The reservoirs at Stillorgan store treated drinking water from water treatment plants at Vartry in County Wicklow and Ballymore Eustace in County Kildare. These reservoirs are open to the environment which is not in accordance with current best practice as it presents quality risks to the water supply. These risks are being managed, however, they will need to be eliminated through the covering of the stored drinking water. This will ensure a sustainable and secure supply of drinking water for the region.

Planning permission for the reservoir works was granted, subject to sixteen planning conditions, by Dún Laoghaire-Rathdown County Council on the 1 June 2017. Irish Water lodged an appeal to An Bord Pleanála seeking the removal of one of the conditions which is to provide publicly accessible open space within the site. In December 2017, An Bord Pleanála approved the planning application to ensure Irish Water will retain the entire site for this future development.

Irish Water’s absolute priority is to protect human health by ensuring the safety and security of the drinking water supply for the 200,000 people served from Stillorgan, while being able to plan for future for growth and development.

The Stillorgan Reservoir Site consists of three open reservoirs of treated drinking water named the Gray, Upper and Lower Reservoirs.  The main element of work at Stillorgan is to drain the Gray Reservoir and to construct a new covered reservoir within the existing reservoir.  The Upper and Lower Reservoirs will be retained as active reservoirs through the construction period (approximately two years).  Once the new covered reservoir is operational, the Upper and Lower Reservoirs will be drained, decommissioned and their areas reserved for future use.  The base of the reservoirs will be landscaped for visual amenity.

Best international practice insists that treated drinking water supplies should not be stored in open reservoirs where they are susceptible to contamination.  This has to be done to ensure the safety and quality of the water supply. 

Following consultation with stakeholders, Irish Water prepared an Environmental Impact Statement (EIS) which was submitted in support of the planning application. This document sets out the impacts (both positive and negative) which the proposed development would have on the environment.

Following preparation of outline designs for the upgrade works, an initial screening assessment of the potential for environmental effects was completed. This included assessment of whether the construction or operation of the elements are likely to have significant effects on any surrounding environmentally sensitive sites or species protected under European Directives (Habitats or Birds Directives), known as Appropriate Assessment.

It is expected that construction will commence in 2018 and will be completed in a single phase of approximately 24 months. A further 12 months will be required to decommission the active open reservoirs and to landscape the remainder of the site.

Works for the Stillorgan reservoir will be confined to the existing Stillorgan site. All potential impacts resulting from construction works have been assessed during an Environmental Impact Assessment and Appropriate Assessment, and submitted as part of the planning application, and suitable management measures identified to reduce or eliminate any impacts.  Works will also be subject to planning conditions and construction legislation which will limit the local disturbance.

The most noticeable impact during the works is likely to be on traffic. Irish Water, and its Contractors, will liaise closely with the community before, during and after construction to ensure a constant flow of information, and to ensure that local considerations are taken into account, such as in developing the traffic management plan, for example.

Security of the Stillorgan Reservoir site and the water supply from the reservoirs will be our priority throughout the project.

The upgrade at Stillorgan Reservoir is being designed and assessed at the same time as works to upgrade the Vartry Water Treatment Plant, Reservoir and Pipeline.  However, the upgrade works to the Stillorgan Reservoirs are required irrespective of the proposed work at Vartry to meet best practice for the storage of treated drinking water prior to supply.  Over half of the water at Stillorgan is now sourced from the Ballymore Eustace Water Treatment plant.

The new covered reservoir will have the capacity to support future growth to 2031. The remainder of the site needs to be reserved for future water services infrastructure to secure drinking water for the community. The site will remain a live drinking water storage, treatment, and distribution centre for over 200,000 customers.  

The Stillorgan reservoir site will remain a strategically important part of Dublin’s water services infrastructure for the long term.

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