Faughan Raw Water Pumping Station (2022)
Faughan Raw Water Pumping Station (RWPS) is located adjacent to the River Faughan and abstracts water from the river. It provides screening by means of bar and band screens before pumping the water via a 30 inch steel raw water pumping main to Carmoney Water Treatment Works (WTW). Carmoney WTW has a minimum daily output of 15MLD and a maximum of 54MLD. Following a one in 200 year storm event in 2017, the pumping station was subject to flooding which rendered the station inoperable. NI Water initiated a project to address the flood risk by reducing the impact of any future flooding at Faughan RWPS. The construction of a the £5m scheme has improved resilience against future flooding events and ensures security of supply to Carmoney WTW.
On 22 August 2017, severe rainfall caused the River Faughan to burst its banks and flood the surrounding areas causing extensive damage to local infrastructure. Faughan RWPS was submerged under approximately 900mm of water as flood defences were breached and the pumping station was rendered inactive. The following damage was apparent after the flooding incident:
- Damage to the weir gates, walkways and perimeter security fencing.
- Water ingress to the 3.3Kv generator and auxiliary equipment and switchgear.
- Water ingress to the 3.3Kv switchboard panel, transformers and variable speed pump drives.
- Water ingress to the 400v low voltage distribution board.
- Pump motors partially submerged under water.
- Site communications and CCTV control systems submerged under water.
- Compressors and local control panel to the surge system were submerged or suffered water ingress.
- The compressor to the air curtain and auxiliary equipment was submerged.
- Monitors within the band screen hall were also submerged, however the band screen motors were elevated and therefore did not experience water ingress and remain operational.
- Building services including power sockets and heaters suffered from water ingress or were submerged.
Following the flood event, NI Water carried out emergency works to clear the flood waters and re-power the equipment to allow the RWPS to operate. This included emergency generators and temporary variable speed drives (VSDs) along with the cleaning of the pumps to ensure that they were ready for operation. Due to the damage caused to the site and the high risk of premature failure of flood damaged equipment the generators remained on the site on stand-by until the project is completed.
NI Water used their existing framework partners to help develop and deliver a solution to reduce flooding risk and upgrade the weir gates bringing all gates back into service. Capita was retained under an NEC 3 PSC Option E Contract to provide project management, cost management and site supervision services. Graham Construction was appointed for the main construction phase of Faughan RWPS Flood Resilience Project under NEC 4 ECC Option A Contract to complete the works. Grahams provided assistance in the development of the design and advising on the constructability of the works from an early stage to ensure Faughan RWPS was operational throughout the construction.
During non-flood conditions, the Faughan River level is controlled by three weir gates installed within the river channel to provide sufficient water level for the pumps to operate whilst maintaining adequate downstream water flow.
Following the 2017 flood event, the weir gates were mechanically inspected and showing signs of significant corrosion and wear with only two of the three weir gates in operation.
The purpose of the resilience works is to reduce the risk from flooding and enable the facility to continue operation throughout a range of adverse weather conditions, thus providing security of supply to Carmoney WTW. The project will include all permanent and temporary works associated with the detailed design, construction, installation and commissioning of work associated with the remedial works of the pump station.
Faughan RWPS remained operational throughout the construction works with no unplanned outages greater than six hours. The contractor had to assume that, from time to time, they may be required to share the working areas with those directly employed by the employer during both normal and emergency operations.
The new Faughan RWPS now employs 4 (No.) 415v VSD driven pumpsets operating in a duty/assist/assist/standby configuration and pumps raw water to Carmoney WTW via a 30inch diameter by 2km long rising main for processing to potable water for supply to the trunk main network. The work included the following key activities and associated support services and construction:
- Installing flood defence barriers around the pumps in the pump hall to provide 1 in 200 year level of protection.
- Refurbishment of Pump No 1 from high voltage to low voltage operation.
- Replacement/refurbishment/relocation to ancillary pump equipment and data systems.
- Replacement and relocation of internal and external lighting.
