Supply Chain - Networks - Sewerage - Pipework Supports & Accessories

The Scunthorpe Wastewater Flooding Defence (WFD) Programme aims to reduce the number of spills from key combined sewer overflows (CSOs) during periods of heavy rainfall. For the South Grange, Brigg Road and Grange Lane North CSOs, a sustainable stormwater management solution was required to retain excess water and reduce intermittent storm discharges at all three CSOs, improving the biological oxygen demand (BOD) concentration in Bottesford Beck. As part of Severn Trent’s commitment to environmental compliance and improving water quality, an effective and efficient delivery was critical. Challenges

Tasked with reducing storm discharges to local watercourses, Avove developed a robust delivery model that ensured a seamless process to achieve key project objectives, whilst minimising disruption to residents. To overcome the project challenges, required blending collaboration and innovation in a way that unlocked measurable long-term benefits for Severn Trent and these included:

Location adjustments: At Brigg Road, the proposed shaft tank location was adjacent to an old building with limited space and difficult access. Following a thorough site review, an alternative location was agreed, delivering significant Health, Safety, Environment and Quality (HSEQ) benefits. Confined space: The confined nature of the site at Grange Lane North presented challenges for construction and operations. These constraints were resolved through the utilisation of an empty building, which was repurposed to provide temporary accommodation and a laydown area for materials. Risk Management: A comprehensive risk register was created to outline potential risks and mitigation strategies. For example, infrastructure risks when crossing a gas pipeline were identified, and through careful planning, were addressed by the Avove project delivery team.

All risk reduction meetings and planning phases were underpinned by collaboration, as the combined expertise of the project team played an important role in strategising an effective response to ensure that the project did not deviate from the scope.

[caption id="attachment_25960" align="alignnone" width="1200"] Work area - Courtesy of Active Tunnelling Ltd[/caption] The approach

Collaborative planning and consistent communication was key to a successful delivery across all three sites. Avove prioritised early engagement with suppliers, particularly for precast items, to secure timely deliveries and reduce the likelihood of budget overruns caused by unforeseen delays. This detailed approach delivered important long-term benefits and facilitated open communication and mutual trust throughout the project’s lifecycle.

With overarching principles of communication and collaboration in place, the technical prowess of the project teams was enhanced. With confidence that key materials would be delivered on time, operatives could begin work, using their expertise to ensure an innovative and sustainable completion. This approach entailed:

Early contractor involvement (ECI): Collaborative input from all stakeholders during the preliminary stages helped to develop innovative solutions and reduce later risks. This was particularly important in terms of design planning, as the Brigg Road shaft tank was relocated following an inspection. Multidisciplinary collaboration: Spanning civil, mechanical, electrical, geotechnical, structural and environmental engineering, multidisciplinary collaboration was facilitated through close engagement with sub-consultants. As such, all designs met the programme’s requirements, maintaining continuous alignment with Severn Trent’s team. Coordinated design process: This process enhanced buildability and reduced environmental impacts through a balance of cost, quality and carbon considerations. From minimising energy usage to cutting waste, the project achieved a significant reduction in emissions by removing the need for additional pumps. Effective programme management: Although it was a complex, multi-phase project, the structured approach comprised of regular project meetings to review progress against detailed schedules, ensuring activities were synchronised.

To complete this approach, Avove supported the communication process between the client and local stakeholders, with the project team assisting with land and planning matters. This involved the distribution of letters to residents, the negotiation of land access with owners and occupiers and following up on any concerns during the execution of works.

[caption id="attachment_25953" align="alignnone" width="1200"] Construction continued throughout the night - Courtesy of Active Tunnelling Ltd[/caption] Scunthorpe WFD Programme: Supply Chain - key participants Client: Severn Trent Delivery contractor/main contractor: Avove Land & planning services: Dalcour MacLaren Shaft construction: Active Tunnelling Ltd Mechanical & electrical works: PJT Pumping Services Ltd VacFlush™ system: CSO Group Ltd Drainage works: VP Groundforce Shorco Core drilling: Matte Black Surfacing Plant: Trenchless Plant Ltd Concreting finishing: Overhall Contractors Ltd Concreting finishing: Groundtech (UK) Ltd Tarmac: Cemex The solution

The Scunthorpe WFD project aligned with Severn Trent’s organisational goals of sustainability, biodiversity and environmental responsibility. By constructing large, off-line shaft tanks to manage stormwater flows from existing CSOs, the BOD concentration in Bottesford Beck was improved.

Effective Design & Delivery: Through effective design and delivery, the South Grange shaft tank (25m x 12m deep), Brigg Road shaft tank (12.5m x 14m deep) and Grange Lane North shaft tank (20m x 15m deep) were all successfully installed along with supporting infrastructure. Technical Expertise: The tanks were connected to the existing combined sewerage system through 1,050mm diameter inlet pipes. A twin-pumped return system was activated by telemetry from Yaddlethorpe Sewage Treatment Works, ensuring stormwater was returned, once permitted. Additionally, MCC kiosks, flushing systems, vent stacks, rising mains and sewers were all introduced as part of the comprehensive works. Sustainable Technology: Sustainability was embedded into every stage of the project. For the South Grange scheme and the Grange Lane North scheme, the initially requested pumped washing facility was replaced with the patented VacFlush™ system from CSO Group Ltd. Not only did this reduce maintenance and operational costs, but it lowered power requirements and cut carbon emissions at two of the three shafts. [caption id="attachment_25956" align="alignnone" width="1200"] VacFlush™ system installation - Courtesy of Active Tunnelling Ltd[/caption] The VacFlush™ system is an automated vacuum flushing system designed to clean storm tanks, holding tanks, and sewer networks without requiring manual entry into the tank. It utilises a vacuum pump to draw wastewater into a flush chamber, which is then rapidly released by a diaphragm valve, creating a powerful surge that cleans the tank floor and removes sludge. Key benefits include safe operation without man entry, efficient cleaning of large tanks, minimal maintenance, and automatic operation, often using the stormwater itself for flushing Landscape Preservation: Through effective programme management and the utilisation of design and construction expertise, we avoided tunnelling under the A1029 highway and crossing strategic assets, preserving mature trees in the process. Budget management: Integral to the project’s success and the feasibility of the solution was effective cost management. We maintained robust budget and cost control throughout the programme of works by implementing comprehensive Cost Value Reconciliation (CVR) reports, which were updated monthly to reflect expenditure and forecast completion costs.

It was through a careful combination of sustainability, innovation and collaboration that a highly effective solution was identified and implemented, helping us achieve a high degree of client satisfaction.

