Supply Chain - Treatment Process Technologies - Rapid Gravity Filters

The primary challenge driving this project was the inadequate storm volume capacity at Ramsey WRC. The existing storm tank could only hold 260m³, far below the required capacity set by the Environment Agency (EA).

Failure to increase the on-site stormwater storage capacity would result in a consent failure leading to the risk of environmental harm and regulatory penalties for Anglian Water.

Additionally, the site’s existing flow to full treatment infrastructure was outdated and in need of major repair and upgrade. The current system could not handle the additional flows required to meet future population growth and environmental obligations. Without intervention, Ramsey WRC faced operational inefficiencies and potential breaches of discharge permits.

To overcome these issues, Anglian Water tasked the @one Alliance to design a dual-scheme solution to address the stormwater storage and FtFT issues.

The new storm tank designed to significantly increase storage capacity and reduce overflow risk during heavy rainfall events. The new tank is 11.1m in diameter and 8.47m high. This provides an additional 693m3 of storage capacity bringing the total volume of stormwater storage to 953m3. This upgrade ensures compliance with Environment Agency requirements and future-proofs the site against climate change impacts and population growth.

To improve operational efficiency and safety, the design incorporates external dry well submersible pumps for automated cleaning. This innovation eliminates the need for manual cleaning and access platforms, reducing health and safety risks for maintenance teams.

Furthermore, the stormwater storage tank has been carefully integrated into the existing infrastructure, optimising the limited site footprint and minimising disruption during construction. This approach allowed the project team to deliver a high-capacity solution without extensive civil works or compromising ongoing operations.

The second element of the project focused on increasing the site’s ability to treat incoming flows during peak conditions.

Modular side-stream: Anglian Water implemented a modular side-stream solution supplied by Siltbuster Group, which offers flexibility and scalability within the constrained site layout. This system includes:

These technologies work in harmony to deliver robust treatment performance even under challenging conditions.

Supporting this advanced treatment process are associated pumps, flow splitters, and access platforms, ensuring smooth operation and ease of maintenance.

Tertiary solids removal: To further enhance effluent quality, the project has incorporated tertiary solids removal (TSR) through twin-stream pile cloth filters and disc filters from FLI Water Ltd, which provide an additional layer of protection for local watercourses.

Power supply: Recognising the increased power demands of these systems, the upgrade also includes a 315kVA electrical power enhancement, installation of a new LV switchboard kiosk, and integration of telemetry systems for real-time monitoring and control.

Collectively, these improvements enable Ramsey WRC to handle an additional 20 litres per second (l/s), bringing the total FFT capacity to 89.4 l/s, while ensuring compliance with stringent environmental standards.

Delivering this complex project posed several significant challenges that required innovative solutions and careful planning.

Coordinating these systems demanded robust design and commissioning strategies. The team mitigated risks by collaborating closely with specialist suppliers, ensuring seamless integration and reliable performance across all components.

The successful delivery of the Ramsey WRC upgrade was underpinned by a highly coordinated and collaborative supply chain strategy. Given the complexity of the dual-scheme approach, combining storm tank capacity upgrades with advanced flow to full treatment (FFT) enhancements, the project required contributions from multiple Tier 2 contractors and specialist suppliers, each playing a critical role in achieving the technical and regulatory objectives.

Work commenced in August 2024 and at the time of writing (January 2026) is scheduled for completion in the upcoming months; ensuring that all regulatory deadlines are met without delays.

The Ramsey Water Recycling Centre upgrade stands as a clear demonstration of Anglian Water’s commitment to resilience, regulatory compliance and environmental stewardship. By investing £10m into advanced treatment technologies and storm capacity improvements, the project not only addresses immediate operational and regulatory challenges but also future-proofs the site for AMP8 and beyond.

This strategic investment ensures that Ramsey WRC can continue to meet the growing demands of population increase and the tightening environmental standards that govern water recycling operations.

The flow to full treatment element of the investment is on track to achieve an 77% reduction against Anglian Water’s capital carbon baseline, which is key to supporting Anglian Water’s commitment to reaching a net zero organisation by 2030.

