- Proposed Regional Wastewater Treatment Plant (WwTP) to cater for 500,000 population equivalent (PE);
- Associated outfall pipeline and orbital sewer linking the proposed WwTP to the existing regional sewer network and to provide future connections for identified developing areas within the catchments;
- Preferred construction methodologies include open cut trenching, trenchless technologies and offshore pipeline installation.
Irish Water is working to deliver the Greater Dublin Drainage Project to serve the Greater Dublin Area, which includes North Dublin and parts of the surrounding counties of Kildare and Meath. The amount of wastewater generated in greater Dublin is projected to increase by over 50% in the period to 2050. This wastewater must be collected and treated so that the treated water can be safely returned to the environment. Greater Dublin Drainage is about providing long term sustainable wastewater drainage and treatment for the Greater Dublin Area (GDA).
The GDD project proposes a new regional wastewater treatment facility to be located in the townland of Clonshaugh in North County Dublin, an underground orbital sewer from Blanchardstown to Clonshaugh, a new pumping station at Abbotsown, a partial diversion of the north fringe sewer, and an outfall pipeline to return the treated water to the Irish Sea. The project also includes a regional sludge treatment centre at the new GDD facility and an associated biosolids storage facility at Newtown near Kilshane Cross.
The Greater Dublin Drainage project will:
- safeguard public health
- improve and protect the environment
- facilitate employment, social progress & economic growth in the wider Dublin region.
From a community perspective, there are clear and long-term benefits in terms of health protection, opportunities for health improvements and access to services. The delivery of this project will result in significant improvements in the level of customer service in terms of supply.
The proposed project will facilitate the continued development of the Greater Dublin Area. There is the potential for socio-economic gains, including economic growth and residential development. There is the potential for increased employment and reduced unemployment. There will also be benefits in terms of social health, including decreased social inequality.
Economic benefits will be realised through operational cost savings made from a reduction in wastewater treatment costs.
The rising mains for the pipeline are designed as full welded high-pressure mains suitable for the variable ground conditions encountered along the route, which is designed to minimise maintenance and repair. The pipeline will be backfilled above the pipe surround using excavated on-site materials, thereby minimising the amount of imported backfill materials required.
The proposed construction methods were chosen for a number of reasons, including the reduction of waster materials generated as a result of the construction works. Trenchless methodologies are proposed at locations which would otherwise result in a significant generation of waste. Trenchless methodologies are also proposed at crossings of significant roads and railways ensuring minimum disruption to traffic.
Furthermore, the construction of outfall pipeline is proposed to be carried out using trenchless methodologies for the entire land-based section of the outfall. It is proposed to construct the subsea section of the outfall using dredging and a “float and sink” method. This construction methodology will require the dredging of the seabed to create a trapezoidal trench ~5m deep and 5m wide at the base. The excavated material will be returned to the trench once the pipe is in place. This construction technique will ensure that there will be no waste generated for this section of the outfall.