[caption id="attachment_25959" align="alignnone" width="1200"] (left) Roof beams in place, and (right) start of the roof panel installation - Courtesy of Active Tunnelling Ltd[/caption] Benefits

The Scunthorpe WFD project delivered a range of long-term benefits, many of which were wide reaching, both in terms of compliance and structural integrity. Beneficial to both the client and their customers, the project achieved:

Long-term compliance: The solution improved the BOD concentration in Bottesford Beck, meeting the Environment Agency’s ‘Good’ standard. Environmental enhancements: The project supported the improvement of nearby rivers, reducing the risk of pollution incidents whilst contributing to Severn Trent’s broader goal of improved watercourse health. Enhanced innovation: Collaborative working between Avove, Severn Trent and other key partners allowed for greater innovation and the successful delivery of robust off-site holding tanks. Future-proof design: The solution’s design ensures long-term compliance and operational effectiveness for years to come. Operational efficiency: Our team demonstrated technical excellence throughout the project’s delivery, ensuring the new solution was fit for purpose and operationally efficient. Time and cost-effectiveness: A proactive and highly collaborative approach streamlined the entire delivery, saving time and reducing costs. Improved safety: Best-in-class construction methods and thorough planning processes ensured the works were completed safely. [caption id="attachment_25957" align="alignnone" width="1200"] Installation of the roof slabs - Courtesy of Active Tunnelling Ltd[/caption] The results

Working diligently to achieve an expedited programme across all three sites, hard work and commitment ensured a seamless delivery, well within time and budget requirements. With regulatory deadlines to meet, it was imperative that a highly collaborative approach was adopted, with open communication and the implementation of a clear structure guiding the project.

The new off-line tanks effectively retain stormwater, reducing pressure from the existing network and improving water quality much to the benefit of the environment, Severn Trent and their customers.

Portadown is a large town in County Armagh, Northern Ireland located approximately 24 miles south-west of Belfast and nestled along the banks of the Upper River Bann. Over recent years, Portadown has transformed from a historically industrial town into a modern hub with a rapidly growing logistics sector and retail environment attracting high footfall and continued economic growth. Meadow Lane Wastewater Pumping Station (WwPS), located within the central retail area of the town, was constructed in 1966. The site forwards flow to a downstream gravity sewer system before subsequently flowing into the southern inlet of Seagoe WwPS, approximately 1.5 miles away. Need for upgrade

Meadow Lane WwPS was identified as requiring significant base maintenance interventions due to the antiquated nature and condition of existing pumps, pipework and control assets which require a high level of maintenance; thus, imposing a risk of potential significant failure. The following observations were made on site:

Existing pumps showed signs of extensive wear (supported by observed power loadings). Control motors were identified as being installed pre-1975. The existing motor control centre (MCC) did not satisfy current asset standards.

NI Water Technical Support had also advised of occurrences of flooding within the dry well as a direct result of leaking pumps which required reactive maintenance and tankering operations.

Additionally, following completion of the 2007 Portadown Drainage Area Study, Meadow Lane WwPS was identified as a required output. It was outlined to NI Water the need for the existing Meadow Lane WwPS to deliver flow to full treatment (FFT) if the upstream network spill performances are to meet the Northern Ireland Environment Agency (NIEA) requirements for the Meadow Lane catchment area.

[caption id="attachment_26864" align="alignnone" width="1200"] Secant piles with reinforced concrete capping beam - Courtesy of BSG Civil Engineering Ltd[/caption]

Model updates were completed in 2016 following flow monitoring surveys, and further inspections confirmed that the existing pumps could not deliver the required FFT. Therefore, the five CSOs identified by the NIEA as Unsatisfactory Intermittent Discharges (UIDs) could not be closed without significant intervention/upgrade at Meadow Lane WwPS. Model updates were also completed in 2020 to reflect predicted future 2040 flows.

The NIEA had identified the following five CSOs as UIDs:

Meadow Lane One CSO. Meadow Lane Two CSO. Portmore Street CSO. Clonavon Avenue CSO. Meadow Lane Health Centre CSO.

Failure to address spills would lead to potential prosecution by NIEA and associated reputational damage due to potential serious sewage flooding and pollution to the Annagh River, Upper River Bann and the surrounding area.

Early Contractor Involvement (ECI)

NI Water appointed BSG Civil Engineering Ltd as the main contractor under an NEC3 Early Contractor Involvement (ECI) Contract. As the main contractor, BSG provided multi-disciplinary design, project and supply chain management and civil engineering and MEICA works for the contract from inception to completion.

The ECI phase allowed BSG to align resources and integrate objectives with the client, NI Water, and project managers, McAdam, at an early stage to benefit overall project delivery. This allowed for enhanced collaboration, innovation, value, efficiency and reduced whole life cycle costs for the project.

[caption id="attachment_26863" align="alignnone" width="1200"] Liner wall formwork using Peri Rundflex - Courtesy of BSG Civil Engineering[/caption] Meadow Lane WwPS: Supply chain - key participants Project delivery: BSG Civil Engineering Ltd Civil, hydraulic & process designer: McAdam Temporary works design: MEA Ltd Earthworks: BSG Civil Engineering Ltd Specialist piling contractor: Quinn Piling Limited Formwork: Peri UK Reinforced concrete works: ONCCE Ltd Tunnelling contractor & TBM: B&W Tunnelling Ltd Open cut pipe installation: Phace Contracts Ltd Open cut pipe installation: O’Neill Contracts & Plant Hire Open cut pipe installation: AG Wilson Civil Engineering Groundworks: RMG Metalwork & FST designer/installer: RJ Smyth Engineering Precast roof beams: Macrete (Ireland) Ltd Precast roof slabs: Creagh Concrete Precast concrete pipes: Tracey concrete Screens: Eliquo Hydrok Ltd Submersible pumps & float switches: Xylem Water Solutions Flow meters: Siemens Control panels: Motrol Ltd Kiosks: Quinshield Ltd Primary drivers

The purpose and drivers of this project were as follows:

Ensure a reduction in spill frequency and volume through the provision of adequate storage facilities within the Meadow Lane catchment area. Closure of the five unscreened UIDs (identified by the NIEA) and subsequent provision of sewer upgrades in the upstream catchment to transfer flows from the closed UIDs and provide online storage. Resolution of three DG5 properties within the Meadow Lane area. Essential replacement of Meadow Lane WwPS with provision of a screened emergency overflow. [caption id="attachment_26865" align="alignnone" width="1200"] Pouring of 400m3 base slab - Courtesy of BSG Civil Engineering[/caption] What the upgrade involved

The upgrade of Meadow Lane WwPS and the associated network was a large-scale infrastructure project located within a complex urban environment. The project saw:

The installation of 380m of 1,500mm diameter tank sewer approximately 7m below ground level. The installation of 350m of sewers ranging in diameter from 300mm to 1500mm via open cut techniques in depths ranging from 2m to 7m below ground level. The demolition of the existing Meadow Lane WwPS. The construction of a new inlet chamber, wet well pumping station and 1,500m3 storage tank at the existing Meadow Lane WwPS site. The installation of a new MCC panel and associated glass reinforced plastic (GRP) kiosk. The installation of three 37kW foul pumps and two 9kW hydro ejectors. The installation of three screens from Eliqua Hydrok Ltd. The closure of five unscreened UIDs. 1,500mm tank sewer installation

Meadow Lane is an arterial route through Portadown town centre, providing access to several shopping facilities, restaurants and medical facilities. It was identified that significant traffic management, potentially involving lengthy diversions, would be required for an extended period to undertake the installation of the 1,500mm diameter tank sewer along Meadow Lane using open-cut methods.

