Supply Chain - Storage Tanks - Precast Concrete

Anglian Water’s Cotton Valley Water Recycling Centre treats flows from Milton Keynes and the surrounding area. The wastewater treatment facility in the Cotton Valley Catchment area serves a substantial population, treating wastewater to stringent regulatory standards before discharge. Over time, the facility has encountered various operational challenges that hindered its efficiency and compliance. These operational challenges included limitations in post-digestion dewatering capacity, recurring pollution incidents during high storm surges, the imposition of a stringent phosphorus standard, and inadequate stormwater storage capacity. Addressing these challenges became imperative to ensure the facility’s long-term sustainability and resilience. Identified Issues

The Anglian Water @one Alliance was tasked with identifying the issues affecting the Cotton Valley WRC and finding and undertaking solution to address each issue. The identified issues were:

Post-digestion dewatering capacity: The existing centrifuges, crucial for dewatering sludge after digestion, operated below the previous AMP6 design throughput. This inefficiency results in inability to ensure treatment capacity and increased operational costs in alignment with the increase working capacity from the storm and TPS schemes. An AMP6 reinvestment scheme installed a third digester on site and increased the capacity of the Cambi plant from 56.6 TDS to 84 TDS.

The throughput is now 70 TDS and the post-digestion dewatering capacity is proving to be a bottleneck to unlocking this full capacity and imports to site have been restricted so that daily throughput does not exceed 60 TDS.

[caption id="attachment_13388" align="alignnone" width="1200"] Terminal pumping station pipework to storm tanks - Courtesy of @one Alliance[/caption]

Pollution incidents and stormwater management: In recent years, pollution incidents, particularly during high storm surges, posed significant environmental and regulatory concerns as the scrutiny of the water industry increases. Therefore, inadequate stormwater storage capacity and outdated pumping infrastructure has enhanced the impact of these incidents in the Milton Keynes area.

These persistent pollution incidents stem from the incoming flows received at the treatment plant station (TPS). Despite previous efforts under an AMP6 scheme, which included the installation of a bypass pipeline to accommodate a hired pump, these measures failed to prevent pollution events. The hired pumps were often unavailable and could not be delivered to the site promptly, leading to asset failure during critical periods.

These pollution events have a detrimental impact on the water quality leaving the WRC due to the treatment process being bypassed which is turn impacts the local environmental ecosystem.

Phosphorus standard compliance: A newly imposed phosphorus standard mandated a reduction in phosphorus levels to be discharged from the WRC. Prior to the new phosphorus investment, the existing chemical dosing infrastructure lacked the capacity to meet the stringent requirements of the new standard.

[caption id="attachment_13379" align="alignnone" width="1200"] Phosphorus removal scheme - ferrous chloride storage tanks - Courtesy of @one Alliance[/caption] Cotton Valley WRC: Supply chain - key participants Principal contractor & designer: @one Alliance Mechanical installation above-ground pipework: Waveneys Electrical installation: Glasswell & Last Glass-coated steel storm tanks: Hayes GFS Ltd MEICA package: FSD Ltd Lagoon clearance: CSG Steelwork: Steelway Ltd Epoxy-coated pipework: Freeflow Pipesystems Chemical storage tank: EPS Water Screens: Huber Technology Transformers: Power Testing Ltd Pumps: Sulzer Pumps Wastewater Ltd Centrifuges: Alfa Laval Ltd Conveyor package: SPIRAC Ltd Poly dosing package: Richard Alan Engineering MCC, panel & kiosk: Paktronic Engineering Company Ltd Proposed solutions

Due to the site’s issues, Anglian Water identified four schemes to be completed at Cotton Valley WRC with a total combined investment of £17m required. Starting in 2022, the @one Alliance initiated all four schemes in alignment with one another.

Digester upgrade scheme: As part of the digester scheme at Cotton Valley WRC, two new centrifuges were installed with enhanced dewatering capabilities to replace the current, outdated units. A modern conveyor system to streamline sludge transport and optimise operational efficiency was also part of the scope.

In addition, a new polymer dosing system was to be installed, including a dedicated polymer silo to improve sludge dewatering performance, and a new motor control center (MCC) within the existing infrastructure was required to facilitate centralised monitoring and control of the upgraded digester system.

Stormwater storage scheme: The biggest financial investment at Cotton Valley was the construction of the additional glass-coated steel stormwater storage tanks to increase the site’s working capacity. These new tanks will operate in parallel with, and overflow from Tank 4, to a new flow meter flume, connecting storm flows to the existing storm discharge chamber on site.

[caption id="attachment_13384" align="alignnone" width="1200"] Construction of the two new storm tanks - Courtesy of @one Alliance[/caption]

The existing working volume at Cotton Valley WRC was 5,795m3, however, the new Environment Agency requirement of having a working volume of 20,502m3, meant the storage capacity needed to be increased by 14,707m3. This would require the construction of two new tanks to accommodate peak storm surges and prevent future pollution incidents.

In addition, new side weir storm overflows and modulating penstocks to regulate stormwater flow and optimise management were installed. Advanced storm feed pumps and gravity collection system tanks to facilitate efficient stormwater transfer and storage during peak flows were also part of the project scope. Other elements of the stormwater storage upgrade included:

A comprehensive cleaning and maintenance regime for the two new storm tanks, including the installation of nozzle cleaning systems for optimal performance. The installation of two new 1.25 MVa transformers based on 500 KVa for storm and 500 kVa for a future TPS inlet scheme with appropriate ancillaries and additional MCC units.

Phosphorus standard compliance: To comply with the new legislation, two 30m3 ferrous chloride storage tanks were installed, equipped with instrumentation for precise dosing control.

This element of the project also included:

A new tanker delivery point and chamber to allow for chemical replenishment and ensure uninterrupted operation when required. A new kiosk. Ducts and draw pits to accommodate advanced chemical dosing equipment. [caption id="attachment_13383" align="alignnone" width="1200"] Terminal pumping station pipework to storm tanks - Courtesy of @one Alliance[/caption]

Treatment plant station (TPS) resilience: To address the TPS issues, two duty/assist pumps with a capacity of 675 litres/second were installed in the TPS inlet well with automatic controls to operate the assist unit.

These pumps will be connected into the existing bypass pipework to ensure continuous operation during peak flows and emergencies.

Downstream pumps with a capacity of 550 l/s were also installed. These pumps were connected to a duty-only 12mm bar screen, which was essential for consent compliance. The discharge is directed into Storm Tank 1, providing additional capacity to manage excess flows during high storm surges.

An unscreened bypass was also installed to enhance the operational flexibility, with screenings directed into a 6.1m3 skip. A new MCert flow meter was also installed to monitor peak flow and screen performance, ensuring regulatory compliance.

Challenges & outcomes

There were a number of challenges that the @one Alliance and their supply chain had to overcome to successfully deliver the four schemes that made up the Cotton Valley WRC Upgrade Project.

Clearance of the existing Cotton Valley lagoons to make way for the new storm tank installations led to an initial delay due to considerable additional material clearance that was required in order to achieve the necessary base foundations. The refurbishment of the TPS wet well, including installation of four additional pumps whilst the existing screw pump and wet well assets remained in operation was a considerable challenge. Not only were the works completely weather dependent resulting in numerous delays over the winter period, the works in the wet well were made up of multiple high-risk activities, requiring two cranes and a man-way basket for access together with a full-time emergency recovery team. The digester upgrade scheme required extensive design and coordination with multiple external package plant suppliers in order develop the overall solution required. With extended material and component lead-times being commonplace across the global supply chain, this led to challenges with the sequencing of the delivery programme. [caption id="attachment_13386" align="alignnone" width="1200"] Terminal pumping station pipework - Courtesy of @one Alliance[/caption] Conclusion

The @one Alliance initiated a comprehensive £17m investment project spanning multiple phases to address operational challenges effectively.

At the time of writing (May 2024), the stormwater storage scheme and phosphorus removal schemes have been completed, whilst work on the digesters and the TPS elements continue.

Through proactive investment and strategic infrastructure upgrades, the wastewater treatment facility in the Cotton Valley catchment will be able to successfully address future operational challenges, and provide enhanced treatment capacity in order to maintain regulatory compliance.

This case study highlights the critical importance of continuous improvement and sustainable infrastructure investment in ensuring efficient wastewater treatment operations and safeguarding environmental health for future generations.

Ballyronan is a small village situated in County Londonderry, within the Mid-Ulster District Council area located on the western shore of Lough Neagh. The towns of Magherafelt and Cookstown are both approximately 4 miles to the north-west, and 11 miles to the south-west respectively. The existing Ballyronan Wastewater Treatment Works (WwTW) was constructed to cater for a design population equivalent (PE) of 571, but in 2021, it was calculated that the existing works was dealing with a PE of 1,020 and that a future PE of 1,520 was anticipated. Existing works

The existing works comprised of an inlet chamber, a rectangular hopper-bottomed primary settlement tank, two percolating filters, a hopper-bottomed humus tank and a sludge holding tank. There was also a brick building which housed the control panel and NIE supply for the WwTW. Interstage pumping was also required to lift the primary settled flows to the biological filters.

The existing works was required to comply with a discharge consent of 40 mg/l BOD, 60 mg/l total suspended solids, and 7.5 mg/l ammonia.

[caption id="attachment_16703" align="alignnone" width="1200"] (left) Existing site on western shores of Lough Neagh, (top right) existing PSTs, and (bottom right) existing percolating filters - Courtesy of NI Water[/caption] Project drivers

Though the treatment process was generally in compliance with the current standard, the Northern Ireland Environment Agency (NIEA) had indicated that a new, more stringent consent would be imposed for future flows discharging to Lough Neagh. In addition, the existing works was operating beyond its capacity, many of the structures were nearing the end of their design life, and regular operator intervention was required to maintain compliance.

Since the existing works was not capable of fulfilling the requirements of NI Water’s long-term strategy to enhance wastewater services, and was expensive to operate and maintain, a new treatment works was deemed essential to ensure compliance with the stricter consents throughout the design horizon.

The provision of a new fully automated rotating biological contactor (RBC) WwTW would provide effective and robust wastewater treatment services for the future catchment area, catering for economic growth (having a design population equivalent of 1,520), and improving the local environment by adhering to a tighter discharge consent of 20 mg/l BOD, 30 mg/l total suspended solids, and 7.5 mg/l ammonia.