The town and immediate area are currently served by a sewage treatment works established at the turn of the last century and upgraded over the years. It is located beside the River Wey, to the north of the A3 trunk road and north of Guildford town centre. It lies just south of Slyfield Industrial Estate. The current STW has a capacity to cater for a population equivalent of around 120,000.

Guildford Borough Council’s Local Plan adopted in 2019 allocates a site to the west of the River Wey wrapping around the eastern side of Slyfield Industrial Estate for mixed use development. Part of the 40 Ha allocated site is currently occupied by the existing sewage treatment works.

Weyside Urban Village is a mixed-use regeneration project which will provide some 1,500 new homes, new community facilities, Gypsy and traveller pitches and 6,500m2 of additional light industrial and trade space. 11Ha of the site are allocated for waste management purposes. The plans include a new council depot, a public recycling centre and a new, relocated sewage treatment works.

In order to bring the development site forward, within the plan period to 2034, Guildford Borough Council (GBC) have entered into partnership with Thames Water Utilities Ltd (TWUL) to build the new STW as the first phase of the redevelopment. The new location is slightly further north on the eastern edge of the Industrial site and is a brownfield site, formerly a gravel quarry and subsequently a landfill tip.

The new sewage treatment works allows for an increase in capacity to serve a population of 125,000 allowing for predicted population growth in the town and surrounding area as well as more stringent effluent discharge standards.

The new site also includes areas within the new works for future expansion and increased treatment capacity as need arises.

The scheme to build a new sewage treatment works (STW) in Guildford is now mid-way through construction. This article provides an update to the project following on from previous articles published in Water Projects. In 2023, Enpure Ltd’s Project Delivery Director Shaun Christopher described in detail the process and assets being provided in the new works and in 2024, Dan Russell, BAM’s Operational Lead, gave an update on the progress of the project one year into the construction.

This article also covers some of the planning considerations and requirements for the scheme.

In 2021 TWUL awarded a contract to a BAM-Enpure Joint Venture to design, build and commission a new STW for Guildford, and once operational, to de-commission the existing works. BAM-Enpure Joint Venture (JV) is a non-integrated Joint Venture, formed specifically to combine experienced civil engineering contractor BAM with the process engineering MEICA specialism of Enpure, to deliver a turnkey solution for TWUL.

Construction began in the spring/summer of 2023 with BAM undertaking design and construction of the civils works and Enpure providing process and MEICA design and installation. BAM have employed Arcadis as their main civils designer and the JV has let a number of specialist sub-contractor design packages alongside.

The project consists of the following:

A detailed description of the process and assets being installed is set out in the previous Water Projects article published in 2023.

The new site comes with additional challenges in that it is brownfield site formerly used for gravel extraction and then landfilled through the 1960s, 70s and 80s, with mainly domestic and some commercial waste. The site is classified as a waste development such that the local planning authority is Surrey County Council (SCC).

The planning permission granted was subject to a number of conditions and commitments, not only relating to the siting and development of the STW itself such as visual impact, odour, noise and traffic generation, but also to the remediation and reuse of the landfill site. Plans and construction methods needed to ensure that there was no temporary or permanent environmental damage to the surrounding area as a result of the impact on or disturbance of the buried waste material and that operatives working on the new STW were protected from any ill effects of the landfill during operation of the site. The landfill also poses particular constraints and hazards during the construction phase.

The strategy for the site was to leave as much of the landfill waste in situ and build above and through the waste. A detailed remediation strategy formed part of the planning requirements. The plan set out how the construction and operation phases of the project would manage issues of ground water and ground gas, potential ground water contamination and leachates, contaminated solid material including asbestos, and short- and longer-term settlement of the landfill.

Dan Russell’s case study in Water Projects 2023 provided a detailed description of the use of a combination of ground improvement and foundation techniques, which consisted of:

Figures 5 (below) show the historic gravel extraction map and depth of landfill determined by ground investigation - both images were extracted from the project’s Detailed Remediation Strategy.