[caption id="attachment_26861" align="alignnone" width="1200"] Pipejacking operation within launch pit - Courtesy of BSG Civil Engineering[/caption]

Therefore, it was determined that a trenchless pipejacking method of installation would be adopted to install the full 380m of 1,500m tank sewer. Additionally, the use of a tunnel boring machine (TBM) would allow for a reduced potential environmental impact due to the reduction in surface disruption, dust, noise and vibrations; and provide enhanced safety for construction staff due to the automated installation process.

Due to the unstable ground conditions, a closed face slurry system was used as this technique allowed the area around the TBM to be supported with a pressurised bentonite mix, preventing collapse and ensuring stability. During this process the excavated material was pumped from the face of the TBM, through the installed tunnel, to an above-ground separation system where the excavated material was removed from the bentonite mix, allowing it to be recycled and returned to the tunnel face for reuse.

The tunnelling operation was undertaken in three stages with launch and reception pits installed to facilitate each drive stage alongside ancillary tunnelling operations; drive stages varied in length between 70m to 230m. Due to the varying and difficult ground conditions present along the proposed tunnelling route, launch pits and reception chambers were installed using a combination of both segmental shafts and traditional cofferdams.

Storm retention tank, inlet chamber & wet well pumping station

The storm retention tank, inlet chamber, and wet well pumping station was designed as one structure. Due to the difficult ground conditions, high water table and proximity to existing NI Water assets, it was determined that secant piling would be implemented as a means of providing temporary support to facilitate safe excavation.

[caption id="attachment_26853" align="alignnone" width="1200"] Installation of concrete beams - Courtesy of BSG Civil Engineering Ltd[/caption]

A specialist piling contractor was utilised to install 140 (No.) 750mm diameter secant piles to a depth of 18m below ground level before the installation of a reinforced concrete capping beam to complete the excavation support system. Once installed, the secant piled wall provided a watertight structure. Localised dewatering within the secant piled structure was used to ensure excavated material remained dry and suitable for reuse on site. Approximately 3500m3 of material was removed from the 21m diameter, and 10m deep excavation.

Construction of the storm tank consisted of a 1200mm deep reinforced concrete base, a 400mm thick external liner wall, and a 500mm internal dividing wall. The liner wall formwork was designed as a single sided system using Peri Rundflex and constructed in two lifts to meet temporary works restrictions.

The roof structure was constructed using 1250mm by 900mm precast beams and 450mm thick precast hollow core slabs. Structural screed was then poured to complete the structure.

The complex roof slab arrangement consisted of a variety of construction techniques including in situ reinforced concrete elements, precast concrete primary and secondary beams, structural steel beams and hollow core precast slabs. The complete design of the roof structure was provided by five different design companies working in collaboration ensuring each element adhered to the tight tolerances required for accurate placement.

Open cut sewer installation

Six sections of open-cut sewer installation were completed in this scheme. Boxed systems were used to provide temporary works excavation support for the pipe installations. Sewers were installed to depths of up to 7m below ground level in sites with limited working room. Traffic flows were controlled by complex traffic management systems.

[caption id="attachment_26858" align="alignnone" width="1200"] Open cut sewer installation at Manhole No. 4 - Courtesy of BSG Civil Engineering Ltd[/caption] MEICA installation

The MEICA installation was completed in two stages. A new MCC was installed within the new GRP kiosk, and once all building services were installed, the NI Electricity supply was diverted to the new MCC panel which then backfed a supply to the existing MCC panel until turn of flows in April 2025.

Once civils construction had sufficiently advanced, the second phase of the mechanical fit out commenced, where the three 37Kw foul pumps and associated pipework were installed from the foul pumping station to the flow meter chamber. A 250mm Siemens MAG 5100w was then installed to measure the outgoing flow-rate. Two pump stools, 9Kw hydro ejectors and pipework were installed within the storage tank to jetwash the tank during storm events.

Three Eliquo Hydrok Ltd screens were installed into the following areas:

Inlet screen chamber: 600l/sec Mecmex™ screen. Foul pumping station overflow screen chamber: 70l/sec static Peak Screen™. Storage tank overflow screen: 264 l/sec static Peak Screen™. [caption id="attachment_26855" align="alignnone" width="1200"] Pump remote enclosures and actuators - Courtesy of BSG Civil Engineering[/caption] Additional construction challenges

The main challenges faced during the delivery of Meadow Lane WwPS were a combination of site-specific constraints, environmental constraints and equipment/asset failures during the construction period. Some of the additional challenges experienced during the construction stage have been outlined below.

Portadown has been identified within the Northern Ireland Flood Risk Management Plan as an area of significant flood risk, due to regular fluvial flooding from the Upper River Bann and its tributaries. The most recent significant flood event was recorded in 2024, which saw substantial flooding across the entire work site. This fluvial flood event led to a halt in works on site for approximately one week and caused damage to plant.

The 500mm diameter outlet pumping main from the existing Meadow Lane Pumping Station ruptured on two occasions during the construction programme. To carry out the repair on the outlet pumping main, both Meadow Lane and Annagh WwPS had to be shut down and seven tankers were mobilised to transfer effluent to other NI Water treatment facilities. BSG Civil Engineering Ltd was able to utilise the newly constructed storm tank to create temporary storage and prevent any out-of-sewer flooding during the emergency repair works. BSG received positive feedback from NI Water on how these critical network emergency repair works were managed and rectified in a safe, collaborative and timely manner.

[caption id="attachment_26857" align="alignnone" width="1200"] (left) Fluvial flooding event in 2024 within the site compound, and (right) utilising the new storm tank for temporary storage following an outlet pumping main failure - Courtesy of BSG Civil Engineering Ltd[/caption] Stakeholder communication

NI Water and the project team recognised the potential negative impacts which could arise from undertaking such a large-scale project within a busy town centre location and from an early stage embarked on a strategic communications strategy to ensure key stakeholders were informed of the works and kept updated throughout.