Project team

As principal contractor, GEDA Construction had overall responsibility to deliver the project on time and within budget. Water Solutions Ireland were responsible for designing and delivering a full turnkey MEICA, process design and build solution for the new works.

McAdam provided civil, structural, and geotechnical design services, including the initial enabling and investigatory works carried out at the Early Contractor Involvement (ECI) stage, as well as the detailed design for construction.

[caption id="attachment_16706" align="alignnone" width="1200"] Early excavation works with compound set up - Courtesy of NI Water[/caption] The contract delivery team worked in a collaborative manner with NI Water, project managers RPS, and key suppliers and subcontractors to deliver a robust, effective and modern treatment solution which allows for future growth in the catchment area and protects the environment by adhering to a tighter discharge consent. Ballyronan WwTW: Supply chain - key participants Project managers: RPS Civil contractor: GEDA Construction MEICA & process designer/contractor: Water Solutions Ireland Civil, structural & geotechnical design: McAdam Electrical design: SBE Design PLC software & commissioning: Ashdale Engineering MCC: R&R Engineering Mechanical storm screen: Jacopa Ltd Static storm screen: Eliquo Hydrok Ltd 6mm inlet screening: M&N Electrical & Mechanical (Hydro International Ltd's UK Wastewater Services Division) Rotating biological contactors & primary/final settlement tanks: KEE Process Ltd Pumps & mixers: Xylem Water Solutions Instrumentation: Park Electrical Systems Flow measurement: Siris Environmental Ltd Flow measurement: AMPM Flow & Energy Services Ltd Penstocks, valves & actuators: Flow Technology Services Storm tank cleaning tipping bucket: CSO Group Ltd GRP kiosks & site-wide metalwork: Victoria Engineering 10mm bar screen, skip rails & trolleys: Graham Steelwork Engineering Potable & FE service water boosters: Dutypoint Ltd Lifting equipment: Columbus McKinnon Co Ltd Access covers: JP Corry Site security fencing & gates: NK Fencing Concrete & precast products: FP McCann Pipes & fittings: APP Welfare unit: Sean Jordan Engineering [caption id="attachment_16704" align="alignnone" width="1200"] Excavation of FSTs to depth of 5m - Courtesy of NI Water[/caption] Project description & scope

The RBC treatment process at Ballyronan WwTW was to be constructed within the same footprint of the existing site. The new treatment works was designed and built to include the following individual process stages for robust and effective treatment of incoming flows:

A preliminary treatment process stage comprising of 6mm mechanical inlet screening and forward flow control equivalent to Formula ‘A’. Any flows greater than Formula ‘A’ are treated via a mechanical storm screen. A new interstage pumping station for passing forward flows equivalent to FFT to the downstream treatment processes. A new storm storage and management facility, providing a total storage capacity of 81m3 for both storm and emergency flows. The storm tank is also equipped with a tipping bucket system for efficient cleaning of the storm tank floor from CSO Group Ltd. The interstage pumps transfer FFT to two primary settlement tanks each of 6m diameter. The primary sludge from the primary settlement tanks is drawn off by the primary sludge pumping station for transferring to the new concrete sludge holding tank. Primary settled flows then gravitate to the biological treatment process; three RBCs from KEE Process Ltd. Following treatment in the three RBCs, the treated effluent gravitates to the two final settlement tanks each of 6m diameter. The sludge from the final settlement tanks is drawn off by the humus sludge pumping station, which can either be transferred directly to the new concrete sludge holding tank or to the primary tanks for co-settling with the primary sludge, before being stored in the new concrete sludge holding tank prior to transporting off-site. Following final settlement, the treated effluent gravitates through a final effluent washwater transfer pumping station, prior to discharge at the final effluent outfall location. [caption id="attachment_16698" align="alignnone" width="1200"] Bottom section of FSTs installed - Courtesy of GEDA Construction[/caption]

The new Ballyronan WwTW includes a new concrete sludge storage tank sufficiently sized for 10 days’ storage prior to being tankered off site.

The site-wide drainage system is segregated between storm and dirty drainage, with any dirty drainage directed to the new return liquors pumping station which transfers additional flows back to the head of the works for treatment.

The old brick building was demolished, and the new works was provided with a new GRP kiosk housing a dedicated main works MCC which controls all mechanical and electrical plant equipment and instrumentation.

As the new works had to be built within the confines of the existing site boundary, a complex construction phasing plan was developed to bring the new treatment works online in four separate stages. GEDA Construction, Water Solutions Ireland and McAdam worked closely with NI Water Operations to ensure effluent compliance was maintained throughout the individual construction phases.

Early contractor involvement

GEDA Construction was awarded an NEC 4 (Option A) Early Contractor Involvement (ECI) contract in February 2021 for a replacement treatment works at Ballyronan WwTW. To assist with the development of a turnkey design and build solution for a replacement treatment works, GEDA appointed Water Solutions Ireland as the MEICA & Process Contractor and McAdam Design as the Civil Designer to deliver both the ECI contract and construction contract.

An extensive ECI process was undertaken for the replacement treatment works at Ballyronan WwTW, which included ongoing collaboration with NI Water for design outputs and workshops such as HAZOP and Value Management. The ECI phase allowed GEDA Construction, Water Solutions Ireland and McAdam to gain an early understanding of the key drivers for the project and achieve buy-in from all stakeholders within NI Water and their project management team from RPS to benefit delivery.

The collaborative approach between the Contractor and NI Water in the ECI contract was an exemplary reflection of NI Water values, purpose and vision. As a result, the ECI led to enhanced value, robustness and operational efficiency for the overall construction project.

[caption id="attachment_16697" align="alignnone" width="1200"] Make up of the FSTs from KEE Process - Courtesy of GEDA Construction[/caption] MEICA & process design

GEDA Construction, in conjunction with Water Solutions Ireland and McAdam, undertook an optioneering exercise to investigate the ideal treatment solution for Ballyronan WwTW under a back-to-back NEC 4 (Option A) ECI contract. This optioneering exercise included the process design requirements of a new treatment works and the potential option of employing temporary treatment facilities to replace the existing works during construction. A full turnkey MEICA design was provided, including steelwork structural drawings and ICA documentation such as PLC architecture and Functional Design Specification for the new process.

Civil design

McAdam was appointed under a bespoke Professional Services Contract to GEDA Construction for all civil engineering design requirements for the ECI and was also engaged by GEDA for the construction contract.  The ECI contract allowed McAdam to develop a turnkey civil design including a detailed construction sequencing plan which included the use of both temporary pipework and permanent pipework for the new structures to enable phasing.

An offline build solution was presented to NI Water as an option during the ECI phase for ease of construction and ongoing process management during construction. However, in agreement with all stakeholders, the preferred design for the replacement WwTW was constructing the new treatment works in a phased manner within the existing site footprint whilst the existing works remained operational. This approach satisfied the long-term operation and maintenance requirements for the new works and negated the need for NI Water to purchase additional land.

Main challenges for design/construction

Existing site: The key challenge around the design and construction of the new Ballyronan WwTW was building a new treatment works in its entirety within the same site boundary as the existing WwTW.

[caption id="attachment_16699" align="alignnone" width="1200"] Installation of RBCs - Courtesy of GEDA Construction[/caption]

Interface between new and old works during construction: The construction of the new treatment works at Ballyronan required a continuous interface between the new and old works during construction. The new WwTW was constructed and commissioned in four individual phases.

Phase 1: Relocation of existing MCC and temporary diversion of NIE connection. The existing brick building housing the MCC was then demolished which provided the required footprint to construct two new final settlement tanks and humus sludge pumping station.

Once the new final settlement process was constructed and commissioned, a temporary diversion of flows from the outlet of the existing percolating filter beds was put in place via a temporary pumping station. This made the existing humus tank redundant and available for demolition.

Phase 2: The new interstage PS and storm tank was constructed. The existing humus tank was demolished which created space on site for constructing the three RBCs. Following construction and commissioning of the new interstage PS, storm tank and RBC process, primary settled flows were diverted to the new RBC flow splitting chamber for seeding.

At the initial stages of turning flows between the two biological treatment processes, any effluent from the RBCs was re-diverted for re-treatment through the existing filter beds to ensure effluent compliance. The effluent from the filter beds was then pumped via a temporary pumping station to the new final settlement tanks before gravitating to the effluent discharge location.

Both the effluent from the new RBCs and the existing filter beds was rigorously tested, and once the RBCs were fully seeded and proved to be treating incoming flows to the required standard, NI Water granted approval to demolish the two existing filter beds. The construction of a section of the site-wide dirty drainage and the new return liquors pumping station also took place in this phase.

Phase 3: The existing two filter beds were demolished in Phase 3 which then created sufficient space on site for constructing the two PSTs. The new inlet works comprising Formula ‘A’ flow control was constructed in the final phase, as was the new concrete sludge holding tank.

[caption id="attachment_16700" align="alignnone" width="1200"] Construction of inlet works, sludge tank & storm tank - Courtesy of NI Water[/caption]

Phase 4: The final phase involved the construction of the two new primary settlement tanks (PSTs) and completing a successful turn of flows from the interstage PS to the new PSTs. Once this was completed, Water Solutions Ireland and GEDA Construction were granted approval to respectively decommission and demolish the existing primary settlement tanks.

The new MCC panel and kiosk were also installed in this final stage, with the entire site transferred across and commissioned as a whole. Other works included:

The construction of the new final effluent outfall configuration which included a new outfall pipe and headwall. FE washwater transfer PS FCOM flow measurement chamber FE washwater booster and potable washwater booster.

At the end of Phase 4, the incoming flows were fully treated by the new RBC works at Ballyronan WwTW.

Turn of flows

As the new works was brought online in four individual phases, a complex turn of flows plan was carefully developed to ensure effluent compliance for NI Water.

GEDA Construction and Water Solutions Ireland managed the individual turn of flow processes between the existing works and new treatment works. A rigorous on-site and external sampling regime was undertaken to regularly monitor the performance of the existing and new works. This sampling regime proved critical in allowing the site team to advise NI Water when the new RBC treatment process was fully functional and treating effluent to the required standard.