However, the impact of the waste material goes beyond its bearing capacity. The site was already being subject to long term monitoring for ground gas and groundwater quality by Thames Water to provide a baseline for the project. Additional boreholes were sunk and a Groundwater & Ground Gas Monitoring Plan was approved by the local authority. Daily and continuous automatic remote monitoring was undertaken during the ground improvement and excavation phases with trigger levels set and exceedances reported back to SCC and a requirement for quarterly summary reporting. Monitoring will continue during commissioning of the site at less frequent intervals.

Asbestos: Asbestos had been discovered in a third of samples taken during the ground investigation and so a monitoring regime was established. Air sampling around the perimeter of the site ensured any airborne particles were detected and works could be stopped if necessary. Proximity asbestos monitoring and identification of asbestos material in excavation has also been used extensively during excavation across the site. The project used Socotec to undertake asbestos monitoring and testing.

Ground gas: A ground gas protection design has been necessary to reduce risk of ground gas entering occupied buildings, kiosks, tanks and chambers where operational or maintenance access is undertaken. A ground gas design protection strategy was set out by Arcadis with PAGeo Contracting Ltd providing expert advice and a detailed ground gas design, PAGeo then supplied gas dispersal matting, venting components and gas membranes. Both the strategy and the detailed design for ground gas protection have been submitted to and approved by SCC.

Independent verification of the gas protection installation has been provided by MTS Ltd as verification of the installation and subsequent reporting to SCC is a planning condition.

Surface drainage: On-site surface drainage has been carefully designed such that new impermeable areas are positively drained to the site drainage system to remove the risk of a spill causing environmental pollution. This surface water is then fed into the inlet pumping station for processing through the works. As the permeable area of the site has been greatly reduced this also significantly reduces leachate mobilisation.

Biodiversity: Another planning condition is the provision of Biodiversity Net Gain (BNG). In conjunction with GBC, the project provides 10% net biodiversity gain by use of on-site planting and off-site enhancement of the land directly to the north of the new STW. A Site of Natural Green Space, biodiversity enhancements to an area of farmland, and a marshy meadow along the River Wey are being provided.

The Environment Agency have also constructed a new fish pass in this area allowing fish to migrate around Old Bucks Weir.

Guildford STW: Civils works supply chain - key participants

As of summer 2025, civils works are nearing completion and MEICA fit out has started.

The installation of piled supports has been undertaken, and all major structures are complete. Installation of the below-ground pipework and buried ducting is in progress and the welfare building is watertight and available for equipment installation. Moving towards installation of MEICA equipment, the water testing of structures started in the February of 2025.

Steel staircases and high-level walkways are mostly complete. The inlet screens and grit removal system are in place. GRP tanks for sludge processing are being installed and many control kiosks are in place. Electrical supply buildings are near completion.

MEICA work commenced in February 2025, overlapping with completion of civils to maximise programme efficiencies. Designed alongside the civils elements of the site, the MEICA installation has taken place apace with the first bridges on the final settlement tanks attached, the larger glass coated steel tanks for the sludge area in place, and generators and some kiosks have been installed.

BAM has started the installation of the above-ground pipework and cable pulling in buried ducts, and the fit out of control rooms will commence shortly. Construction of MCC basements has been completed and two of the three MCC kiosk, and power supply and distribution works are nearing completion.

A 1.5m diameter gravity tunnel, 1.5km long, transfers flows from the existing works and intercepts minor sewers en route. There are six shafts along the tunnel route, some of which act as junctions between the new tunnel and the existing sewers. Shafts were sunk by Joseph Gallagher using the caisson method and the tunnel was driven between them using a full-face tunnel boring machine, (named Daphne by a local school). The tunnel and shafts were completed in 2024 and the final work remaining are the completion of the large inlet pumping station (IPS), shaft (E2) at the new works and connection of Guildford’s main sewer to the head of the tunnel, which will allow all flows to be diverted to the new tunnel.

