. Consumers reported that the water had a strange smell and feel, and some reported that bathing in the water caused skin irritation. Late that evening, the true extent of the issue was realised, and attempts were made to flush the high-pH water out of the system.
The following morning, the operator attended Blairnamarrow WTW and saw that the sodium carbonate was again being overdosed. Urgent arrangements were made to repair the pump properly, and the full scale of the problem was communicated to Public Health staff in Scottish Water and health professionals at NHS Grampian, who requested a “Do not Use” notice be placed on the supply in view of the high pH values.
The “Do Not Use” notice was communicated to residents and alternative supplies were delivered. At this stage the problem was escalated to senior management within Scottish Water, who implemented the appropriate recovery plan. Flushing continued through the day in order to remove the high-pH from the supply network. By the morning of Thursday 22 October, pH levels were restored to normal and NHS Grampian were sufficiently reassured to enable the lifting of the restriction on supply.
DWQR Assessment of the Cause of the Incident
The root cause of this serious incident was the malfunction of the sodium bicarbonate dosing pump on an intermittent basis. The extent and severity of the incident was compounded by a number of further issues, namely:
· A very basic standard of dosing system, with a fixed dose of sodium carbonate being applied to the water and no feedback mechanism to control this according to the pH being measured;
· The suppression of the pH alarm at the treatment works that prevented the effect of the overdosing on water quality to be identified and responded to appropriately;
· The absence of a “day tank” at the treatment works that could have limited the amount of sodium carbonate available to dose into the supply.
This situation is completely unacceptable at a modern treatment works, regardless of size and location. DWQR is highly critical of Scottish Water for allowing the circumstances that lead to the incident to have occurred and has submitted a report to the Procurator Fiscal outlining a case for prosecution for the offence of supplying water unfit for human consumption under Section 76C of the Water (Scotland) Act 1980.
DWQR Assessment of Actions Taken by Scottish Water
Actions for Recovery
Once the problem with the pump was discovered, Scottish Water’s operational response was delayed and inadequate. The following specific deficiencies have been identified by DWQR:
· The failure of treatment works staff who attended the site to initially identify the problem and respond to it promptly;
· The failure of operational staff to make an effective repair to the faulty pump;
· Once the problem with the sodium carbonate pump was noticed the potential impact on consumers due to the water already in the service reservoir and distribution system was not appreciated and no action was taken to protect them;
· The “Do Not Use” notice was not issued to consumers until 45 hours after the overdosing had commenced, meaning that consumers could still have been consuming the water until this time;
Once a full appreciation of the severity of the incident was realised, Scottish Water implemented a full incident response, albeit two days late. DWQR considers that actions taken by Scottish Water from this point on were appropriate.
Reporting and Notification
DWQR considers that there were inadequacies associated with Scottish Water’s reporting of the incident internally and to external bodies:
· Escalation of the incident to senior staff within Scottish Water was unacceptably delayed, meaning that the wider understanding of the incident and appreciation of its scale only occurred two days after the overdosing commenced;
· Notification to the CPHM and Moray Council only took place two days after the overdosing started, meaning that timely advice to protect consumers could not be given.
Actions Taken by Scottish Water to Prevent a Recurrence
Scottish Water carried out a full investigation in response to this incident and has identified 30 actions to prevent a recurrence. These have all been completed. Tomintoul is now supplied by a completely new membrane treatment works at Blairnamarrow.
Action Taken by DWQR
Having investigated the incident, DWQR considered that there was clear evidence that an offence had been committed. A report was submitted to the Procurator Fiscal in February 2010 outlining a case for prosecution for the offence of supplying water unfit for human consumption under Section 76C of the Water (Scotland) Act 1980.
The case was heard at Elgin Sheriff Court on 20 January 2012.