As part of the public relations programme the project team and NI Water Communications held early briefings with a range of stakeholders including elected representatives, town centre management, chamber of commerce, health care centre, council, roads authority, landowners and local businesses.

In addition to the numerous one-to-one meetings, letter drops were carried out in advance of each section of road works commencing and press releases issued to the local media to advise the wider public of traffic management. Variable message boards were erected on main routes and large-scale project boards helped to convey the huge investment being made by NI Water and the resulting benefits for the public.

Key project milestones were publicised along with facts and figures relating to the construction work and tunnelling exercise.

Regular project updates and lookahead bulletins were issued to stakeholders to keep them up to date on progress and advise them of future traffic management requirements. Town centre management were invited to site at key stages of the project to view progress and hear firsthand about the benefits the NI Water investment will bring to Portadown.

BSG provided a point of contact for operational queries and this, along with NI Water’s wider stakeholder communications, helped to ensure a smooth-running construction programme.

[caption id="attachment_26859" align="alignnone" width="1200"] Completed Meadow Lane WwPS (July 2025) - Courtesy of BSG Civil Engineering Ltd[/caption] Outcomes

NI Water directed significant financial investment into upgrading the existing sewer network and Meadow Lane WwPS within the Meadow Lane area of Portadown. The proposed works oversaw the closure of five CSOs within the Meadow Lane WwPS catchment area through connection into the new 1,500mm tank sewer alongside the resolution of three DG5 properties.

The collaborative effort between NI Water, BSG Civil Engineering Ltd and McAdam resulted in the smooth completion of the programme and successful testing, commissioning and handover to NI Water in July 2025. The benefits of the new infrastructure will be realised almost immediately through a reduction in spill frequency and volume within the Upper River Bann and Annagh River.

This project showcased the capabilities of NI Water, BSG Civil Engineering Ltd and McAdam to coordinate and undertake sensitive high-risk activities such as a large-scale turn of flow without issue and within a complex urban environment.

Leamington Spa is a historic spa town with a growing population and significant development pressures. The River Leam, which flows through the town centre, is a focal point for recreation, including wild swimming, boating, and public parks. The sewerage catchment includes Leamington, Warwick, and surrounding villages, all draining to Longbridge Sewage Treatment Works (STW). Six CSOs were identified for improvement. This requirement was designed to safeguard public health and ensure compliance with the Bathing Water Directive and related water quality with the aim to reduce spill volumes and spill frequency with a variety of interventions; to give an insight into the best approach for bathing waters. Endorsed by Ofwat in 2021, the scheme is part of a broader strategy to support post-pandemic economic recovery through environmental infrastructure investment. The Leamington scheme exemplifies innovation in hydraulic modelling, and collaborative delivery within tight regulatory timeframes. Project overview

The Green Recovery Leamington Spa Sewerage Scheme is a flagship initiative under Severn Trent’s Green Recovery programme, aimed at moving a stretch of the River Leam towards bathing quality. This ambitious project addresses the performance of six critical Combined Sewer Overflows (CSOs) in Royal Leamington Spa, Warwickshire, through a suite of technically advanced designs that test a variety of complementary solutions.

Few projects manage to balance technical complexity with community benefit as seamlessly as the Leamington Spa Sewerage Scheme with live public functional spaces is technically complex but also requires attentive and agile stakeholder engagement, delivering large measurable environmental improvements.

[caption id="attachment_26765" align="alignnone" width="1200"] Surface water separation - Courtesy of Forkers Ltd[/caption]

While early guidance targeted storm overflows with direct discharges into these areas, the programme has since expanded to include overflows that pose wider environmental and public amenity impacts. This includes high amenity areas such as recreational waters and areas of interest to businesses and other organisations, even if they are not formally designated as bathing waters.

The shift reflects a more holistic approach to water quality management, prioritising interventions based on environmental sensitivity, public usage, and the potential impact of overflows. This broader targeting ensures that improvements are aligned with community expectations and environmental stewardship goals.

Hydraulic modelling & option development

The project leveraged the Longbridge Strategic Sewerage Growth model, enhanced with updated flow monitoring and surface water network refinements. Hydraulic solutions were identified early through iterative hydraulic modelling and refined through feasibility and Early Contractor Involvement (ECI) with Forkers Ltd.

By integrating advanced hydraulic modelling and real-time control, the scheme exemplifies the kind of forward-thinking infrastructure needed to meet the challenges of climate resilience and urban growth.

Preferred interventions included surface water separation, pumped and gravity storage, and network optimisation.

[caption id="attachment_26764" align="alignnone" width="1200"] Shaft storm tank precast concrete segments - Courtesy of Forkers Ltd[/caption] Leamington Spa Sewerage Scheme: Supply chain - key participants Deliver contractor: Forkers Ltd Designer: WSP Tunnelling/shafts/timber headings: Active Tunnelling Ltd Electrical/mechanical: STAL (UK) Ltd Ground support & shoring: MGF Ltd Vacuum excavation: VAC UK (Kilkern Ltd) Drainage sub-contractor: Arthur Civil Engineering Ltd Emergency temporary pumping: Selwood Precast concrete pipe & rings: Marshalls Civils & Drainage Precast concrete rings: FP McCann Ltd Plastic storage pipes: Aquaspira Ltd GEOlight® storage tank: SDS Limited Concrete & aggregates: Aggregate Industries | Cemex Plant hire: Flannery Plant Hire (Oval) Ltd Traffic management: RouteOne Traffic Management Ltd Carriageway surfacing: JMC surfacing Ltd Surface water separation (SWS)

A major surface water separation scheme was implemented between Campion Road and Milverton School, delivering significant benefits in surface water management. The project successfully disconnected impermeable areas from the combined sewer network, reducing the volume of stormwater entering the system. Additionally, it incorporated below-ground storage to help manage flood risk, enhancing the area’s resilience to heavy rainfall events and contributing to improved environmental outcomes.

[caption id="attachment_26763" align="alignnone" width="1200"] Surface water separation - Courtesy of Forkers Ltd[/caption] Pumped & gravity storage

The Lower Avenue Combined Sewer Overflow (CSO) scheme involved the installation of an 880m3 shaft tank with a return flow capacity of 30 l/s, located in the Station Approach car park. The shaft tank was designed and constructed by Active Tunnelling Ltd. At Princes Drive 19B, the scheme increased the flow into the existing storm tanks by an additional 75 l/s. Both storage systems were equipped with real-time control (RTC) logic to optimise return flows and minimise the risk of spills into the river, ensuring more efficient and environmentally responsible stormwater management.