The new inlet pumping station (IPS) is a 12.5m diameter shaft with a depth of 17m, which houses six pumps with the capacity to lift flows of around 2,500 l/s from the tunnel entry, at the base of the shaft, to the inlet works where all flows are screened. The shaft is complete except for the internal walls and installation of penstocks which allow isolation of half the well at any time for maintenance of the pumps. This will be completed in the autumn of this year.

Two storm tanks provide a combined capacity of approximately 8 million litres to which flow can be diverted to temporarily hold sewage arriving at the new works should flows exceed the capacity of the works. Constructed onto in situ bases, the walls of the storm tanks were prefabricated, placed and post-tensioned by A Consult Ltd.

The inlet works and larger chambers were entirely cast in situ due to lack of repeatable sections and logistics. In situ concrete work for these was undertaken by Kelly Formwork. The inlet screens have been installed and walkways are in place.

Screened flows from the inlet works will then pass through primary and secondary treatment tanks comprising rectangular primary settlement tanks (PSTs) and activated sludge plant (ASP) tanks. The walls for these tanks were designed and supplied by FLI Precast Solutions Ltd and installed by BAM and DJ Civils Ltd on in situ bases prepared by Kelly Formwork Ltd. These tanks are complete with pipework being fitted and the ASP has commenced water testing.

To ensure watertightness of the larger rectangular tanks, Heidelberg Materials and Sika’s concrete technology were used.

Concrete containing Sika WT-200 P was utilised for the PSTs and the ASP. Sika WT-200 P is a combined water-resisting and crystalline waterproofing admixture used to reduce the permeability of concrete, making it suitable for water retaining structures.

Gas protection has been laid under all large tanks. Materials were supplied by PAGeotechnial Ltd and verified by MSL Ltd. Void former mating laid on a bed of single grade 40mm stone provides a preferential escape path for ground gases and is connected to vents at the tanks periphery allowing ground gases to vent to atmosphere.

These tanks are not habitable spaces and only require a dispersal system to discourage any build-up of gas below the large tank bases.

The four final settlement tanks were also precast, supplied, installed and post-tensioned by A-Consult Ltd onto in situ bases prepared by Kelly Formwork Ltd. The FSTs are complete with bridges and scrapers installed and are currently being water tested.

Following final settlement, flows will pass through final filtration in the tertiary treatment plant before being discharged to the River Wey via new, twin outfall pipes. Civil construction is complete and MEICA installation of cloth pile filters and drums from Eliquo Hydrok Ltd is underway.

The outfall pipework has been fully installed across the water meadow and the headwall has been constructed at the discharge point into the River Wey.

The project also provides a dewatering facility for imported sludge from other small treatment works. This area is nearing completion with the larger coated glass sludge blending tanks in place and the smaller buffer tanks being installed. Gas vent pipes have been installed below the extensive concrete slabs to allow venting of ground gases to the atmosphere.

The sludge belt presses from Kent Stainless Ltd for sludge dewatering and thickening have been installed adjacent to the bases for the elevated sludge cake silos. The silos from Saxlund International have been sized to provide storage of seven days’ worth of processed sludge, which can be discharged to trucks for export from site.

Power supply and distribution infrastructure is now in place. The three MCCs have been constructed in sequence and the first two are being fitted out.

A new welfare building houses the automated systems for running the new plant and controlling effluent quality as well as office and mess space for Thames Water staff and operatives. The building is watertight with cladding being installed and the fit out of building fixtures and plant control equipment is in progress.

Design has utilised a 3D model hosted by Arcadis with each designer adding in modelling information as their design capabilities have allowed. This has enabled precise integration of designers individual input and interrogation of the integrated design

The model is used extensively by engineers on site. 3D modelling has, for example, allowed duct chambers to be precast with precision positioning of cable openings, saving on in situ working and substantially reducing programme on these installations.

To enable the STW to be constructed on the site without the waste being removed a combination of ground improvement techniques have been employed including driven concrete piles, Rapid Impact Compaction, and Vertical Rigid Inclusions.

