Construction work for water and sewage pipelines

Description

Irish Water plan to undertake the duplication of the existing 9C sewer and associated storage as part of the Blanchardstown Regional Drainage Scheme (BRDS) project. The planned works are necessary to ensure compliance with EU directives, Irish National Standards and Regulations relating to treated water for human consumption. It is intended that the works will be implemented under a Design Build (‘DB’) contract with a 24-month operation service period with a possibility to extend to 48 months. Further details are in the PQQ document. Irish Water plan to undertake the duplication of the existing 9C sewer and associated storage as part of the Blanchardstown regional drainage scheme (BRDS) project. The planned works are required to cater for future domestic population growth and the full development of the development plans within the 9C catchment (including Fingal, Meath and Kildare areas). The 9C-Trunk Sewer was constructed in the 1970s along the Tolka Valley to provide drainage for the planned towns of Blanchardstown, Mulhuddart and Castleknock. It connects into the Grand canal trunk sewer (GCTS) at Dolphin Road via twin siphons under the River Liffey and flows are transferred to Dublin City’s Ringsend Wastewater Treatment Works for treatment prior to discharge to the Liffey Estuary. Under the Greater Dublin Strategic Drainage Study (GDSDS) flow from the 9C to the Ringsend WwTW is to be limited to 2,7 m3/s. This is the maximum flow that the twin Liffey Siphons can transfer to the Dublin City Council (DCC) Sewer. However, peak flow from the catchment is predicted to be greater than this. Storage is therefore required to balance peak flows due to the pass forward limit, and prevent uncontrolled spills to the Tolka. Off-line storage will be provided by constructing large underground tanks with pumps returning the stored flow to the existing pipeline once capacity becomes available. The design philosophy for the 9C Duplication and Storage is to duplicate the 9C for a distance of approximately 3,2 km from Parslickstown Bridge to the off-line storage tank adjacent to Mill Road, in Tolka Valley Park at Waterville. Based on the current modelling the storage capacity proposed for the tanks is approximately 30,000 m3. The tank configuration is currently proposed as comprising 4 underground storage tanks, with approximate dimensions of 25 metre internal diameter and 30 metre depth.