Coffey Construction Ltd (CCL) were the civil works main contractor on this project to extract water from the River Mahon and to pump the raw water through 10km of 600mm rising main to Ballyshonock Reservoir in County Waterford. A separate contract was let to Response Engineering for the pumping station MEICA installation.
The project consisted of the construction of a new river weir, water intake structure, 26Ml/day raw water pumping station with three multi-stage turbine pumps (duty, duty-assist, standby), substation and switchroom, 9,824 metres of 600mm rising main and associated valve chambers, inlet and outlet works at Ballyshonock Reservoir and 905 metres of 700mm raw water trunk main between Ballyshonock Reservoir and the N25 Trunk Road. Approximately 16,000 m3 of material was excavated for the pumping station structure, much of which was used for landscaping and the access road.
The project was client designed, with some contractor-designed elements. Following an intrusive investigation, CCL produced a full design for the reservoir inlet structure which took account of the condition of the existing shotcrete slipway. This design was reviewed and approved for construction by the client.
CCL arranged a risk workshop to develop the risk register for the implementation phase, which included the identification, avoidance and reduction of risk to provide greater cost certainty, and this workshop effectively became the first of several value engineering forums with the client’s representative. Project benefits arising from these meetings included:
- Replacement of 25% of the RC pumping station roof structure with a structural timber roof to allow future removal of the surge vessel by crane;
- Pipeline alignment and valve redesign to obtain the most cost-effective horizontal alignment in unexpectedly rocky ground conditions, following detailed SI by CCL;
- Pipeline realignment to avoid existing services on the 3km section laid in road verges;
- A decision to temporarily divert the River Mahon away from the construction works and within its floodplain as acceptable and practical temporary works.
In-river working consisted of the temporary diversion of the River Mahon, the construction of a 1200mm high concrete weir and a new 40m long by 15m wide river inlet channel, RC sump structure, baffle walls and smolt screen. CCL assessed the size of river channel needed for the river diversion and produced a construction sequence design and method statements which were reviewed and approved by the client’s representative and local fisheries board.
A suite of standard documents and a document control procedure was agreed with the client for use on the project.
The intake structure and associated valves were fully inspected and handed over in advance of the joint commissioning programme for the pumping station. CCL and the client agreed on a regime where each completed element of work was thoroughly inspected by CCL’s Site Agent, and any remedial works were carried out before the client was invited to accept the works. This process worked successfully and resulted in a smooth handover.