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Arklow
Since 2014, the Environmental Protection Agency (EPA) has identified multiple locations across Ireland where raw sewage continues to discharge untreated into rivers and seas—posing serious environmental risks. In response, Uisce Éireann (Irish Water) has made significant infrastructure investments to tackle these long-standing wastewater challenges. One such investment is the Arklow Wastewater Treatment Plant, which serves a rapidly growing commuter town just 90 minutes south of Dublin.
The project follows decades of delays and setbacks. First proposed in 1988, it encountered numerous challenges—including a controversial site change in 1993, initial planning permission granted in 1994 that stalled for more than 30 years, renewed approval in 2005, and lapsed permissions in 2015. Real progress only began after Uisce Éireann took over responsibility in 2016. Planning permission was granted by An Bord Pleanála in 2019, with the project going to tender in 2021 and construction starting the same year at the North Dock site. Remarkably, the facility was completed six months ahead of schedule in November 2024 and commissioned in January 2025.
Delivered under a Design-Build-Operate contract with a four-year delivery timeline, the project team included Wicklow County Council, Ayesa, Ward & Burke Construction Limited, and Clancy Moore Architects. Already recognised with the prestigious Downes Medal—an exceptional honour for utility infrastructure—the facility sets a new benchmark in sustainable civic design.
The plant will prevent untreated wastewater from entering the Avoca River and the Irish Sea, bringing Arklow into compliance with EU environmental regulations. It has an initial treatment capacity of 24,000 population equivalent (PE), scalable to 36,000 through modular upgrades. Beyond regulatory compliance, the facility supports a growing population, strengthens flood resilience, and represents a major investment in the long-term health and wellbeing of the local community.
Uisce Éireann appointed Ayesa to provide consultancy services across all phases of this critical wastewater treatment plant (WWTP) project. Our role is based on our extensive experience in delivering water infrastructure in the area, having previously been appointed as engineers for the Arklow Water Supply Scheme and the Arklow Flood Relief Scheme (FRS). This deep understanding of the full water cycle within the catchment allowed us to adopt a strategic and holistic approach, particularly in managing the shared interfaces between wastewater, flooding, and climate resilience.
Phases 1 & 2: Design of Preferred Routes
Ayesa, working in collaboration with Arup, developed the preferred design for the new interceptor sewers that would transport wastewater to the plant and the outfall pipe that would safely discharge treated effluent into the Irish Sea. This phase was highly complex, requiring detailed hydraulic modelling, environmental impact assessments, and strategic stakeholder engagement.
Key tasks included:
One of the most challenging aspects of the design was selecting the best route for the interceptor sewers. The topography of Arklow and the termination of all outfalls at the river provided only two viable locations for these sewers—at the North and South Quays. This required the construction of a tunnel pipeline linking both sides, allowing wastewater to be transferred to the new plant.
Gates 3 & 4: Construction & Delivery
With planning, land acquisition, and environmental licenses secured, Uisce Éireann (Irish Water) appointed Ward & Burke as the contractor for the scheme. Following a competitive tender, Ayesa was selected as Employer’s Representative, providing contract administration and overseeing project delivery.
Key construction milestones included:
Construction also included:
Outfall and intake Selection & Marine Engineering
A key part of the project was determining the most efficient solution for discharging treated effluent. Ayesa and Arup conducted a series of feasibility studies to evaluate whether a river or marine outfall would be more appropriate.
In September 2022 the installation of the one-kilometre long sea outfall (LSO) off the coast of Arklow, Co. Wicklow was completed. Designed by Royal HaskoningDHV for Van Oord Ireland Ltd, the high-density polyethylene (HDPE) pipeline measures 630mm in diameter and extends approxi-mately 927 metres offshore to a discharge point located in 13 metres of water. The outfall termi-nates in a diffuser structure comprising six 355mm risers and four 160mm ports, each fitted with duckbill valves to ensure even horizontal dispersion approximately one metre above seabed level.
