Northern Ireland: Newcastle WwTW Extension

DAWSON-WAM were the principle contractor on the multi-million pound design & build extension and upgrade to the Newcastle Sewage Treatment Works. The scheme has incorporated an extension to the existing treatment works to house a secondary treatment stream, storm storage facilities, an inter-stage pumping station, UV disinfection, a replacement standby generator and other ancillary equipment including the main control panels.

Newcastle WwTW Extension and Upgrade, future-proofed for additional 5,000 PE, included secondary treatment stream, storm storage facilities, an inter-stage pumping station, UV disinfection & a replacement standby generator. This Design & Construct project was one of the most challenging wastewater facility upgrades undertaken for NI Water in recent years.

A Marine Environment project; Newcastle WwTW is located on the coastline, immediately adjacent to the Scheduled Monument harbour on South Promenade. The site lies within or adjacent to the following environmental designations: Murlough SAC, Murlough ASSI, Mourne Coast ASI and Mournes ANOB.

Due to the shoreline location the extension to the existing WwTW structure is concealed and contained entirely within a reinforced concrete box 50m long x 40m wide x 14m tall; on 1m deep concrete foundations. External sea walls were 1600mm thick at the base tapering in to 1200mm at the top. 5675m3 of SR Concrete, 671t of rebar and 2000m3 of Greywacke rock extraction from the shoreline were required for construction.

Planning permission conditions required a FEPA licence for construction and a site boundary cofferdam to contain the entire construction process within a leak proof environment to protect the adjacent Murlough ASSI/sea environment. Cofferdam: 210m of LX25 sheet piles 14m long with 16000t of 5-8t rock armour breakwater & 13000t of imported berm stone constructed in inter tidal zone. Rock armour protected works from Irish Sea’s winter gales/high tides. Waler/capping beam stabilised sheet piles from storm wave energy. 10000t of existing rock armour breakwater was temporarily double handled to the cofferdam & the whole 16000t reinstated as a raised rock armour breakwater sea defences in front of the new & existing WwTW wave walls. Sustainability: 13000t of imported berm stone exported off-site, for re-use at Newry Road, Warrenpoint WwPSs & pipelines project. At completion 58000t of rock armour/stone; consisting of; 32000t of 5-8t rock armour & 26000t of berm stone was double handled, removed or replaced.

Our high frequency resonance free piling rig/plant with effective silencers in tandem with Acousti-bloc noise barrier maximised the acoustic shadow mitigating all potential noise impact. Noise/vibration monitoring ensured regulations met & the residents/community were never impacted.

Part of the works required the installation of 35nr 450mm diameter auger bored piles were the existing soils were very weak. The external walls were 11m high and 1.2m wide. Total structural concrete - 5000m3, Rebar - 800T. Structural steel was erected to support the precast concrete roof on the extension. A green roof was installed on the new roof to help blend the new structure into the surrounding environment

Running concurrently with the construction of the new extension a vast programme of refurbishments inside the existing treatment works took place. In a carefully planned and programmed way, all of the existing treatment streams were completely refurbished sequentially so that the treatment works remained operational at all times. The existing sea outfall pipe was cleaned by divers from the diff user end in the sea working from a boat.

The scheme achieved Considerate Constructor Silver due to the efforts made by the site team to minimise disruption and promote close working relationships with community groups. Exemplary Customer Care delivered by: early/sustained consultation with the local community, businesses & elected representatives through information events/evenings; project leaflet drops; council briefings; Site Agent’s personal contact with impacted third parties, progress notice board & informed site visits for invited community members.

‘Green’ roof reinstatement in harsh marine environment provided sustainable natural habitats for local flora, fauna, birds & insects and this helped the scheme achieve CEEQUAL Excellent and an ICE(NI) 2016 Sustainability Award

WwTW Scope included:

• Construction of 5th FST lane 12m diameter x 6m deep. Storm tanks 1000m3 storage
• Storm return & Interstage pumping station with associated pipe-work
• Construction of interstage 1250m3 storage tank. UV disinfection channels
• Effluent washwater tank, pumps and booster set. Sludge decant pumping station
• Rivers Agency culvert extension; 35m of 900mm dia concrete pipes.
• Sea outfall inspection & rehabilitation, 283m of 1016mm dia steel pipe
• FFT overflow with 6mm Huber storm screen/Replacement 6mm inlet screens
• Rationalisation of 4nr digestion tanks into 2no thin sludge holding tanks
• Replacement mechanical sludge thickener and associated poly dosing plant
• New odour control, upgraded ventilation and building services
• Replacement blowers, standby generator, fuel delivery and storage
• MEICA refit of Harbour and Blackrock pumping stations inc Archimedean Screw Pumps
• 1400m2 of Hydro-demolition/concrete repair to existing walls & 252nr CP Anodes
• Beach reinstated as original

Process and MEICA elements were delivered by Ovivo.

Newcastle WWTW Extension was awarded a CEEQUAL 'Excellent' Whole Life Award in 2020, for more information please see https://www.ceequal.com/news/newcastle-wastewater-treatment-works-upgrade-hailed-as-excellent/.