[caption id="attachment_16701" align="alignnone" width="1200"] Completed Ballyronan WwTW - Courtesy of GEDA[/caption]

As a result, NI Water granted approval for the decommissioning of the existing filter beds. From this, the existing biological filter beds could be demolished to allow further construction to progress.

The turn of flows process, particularly from the old filter beds to the new RBCs, had to be carefully managed both hydraulically and biologically to ensure the treatment process was optimised and effluent compliance was maintained at all times.

The various turn of flow processes required both temporary gravity-fed lines and temporary over pumping lines to demolish existing structures. For example, GEDA Construction had to lay a temporary sewer to divert flows from the existing primary tanks to the new interstage pumping station in Phase 2.

Both GEDA and Water Solutions Ireland had to construct and fit-out a temporary pumping station to direct flows from the outlet of the existing percolating filter beds to the new final settlement tanks.

Commissioning

Construction work on the new Ballyronan WwTW was completed early September 2024 with site-wide testing and commissioning of the plant successfully undertaken for handover to NI Water in October 2024.

Speaking about the economic and environmental benefits of the project, Senior Project Manager, Sean Milligan commented:

“NI Water’s substantial investment of around £5m has provided a robust wastewater treatment solution for the Ballyronan area that will support local development and help improve water quality in Lough Neagh.”

The town of Giffnock is situated approximately 6 miles south-west of Glasgow and has a population of around 12,500. In June 2022, Scottish Water launched a £6.8m, year-long, investment project aimed at mitigating the risk of sewer flooding on Braidholm Road. This initiative is intended to significantly improve conditions for households that have previously experienced internal property flooding. A new offline underground storage tank with a capacity of 1.6 ML was installed beneath the grassed open space on the south side of Braidholm Road next to the junction with Whitton Drive and Graffham Avenue. Project scope

The project involved constructing a storm overflow chamber, a storm overflow diversion pipe, and a 13m wide x 13m deep underground stormwater storage tank, as well as enhancing the current sewer infrastructure, to safeguard residences on Braidholm Road against sewer flooding during extreme weather circumstances.

Project challenges

The logistics of constructing the stormwater storage tank in the middle of a residential area were huge and residents faced significant disruption. The project team had to overcome several challenges, such as:

Managing groundwater levels and ensuring adequate dewatering throughout the construction process. Protecting the existing sewer network and other underground services from damage or interference. Minimising noise and vibration during the excavation and piling works, which involved driving 120 piles to a depth of 14m. Securing access and traffic management for the delivery of heavy plant and equipment, including a 120-tonne crane and a 35-tonne excavator in a built-up residential area. Maintaining communication and engagement with the local community and stakeholders, providing regular updates and addressing any concerns or complaints. [caption id="attachment_14764" align="alignnone" width="1200"] Site establishment - Courtesy of Whitehouse Studios[/caption] Constructing the shaft

One of the key features of the project was the construction of a segment ring shaft, which is a novel and innovative method of creating a deep circular shaft using precast concrete segments from Macrete (Ireland) Ltd. Over a period of five months, eleven segments measuring 12.5m each were carefully lowered into an excavation and sequentially stacked to create a sealed shaft structure. In total, approximately 1800m3 of material were dug out and 400m3 of concrete were utilised in the construction.

This technique reduces the amount of concrete and steel required, as well as the carbon footprint and disruption associated with traditional shaft construction methods.

Braidholm Road Flood Alleviation: Supply chain - key participants

The project was managed by Investment Delivery, Scottish Water’s in-house delivery vehicle, and delivered by George Leslie Ltd, one of Scottish Water’s capital delivery partners.

Principal contractor: George Leslie Ltd Design consultant: AECOM Civil engineering: JOS Civil Engineering Tunnelling: Pipeline Drillers Ltd Ground support systems: Groundforce Ground support systems: Mabey Hire Ltd Piling: Burnside Plant Hire Ltd Steelwork: MacGregor Technical Services Ltd MEICA: ID Systems Kiosk: Quinshield Ltd Shaft segments: Macrete (Ireland) Ltd Pumps: Xylem Water Solutions Landscaping: MW Groundworks Ltd Project adopts low carbon approach

The Braidholm Road project is one of the first in Scotland to adopt a low carbon approach for the construction of sewer infrastructure.

Over 1,000 tonnes of low carbon concrete was used to construct a 13m deep stormwater tank and overspill chamber, whilst hydrotreated vegetable oil (HVO) was used as fuel, ‘huge’ electric batteries came in place of generators, and recycled aggregates were utilised.

Scottish Water are committed to delivering net zero emissions by 2040 and beyond and every project we undertake is a step towards achieving that aim. The carbon saving in Braidholm Road is the equivalent of 220 return flights from Paris to New York.

[caption id="attachment_14761" align="alignnone" width="1200"] Work on Braidholm Road - Courtesy of George Leslie Ltd[/caption] Benefits

Scottish Water is a public sector body answerable to the Scottish Parliament through Scottish Ministers and our principal activities are the supply of water and wastewater services to around 5.4 million customers in homes and businesses across Scotland covering an area of 30,810 square miles.

Our vision is to be trusted to care for the water on which Scotland depends. Reflecting that, our customers expect us to provide excellent customer service by delivering high levels of water quality and environmental performance, all for an affordable price. Using Scotland’s natural resources and the skills of our people, Scottish Water is committed to improving our services for customers and communities while protecting and enhancing the environment of Scotland.

The new stormwater storage tank can hold the equivalent of more than half an Olympic size swimming pool of water (1.6 megalitres) during periods of extreme weather events, providing extra capacity, both within the tank and the local sewers alleviating pressure on the wastewater network.

This project is important to Scottish Water as it continue to build the trust and confidence of our customers and communities across Scotland through maintaining and investing in our assets.

Engagement

In the initial phase prior to construction, a plan for entry and exit was developed through early discussions with stakeholders, pinpointing all community members and stakeholders impacted and establishing the most effective routes and locations for the site compound and work area. A traffic management plan was drafted in consultation with the residents, ensuring ongoing access while reducing any disruptions from the construction activities within the community.

The key site compound was positioned at a central main location to include the project office and material storage; this was purposefully set some distance from the construction site to diminish any disturbance to the residents.

The Scottish Water and the George Leslie joint project communication team organised a community open day to share details about the upcoming works, allowed for engaging with the locals, and addressed any issues or needs they might have had. Prior to starting on-site work, they distributed informational letters to all stakeholders affected, which included direct contacts for any project-related inquiries.

[caption id="attachment_14760" align="alignnone" width="1200"] Site reinstatement - Courtesy of Whitehouse Studios[/caption]

During the construction, all interactions regarding information requests, complaints, or consents were formally documented, responded to, and resolved according to the management plan.

The commitment and cooperation of the community were crucial to the success of this significant and multifaceted engineering project, and Scottish Water is grateful for the community’s goodwill and understanding throughout the process.

Conclusion

The Braidholm Road project, delivered by Scottish Water partner George Leslie Ltd, has successfully implemented a multi-million-pound, year-long initiative to prevent sewer flooding in Giffnock for Scottish Water.

Despite the challenges of managing logistics, noise, vibration, groundwater levels, and maintaining community engagement, the project team overcame these obstacles to deliver a low carbon approach to sewer infrastructure.

This project not only alleviates pressure on the wastewater network by providing extra capacity but also demonstrates Scottish Water’s commitment to net zero emissions by 2040, building trust and confidence in customers and communities across Scotland.

