Environmental Protection Agency audit report on Incident at Leixlip Water Treatment Plant

Date released: Oct 30 2019

The EPA’s report of the audit undertaken at Leixlip Water Treatment Plant on Thursday 24th October 2019 is now available on the EPA website.

The purpose of the audit was to establish the full facts of the incident which occurred on Monday 21st October, which resulted in a boil water notice being put in place on Tuesday 22nd October, affecting over 600,000 customers. The audit also assessed the corrective actions taken by Irish Water and Fingal County Council, verified the performance of Leixlip Water Treatment Plant and provided evidence to facilitate the lifting of the boil water notice. The audit also reviewed the recommendations of the EPA’s previous audit of 22nd March 2019 and assessed the implementation of the actions taken to address those recommendations.

The main findings of the audit were:

  • The primary cause of the incident was a blockage in one of the treatment processes, the alum (coagulant) dosing line, which occurred at Leixlip Water Treatment Plant on 21st October 2019 giving rise to elevated turbidity levels in treated water.  This compromised the integrity of the treatment barriers for the removal of Cryptosporidium/Giardia creating a significant risk to the safety of the water supply.
  • There was then a failure to respond to multiple process alarms that activated at the plant as a result of the elevated turbidity levels in the water. 
  • That Irish Water and Fingal County Council had failed to implement the main recommendations of the EPA’s previous audit of Leixlip Water Treatment Plant in March 2019.  In particular there was a failure to install automatic shutdown when critical plant alarms are not responded to, as previously recommended, which was a contributory factor to the incident. Since the incident, Irish Water and Fingal County Council have implemented automatic plant shutdown on high turbidity levels, and if there is a failure to respond to a turbidity alarm within 15 minutes.
  • Whilst the Leixlip Water Treatment plant is now operating satisfactorily, the level of treatment at this plant is not sufficient to manage the risk posed by the River Liffey source water. To address this, the EPA has recommended that Irish Water consider installing ultraviolet disinfection to further ensure drinking water quality and the protection of public health.

The audit report includes recommendations which should be addressed by Irish Water as a matter of priority.  Irish Water is required to submit a report to the EPA no later than 30th November 2019, detailing how it has addressed the audit recommendations.

View the full report online here.