- Relocation of all building services (socket outlets, heaters, instrumentation, junction boxes, etc.) above the flood resilience level (For reference, this is considered +1.2m above the existing building floor level).
- Replacement of overhead crane pendant.
- Installation of new mezzanine floor in generator room (to become new MCC room above flood resilience level).
- Installation of new ventilation system to MCC and transformers.
- Installation and commissioning of new MCC panel and VSD.
- Installation and commissioning of new roller shutter doors for new MCC and existing switch gear room.
- Upgrade of access road to accommodate articulated, large goods vehicles.
- Installation and commissioning of two new cast resin transformers (33 KV to 0.4 KV).
- Construction installation and commissioning of new HV/ LV kiosk.
- Install new auto-dim lighting to all internal rooms.
- Refurbishment (re-pointing and re-painting) of building walls and floor.
- Install new inlet screen to pump station, new task lighting to intake sump.
- Install and commission new weir gates and ancillary items.
One of the biggest challenges faced throughout the project was to ensure continuity of raw water supply to the nearby Carmoney WTW, whilst at the same time undertaking a complete replacement of and relocation of all electrical plant and equipment, this included everything from the 33kV transformers down to the light switches on the walls. This was successfully achieved by way of forming and maintaining a ‘highly collaborative’ team, consisting of the client, consultant, principal contractor and electrical subcontractor and involved meticulous planning, management and supervision across the board throughout the project.
The weir gates posed a significant challenge from ECI stage through to construction stage. Continuous impounding of river flow is needed to maintain levels for extraction and ensure the continuity of supply to the WTW. Unfortunately, due to the extremely poor condition of the existing ‘temporary’ sectional barriers, designed to dam the upstream and downstream side of the existing gates for maintenance and repairs, these were unusable. As the envisioned ‘dry’ access was not achievable, the use of divers had to be employed to complete a survey of the submerged sections of the gates and river channels to assist with the design process.
Stoplogs were installed at each location to allow the new weir gates to be placed within the new guide channels. All three weir gates along with the guide rails and cables were replaced.
- NEC4 project manager: Capita Real estate & infrastructure
- Principal designer & contractor: GRAHAM
- Civil & structural designer: AECOM
- Weir gates design/supply/installation: Aquatic Control & Engineering
- Generators: FG Wilson
During the development of the solution for Faughan RWPS, a number of H&S improvements were incorporated including:
- Replacement of the old ‘segmental’ stoplogs with new ‘one piece’ stops logs for ease of installation and additional stability and protection of the works area during pumping out and gate inspections etc.
- Raising of all electrical services and electrical terminations/connects above 1 in 200 year flood level (circa 1.65m above FFL) to ensure no live/unprotected cables or equipment can come into contact with water during 1 in 200 year flood event (plus circa 450mm freeboard).
- Installation of a single ‘kill switch’ at the front of the building so as the entire plant can be easily electrically isolated without the need to enter the plant rooms or access the transformers etc, this is located just inside the pedestrian door to the foyer entrance at the pump hall.
- Mechanical and software ‘interlocks’ introduced to the MCC to ensure only one transformer can be on load at any time.
- All original handrailing and the existing metal inlet screen platform replaced with new galvanised systems.
- Davit sockets and ‘lockable self-closing gates’ fitted to raised platforms to facilitate future access and maintenance.
- All existing fuel transfer pumps, fuel transfer pipework, bunding and controls replaced with new fully compliant systems, existing diesel storage capacity significantly reduced in-line with minimum ‘site’ generator requirements
- All works undertaken in accordance with the Critical National Infrastructure guidance and requirements.
The works at Faughan RWPS are due for completion in Summer 2022. Successful delivery of this project will ensure that the pumping station can continue to operate during a flood event and ensure supply to Carmoney WTW while keeping NI Water operatives safe at work. Further works have been undertaken to upgrade the grounds of the site including the NIE generator located within the boundary of the Faughan RWPS.
The editor and publishers would like to thank Rosie Griffin, Principal Project Manager, and Damien Graham, Senior Project Manager, both with Capita Real estate & Infrastructure, for providing the above article for publication.