The Rapid Impact Compaction work undertaken by Cofra was completed in late summer of 2023. From July 2023 to the spring of 2024, to support the larger structures, tanks and main process critical pipelines, 3500 concrete piles were driven through the landfill into the clay. The design and installation of this piling operation was undertaken by Aarsleff Ground Engineering.

In areas where settlement criteria were less critical, but needed controlling (for example roadways and minor pipework), a Vertical Ridged Inclusion (VRI) piling technique was used. The system involves displacement drilling a column in the landfill and filling the void with concrete. This works by consolidating the soil around the pile, transferring load to lower layers, thus increasing bearing capacity and reducing settlement over time.

Since 2024 the installation of VRIs by Foundation Piling has been completed with 7500 inclusions installed across the site. During detailed design, the project was able to remove the need for a load transfer platform above the VRIs across much of the site. This was done by detailed analysis of the 3D model to target differing requirements for support and by reducing inclusion spacings, thereby reducing the expected landfill removal by 37,500m3.

The load transfer platform remains below roads, but pipework sits within the grid of VRIs.

Completion of the mechanical works is expected in the first part of 2026 with installation of electrical and control systems expected to complete in the second part of 2026. Dry and wet commissioning will be undertaken sequentially across the site throughout the coming year, ensuring the new works is ready to commence process commissioning.

The final, and arguably most challenging activity, will be to connect the existing sewer network to the new tunnel, diverting flows from the existing STW to the new STW. A series of interventions will be required to intercept the various sewers, along the route of the tunnel, all the whilst ensuring the new STW is performing within strict limits and the existing STW is able to maintain its performance during the ramp down of flows.

During the optioneering stage, a range of interventions were assessed to address the storm overflow impact, including catchment‑scale rainfall disconnection, increased pass‑forward flow, nature‑based treatment and conventional storage. Catchment disconnection was discounted due to the high levels of customer disruption required, while increasing pass‑forward flow was not feasible due to downstream hydraulic constraints. Given the overflow’s location adjacent to open land by the river, a nature‑based solution was identified as the most effective and deliverable option.

A two-stage approach was chosen to maximise success, with an aerated reed bed providing initial intensive solids capture followed by two Integrated Constructed Wetland (ICWs) in series, providing effluent polishing and an opportunity for the industry to research wetland treatment in this application.

The favourable topography enabled a gravity system, eliminating the need for lifting flows and in turn, reducing operational energy demands. The field’s proximity to New Inn’s residents also allowed for place-making features for the local community, such as footpaths, an outdoor classroom and natural play areas, enhancing community engagement and educational opportunities.

The indirect monetary value of these wider benefits was captured in the decision-making stage via the use of CIRIA’s B£ST estimation tool, which estimated £12m in realised benefits over the next 40 years across social, natural and other capitals; something none of the grey solutions offered.

The existing storm overflow (SO) was located amongst trees on the edge of the field. The incoming pipe laid in the eastern corner of the field meant the SO could be relocated into a new compound, which will contain the following chambers and plant:

Design for Manufacture and Assembly principles were adopted to several elements of the compound. The screening and bypass chamber were fabricated off site by FP McCann Ltd, reducing the need to cast these chambers in situ.

Both the kiosks were prefabricated off-site by Morgan Marine Ltd to save time and reduce on-site activities in the construction phase.

The design team carried out a catchment Flow & Load Survey to ensure a better understanding of the design parameters required to achieve the ‘No Impact’ outcome. The survey gave insight into the challenges around pollutant loads in intermittent discharges, with varying concentrations of biochemical oxygen demand (BOD) and ammonia found in the excess diluted sewage; especially the difference between accommodating the ‘first flush concentration’ and weaker dilutions as a storm event continued.

Working collaboratively with the reed bed and ICW suppliers early in this stage, increased confidence in achieving the necessary pollutant removal in the final effluent.