The Ards Peninsula is a scenic area in County Down, situated on the north-east coast of Northern Ireland. It separates Strangford Lough from the north channel of the Irish Sea and its coastal towns and villages are popular with day trippers and caravanners alike. By 2020, the wastewater treatment works serving the villages of Carrowdore and Ballywalter were operating at full capacity. NI Water investment was required to ensure that these areas could meet future EU and Northern Ireland Environment Agency (NIEA) standards. The area of Ballywhiskin only had primary settlement, which was not deemed sufficient, and the caravan parks and small settlements in the Ballywalter area were served by septic tanks, which again only offered primary settlement of wastewater before discharge to nearby watercourses. The beaches in the area represent significant tourist amenity and an extensive treatment scheme was essential to meet future bathing water quality standards in line with NIEA standards. What the scheme involved The two-year Ards North Wastewater Improvement Scheme involved the rationalisation of the Carrowdore, Ballywhiskin and Ballywalter catchments so that all wastewater flows from these areas could be transferred to a new state-of-the-art wastewater treatment works (WwTW) constructed on a greenfield site off the Ganaway Road in Ballywalter. In addition to these catchments, the new treatment works has been designed to treat wastewater flows from nearby caravan parks and small settlements, which previously had no treatment facilities. The scheme was split into two contracts; one for the design and construction of new pumping stations, pipelines and a modern wastewater treatment works, which was awarded to BSG Civil Engineering, and another for the design and installation of a new long sea outfall, which was awarded to Farrans. Project management/technical support for both contracts was provided by Tetra Tech. This article focuses on the work carried out to construct the new WwTW, pumping stations and pipelines by BSG Civil Engineering to serve the combined catchments and cope with seasonal fluctuations in population to protect the tourism potential of the area for many years to come. [caption id="" align="alignnone" width="1200"] Bulk excavation - Courtesy of BSG Civil Engineering Ltd[/caption] Early contractor involvement/design and build contract BSG Civil Engineering was appointed by NI Water as the main contractor in November 2018 under an NEC 3 Early Contractor Involvement (ECI) contract. BSG provided multi-disciplinary design, project and supply chain management and all civil engineering, process and MIECA works for the contract from start to completion. The ECI phase allowed BSG to align resources and integrate objectives with NI Water and their project management team from Tetra Tech at an early stage to benefit delivery. This proactive approach led to enhanced collaboration, innovation, value, efficiency and reduced whole life costs for the project. Primary drivers The purpose and drivers for this project were as follows: Achieve compliance with current and future EU directives on effluent discharge standards. Meet Registered Discharge Standards set by the Northern Ireland Environment Agency (NIEA). Provide a flexible design to cater for future flows and the significant summer/winter fluctuations. Minimise impacts to community and environment. Support local development, tourism and economic growth. Deliver best value for money construction making use of existing assets. [caption id="" align="alignnone" width="1200"] Ards North WwTW - Inlet works overview - Courtesy of BSG Civil Engineering Ltd[/caption] Scope of works The main elements of work included: Installation of 14km of pumping main between WwTW & new/upgraded pumping stations via directional drilling and open cut methods. 2km of gravity sewer installed between pumping stations. 6mm inlet screening and storm storage for 2 hours/3x DWF) Grit treatment and removal. 3 (No.) 131m3 primary settlement tanks with automatic desludge and scum removal. Return activated sludge (RAS)/surplus activated sludge (SAS) pumping station. Anti-septicity treatment at source at the pumping stations. 3 (No.) 12m diameter final settlement tanks with automatic desludge and scum removal. Sludge holding tank. Sludge thickening and processing. Two-stage odour control plant. 330KVA standby power generation. 52.28 kwP roof mounted solar PV array, complete with dual 22kWh EV charging points. Process flows, levels, and quality monitoring; ancillary processes to support the main process units and intelligent motor control centre (MCC) with telemetry. Programmable logic controller (PLC) and human machine interface (HMI) control system. Installation of new long sea outfall pipe (detailed in a separate article). Design criteria for the Ards North WwTW Due to the large number of caravans in the area expected to be served by the new Ards North WwTW, the plant needed to be designed to deal with significant variations in flow and load to ensure satisfactory treatment could be achieved throughout the year. This meant that the works had to cope with a summer population equivalent (PE) of 8508 and a PE of 4809 in winter months. Inlet works & flow control/balancing Flows up to Formula A from the outlying stations can arrive at WwTW simultaneously. The inlet balancing chamber balances out flows going forward to the inlet screening plant. The inlet screening plant consists of two duty/standby incline screens and a cross conveyor. Each screen has a manual inlet penstock installed to enable isolation for maintenance purposes, or for bypass through the static 6mm bar screen. [caption id="" align="alignnone" width="1200"] Inlet works side view - Courtesy of BSG Civil Engineering Ltd[/caption] Screened raw sewage continues to the grit removal plant. The grit settles in a sump underneath the grit paddle. Any grit that settles in this sump is periodically aerated using the grit blower and then removed. From here the grit is transported out of the grit plant by the grit classifier and is deposited into the grit skip. From here it is removed off site for disposal. After the wastewater has passed through the grit removal plant, flow continues to the FFT pumping station. Here influent is collected, and FFT of 48.2 l/s (summer) & 29.6 l/s (winter) is pumped to the PST flow splitting chamber. Ards North Wastewater Improvement Scheme: Supply chain - key participants Client: NI Water Project management: Tetra Tech Principal designer/contractor: BSG Civil Engineering Ltd Structural, hydraulic & process design: Doran Consulting MEICA design: BSG Civil Engineering Ltd Temporary works design: MEA Ltd Electrical installations: AW Control Systems Dewatering: Causeway Geotech Aeration equipment: Xylem Water Solutions Aeration blowers: Aerzen Machines Sludge thickeners: Huber Technology MCC: LMP Controls Inlet screening: M and N Electrical and Mechanical Services | Hydro International Grit treatment: Jacopa Storm screening: Eliquo Hydrok Ltd Actuators: Rotork Septicity dosing & booster pumps: FM Environmental Half bridge scrapers & access flooring/metalwork: Graham Steelworks & Engineering Ltd Odour control plant: John Cockerill Environment Pipes & fittings: APP Fusion Group Standby generators: PM Power Poly dosing plant: ProMinent Fluid Controls (UK) Ltd Micro-strainers: Whitewater Care Photovoltaic solar farm: Solmatix Renewables Ltd DO/MLSS & turbidity instrumentations: Hach Lange Flow meters & ultrasonics: Siemens Tipping buckets: CSO Group Ltd Precast concrete supplies: FP McCann Stormwater storage When incoming flows exceed FFT, the FFT pumping station will start to fill and eventually overflow to the blind storm tank. Once the blind storm tank has reached maximum capacity, flow will backup, allowing the level within the FFT pumping station to increase further. A higher-level overflow pipe allows flows to pass to the online storm tank. Once maximum capacity is reached here, flows will pass to the Ganaway Burn via the 6mm overflow screen and flow meter. Storm return will occur when the FFT pumping station is at a suitable low level. The storm tanks will return flow to the FFT pumping station in sequence i.e. blind tank first. Both tanks are fitted with automated penstocks which will open to return the contents of each storm tank to the FFT pumping station. Both storm tanks are fitted with tipping bucket cleaning systems from CSO Group Ltd, which help prevent build-up on the tank floor to achieve that ‘brushed floor effect’ when empty. The tipping bucket will operate when each of the storm tanks has reached the empty level. [caption id="" align="alignnone" width="1200"] (left) Ards North WwTW - Courtesy of NI Water, and (right) storm tanks tipping bucket installation - Courtesy of BSG Civil Engineering Ltd[/caption] Primary treatment The PST flow splitting chamber receives flows from the FFT pumping station and return liquors pumping station. Flow from the PST flow splitting chamber passes to three primary settlement tanks. These tanks are hopper bottomed and are desludged using automated valves to the primary sludge pumping station. Wastewater continues through to the PST collection manhole which mixes with RAS upstream of the ASP distribution chamber to feed the three ASP lanes. Sludge and scum drawn from the three PSTs arrives in the primary sludge pumping station. This station consists of two submersible pumps in duty/standby arrangement and is used to transfer sludge and scum removed from the PSTs to the thin sludge tank. Activated sludge plant The ASP lanes are identical in design and equipment. Each lane comprises an anoxic zone and an aeration zone. Each anoxic zone is equipped with a mixer. Each aeration zone is equipped with an aeration grid, air control actuator, air flow meter transmitter, two dissolved oxygen probes and an MLSS probe. Each aeration zone is fitted with mixers and aeration grids with fine bubble disc diffusers, which are attached to a central manifold which then connects to the ASP blowers. The influent entering these zones is controlled to maintain a set dissolved oxygen and MLSS level. The dissolved oxygen demand is supplied via the ASP blowers, configured in a duty/assist/standby arrangement. The blowers’ manifold is monitored by a pressure transmitter, a temperature transmitter and an air flow meter transmitter. [caption id="" align="alignnone" width="1200"] Aeration plant air manifold control valves and instrumentation - Courtesy of BSG Civil Engineering Ltd[/caption] Final treatment Flow from the ASP Lanes gravitates to the FST flow split chamber, fitted with adjustable weirs where the flow is split evenly to the three final settlement tanks. Each tank is identical and is equipped with a half bridge scraper, sludge blanket detector, ladder position switch and a proximity switch. Scum travels to the scum collection chamber and furthermore to the FST scum pumping station. The