Climate change & resilience

To ensure long-term resilience and performance under changing climate conditions, the design rainfall was uplifted by 15% to reflect projected 2050 scenarios. Spill frequency assessments were carried out using Severn Trent’s Technical Standard Rainfall Dataset, representing worst-case conditions to ensure robust system performance. All conveyance infrastructure was sized accordingly to accommodate future climate impacts, supporting sustainable and reliable operation over the asset’s lifetime.

Construction & delivery

The project was delivered under tight AMP7 deadlines, requiring early contractor involvement and agile design development. Forkers Ltd and WSP played key roles in feasibility, site investigation, and outline design.

Key construction innovations included the use of GEOlight® blocks from SDS Limited for modular storage. GEOlight® blocks offer a significant advantage in large-scale infrastructure projects due to their lightweight, corrosion-resistant design, which simplifies installation and reduces long-term maintenance costs compared to concrete or steel alternatives.

[caption id="attachment_26767" align="alignnone" width="1200"] GEOlight® modular storage tank - Courtesy of Forkers Ltd[/caption] Environmental & community benefits

Reducing the impact from CSOs has had significant social implications. Access to clean and safe recreational waters promotes public health and well-being, encouraging outdoor activities and fostering a connection with nature. This initiative does not just solve a problem, it redefines what is possible in urban water management, setting a precedent for future projects across the UK and beyond.

Spill reduction. Flood risk: No detriment demonstrated; some areas show betterment particularly through the implementation of surface water separation in the north-east, the construction of stormwater storage tanks in the south, and comprehensive improvements along the River Leam corridor aimed at enhancing water quality and resilience. Education: Engagement with Milverton School on drainage and sustainability. Broader significance & replicability

The Green Recovery Leamington Spa Sewerage Scheme stands as a testament to the power of innovative engineering and sustainable practices in addressing modern environmental challenges. This project not only resolves immediate issues related to CSOs but also sets a benchmark for future initiatives aimed at enhancing urban wastewater management.

The Leamington Spa Surface Water Separation Scheme, delivered as part of Severn Trent’s Green Recovery Programme, exemplifies a forward-thinking approach to sustainable water management.

Central to the project was the installation of a two megalitre GEOlight® attenuation tank from SDS Limited beneath a playing field adjacent to Milverton Primary School. The tank, connected to newly laid surface water sewers across several roads in Leamington Spa, significantly increases stormwater storage capacity within the network. This enhancement plays a critical role in protecting downstream sewage treatment infrastructure from overload and reducing the frequency of combined sewer overflows into the River Leam.

[caption id="attachment_26768" align="alignnone" width="1200"] Construction of the 2 megalitre attenuation tank - Courtesy of Forkers Ltd[/caption]

The project not only supports Severn Trent’s ‘Get River Positive’ commitments but also aligns with local and national planning policies. By integrating innovative technology with sustainable construction practices, the scheme delivers measurable environmental benefits. It demonstrates how targeted infrastructure investment can contribute to long-term river health, climate resilience, and community wellbeing; setting a precedent for future water management initiatives across the region.

Its success lies not only in the numbers (reduced spills, increased storage, improved water quality) but in the way it brings together engineering excellence, ecological sensitivity, and community engagement. The project’s legacy will be felt not just in the River Leam’s improved health, but in the model, it provides for sustainable, scalable, and socially conscious infrastructure.

Conclusion

The Green Recovery Leamington Spa Sewerage Scheme is a model of integrated water management, combining hydraulic engineering and community recreational benefit. It demonstrates how ambitious environmental goals can be achieved through technical excellence, collaboration, and innovation.

In a sector where impact is often measured in compliance, this scheme goes further; delivering outcomes that resonate with local communities, regulators, and the environment alike.

The project not only safeguards the River Leam for recreational use but also sets a precedent for inland bathing water schemes across the UK and beyond.

The Water Industry National Environment Programme (WINEP), developed by the Environment Agency, Defra, Natural England and Ofwat, is a regulatory framework that outlines the environmental obligations for water companies in contributing to the wider national objectives for the natural environment. One of its aims is to ensure that pollution incidents resulting from spills of untreated wastewater are better monitored and managed. The most significant requirement in this context is the retrofitting of event duration monitoring at sewage treatment works. EDM records the time and duration of storm water releases into rivers, lakes, oceans, or the surrounding land from combined sewer overflows (designated as U_MON1 under WINEP), when stormwater is diverted to a storm storage facility before being returned to the treatment process (U_MON3) and recording the flow being passed forward for treatment (U_MON4). The programme

Southern Water required the delivery of UMON_4, final stages of UMON_3, and MCERTS qualification for all monitoring equipment on spill overflow points by 31 March 2025.

Initially, Southern Water contacted Trant Engineering to carry out U_MON4 and EDM installations at 20 wastewater treatment works to be completed in AMP7, with Trant having previously installed 645 EDM and U_MON monitors for Southern Water in AMP5 and AMP6.

Prior to beginning design work, detailed site surveys were carried out to establish existing assets, the details of power, communications and telemetry hardware and to ensure that the new installations would not interfere with any other site processes.  Design work was all conducted by Trant’s inhouse electrical engineers working closely with Southern Water’s team to ensure a ‘right first time’ approach.

[caption id="attachment_26776" align="alignnone" width="1200"] FFT Radar at Petersfield WwTW - Courtesy of Trant Engineering[/caption] Challenges

Installing flow metering and EDM equipment sounds straightforward but, as is always the case in engineering, challenges arise. Although the concept design was identical for each site, the detail varied depending on individual site conditions: civil works, cable ducts, flow meter positioning, power supplies and many other factors.

Initial scoping is required to identify environmental considerations, including wildlife which may need to be moved or invasive species and the effect on programme. For example, a colony of bats had taken up residence in one of the existing kiosks, but fortunately, after careful monitoring, by the time installation was due to commence the colony had moved on.

Another challenge was that completed installations had to be certified by Environmental Flow (one of only four independent MCERTS approved bodies in the UK). With so many EDM schemes being installed around the country, Environmental Flow Ltd was very busy, so any missed scheduled sign-off date could have resulted in long delays. Thus, commissioning was completed strictly to a year-long rolling programme.

Project management

Installations were made ready for switchover in a brief window to ensure that reporting time would not be compromised. Installation and commissioning at several sites were carried out simultaneously and the region was split into two sectors. Each with its own delivery team including electrical, installation along with civils, and mechanical operatives to enable the delivery to be met.

To cover all the work in such a condensed time, staff were allocated allowing back-to-back design, installation and commissioning. The programme evolved collaboratively with Southern Water as the requirements become known, and Trant was able to build, invest and recruit into the programme.