The pipeline was installed using a float-and-flood methodology. To ensure long-term seabed stability under wave and current loading, concrete collars (290kg/m) and interspaced 2.3-tonne concrete kennels were added along the pipe at 3.5-metre intervals, providing a submerged specific gravity greater than 1.35. The trench was backfilled with side-cast material, and the pipe was designed to maintain a minimum 1.5m cover depth—even under fluctuating seabed conditions or potential anchor drag.
Installation was not without challenges. Working within a small, active port meant strict delivery and access constraints, while offshore preparations were limited by weather conditions This critical in-frastructure project was delivered through collaboration between Ward & Burke (main contractor), Van Oord Ireland Ltd (marine works), Royal HaskoningDHV (marine design), Pipelife Norge AS (HDPE pipe), Tracey Concrete (concrete collars and kennels).
Water Infrastructure with a Civic Identity and Design by Collaboration
Built on a former industrial site, this wastewater facility reimagines public architecture. The project was true collaboration between the people of Arklow, architects and engineering design teams. In early consultations and design workshops, local knowledge, history, and aspirations were gathered and shared. These community conversations shaped the design approach, resulting in a facility that responds not only to environmental needs but to cultural and civic values as well. Architects Clancy Moore Architects won Irish Water’s public competition with a design that integrates the plant into the town’s maritime and industrial past. The result is a low-energy, above-ground system that minimises site disturbance and integrates sustainable features such as rooftop solar panels, and gravity-assisted flow.
Two low-slung, teal-clad buildings reflect the colours of local boats and flora, with louvred façades that support ventilation, odour control, and even offer habitats for bats and birds. The building’s louvred façades are engineered to promote natural ventilation and soften the visual impact over time. This layered cladding system, along with modulated structural proportions, ensures the building is visually engaging up close and from a distance. The result is a compact, low-energy approach to wastewater infrastructure. All treatment processes are placed above ground, avoiding the disturbance of pollutants left by the site’s former industrial use, with no need to remove soil. The processes are vertically stacked to minimise site coverage, and unlike a conventional plant that requires multiple energy-intensive pumps, this system relies on a single pump with gravity assisting the remaining flow — significantly reducing energy demand. To service the stacked forms, a gantry crane runs along the roof, which also hosts a PV solar farm to offset energy use. The main treatment functions are housed in two primary volumes, each clad in a louvred skin that distributes air, controls odour, and screens operations from view.
Materials and Sustainability
The design prioritises durable, low-maintenance materials that are both environmentally responsive and sensitive to the cultural context. The primary structure consists of reinforced concrete, forming the base and tank walls, while steel portal frames rise to support the superstructure. Main process buildings are clad in fibre cement panels—a non-toxic, fully recyclable material with a long service life and a reduced whole-life carbon impact. Sustainability is embedded throughout: a compact and efficient layout limits the footprint, avoids disturbing contaminated ground, and uses gravity-assisted flows to reduce energy demand. Rooftop solar PV panels further offset operational energy. Together, these strategies deliver a resilient, low-energy, and low-maintenance future.
Stakeholder Engagement & Community Impact
Minimising disruption to the local community was a key priority throughout the Arklow Wastewater Treatment Plant project. Several strategies were implemented to ensure smooth integration within the town:
This approach successfully mitigated environmental impacts kept a positive relationship between the project and local residents.
Project Benefits & Innovations
This wastewater treatment plant delivers multiple benefits for Arklow, including:
Decades in the making:
40months
Total time on site
1200metres
Total length of interceptor sewer tunnelling
360metres
Total length of new wave defences
1400000kWh/year
Operational energy (The energy use of the plant) Approx.
19280m³
Concrete
2300tonne
Steel reinforcement
760tonne
Structural steel
160180.3kWh/year
Total of PV electricity power generation on site
12234m²
Area
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