A Flood Consequence Assessment (FCA) was completed as part of the planning application and the findings required the reed bed and wetlands to be moved further away from the river, reducing the size of the originally allocated footprint. The revised layout however, still provided sufficient treatment area (3,000m2 for the reed bed and a combined ICW treatment area of 2,400m2) and created additional space for the public to enjoy.

The planning application was critical to the success of this project, which was well received by local councillors and relevant bodies, in part, due to the extensive up-front work done by Arup’s planning team. Arup specialist teams carried out predictive odour and noise modelling of the solution to address concerns raised by the planning authority. The project team also engaged extensively with the local community through both in-person and online events, ensuring the design met local needs and preferences.

To align with the Sustainable Approval Body (SAB) requirements as part of planning approval, the design team implemented sustainable drainage features across the site. The maintenance track and vehicle areas in the compound were constructed from permeable TruckCell™ paving, made from recycled plastic, whilst vegetated swales and depressions were incorporated alongside the impermeable access track and footpaths. This reinforced the project’s low‑carbon and sustainable design ethos.

Construction started in January 2024, with Morgan Sindall Infrastructure mobilising to bring the nature-based solution system online before the regulatory deadline of 31 March 2025. The team navigated challenges including invasive species within the compound area and persistent groundwater during the large excavations, requiring an extensive dewatering activity (under approved Abstraction Licences).

Working with the sub-contractors, Natural Wastewater Solutions (NWS) for the reed bed, and Salix River and Wetland Services and Vesi Environmental Ltd for the integrated constructed wetland, 33,904 tonnes of soil were removed and the ground re-profiled. 30,000 tonnes was re-used off site, whilst 3,000 tonnes was recycled and re-used on site, with the final 904 tonnes taken to landfill, due to the presence of Japanese knotweed.

Due to the impermeable nature of the soil, the reed bed and constructed wetland both required under-draining to minimise the impact on the groundwater table. Once the under-drains were installed, the basins were constructed, which included the following:

The site team pushed to see the first flows through the system just 12-months later, ahead of the 31 March deadline and handled the heavy rainfall from Storm Eowyn on 24 January without any issue.

A robust sampling regime is currently underway to understand the performance of the individual stages and final effluent from the nature-based solution. This will inform future permitting of these types of solutions in cooperation with the environmental regulator, Natural Resources Wales (NRW).

The initial sampling results are promising, with significant reductions in BOD, ammonia, total suspended solids (TSS) and phosphorus in the final effluent. River water quality sampling upstream and downstream of the outfall is also being carried out to understand the impact of the scheme on the Afon Lwyd.

Welsh Water is participating in the Chemical Investigation Programme (2025–2030) with UKWIR, where samples from the wetlands are currently being used to help understand bio-accumulation of emerging substances such as pharmaceuticals in intermittent discharges.

With the site due to open to the public soon, Pont-y-felin Lane exemplifies a paradigm shift in storm overflow management, demonstrating how nature-based solutions can deliver technical excellence, environmental restoration, and community enrichment, all while setting a precedent for low-carbon infrastructure in the water sector. The forward‑thinking optioneering, combined with the client’s commitment to selecting a nature-based solution, over traditional ‘grey’ options, has resulted in a scheme that proves natural solutions can deliver more sustainable outcomes, for less.

In recent times Seagahan WTW has faced ongoing issues including:

Unaddressed, these deficiencies could pose risks to regulatory compliance, limit future growth capacity, and increase the potential for Cryptosporidium contamination.

The Seagahan WTW Treatability Improvements Project has implemented a series of targeted upgrades to enhance water quality, improve operational resilience and maintain compliance. Key interventions included:

These upgrades are informed by a treatability appraisal conducted by Arup, which identified critical shortfalls and recommended improvements to ensure the facility could meet current and future regulatory standards.

NI Water engaged Arup and Murphy DAWSON-WAM (MDWAM) early in the project through an Early Contractor Involvement (ECI) approach, fostering a collaborative environment that allowed the project to evolve efficiently. As Principal Contractor, Murphy DAWSON-WAM, supported by strong coordination across all parties, successfully delivered the project on time and within budget. Arup played a dual role, providing NEC Project Management and Supervision throughout the construction phase, while also leading design reviews and approvals. Their involvement extended to managing stakeholder engagement within NI Water and liaising with external bodies such as the Department for Infrastructure.