station is equipped with a duty/standby pump set which pumps its contents to the thin sludge tank. The tanks desludge is controlled via flow meters through actuated hydrostatic valves located in separate chambers that adjoin the RAS/SAS pumping station. Each tank’s settled effluent hydraulically discharges into the tank’s outlet launder channel to the final effluent/washwater pumping station. Final effluent Final effluent flows into the final effluent/washwater pumping station and on to the final effluent sample chamber. Here, the final effluent is monitored for turbidity and temperature levels and is also the dedicated location for the auto sampler. The final effluent/washwater pumping station contains two submersible fixed speed final effluent/washwater pumps in a duty/standby arrangement. These are used for supplying the washwater tank with the necessary effluent for washing the screens, sludge thickeners, etc. Final effluent is returned through a packaged plant automatic backwash strainer system located inside the control building. The automatic backwash strainer system, situated inside the sludge thickening building, is a filter that is used to remove particles from the final effluent returned from the final effluent/washwater pumping station. Final effluent flows from the sample chamber which is connected to the long sea outfall pipe. Sludge pumping, treatment & storage The RAS/SAS pumping station is equipped with two sets of pumps. RAS pumps and SAS pumps, a level ultrasonic and high-level floats are used to control both sets of pumps. The duty pump returns the desludge from all FSTs back to the PST collection manhole, continuing to the aeration distribution channel. The SAS pumps, also arranged in a duty/standby configuration, periodically pump forward sludge to the thin sludge tank. The frequency is operative set to maintain a desirable MLSS level within the ASP lanes. [caption id="" align="alignnone" width="1200"] RAS/SAS pumping station - Courtesy of BSG Civil Engineering Ltd[/caption] The thin sludge tank is equipped with an external mixer for the blending of the tank’s contents to feed the sludge thickening plant. A level ultrasonic with low and high-level floats are used in the control of the mixer. Mixed sludge from the thin sludge tank is pumped to the sludge thickening plant via the two thickeners feed pumps. These pumps are progressive cavity pumps and are arranged in duty/standby configuration. The pumps are VSD controlled to allow the flow to the thickening plant to be controlled. There are two sludge thickeners, with an individual throughput of 8.3 m3/hr @ 1.3% DS with a discharge of no more than 6%, based on a 5-hour day, 7-days per week operation at 100% of the maximum design load. The thickeners are arranged in a duty/standby configuration with two actuated isolation valves installed on the feed pipework allow this to be fully automated. If one thickener was to develop a fault, the standby thickener can resume operations without manual intervention. Polyelectrolyte is made up on site to be added to the sludge fed to the sludge thickening plant. The addition of this chemical aids flocculation and makes thickening easier. This plant is a liquid polymer set. The liquid poly is delivered within IBCs for the makeup process. The set mixes the poly from the IBC with water to a preset concentration rate and is then transferred to the poly storage tank. The duty poly dosing pump doses to the thickener’s sludge feed pipework from here. Thickened sludge from the sludge thickening plant is transferred to the thick sludge tank. Here thickened sludge is stored for removal off site. A collection tanker removes the tank’s contents off site by coupling to the tank’s Bauer Coupler connector. [caption id="" align="alignnone" width="1200"] PST No 1 & control building - Courtesy of BSG Civil Engineering Ltd[/caption] The tank is equipped with a decant valve arrangement to facilitate settlement of the tank’s contents. The tank is also equipped with a level ultrasonic, low and high-level floats for level status and control of an externally fitted mixer for tank agitation. The return liquors pumping station receives liquors from the following areas: inlet works drains, thin sludge tank decants and overflow, thick sludge tank decants and overflow, sludge thickening plant bund, FE and washwater drains and odour control plant drains. The station comprises of two fixed speed pumps, which are arranged in duty/standby arrangement. These return liquors to the activated PST splitting chamber. Washwater pumping The final effluent washwater & potable water booster sets are positioned within the sludge building. A ’dual washwater tank’ system is in place to feed both sets of pumps. The GRP dual washwater tank is designed with a lower compartment which holds 6m3 and an upper compartment which holds 1m3. The lower compartment is designed to contain the final effluent delivered via the final effluent/washwater pumping station, which in turn feeds the final effluent booster set which boosts the pressure as required for the washwater of the inlet screens, sludge thickeners, odour control, and the storm tank tipping buckets. The upper compartment is designed to contain potable water which in turn feeds the potable water booster set, which boosts the pressure as required for the nine retractable hose reels around the site for wash down, poly makeup plant water and poly carrier water. [caption id="" align="alignnone" width="1200"] Low level structures RC concrete installation - Courtesy of BSG Civil Engineering Ltd[/caption] Odour control plant The 2-stage odour control unit (bio & carbon filter) is connected to the various strategic areas. The odour control unit comprises of two odour fans, which are arranged in duty/standby arrangement. Actuated valve, flow meters, pressure transmitters and temperature transmitters are used to control the odour control system. Only odour omitted from the sludge thickening building (due to their extreme odorous compounds) will bypass the biofilter and go directly to carbon filter for treatment. Outlying pumping stations Existing treatment facilities at Ballywhiskin and Carrowdore were decommissioned and replaced with new pumping stations, while a completely new pumping facility was constructed at Sandycove Caravan Park where no NI Water asset previously existed. The last of the outlying WwPS to be upgraded was Ballywalter Fowler Terminal Pumping Station (TPS). This facility was completely refurbished with larger capacity pumps, a new MCC and additional storm storage capacity. Fowler Way TPS pumps to Sandycove WwPS which in turn pumps to the new Ards North WwTW, while the pumping stations at Ballywhiskin and Carrowdore pump directly to Ards North. [caption id="" align="alignnone" width="1200"] (left) Ballywhiskin TPS - Courtesy of NI Water, and (right) Carrowdore WwPS - Courtesy of BSG Civil Engineering Ltd[/caption] Civil construction challenges There were various challenges throughout the construction phase of the works that had to be overcome to ensure that the contract programme was achieved. As the project spanned over a 20km distance, there were varying ground conditions to deal with from very loose running sand in the gravity pipeline sections at Sandycove; soft, deep peat at Carrowdore WwPS; extremely hard rock at Ballywhisken to stiff clays with loose gravels at the WwTW site. This led to a variety of temporary works systems having to be designed and employed to deliver the works safely. Groundwater levels also varied across the scheme with various dewatering techniques used to maintain dry working spaces. Artesian water pressure and groundwater under tidal influence presented difficulties during the construction of these works. Overhead services also presented a construction issue at the WwTW site. As a result, carefully planned construction sequencing and specialised plant were employed. 13.5km of pumping main was installed along roads within this rural area. In order to keep to programme, pipe installation had to be carried out using a minimum of two separate teams at all times. Due to the limited options for suitable diversionary routes in the area, the pipe installation programme had to be carefully managed and continually communicated to the roads authority to ensure both pipe installation squads had consecutive sequencing of works throughout the pipeline installation phase of the scheme. [caption id="" align="alignnone" width="1200"] (left) Sandycove WwPS and (right) Ballywalter Fowler Way TPS - Courtesy of NI Water[/caption] Sustainability To boost the sustainability of the treatment facility, 138 solar PV panels from Solmatix Renewables Ltd were fitted to the roof of the new control building which will produce over 45,000 kWh per annum. This renewable energy could save NI Water up to £300k over 25 years. Charging points for NI Water’s growing fleet of electric vehicles have also been installed at the new treatment works. Communications & PR NI Water and its project management team developed a proactive comms and PR strategy for the Ards North Wastewater Improvement Scheme which included circulation of project brochure, issuing of regular press releases, letters to residents, briefings for elected representatives, circulation of progress updates, safety events with children, and face-to-face meetings with landowners. Myriad stakeholders were kept up to date with progress and informed in advance of pipelaying works and associated traffic management arrangements. Following completion of the project, a site tour of the new WwTW was organised to give local elected representatives the opportunity to view the modern facility first hand. Feedback from the visit was extremely positive. [caption id="" align="alignnone" width="1200"] NI Water, TetraTech, BSG Civil Engineering Ltd and Farrans along with local elected representatives to mark completion of the £18m Ards North Wastewater Improvement Scheme - Courtesy of NI Water[/caption] Conclusion A collaborative, forward-thinking approach between NI Water, BSG Civil Engineering and Tetra Tech has produced whole-life cost, programme and carbon savings in the delivery of this project. Phased flows were brought into the new Ards North WwTW between the months of November 2022 and January 2023. During this time, a process optimisation phase took place before the plant was rigorously tested and commissioned under varying flow and load scenarios. The plant was then put through a period of intensive detailed process sampling achieving highly performing results during separate 14 and 28-day sampling periods during Spring 2023. The project was successfully completed and handed over to NI Water ahead of the 2023 summer tourist season. The new Ards North WwTW is ensuring that high-quality effluent is being discharged out to sea, helping to improve the bathing water quality along this part of the Ards Peninsula in line with the project objectives.

