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Statement from Mayo Co Council re Lough Mask Water Supply

Mayo County Council is satisfied that the drinking water on the Lough Mask Water Supply Scheme is entirely safe to drink.

Up to 2009, the allowable level for Trihalomethane parameter (THMs) in drinking water was 150 microgrammes per litre and Mayo Co Council has complied with that standard at all times.

Since 2009, the standard has been changed so that the upper limit for THMs is now 100 microgrammes per litre.

In order to reach that standard certain works have to be put in place by Mayo Co Council.

The Council has been engaged in the complex approval process with the Department of Environment Community and Local Government (DECLG) to undertake the works to upgrade the capacity of the water treatment plant to enable it to comply with the new standards.

The Environmental Protection Agency (EPA) issued Mayo Co Council with a deadline of May 2011 to have the upgrade works completed.

However, approval for the works was not received from the DECLG until September 2011 - after the EPA May 2011 deadline for the completion of the required works had been set .

Hence the EPA brought a prosecution for a technical breach of the EPA direction against Mayo Co Council. 

The Council could not comply with the deadline because, without approval from the Department, it was not in a position to move the project forward.

On receipt of the approval Mayo County Council commenced the public procurement process and expects  to be in a position to  commence works in the coming months.

A useful reference is the recently published Report by the EPA on “The Provision and Quality of Drinking Water in Ireland” for 2010.

  • The Report describes THMs as the by-product of the chlorination process which is used to disinfect drinking water. 
  • THMs, according to the report, are regarded as “undesirable in drinking water and there is an uncertain, small and long term risk associated with elevated THMs”.  
  • However the EPA also stresses that “care should be taken not to reduce chlorination in such a way as to compromise the microbial safety of drinking water.”
  • In addition the EPA report asserts that “evidence for a causal association between cancer and exposure to chlorination by-products is limited, and any such association is unlikely to be strong”.

In providing drinking water from the Lough Mask Scheme, Mayo Co Council agrees with the EPA that “A balance should be struck between an uncertain, small, and long term risk associated with elevated THMs and the significant, large, immediate and serious risk associated with inadequate chlorination”.

Mayo County Council is committed to upgrading the Lough Mask Water Treatment Plant as quickly as possible and is satisfied that, in the interim, the quality of the drinking water is entirely safe.      



Posted: 13/02/2012
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