A key success factor was the strong working relationship developed with NI Water’s Operations, which enabled a clear understanding of practical operability challenges. This collaborative approach informed strategic decisions around infrastructure layout, including pump and panel positioning, freeing up space for storage and maximising the use of existing buildings. These efforts not only streamlined project delivery but also ensured the long-term resilience of water treatment at Seagahan WTW.

ECI with MDWAM and Arup enabled a collaborative and informed approach from the outset of the project. Arup provided up-front technical input through treatability studies, which were instrumental in shaping Business Case submissions and developing focused Basis of Design reports. This proactive engagement supported scope progression and ensured a robust design strategy. Throughout the process, NI Water stakeholders were actively involved in decision-making, fostering transparency and alignment across all phases of delivery.

As designs evolved, a number of design review workshops were held which involved the use of walkthrough models to highlight pinch points and process walk-throughs.

Preference was for the new soda ash storage silo to be located indoors, restricted space for which was determined in the existing GAC building. MDWAM introduced innovative methods, including a 3D scan of the existing GAC building, to validate the feasibility of initial design proposals and facilitate the reuse of existing storage space. The volume and design of the storage silo were influenced by these constraints. The 3D scanning of the existing GAC building was instigated in the absence of record drawings, with new equipment designed to fit head height constraints and roller door access for installation.

A key design decision identified during a design review meeting was the introduction of a structural steel mezzanine platform level to locate the new MCC as floor space was limited.

During the initial investigations, the team identified gaps in the existing information relating to original structures, highlighting the need for further exploration. In several instances, monitoring data was unavailable, so dosing pump and process design had to be guided by SCADA trend analysis where possible. Temporary instruments were also set up during ECI to capture critical analytical data that was otherwise missing. These proactive measures ensured that design decisions were grounded in accurate, site-specific information, ultimately enhancing the reliability and efficiency of the final solution.

The project was delivered within a live operational environment, requiring meticulous planning and coordination to ensure continuity of service and safety. Construction on site began in December 2023 and completion was at the beginning of July 2025. The works were sequenced to minimise disruption to ongoing treatment operations, with close collaboration between the design, construction, and operations teams throughout. A key inherent risk exists when interfacing with existing operational works, live instruments and electrical assets, and this collaboration and careful planning helped to ensure no negative effect on network assets or output during the upgrade.

Early challenges included the failure of legacy equipment originally earmarked for reuse, such as manganese blowers and seized valving arrangements. These issues were addressed through rapid redesign and procurement, ensuring the programme remained on track. Spatial constraints within the site presented further complexity, particularly during the construction of the new dosing chamber and associated pipework diversions. Temporary works and phased excavation strategies were implemented to maintain access and operational integrity.

Modifications to the clean water tanks (CWT1 and CWT2) were carried out under confined space protocols. The installation of actuated valves and bell mouth fittings required innovative approaches due to restricted access openings. Sequencing was critical, with CWT2 brought back into service prior to converting CWT1 into a dedicated un-chlorinated backwash tank.

All works were delivered on a live site, with embargo periods and planned maintenance activities carefully managed. Temporary dosing systems were installed to facilitate safe changeovers, and effective stakeholder engagement with NI Water operations teams ensured that risks were mitigated and service continuity maintained. The new soda ash plant was commissioned in April 2025 and has since been used as the pH controlling process, taking over from the old system.

The project also included the installation of a new potable water supply to the site, with future-proofing measures incorporated to support additional connections. Engagement with DfI Roads and NI Water Distribution Teams ensured compliance and coordination with wider infrastructure planning.

As part of the project, several process-driven improvements were implemented to enhance operational reliability, chemical dosing accuracy, and overall treatment efficiency.