The Burnley integrated catchment scheme is one of United Utilities' (UU) largest AMP7 projects with a value of £77m. The project is being delivered by UU’s construction delivery partner (CDP) framework by Advance-plus, a joint venture between MWH Treatment, J Murphy & Sons (JMS) and Stantec UK. The project commenced in 2020 and through two previous articles, UU and Advance-plus have shared the project background, the story of developing the solution and design, and commencing the build. In this year’s article, the project delivery team is pleased to provide an update on the construction progress and a look at the journey ahead as the project remains on course to achieve the December 2024 regulatory completion date. A summary of the project requirements and the integrated catchment solution scope The integrated solution scheme requirement is River Water Quality Improvement for the Water Framework Directive (WFD) driver identified in the Water Industry National Environmental Programme 3 (WINEP3) to achieve a ‘good status’ in the defined reaches of Pendle Water and the River Calder. To meet this, the treatment capability at Burnley Wastewater Treatment Works (WwTW) is to be enhanced to achieve compliance with the new enhanced, treated effluent permit standards, and management of storm discharges in the defined reaches, to achieve a compliance with the WFD 99%ile wet weather intermittent standards. The project also includes the U_MON3 spill monitoring and U_MON4 flow monitoring drivers. Through complex river water quality and network modelling, the lowest whole life cost integrated catchment solution was determined and developed. Four sites make up the integrated catchment solution which are all interdependent in delivering a total of ten regulatory outputs. [caption id="" align="alignnone" width="1200"] ASP under construction - Courtesy of United Utilities[/caption] Burnley WwTW Burnley WwTW serves a domestic population equivalent (PE) of 107,115 plus trade load. The site is undergoing a significant upgrade with the scope comprising design, construction, and commissioning of: New 12,000m3 detention tank with associated pumping station. New additional primary settlement tank (PST). New 1300 l/s inter-stage pumping station. New activated sludge plant (ASP) with BioMag® process. The BioMag® System enhances conventional biological wastewater treatment by using magnetite (Fe3O4) to ballast floc allowing an increase in mixed liquor suspended solids (MLSS) in the ASP and enhanced performance in the final settlement tanks (FSTs). Refurbishment of existing final settlement tanks. New surplus activated sludge (SAS) thickening process. New ferric and caustic dosing plants. Associated motor control centres (MCCs), SCADA upgrade, and power upgrade. Pipework The last year has seen great strides being made across the site and various process areas, with major civils structures constructed and taking shape. The very constrained nature of the site, existing processes and services, and the need to lay many kilometres of small and large diameter underground pipework has proven to be a major constructability challenge. Most of the pipework installation has been self-delivered by J Murphy & Sons with Saint Gobain PAM UK being the main supplier of the pipework and fittings. Detention tank The new detention tank, has been constructed by A-Consult Ltd using 64 precast concrete panels, standing 10.4m high. The panels were precast in their factory before being transported to site for erection and subsequent post tensioning. Utilising this construction technique, with design for manufacture and assembly (DfMA) brings benefits in terms of quality, time and safety. The tank has successfully passed its water test and is currently being drained. The feed pumping station has been constructed and the mechanical installation of pumps, mixers and pipework is now in progress. [caption id="" align="alignnone" width="1200"] Detention tank on water test - Courtesy of United Utilities[/caption] Primary settlement tank The new primary settlement tank (PST) civils construction is also complete, again undertaken by A-Consult Ltd using the precast concrete panel method of construction. It has also successfully passed its water test. Mechanical installation by EPS Water is now in progress on the ‘H’ frame steel structure which will support the scraper bridge. The design of the PST incorporates a fixed bridge arrangement with rotating scrapers beneath. This arrangement is necessary as the PST will eventually be covered with a GRP roof for odour mitigation. The odour control fans, ductwork and vent stack are scheduled to be installed in December. [caption id="" align="alignnone" width="1200"] PST4 and ASP lane 1 on water test - Courtesy of United Utilities[/caption] Interstage pumping station Due to the topography and hydraulic levels across the site, a new interstage pumping station (IPS) is required to pump the effluent leaving the four PSTs up to the new activated sludge plant (ASP) distribution chamber. Civils FRC works are being undertaken by STAM Construction Ltd and contain 94 tonnes of rebar and 900m3 of in situ poured concrete. The pumping station structure is complete and has undergone successful water testing. The internal benching is complete and the next activities planned for the coming period will be the mechanical installation of the pumps and pipework. As the pumping station is vital to keep all flows passing through the treatment process, a standby generator will also be installed. The IPS is a two compartment design to facilitate future maintenance activities preventing the need to take it completely out of service. The new pumps have been supplied by Xylem Water Solutions who have supported the designers in providing efficient selections for the large submersible pumps and optimising the layouts of the pump chambers. Activated sludge plant The ASP distribution chamber is currently being constructed with all four concrete walls having now been poured. These are curing and the structure will undergo a water test in September 2023. [caption id="" align="alignnone" width="1200"] ASP constructed and water tested - Courtesy of United Utilities[/caption] In constructing the new ASP, STAM Construction Ltd have installed 650 tonnes of rebar and poured 4500m3 of concrete. The overall size of the ASP is 48m x 48m x 6.6m deep, has a capacity of 14,500m3 and comprises four lanes. Civils construction of the ASP is complete and fully water-tested with the mechanical installation of the internal pipework, aeration grids, diffusers and access platforms and walkways taking place over the next few months. Suprafilt Ltd will be supplying and installing the internal pipework, aeration grids and diffusers. Mechanical installation of the pump stations and access steelwork etc will be undertaken by Fluid Sealing & Engineering (FSE). BioMag® The Evoqua Water Technologies detail design for the new BioMag® process has been finalised and the building layout confirmed. The main equipment including four Magdrums and two shear mills, process tanks, silo and pumps, which have been manufactured and are ready for delivery to site when required. The BioMag® building is currently under construction by Gallaway Construction. The steel frame has been erected and the gantry crane and roof cladding have been installed. External wall cladding is in progress, after which attention will turn to the internal fit-out and installation of the BioMag® equipment. [caption id="" align="alignnone" width="1200"] BioMag® building being erected - Courtesy of United Utilities[/caption] Final settlement tanks (FST) There are four existing final settlement tanks which required refurbishing to ensure adequate performance and asset life are achieved. The scope includes civils refurbishment of the tank walls which involves cutting approximately 300mm from the top of the walls before installing new reinforcement and re-casting concrete to the required coping levels. Cutting works is being undertaken by Holemasters and FRC works self-delivered by JMS. The mechanical and electrical work is being delivered by Jacopa and comprises refurbishment of the bridge, scraper assemblies, and other ancillary equipment. Three of the four FSTs have now been refurbished with the final one due to be undertaken towards the end of the year. Surplus activated sludge (SAS) thickening Civils works has been ongoing in the SAS thickening process area for the last couple of months with the storage tank, drum thickener, poly plant and kiosk bases all constructed. Underground services, ducts and pipework have also been installed and tested. The filtrate return pumping station construction is in progress with the mechanical installation due to follow on. Chemical dosing The new ferric and caustic dosing plants comprise storage tanks, dosing rigs and dosing pipelines, all of which have been designed and well progressed in manufacture. These are being supplied by NPS Engineering Group. A new chemical delivery facility will also be provided with civils construction in this area commencing towards the end of the year and installation of the new dosing plants taking place early 2024. [caption id="" align="alignnone" width="1200"] 3D model of chemical dosing area - Courtesy of United Utilities[/caption] HV works A new, uprated HV cable has been installed from the off-site substation to the wastewater treatment works, a length of approximately 900m, passing through a number of fields and third-party land. Motor control centres (MCCs) To control all the new assets a number of new MCCs housed within kiosks are required around the site, along with a new site-wide SCADA system. The MCCs are all in various stages of manufacture and factory testing. The electrical installation and system integration works, including dry testing, will be undertaken in phases over a period of months as the programme for each of the new process areas dictates. The MCCs are being built by Technical Control Systems Ltd, electrical installation will be by PICOW Engineering Group and system integration by Tata Consultancy Services. Looking forward to commissioning Commissioning of the new treatment process, and transitioning from the old process in a controlled staged approach, will be complex. The existing treatment stream and process compliance cannot be put at risk or compromised and months of hard work and planning for commissioning has already taken place. Wet commissioning is due to start in April 2024, gradually increasing flows into the new treatment process over several months while the new biological process builds up and matures to a point where the improved treatment standards are being met. The forecast project in use date is October 2024. [caption id="" align="alignnone" width="1200"] Aphex construction planning software map view - Courtesy of United Utilities[/caption] Burnley WwTW Catchment Strategy: Supply chain - key participants Construction Delivery Partner: Advance-plus JV MWH Treatment (Advance-plus jv) J Murphy & Sons (Advance-plus jv) Stantec UK (Advance-plus jv) CFD modelling: CER Technologies Ltd GPR & topo surveys: Atlantic Geomatics (UK) Ltd Flood risk assessment: Ambiental Environmental Assessment Ltd Physical modelling: Hydrotec Consultants Ltd Dewatering design: OGI Groundwater Specialists Ltd Concrete construction: STAM Construction Ltd Concrete supply: CEMEX UK 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 Earthworks: D Morgan plc Blower building: Saredon Steel Buildings Ltd Access metalwork: Tushingham Steel Fabricators BioMag process: Evoqua Water Technologies (Xylem Water Solutions) BioMag building: Gallaway Construction Ltd BioMag mechanical installation: Alpha Plus Ltd Ventilation: Air Technology Systems Ltd Pumping station mechanical installation: Fluid Sealing & Engineering (FSE) HV cable installation: Smith Brothers Ltd Transformers: Winder Power Electrical installation: PICOW Engineering Group MCCs: Technical Control Systems Ltd Systems integration: Tata Consultancy Services Standby generators: DTGen SAS glass coated steel tank: Stortec Engineering Ltd PST fixed scraper bridge: EPS Water Epoxy coated carbon steel pipework & wall starters: Freeflow Pipesystems Ltd Dosing systems: NPS Engineering Group 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 Water & Wastewater Aeration system: Suprafilt Ltd SAS tank air mixing system: Utile Engineering Submersible pumps: Xylem Water Solutions Valves: AVK UK Ltd Kiosks: Industrial GRP Lindred Road CSO (PEN0056) Work at this existing combined sewer overflow (CSO) site comprises the construction of an online 1,950m3 detention tank which will hold stormwater during times of heavy rainfall, reducing discharges to the watercourse. New pumps within the tank will return the effluent to the sewer for onward treatment at Burnley WwTW. The 15m diameter x 20m deep detention tank, is of segmental shaft construction and is located within the very busy and congested Lomeshaye Industrial Estate in Nelson, and was constructed by Joseph Gallagher Ltd. This was a highly challenging build within a car park of one of the local businesses and an enormous amount of planning and stakeholder management has been required. [caption id="" align="alignnone" width="1200"] Lindred Road detention tank during construction - Courtesy of United Utilities[/caption] Work started on site in July 2022, with the first phase involving the diversion of numerous services, including gas, fibre, BT, water and power, to clear the area for the tank construction. Enabling works to provide safe access routes, segregation, and procurement of alternative car parking for the impacted business employees was also required before the main construction work could commence. Ground was broken in August 2022 with the tank construction continuing through to December 2022 when full depth was reached. Construction of the pump sumps, inlet channel and complex benching arrangement followed. The spring months of 2023 saw the mechanical works inside the tank take place with the installation of the pumps, pipework and access ladders and platforms. Once the internal works were complete, the roof beams were installed and the roof slabs placed on in May 2023. The inlet and outlet pipework for the tank has now been installed, including associated manholes and chambers. To facilitate the connection of the 1200mm inlet pipe into the existing CSO chamber, a complex timber heading arrangement needed to be constructed in order to access beneath, and protect a myriad of services crossing the vicinity. All buried pipework, chambers and ducts etc have been completed and reinstatement of the area is in progress. The civils and pipework has been undertaken by SGC Civil Engineering Ltd and the mechanical works by Fluid Sealing & Engineering (FSE). A new motor control centre and power supply is being installed for this facility. The new control kiosk was delivered and installed in July 2023 and the electrical installation is currently ongoing with the new power supply due to be energised in October. Testing and commissioning is scheduled to start in November, with the site achieving project in use in February 2024. Lindred Road Detention Tank: Supply chain - key participants Civil design detention tank: COWI UK Ltd Detention tank shaft: Joseph Gallagher Ltd Civils & pipework: SGC Civil engineering Ltd Mechanical works: Fluid Sealing & Engineering (FSE) Precast roof sections: Macrete (Ireland) Ltd Precast shaft segments: FP McCann MCCs: Technical Control Systems Ltd Kiosks: Industrial GRP [caption id="" align="alignnone" width="1200"] Lindred Road: Aerial view of detention tank - Courtesy of United Utilities[/caption] Altham Outfall Fennyfold CSO (BUR0026) This existing CSO site is located in Padiham, near Burnley, and is part of the sewer network that transfers flows to Hyndburn WwTW for treatment. The solution here is to construct a new chamber over the downstream sewer, and install a new real time controlled actuated penstock valve that will regulate and optimise flows passed forward to Hyndburn, whilst reducing spills from the existing CSO. A new control kiosk and power supply are also required. This new facility is situated within an environmental and stakeholder sensitive area, adjacent to a number of allotments and the River Calder. The parcel of land required for the new kiosk and chamber has been procured and a new access track for future operation and maintenance, as well as the build, will be required and constructed. The detailed design is complete and some enabling works to set up site have been undertaken. For the main construction activity, a complex temporary works arrangement will be required, with large scale over-pumping, to carry out the works on the live sewer. Plans are currently being made to install temporary isolation rails and plates during a suitable dry weather period in preparation. This site is scheduled to be complete in spring 2024. Hyndburn WwTW To cater for the change in flows being presented at Hyndburn WwTW through the inlet sewer from the BUR26 catchment, the solution modelling has identified that by reducing the time it takes for the storm tanks to be returned into the treatment stream would ensure that the river water quality objectives could be achieved. The existing storm return pumping station is made up of fixed speed pumps operating at a duty of 100 l/s. A new variable speed storm return pumping station will be constructed which will be capable of returning flows across the range of 30 l/s to 330 l/s. This means that the contents of the storm tanks can be returned much quicker after a storm subsides. [caption id="" align="alignnone" width="1200"] Hyndburn WwTW - 3D model of storm return pumping station - Courtesy of United Utilities[/caption] A new below-ground wet well type pumping station will be constructed with three high-flow pumps and two low-flow pumps which provides a more flexible and efficient system with greater turn down capability. A new single rising main will return the storm flows back to the head of the treatment works. A new kiosk and motor control centre will also be installed. Planning permissions are in place and all pre-start surveys and investigations have been completed. Detailed design is nearing completion and the site has just been established. Construction is due to start in earnest in September on the new pumping station excavation. The winter months will see the civils works progress, with mechanical and electrical works due to start in spring. The project in use is forecast for July 2024. The digital toolbox 4D digital rehearsals which link the 3D model to the programme have been used extensively by the site team to validate the constructability and sequencing of the works. Visualisation allows all parties to truly understand the construction sequence, interfaces and interdependencies which is relevant on such a congested work area with multiple subcontractors operating in close proximity. They have helped to identify high risk activities and plan mitigation measures. They also help provide programme and cost certainty and facilitate stakeholder engagement. Over the last year Aphex, a powerful construction planning software tool which enables the delivery teams to better plan and work together has been introduced. This has been used for short term, look-ahead planning, which is linked to, and aligned with the master schedule in P6. It has also enabled the construction teams to control the build, assign ownership, communicate and track plans on a daily basis. [caption id="" align="alignnone" width="1200"] Aphex construction planning software Gantt chart - Courtesy of United Utilities[/caption] Challenges and collaboration A large and complex project of this type, across several sites, brings enormous and numerous challenges. These include health and safety management of large scale, complex construction in constrained working areas, on live operational sites and in 3rd party and public areas, while also working in environmentally sensitive areas and requiring engagement and interfacing with customers. Successful delivery would not happen without true collaboration. From the outset of the project we delivered a team development programme and established a co-located office which has proven to be invaluable in creating a great culture and an open and collaborative working environment over the last three years. Challenges and emerging risks and issues are dealt with almost on a daily basis as a team. The project teams continually work together to ensure that delivery stays on track, the highest standards are maintained and everyone goes home safe and well.

