North Coast WwTW

North Coast, Co-Antrim

The North Coast Scheme was the largest standalone contract ever procured by DRD Water Service (now Northern Ireland Water).  The project comprised four separate packages:

PACKAGE A - Pumping Stations

This package of work included the construction of new and refurbishment of existing pumping stations which have to transfer flows to the new regional wastewater treatment works at Craigtown More. The stations also provide storm water storage and ensure that emergency discharges during storm conditions comply with statutory requirements.  Construction techniques utilised included precast concrete segmental shaft construction, for example, Riversdale Pumping Station had two such shafts installed one of which was 15m diameter and 18m deep.

New pumping stations were constructed at:

• Articlave - within the site of and replaced the existing wastewater treatment works.
• Castlerock - within the site of and replaced the existing pumping station. The new building is buried and landscaped.
• Coleraine Terminal - within the site of and replaced the existing wastewater treatment works at Ballycairn.
• Dhu Varren, Portrush - adjacent to the railway line at West Strand. The new buildings - designed in conjunction with Coleraine Borough Council - incorporate public toilets, baby changing and water sports/changing facilities.
• Causeway Street, Portrush - on the open amenity land near the Crocknamack Road junction. Again this building is fully integrated and landscaped.
• Lansdowne, Portrush - adjacent to the old lifeboat station. The new visually pleasing pumping station incorporates a public viewing platform.
• Riversdale - within the site of and replaced the existing pumping station
• Salmon Fisheries - within the site of and replaced the existing pumping station.

Existing pumping stations were refurbished at: Castlerock Promenade, Ardina Cottages, Ballycairn, Harbour and Blackrock.

PACKAGE B - Pipelines

The construction of the new wastewater treatment works necessitated the laying of some 24km of pumping mains and gravity sewers to provide the interconnecting pipework between each of the various pumping stations, to connect the pumping stations with the main works site at Craigtown More and to divert existing sewers into the new pumping stations.

To reduce the environmental impact and to minimise disruption, almost half of the pipelines were installed using trenchless techniques (where ground conditions and absence of rock permitted). These innovative and sustainable methods of pipelaying avoided the excavation of a continuous trench and only required pits to be dug at intervals.  Pipelaying techniques included:

• Directional drilling under River Bann
• Auger boring under the railway
• Micro tunnelling in sandy conditions along roadways
• Pipe jacking
• Open cut

PACKAGE C - Wastewater Treatment Works

This involved the construction of a state-of-the-art wastewater treatment works (WwTW) at Craigtown More for a PE of 105,000.  The activated sludge process includes inlet works, aeration tank, final settlement tanks and sludge storage and dewatering plant. The main elements of the WwTW were constructed in a natural hollow and all excavated material used to landscape the perimeter and hence minimise the visual impact.

PACKAGE D - Long Sea Outfall

The 630mm diameter outfall is approximately 1,275m long and replaced the original discharge point.  It was constructed using a jack-up barge and rock blasting methods. This outfall system places the treated effluent at a location off the coast at Port Gallen, where the depth and natural currents will provide effective dispersion.