Some of the sites had a history of power outages, which created some concerns for Southern Water about potential loss of data reporting. As a result, Trant proposed to install individual uninterruptable power supplies (UPS) to maintain power for 12 hours. Southern Water decided that the additional cost presented real value in terms of security and their MCERT coordinator was sufficiently impressed to request that a UPS be installed on all the schemes, including retrofitting at those already completed.

[caption id="attachment_26774" align="alignnone" width="1200"] Instrument board including new FFT monitor, FTS monitor and storm return MAG - Courtesy of Trant Engineering[/caption] Undertakings

Running many small, live sites concurrently meant a large volume of paperwork to ensure that there was minimal interruption to normal service: risk-assessed method statements, permits to work had to be submitted in a timely manner, and this needed close cooperation between all stakeholders. Trant demonstrated organisational proficiency as further sites were given with the final 35 sites to be completed in an eight-week period to meet tight accelerated WINEP deadline of 31 March 2025. Following which, Southern Water awarded Trant a further 40 sites. Later increasing to 91.

EDM & U_MON4 Programme Supply chain: Key participants Client: Southern Water Principal designer & contractor: Trant Engineering Civil design: Godsell Arnold Partnership Ltd Electrical installation: SRE Services Ltd Civil installation: DR Clark Services MCERT inspections: Environmental Flow Ltd FFT instrumentation: Vega Controls Ltd Flow meters: Siemens Project success

Whilst Trant were completing the initial schemes, Oliver Lockwood Southern Water’s Capital Delivery Project Manager was impressed by the performance.

“The Trant team has delivered incredible work across the U_MON projects, their exceptional efforts over AMP7, successfully delivering our U_MON3 regulatory outputs, as well as the challenging U_MON4 project while simultaneously finishing the final EDM programme deliverables. The work has not gone unnoticed.

“The team has demonstrated flexibility under numerous pressures and collaborated seamlessly with Southern Water and other delivery partners. Your experience has been a significant factor to the overflow monitoring performance, and I can confidently say that the successes of these projects would not have been possible without your collective skill and dedication.”

[caption id="attachment_26775" align="alignnone" width="1200"] New Storm Return MAG Sensor at Cowfold WwTW - Courtesy of Trant Engineering[/caption]

In all, Trant completed a total of 496 EDM installations for Southern Water during AMP7 by the regulatory date of 31 March 2025 and have now delivered over 1,000 such monitoring installations over the past three regulatory periods for Southern Water.

Southern Water’s EDM & U_MON4 Programme provides full visibility of events from every overflow in Southern Water’s network as well as monitoring Flow to Full Treatment (FFT) to meet the regulatory deadlines. The works saw just under 100 sites upgraded across Kent, Hampshire, the Isle of Wight, and East & West Sussex.

The requirement of the Burnley Integrated Catchment Scheme is the River Water Quality Improvement for the Water Framework Directive (WFD) driver identified in the Water Industry National Environmental Programme (WINEP) to achieve a ‘Good’ status in the defined reaches of Pendle Water and the River Calder. The project, which commenced in 2020, is one of United Utilities’ largest AMP7 investments and is being delivered by Advance-plus, a joint venture between MWH Treatment, J Murphy & Sons (JMS) and Stantec UK. In previous articles published by Water Projects, United Utilities has shared the project journey from concept, solution design development, and construction. This case study focuses on the project team’s experience in achieving effective project outcomes. Project requirements & summary

To meet ‘Good’ status in Pendle Water and the River Calder, the treatment capability at Burnley Wastewater Treatment Works (WwTW) had to be enhanced to achieve compliance with the new treated effluent permit standards, coupled with management of storm discharges in the defined reaches, to achieve compliance with the WFD 99%ile wet weather intermittent standards. There are eight regulatory drivers attached to this WFD element of the scheme.

The project also includes two additional regulatory drivers for U_MON3 spill monitoring and U_MON4 flow monitoring.

Through complex river water quality and network modelling, the lowest whole life cost integrated catchment solution was determined and developed.

The Integrated Catchment Solution comprised four sites, which are all inter-dependent in delivering the regulatory outputs.

[caption id="attachment_26729" align="alignnone" width="1200"] Modification of existing PSTs 6, 7, 8 and 9 - Courtesy of United Utilities[/caption] Burnley WwTW

Serving a domestic population equivalent of approximately 107,000 plus trade load, Burnley WwTW has undergone a significant upgrade during this AMP7 project with the scope comprising the design, construction, and commissioning of:

A new Evoqua BioMag® activated sludge plant (ASP) from Xylem Water Solutions. The BioMag® system enhances conventional biological wastewater treatment by using magnetite (an iron oxide powder) to ballast the microbiological floc, creating an increase in mixed liquor suspended solids (MLSS) in the ASP and enhanced performance in the final settlement tanks (FSTs). A new 64-panel, 12,000m3 detention tank constructed by A-Consult Ltd with associated feed pumping station. A new additional (4th) primary settlement tank. A new 2500 l/s interstage pumping station (pass forward of FtFT and RAS flows). Refurbishment of the four existing FSTs. A new surplus activated sludge (SAS) thickening process. A new ferric and caustic chemical dosing plants. New MCCs, SCADA upgrade and power upgrade. U_MON3 event duration monitoring on spills to storm tanks. U_MON4 flow monitoring.

The final effluent quality for the new works at Burnley WwTW is to comply with both WRA (spot samples) and UWWTD (composite samples):