Soda ash system upgrade: The existing soda ash silo was experiencing structural issues and material bridging, leading to inconsistent dosing. A new soda ash system was installed, comprising a silo with integrated shakers, blowers, and a batch tank. A third mixing/maturation tank was introduced to stabilise pH levels and eliminate dosing spikes. Strategically positioned at the opposite end of the building, it also shortens suction lines and improves soda ash solubility. This upgrade ensures consistent material flow and improved pH control, particularly important given the variable pH levels observed due to temperature fluctuations in Seagahan Reservoir.

Potable water protection measures: To prevent back siphonage and protect potable water quality, the supply to the backwash tank was removed following its conversion to an un-chlorinated backwash tank. A new supply line was established from the main distribution network, ensuring compliance with water safety standards.

Centralised control via MCC panels: Motor Control Centre (MCC) panels were installed to provide centralised control of all newly commissioned equipment. This integration enhances operational oversight and simplifies maintenance procedures.

Efficiency gains in backwashing: The transition to unchlorinated water for backwashing has led to reduced chemical wastage and improved backwash efficiency, especially during periods of poor water quality. This required careful reconfiguration of valving arrangements and blanking off interconnections between tanks to prevent contamination of clean water leaving the site.

Flow monitoring & chemical dosing control: A dedicated flow meter chamber was constructed to monitor flow rates of orthophosphate and chlorine dosing. The flowmeter also interfaces with an actuated valve to regulate the filling of CWT1, now designated as the backwash tank. This setup allows for precise control of chemical dosing and tank filling operations.

To protect operatives, the chlorine and orthophosphate are installed in separate chambers to reduce the risk during leaks. This item was identified during a hazard identification meeting.

Hydraulic improvements: The upstand level of CWT2 was increased to enhance hydraulic head, supporting improved flow dynamics across the system. An actuated valve was installed to prioritise flow between the backwash line and CWT2, ensuring that neither system is starved during simultaneous operations.

Water recovery gains: The backwash system was previously a bottleneck to reliable output, following review a hydraulic restriction in the lamellas was identified and addressed which allowed a greater flow to pass through them to reach their design capacity. This improved the overall efficiency and removed the bottleneck, providing headroom in the dirty wash water system and ultimately providing the works with more frequent backwashing facilities.

The Seagahan WTW Treatability Improvements Project incorporated a range of innovative and sustainable measures that enhanced delivery and long-term operational performance. By maximising existing assets and deploying efficient technologies, substantial carbon and financial savings were achieved, both in construction and ongoing operation.

A 3D scan of the GAC building was undertaken to address the absence of reliable as-built records. This enabled accurate coordination with the BIM model and informed the design of new equipment, including a bespoke mezzanine platform for the MCC panels, optimising use of available space.

Sustainability was embedded throughout the project. Excavated material was reused on-site for landscaping and reprofiling, eliminating disposal costs and reducing carbon emissions. Modular blocks were re-purposed for use on other sites, supporting circular economy principles.

The introduction of a third process tank and the use of un-chlorinated water for backwashing improved chemical efficiency and reduced waste, particularly during periods of algal blooms. Additional measures included the installation of a spill tank with integrated safety features and the design of dosing skids with enhanced access and flushing capabilities.

These innovations supported efficient delivery, reduced environmental impact, and aligned with NI Water’s long-term sustainability goals.

The project exemplifies sustainable infrastructure delivery, with substantial environmental and financial benefits realised through three key initiatives:

Overall, the combined impact of these measures in the first year is estimated to deliver a total carbon saving of 64 to 105 tonnes of Co2e and a cost saving of between £351,216 to £502,432.

The Seagahan WTW Treatability Improvements Project was successfully delivered on time and within budget driven by early contractor involvement, innovative design solutions, and a shared commitment to operational excellence and sustainability. With this project NI Water has been able to enhance operational efficiency, enable real-time monitoring via advanced SCADA telemetry, and has future-proofed the system for further instrumentation upgrades. Collaboration between the client, project manager, contractor and other key stakeholders was central to the execution of the project and its overall success.