Storm overflows are a critical component of sewer networks, acting as relief points within the network and preventing systems from being overloaded and causing flooding. In the UK, this legacy Victorian sewer infrastructure is under growing pressures from climate change and increasing urban development. As stated in the UK Government’s ‘Storm Overflows Discharge Reduction Plan’ (SORP) (Defra, 2023), reducing storm overflows and improving water quality is a core part of the largest infrastructure investment in UK history. To address this, Wessex Water Services Limited (WWSL) is integrating Nature-based Solutions (NbS) as key interventions into their asset base through their commitment to restoring the environment. Background

Mott MacDonald (MM) has been working closely with WWSL to assess several of their storm overflow sites for installation of constructed treatment wetlands. MM is designing both traditional and innovative wetland approaches to deliver schemes at different scales and approaches, whilst maximising sustainability through retrofitting existing and decommissioned infrastructure.

The focus of this case study is to outline the regulatory drivers, the overall design approach taken by MM and detail how the design has gone beyond simply seeking to limit environmental impact.

[caption id="attachment_15838" align="alignnone" width="1200"] Example of a separated storm overflow and final effluent discharge point - Courtesy of Mott MacDonald (David Naismith)[/caption] Regulatory drivers

Under the Environment Act 2021 (Parliament of United Kingdom), all water companies in England are legally required to progressively reduce the adverse impacts of discharges from storm overflows. Under the SORP (2023), all water companies are required to achieve the following three specific targets:

By 2035, water companies will have improved all storm overflows discharging near every designated bathing water and improved 75% of storm overflows discharging into or near ‘high priority sites’. By 2045, water companies will have improved all remaining storm overflows discharging into or near ‘high priority sites’. By 2050, no storm overflows will be permitted to operate outside of unusually heavy rainfall or to cause any adverse ecological harm.

These targets need to be achieved in addition to all legal duties stipulated under the Urban Waste Water Treatment Regulations (England and Wales) (1994) and the Water Industry Act (1991).

Storm overflow operation is influenced by rainwater and/or groundwater contributions. Where groundwater is the key contributor causing the overflow to operate, often for prolonged periods of time, NbS can provide treatment to ensure no adverse ecological harm. This aligns with the requirements set out in the relevant legislation.

Suitable regulation is and will be key to ensuring wetlands are appropriate and adequately designed to address needs. Wessex Water has been working with Defra and the Environment Agency to develop a permitting approach suitable for use at their sites with groundwater influenced storm overflow wetlands. It is anticipated that through using existing wetland sites as research and case study systems, under Operating Techniques Agreements (OTAs), suitable permitting can be developed for future use.

To date, there is a requirement to satisfy the requirements of the Urban Wastewater Treatment Regulations (England and Wales) (1994), specifically Schedule 3 Table 1, which sets out effluent quality requirements with respect to BOD5 and demonstrate that the Best Technical Knowledge Not Entailing Excessive Cost (BTKNEEC) tests have been satisfied.

[caption id="attachment_15846" align="alignnone" width="1200"] Example of a wetland with established vegetation - Courtesy of Mott MacDonald (David Naismith)[/caption] Design approach - phased delivery

Since 2022, Mott MacDonald has assisted Wessex Water to review their most frequently spilling groundwater induced storm overflows and assess the suitability of each for the installation of constructed treatment wetlands. Overflows that are governed by groundwater infiltration into the sewerage system in the upstream catchment typically exhibit a lower peak flow and overflow for a longer duration. Initial screening was undertaken to derive a candidate list of sites - where installation of treatment wetlands may be a feasible option to reduce untreated discharges to the environment and prevent subsequent ecological degradation of the receiving waterbody. This screening primarily consisted of the review of all available data sets (e.g., storm overflow water quality, quantity, and spill frequency data) and undertaking initial site visits.

It is recognised that the use of treatment wetlands systems in Europe to treat storm overflows has occurred, but their use in the UK is limited. The integration of non-traditional and unfamiliar technology within the UK water industry comes with associated risks and opportunities. Wessex Water has used a phased delivery approach which allows for a gradual implementation, facilitating easier planning and control of delivery. Key blockers are identified at the initial stages of delivery, allowing for issues to be solved with a minimised impact and will make the process smoother in the long run. A staggered approach has allowed for the growth of expertise and capacity, development of efficiencies and best practice and lessons learnt to be implemented from earlier phases.

[caption id="attachment_15840" align="alignnone" width="1200"] Soft engineered bank, pond and marginal planting - Courtesy of Mott MacDonald (David Naismith)[/caption] Overview of constructed wetlands solutions

There is good evidence of the use of constructed wetlands (CWs) for treating storm overflows in Europe and the USA, with the most recent information available for systems in Germany, Italy, France and the USA. At present there is little published literature on the use of CWs for CSOs/SOs for the UK.

One of the first storm overflow filters was built in Germany in 1989, these were referred to as Retention Soil Filters (RSF) as they were constructed with a soil and compost filter media. Following early experience with these systems, the filter media was changed to technically mixed sands to prevent clogging (Meyer et al., 2013).

The German Association for Water, Wastewater and Waste (Deutsche Vereinigung fur Wasserwirtchaft, Abwasser und Abfall, DWA), released national guidelines on design and operation in 2005, based on the improved RSF design with sands and gravels as the filter media. These guidelines were updated in 2018 (DWA, 2018; Nivala et al., 2018) based on the experiences since the first issue. Further development of the design of storm wetlands in France and Italy began in the late 2000s, with national guidance being produced.

Treatment process

A typical storm overflow wetland is installed between the overflow point from the storm tank and the existing storm outfall. Irrigation flow can be taken from the final effluent stream or a potable water source. The figure below illustrates a flow diagram for an example site with Vertical Flow (VF) wetlands installed. It should be noted that at some sites, storm overflow and final effluent share a common outfall to an adjacent watercourse.

[caption id="attachment_15832" align="alignnone" width="1200"] Example treatment process of a vertical flow wetland used to treat storm overflow - Courtesy of Mott MacDonald (David Naismith)[/caption]

The typical performance for CSO/SO wetlands is provided in the table below.

The pollutant reductions ranges are derived from a review of literature and cover a range of system configurations but provide a general indication of the water quality improvements that can be expected.

Parameter Typical Reduction Range Parameter Typical Reduction Range Total suspended solids 50-95% Nitrate 45-50% Biological oxygen demand (BOD) 60-90% Total phosphorus 40-90% Chemical oxygen demand (COD) 80-90% E. Coli 1.2-2.3 log10 Ammonia 40-90% Enterococci 0.9-2.2 log10 Typical Performance of CSO/SO Wetlands Wetland types

Selection of the type of treatment wetland to be implemented has been very site specific, as each site has offered unique challenges and opportunities, though with some commonality. Typical constraints have been land area available, topography (especially levels of existing chambers where flows have to be intercepted), ecological aspects, and existing services.

The design has sought to select the most suitable wetland type for each site. The following wetland types are being designed by MML and are elaborated upon in the following sections:

Free water surface (FWS) wetlands. Vertical flow (VF) wetlands. Floating treatment wetlands (FTW). Swales and bioswales. [caption id="attachment_15839" align="alignnone" width="1200"] Example of a free water surface wetland - Mott MacDonald (David Naismith)[/caption] Free water surface (FWS) wetlands

This type of wetland most closely resembles natural wetlands and take the form of a marsh habitat. They consist of soil media in the base, a permanent flooded water depth of at least 300-500mm and are usually densely planted with mixed native species of submerged, emergent, and marginal aquatics. These wetlands are typically used for secondary and tertiary treatment and are effective at reducing BOD, COD, oxidised nitrogen, total phosphorus, and suspended solids concentrations.

FWS wetlands are good for high flow sites as attenuation capacity can be built in, they are continuous flow so do not require measured volumes or inflow control like VF wetlands. They do require a larger surface area and land-take than VF wetlands so are only suitable on sites where land is available, and the soils and topography are favourable. They can be incorporated into the landscape and designed to reflect more natural wetland features, so can appear less engineered than VF wetlands with less visual impact.

Vertical flow (VF) wetlands

VF wetlands consist of a sand and gravel filter with wetland plant species (typically Common Reed ‘Phragmites australis’) present on the surface. Influent is delivered in measured volumes to the surface of the wetland where it floods the top sand layer to a design depth. The influent then filters vertically down through the sand and gravel layers receiving treatment before being collected in the base of the wetland and directed to the next downstream stage. These wetlands usually operate in a minimum configuration of two cells that are alternately fed with influent, with each cell having a rest period between feedings. These wetlands are particularly effective at reducing biological oxygen demand (BOD), chemical oxygen demand (COD), and ammonia concentrations.