Design Permit WRA Parameter Average 95% ile Upper Tier Limit BOD 9 mg/l 50 mg/l Solids 40 mg/l Ammonia 2 mg/l 12 mg/l Total P 0.25 mg/l Iron 4 mg/l 8 mg/l Design Permit UWWTD Composite Samples Parameter Compliance Requirement Upper Tier Limit BOD 25 mg/l (or 70% removal) 50 mg/l COD 125 mg/l (or 75% removal) 250 mg/l Total P 2 mg/l (or 80% removal) [caption id="attachment_26728" align="alignnone" width="1200"] Evoqua BioMag® activated sludge plant - Courtesy of United Utilities[/caption] Burnley WwTW Catchment Strategy: Supply chain - key participants Client: United Utilities Construction Delivery Partner: Advance-plus JV MWH Treatment (Advance-plus jv) J Murphy & Sons (Advance-plus jv) Stantec UK (Advance-plus jv) Civil design detention tank: COWI UK Ltd Physical modelling: Hydrotec Consultants Ltd Dewatering design: OGI Groundwater Specialists Ltd Dewatering: Alba Dewatering Services Ltd Concrete construction: STAM Construction Ltd Detention tank shaft: Joseph Gallagher Ltd Pump station shaft: EJ Kelly Sheet piling: Sheet Piling (UK) Ltd PCC driven piling: Van Elle Concrete cutting: Holemasters Temporary works/shoring: MGF Ltd Precast post tensioned tanks: A-Consult Ltd Precast roof sections: Macrete (Ireland) Ltd Precast shaft segments: FP McCann Blower building: Saredon Steel Buildings Ltd BioMag® building: Gallaway Construction Ltd Access metalwork: Tushingham Steel Fabricators Evoqua BioMag® process: Xylem Water Solutions BioMag® mechanical installation: Alpha Plus Ltd [caption id="attachment_26724" align="alignnone" width="1200"] Detention tank water test - Courtesy of United Utilities[/caption] Civils & pipework: SGC Civil engineering Ltd Pumping station mechanical installation: Fluid Sealing & Engineering (FSE) Transformers: Winder Power Electrical installation: PICOW Engineering Group MCCs: Technical Control Systems Ltd Systems integration: Tata Consultancy Services SAS glass coated steel tank: Stortec Engineering Ltd Dosing systems: NPS Engineering Group PST fixed scraper bridge: EPS Water Epoxy coated carbon steel pipework & wall starters: Freeflow Pipesystems Ltd SAS drum thickeners: Huber Technology Odour control system: Air-Water Treatments Ltd PST odour covers: Corporate Engineering Ductile iron pipework: Saint Gobain PAM UK Ductile iron pipework: Electrosteel Castings (UK) Ltd FST scraper bridge refurbishment: Jacopa Ltd Blowers: Sulzer Pumps Wastewater Ltd Aeration system: Suprafilt Ltd SAS tank air mixing system: Utile Engineering Submersible pumps: Xylem Water Solutions Valves: AVK UK Ltd Standby generators: DTGen Kiosks: Industrial GRP Ventilation: Air Technology Systems Ltd Lindred Road CSO (PEN0056)

Work at this existing combined sewer overflow (CSO) site comprised the construction of an online 1,950m3 detention tank to store storm waters during times of heavy rainfall and reducing discharges to the watercourse. New pumps within the tank return the effluent to the sewer for onward treatment at Burnley WwTW. A new MCC and power supply were installed for this facility.

[caption id="attachment_18286" align="alignnone" width="1200"] Lindred Road detention tank during construction - Courtesy of United Utilities & Advance-plus[/caption] Altham Outfall Fennyfold CSO (BUR0026)

This existing CSO site is located in the local town of Padiham and on the sewer network that transfers flows to Hyndburn WwTW for treatment. The solution at this site was to construct a new chamber over the downstream sewer, install a new ‘real time’ controlled actuated penstock valve that regulates and optimises flows passed forward to Hyndburn, whilst reducing spills from the existing CSO. A new control kiosk was also provided.

Hyndburn WwTW

Value engineering and engagement with the Environment Agency enabled a no-build solution to be accepted at Hyndburn WwTW site, with only the optimisation of existing storm tank emptying system necessary for compliance.

Process optimisation: update to previous report

New primary settlement tank No. 4

New primary settlement tank (PST) No. 4 desludge pump run/dwell timers have been optimised to provide primary sludge concentration to a target of ~3.5% ds w/w. Daily PST No. 4 sludge blanket dips are undertaken by ADP and UU Operations undertook routine measurement of primary sludge concentration to inform any occasional minor changes to desludge pump run/dwell timers. The set-points for the run/dwell timer of the PST No. 4 desludge pumps typically range from 9-12 minutes for the run phase and 45-60 minutes for the dwell phase. These set-points will be adjusted in the future to accommodate changes in operational conditions at the site, including those related to the current sludge treatment center. [caption id="attachment_26733" align="alignnone" width="1200"] PST4 with odour control cover - Courtesy of United Utilities[/caption] Interstage pumping station The new interstage pumping station (IPS) has been commissioned with close consideration of the operating level set-points as determined during detailed hydraulic design. Further optimisation of the recycled activated sludge (RAS) control flow rates was undertaken following an exceptionally dry and warm weather period during April-June 2025 which has then resulted in supplementary further optimisation of the IPS control set-points. To maintain a stable hydraulic gradient for control of RAS (via gravity) from the final settlement tanks, the IPS top water level has been further optimised at 2.5m set-point with an operating level set-point control band optimised across a 0.5m depth (as per design). The IPS pumps minimum/maximum operating speeds (32.5Hz and 50Hz respectively) have been further optimised to provide stable control to level set-point across the 0.5m operating level band and avoiding, as much as possible, pump start/stops during dry weather flow periods where pump minimum performance exceeds received flows into the pumping station. The IPS has operated generally in accordance with the initial duty/assist/assist cascading level control with PID control loop tuning set-points remaining generally unchanged since original turn of flows in early October 2024. Further optimisation of the IPS process control set-points is not envisaged in the future. [caption id="attachment_26725" align="alignnone" width="1200"] Interstage pumping station - Courtesy of United Utilities[/caption]

Process air blowers: The new process air blower package was initially commissioned with support from the supplier, Sulzer Water & Wastewater. The majority of operational set-points within the blower package system are standard defaults and did not require further optimisation. The assist blower start/stop changeover set-points were optimised during a subsequent Sulzer site visit to ensure stable operational transition, avoid unnecessary noise and prevent nuisance under/over pressure process trips.

The process air blower discharge header control set-point has been further optimised to 640 mbarg in attempt to minimise dissolved oxygen depletion during storm events. The occasional depletion of dissolved oxygen remains an issue during the extraordinary rate of change of incoming flows and loads often associated with these storm events.

The addition of alternative ‘Storm Mode’ process control may ultimately be required to fully remedy the situation. Further optimisation of the process air blower process control set-points may therefore be required in conjunction with implementation of future ‘Storm Mode’ process control philosophy.

New primary ferric sulphate dosing: Extensive and routine jar-testing to monitor the optimal primary ferric dose molar ratio dose to achieve target residual orthophosphate and Total Iron concentrations was undertaken during May and June 2025.

The primary ferric molar ratio dose providing optimal phosphate and iron control (~1mg/l orthophosphate and <20mg/l Total Iron concentrations in PST effluent), as determined during the Summer Completion Test, was 4.15 MR. For reference, the ‘as-commissioned’ diurnal orthophosphate base load profile is shown below.

