Upgrading a historical water supply scheme in Dublin, Ireland

Project summary

Nicholas O’Dwyer led a complex project to upgrade a major historical water supply scheme.

The background

Developed by the Dublin Corporation in the 1860s, The introduction of the Vartry scheme resulted in the reduction of cholera outbreaks and huge improvements to public health, thanks to the availability of clean drinking water.

The original scheme is still in use and provides safe, clean drinking water to over 200,000 people: satisfying most of the South Dublin and Wicklow drinking water demand. In 2015, Uisce Éireann (formerly Irish Water) invested €150 million in an upgrade to the original water supply scheme.

Nicholas O’Dwyer Ltd (NOD) was appointed by Uisce Éireann to bring the project from concept stage through planning, design, procurement and construction supervision to the handover stage.

The main work carried out by NOD on the project included:

• an upgrade to a dam to ensure its safe operation and a back-up siphon to enable future maintenance
• a new water treatment plant (WTP) to ensure the delivery of 80 million litres per day into the supply, to drinking water standards
• a pumped pipe system to replace a tunnel, including the installation of a new generator to prevent water supply interruptions; the design included a turbine to enable energy recovery on a section of the gravity main160 million litres of covered storage to replace the open storage reservoir and reduce public health risks.

The challenges

Age of construction

Owing to the age of the original Vartry Water Supply Scheme, several issues were identified. Firstly, dam safety issues were identified at the raw water dam constructed under the original scheme. The spillway was undersized and the functionality of the pipework and valving under the dam were unreliable.

Furthermore, the old slow sand filter WTP regularly had a 40–50% reduction in output due to its age and had difficulties treating seasonal algal blooms in the raw water.

Lastly, the original scheme had a 4-km tunnel between the WTP and Callowhill in Co. Wicklow to transfer treated water into the supply. This asset risked collapse, which would cut off the supply. High infiltration rates into the tunnel were also causing water quality issues.

Contamination concerns

The treated water storage at Stillorgan was an open reservoir, which could lead to associated contamination risks.

Project complexity

The Vartry Water Supply Scheme was an exceptionally complex project, spanning three local authorities, involving a very large number of project stakeholders and interest groups and highly complex project sites with numerous critical interfaces.

The solutions

The complexities of the project were managed using a highly collaborative partnership approach with Uisce Éireann.

NOD implemented a unique methodology in working through this project. Through this, obtaining planning permission was identified as a significant project risk. To mitigate this risk, the team divided the overall project into three distinct contracts, each scoped independently, with the delivery of each contract providing individual benefits to the water supply. This reduced the overall risk and offered the client flexibility in project financing and programme, and also allowed for different forms of contract to better manage the work undertaken in each one.

The design stage was approached with sustainability and energy conservation at the heart of it. Significant work was undertaken to ensure this was considered at every stage, such as designing a green roof covering the entirety of the 160 ML Stillorgan Reservoir and planting wild flowers on it to support biodiversity and maintaining some of the existing slow sand filters near the dam, complete with a small flow of raw water through the filters to support and maintain biodiversity at the site and to preserve a heritage aspect of the site.

At the project’s conception, a detailed stakeholder engagement plan was developed with Uisce Éireann. This included assigning a senior team member to the role of communications and management of stakeholders. Engagement and communication with stakeholders was mutually beneficial for the project and for stakeholders, who held valuable knowledge of the project sites and surrounding areas, and their input considerably benefited project delivery.

For the construction stage of the contracts, NOD maintained its management team that had been in place since project commencement, ensuring continuity through the project phases. This ensured that risk management and mitigation remained paramount until construction completion, which in turn enabled project completion on schedule and within budget. When required, NOD also employed external expertise. In order to mitigate the risk of dam failure at the Vartry WTP site, it employed the services of an All-Reservoir Panel Engineer for the entire project’s duration to specify the reservoir upgrade works and at construction stage, to review contractor method statements and risk assessments and to inspect the works during construction.

The impact

This project took around seven years from conception to delivery. The scheme benefits the 200,000 Uisce Éireann customers who were at risk of their water supply being cut off due to the collapse of a section of the Callowhill tunnel, and whose supply was on the Environmental Protection Agency’s Remedial Action List. The delivery of the project has resulted in the removal of supply risk and the removal of the supply scheme from the list. The project also delivered an important safety upgrade to the dam at Vartry. The upgrades greatly improved the water quality delivered to customers, while reducing water quality risks.

Furthermore, the project resulted in additional benefits to the area. The project provides an additional 40 million litres of water per day, which is vital for the provision of new housing in the region and the continued development of employment opportunities for communities. This was achieved through the development of a new WTP at Roundwood (Vartry WTP) and improvements to existing infrastructure.

This project won the Project Management category at the annual Association of Consulting Engineers of Ireland (ACEI) Engineering Excellence Awards in 2022.