[caption id="attachment_26740" align="alignnone" width="1200"] Burnley WwTW: Orthophosphate diurnal load profile - primary ferric LUT set-points (as commissioned November 2024) - Courtesy of United Utilities[/caption]

A summary of initial and subsequent primary ferric dosing MR dose ‘optimisation’ is provided below:

28 November 2024 Dosing commences at 5MR 11 December 2024 Dosing increased to 6MR to target 1mg/l orthophosphate in PST effluent 20 December 2024 Dosing reduced to 5MR in response to ASP ammonia breakthrough spikes 24 December 2024 Dosing reduced to 4MR in response to ASP ammonia breakthrough spikes 2 January 2025 Dosing paused in response to observed ASP ammonia breakthrough spikes 9 January 2025 Dosing recommenced at 2MR 11 February 2025 Dosing increased to 3MR to target 1mg/l orthophosphate in PST effluent 25 February 2025 Dosing increased to 3.5MR to target 1mg/l orthophosphate in PST effluent 6 March 2025 Dosing increased to 3.75MR to target 1mg/l orthophosphate in PST effluent 17 March 2025 Dosing reduced to 3.5MR in response to ASP ammonia breakthrough spikes 24 April 2025 Dosing increased to 3.75MR to target 1mg/l orthophosphate in PST effluent 30 April 2025 Dosing paused in response to observed FST iron breakthrough spikes 3 May 2025 Dosing recommenced at 4.5MR following jar testing 8 May 2025 Dosing reduced to 4.15MR in response to jar test results N/A No primary ferric MR change since 8/5/25

Routine, minor, operational changes to the primary ferric dosing set-points will remain a business-as-usual activity associated with normal wastewater treatment works operation in the future; and most notably, in response to envisaged seasonal variation and catchment characteristics.

Caustic dosing: An initial set-point of 7.1 pH units was adopted for interstage pH process control upon commencement of the Summer Completion Test. This control set-point has been further optimised on occasion and in agreement with/request by United Utilities Operations to 7.15 pH units to either reduce chemical consumption or in consideration of prevailing final effluent alkalinity measured value.

Routine, minor, operational changes to the interstage pH setpoint considering prevailing final effluent pH and alkalinity will remain a business-as-usual activity associated with normal wastewater treatment works operation in the future.

[caption id="attachment_26726" align="alignnone" width="1200"] Chemical dosing area - Courtesy of United Utilities[/caption]

Liquid polyelectrolyte dosing: The ‘sweetening’ dose set-point of 25 l/h per FST has been retained and a storm event %FtFT trigger setpoint of 75% (in line with Evoqua recommendation). During periods of low FtFT, the 25 l/h ‘sweetening’ dose set-point results in the liquid poly system batching around four times per day; ensuring that a fresh, but matured, make-up solution is available at all times in readiness for flash increase in FtFT or prolonged storm event.

The poly dose proportional set-point has been gradually reduced to the current value of 0.6 mg/l as active product. It is noted that the product selection and amount of liquid polyelectrolyte dosed is subject to EA permitting and, as such, strict limits on maximum poly dose rate applies (currently 3.2 mg/l maximum as active product).

Further optimisation of the liquid poly ‘proportional’ dose process control set-points is not envisaged as necessary in the future.

[caption id="attachment_26734" align="alignnone" width="1200"] New assets at Burnley WwTW - Courtesy of United Utilities[/caption]

Magnetite addition & recovery: Magnetite, an iron oxide powder, is added to the activated sludge process via the BioMag® system to provide mixed liquor enhanced settleability in the final settlement tanks by microbiological floc ‘ballasting’.

The new works was operated during Q1 of 2025 to maintain the magnetite : MLSS ratio at the target of approximately 2:1, which was necessary to achieve the necessary mixed liquor settleability performance as measured by Specific Stirred Volume Index (SSVI).

Control to the target ratio is effected by management of magnetite ‘top-up’ addition, and in consideration of daily surplus activated sludge wastage volume, which relies upon having a disposal route for SAS. Mixed liquor settleability performance matured naturally during Q2 of 2025 and the magnetite : MLSS ratio was coincidentally reduced to target of 1:1 by the reduction of magnetite ‘top-up’ addition to the design anticipated amount of 500 to 600 kg/d.

The historic magnetite : MLSS ratio data is shown in the graph below. It can be seen that magnetite : MLSS ratio has trended down since the Summer Completion Test and as such, the ‘top-up’ magnetite loading set-point has been increased slightly to compensate.

Routine operational changes to the daily magnetite loading rate will therefore remain a business-as-usual activity associated with normal wastewater treatment works operation in the future. [caption id="attachment_26722" align="alignnone" width="1200"] MLSS minus magnetite (true MLSS) and true MLSS : Magnetite ratio on-site tests and laboratory results - Courtesy of United Utilities[/caption]

Recycled activated sludge control: Further optimisation of the RAS control set-points was undertaken following the extended period of exceptionally dry and warm weather period during April-June 2025. During this dry weather period the RAS flow rate was maximised to design limitation of 1,040 l/s to best manage potential for denitrification within the FSTs and avoid rising sludge and scum formation where possible. RAS control to ‘FtFT Mode 1’ was adopted for control of RAS flows during the Summer Completion Test in accordance with a three-tiered banded philosophy as follows:

FtFT flow (l/s) RAS flow (l/s) <600 400 >600 <1000 600 >1000 750

The RAS control system has operated stably for many months, and no significant further optimisation is envisaged. However, routine operational changes to the RAS control rate or mode of operation will remain a business-as-usual activity associated with normal wastewater treatment works operation in the future.

Activated sludge plant: Routine control of MLSS concentration has remained by the conventional method of monitoring food to micro-organism ratio (F/M) to the design target ~0.08d-1, by assessment of sludge age against target of ~14 days and then by manual adjustment of the surplus activated sludge daily wastage volume.

Routine monitoring of the biological load on the ASP and as-required operational changes to the daily SAS wastage volume to maintain F/M ratio and sludge age within an acceptable range will remain a business-as-usual activity associated with normal wastewater treatment works operation in the future. The historic F/M ratio and sludge age data is shown below.

[caption id="attachment_26739" align="alignnone" width="1200"] F to M ratio and sludge age - Calculated using on-site tests and laboratory test results - Courtesy of United Utilities[/caption]

Similarly, routine microscopic analysis has been undertaken by UU labs to monitor and track filamentous (and other indicator bacteria) abundance.

Summary/conclusion

The Summer Completion Test was carried out by Advance-plus over a 28-day period between 21 July and 18 August 2025. From the test results, it is concluded that the new works has successfully demonstrated compliance with the requirements of:

CT1: Final effluent water quality compliance with site WRA Regulatory Permit limits for BOD, TSS, ammonia, Total Phosphorus, Total Iron and pH. The final effluent water quality adequate compliance with asset standard for alkalinity residual (noting routine pH set-point change made during completion test in response to slight reduction in background alkalinity). CT2: Final effluent water quality compliance with site UWWTD Regulatory Permit limits for BOD and COD. CT3: Final effluent water quality compliance with site UWWTD Regulatory Permit limits for Total Phosphorus. CT4: Magnetite recovery rate of the BioMag® process.