VF wetlands provide high performance for area footprint but do require wastewater to be delivered in measured volumes, therefore pumping or gravity siphons are required. They were selected where space was limited, and available flow data indicated they would be suitable.

[caption id="attachment_15842" align="alignnone" width="1200"] Example of a vertical flow wetland - Mott MacDonald (David Naismith)[/caption] Floating treatment wetlands (FTW)

This type consists of module units that comprise a floatation and substrate support system, planting substrate, and plants. They are typically installed on open water areas with multiple anchoring points to the bed and/or banks to hold them in position. They have the advantage of being able to accommodate relatively large fluctuations in water level while providing water quality improvement and ecological benefit. They can be used to improve the performance of settlement ponds by promoting greater suspended solids removal.

The modules are fabricated off site with media installation and planting undertaken on site. The modular construction, ability to build different configurations and shapes, and low infrastructure requirements make FTWs an effective solution for retrofitting to existing ponds, lagoons and tanks.

Swales & bioswales

Traditionally used for sustainable drainage systems (SuDS) applications, dry and wet swales are shallow ditch like features with dense vegetation. Bioswales are deeper features with a saturated, anaerobic zone in the base. Swales have been considered here in specific situations where spill volumes could be low, space is limited and irrigation between events is a challenge, as they are more resilient to dry periods. Adopted from the Catchment Sensitive Farming (CSF) approach, they are proposed on an experimental basis for network pump stations and low volume spilling sites to improve water quality and reduce impact on the receptor. However, they are likely to have lower water quality improvement potential than the other wetland types.

[caption id="attachment_15836" align="alignnone" width="1200"] (left) Example of a floating treatment wetland - Courtesy of Biomatrix Water and (right) example of a swale - Courtesy of Mott MacDonald (David Naismith)[/caption] Wider benefits during solution development

An appropriate balance between grey and green infrastructure has been sought during design development at existing Wessex Water WRCs (water recycling centres) and SPSs (sewage pumping stations). The design approach of the schemes has focused on wider benefits alongside reducing construction, carbon, and energy requirements. The team has taken a collaborative approach to design working with multiple stakeholders and disciplines, including operational and specialist technical teams, statutory agencies, contractors, and suppliers. This included early engagement, where possible, to mitigate risks and maximise opportunities.

Retrofit & reuse

Where possible, the design has investigated the use of existing but decommissioned or under-used infrastructure for the installation of wetland systems. This has included the conversion of disused sludge or filter beds into vertical flow (VF) wetlands and re-use of redundant storm tanks or oxidation ditches into floating treatment wetland (FTW) settlement tanks. If existing infrastructure can be re-purposed where possible, this will reduce materials and construction costs and potentially reduce carbon impacts. The other advantage is to utilise space within sites more effectively, reducing the potential land take of a system and the need to purchase further land outside of the works.

The design process has also sought to maximise reusing material, such as biofilter media, to encourage responsible material consumption, reducing the required transport and volume of material sent to landfill.

[caption id="attachment_15864" align="alignnone" width="1200"] (top left) Decommissioned filter beds being considered for retrofit, (top right) filter media being considered for reuse, (bottom left) decommissioned oxidation ditch being considered for retrofit - All courtesy of Wessex Water, and (bottom right) planting within an existing floating wetland - Courtesy of Mott MacDonald[/caption] Sustainability

The design has considered the whole life cycle of the wetland and mitigated the risk of potential degradation of habitat during dry periods when selecting the type of wetland to be installed at a site and irrigation required. To reduce energy consumption, designs have been exploring the use of renewable energy using solar pumps for irrigation of wetlands during dry summer periods. Where topography and site constraints have allowed, the designs have sought to install gravity systems to avoid pumping and have adopted greener engineering solutions to provide additional value and sustainability benefits.

Where possible, the designs include viewing platforms and interpretation boards for recreational users of adjacent land to use to view and learn about the proposed wetland and surrounding area. The incorporation of these elements provide opportunities to educate on the importance of water management and biodiversity and also directly benefit people’s wellbeing through the creation of interactive spaces.

The design process has considered how multiple benefits for local wildlife and enhancements to existing habitat could be achieved. The use of soft engineered banks to retain wetlands has been prioritised where land and site-specific constraints allow. This, in addition to planting of mixed native species with attention to locally important species, has the potential to support the local ecosystems and enhance biodiversity. Where excavation has been unavoidable, enhancements such as: utilising excavated chalk to enrich surrounding chalk grassland; creation of butterfly and invertebrate mounds; and strategic planting have been included in the design. For example, at Maiden Newton WRC, the design includes scrub planting for the enhancement of local reptile habitat and hedge planting and management, using traditional hedge laying techniques, to both screen the existing WRC works and provide ecological, landscape, and heritage educational opportunities

[caption id="attachment_15843" align="alignnone" width="1200"] Soft engineered bank, pond and with established vegetation - Courtesy of Mott MacDonald (David Naismith)[/caption] Conclusion/summary

Working towards achieving targets set out in the SORP, Wessex Water is trialling NbS schemes across the region which shall inform the long term NbS strategy. The systems will be monitored for performance but also for ease of operation and maintenance. This monitoring will feed into capturing performance trends, lessons to be learnt and efficient maintenance operations. The information captured can then be fed back into various elements of the business to inform the development of NbS for this application.

From this, there is potential to educate and inform the national narrative and provide the evidence for other water companies to take up these solutions. Promoting the wider benefits (biodiversity, carbon, energy reduction, research, and education), resilience to climate change impacts and landscape fit, backed up with evidence, should increase the uptake of NbS within the water industry.

At time of writing (August 2024), Mott MacDonald has commenced design on a total of 11 sites whose construction phase is programmed to occur in AMP8 (2025-2030) and AMP9 (2030-2035).

The list below provides a high-level overview of the types of wetlands being designed for the sites*.

Gurney Slade SPS: Swale with engineered soil. Bradford on Tone WRC: Vertical flow wetland. Hatch Beauchamp WRC: Bioswale (deep swale with engineered soils and a saturated, anaerobic zone). Maiden Newton WRC: Combination of vertical flow & free water surface wetlands. Wookey WRC: Re-purposing of decommissioned filter beds and retrofit with a vertical flow-style wetland using existing filter bed media. Cheddar WRC: Re-purposing of decommissioned oxidation ditch and retrofit with floating treatment wetland. North Cadbury WRC: Vertical flow wetland and/or bio-bed or bioswale. Sydling St Nicholas WRC: Potential short term swale solution and long term vertical flow wetland. Chew Stoke WRC: Re-purposing of decommissioned primary settlement tanks and creation of a free water surface wetland. Hullavington WRC: Vertical flow wetland. Great Badminton WRC: Free water surface wetland.

* Subject to change upon receipt of surveys and/or review of guidance pertaining to permitting and monitoring requirements for storm overflow treatment wetlands, anticipated to be released by the Environment Agency in 2024.

Dawlish is a traditional seaside town on the south coast of Devon, approximately 12 miles south of Exeter and is a popular holiday and day trip destination. South West Water (SWW) and Galliford Try’s objective was to ensure that the bathing water quality did not deteriorate within the next 20 years by ensuring that there are no more than two significant (>50m3) spills from the Brook Street CSO per bathing season by 31 March 2022. The proposed solution was to be achieved by providing 30m3 of offline, pumped return stormwater storage in the Manor House council office car park on Brook Street to improve spill performance at Meadow Road CSO in line with SWW/Environment Agency targets, in combination with the removal of surface water from the combined system; being delivered as a separate element of the overall project by another delivery partner. Description As part of the overall SWW objective to achieve less than two significant spills from Brook Street CSO per bathing water season, this project supplemented the scope from the infra delivery partner. Provision of 30m3 of unscreened, stormwater storage upstream of the Brook Street CSO, by the installation of a 4m diameter x 3m deep tank with duty pump return. Provide a flow control device (Hydro-Brake®) to limit PFF to 10 l/s with an unrestricted bypass arrangement within an overflow chamber. Once the tank is full, additional flow will bypass the Hydro-Brake® via a high-level weir. The agreed storage tank volume, flow control device and overflow weir levels have been derived from the Stantec UK modelling report and taken as the scheme output for the storage element. The final tank volume selection/spill performance of the promoted option has been selected at SWW IPC and has been operationally reviewed by SWW operations team, commissioning engineer and asset management. [caption id="" align="alignnone" width="1200"] (left) Flow control chamber showing overflow weir and Hydro-Brake® and (right) looking down into the 30m3 stormwater tank showing the float controls, pump, pump guides and sump - Courtesy of Galliford Try[/caption] Project scope Site mobilisation and temporary works, to include road closure of Brook Street and suitable traffic management/diversion. Construct 4m diameter x 3m deep (internal) PCC shaft in Brook House car park. Construct 30m of connecting pipework and associated manholes to connect new tank to existing sewerage network. Construct PCC overflow chamber to include Hydro-Brake®, spill weir and bypass weir. Install new single 5 l/s return pump and associated control cabinet, cabling, ducting, instrumentation and return rising main. Site reinstatement. In-house capability Galliford Try self-delivered this project, designing all civils and MEICA elements, as well as being the principal contractor and lead designer on the scheme. Galliford Try managed the site, direct labour, installation and commissioning, all within an incredibly tight programme (made tighter by severe storms). Brook Street CSO: Supply chain - key participants Design & construction: Galliford Try Modelling: Stantec UK Shoring/temporary works: MGF Ltd Hydro-Brake®: Hydro International Ltd Pumps: Xylem Water Solutions Access covers: Technocover Ltd Traffic Management: Amberon Ltd Fabrications: Thorne Fabrication Limited Electrical items: Edmundson Electrical Ltd Diamond drilling works: 24-7 Diamond Drilling & Sawing Services Ltd Civils items: Keyline Civils Specialist Plant hire: Gap Group Ltd Aggregates: Hanson Aggregates Construction Products: Jewson Plant hire: Plantforce Rentals Ltd Crane hire: Spence Crane Hire Ltd Tarmac surfacing: Devon Tarmasters Planning & collaboration The site footprint consisted of a small section of The Manor House carpark (which belongs to the Dawlish Council offices), a 20m x 20m area in which Galliford Try managed to contain their welfare facilities and site office, working area and laydown of plant, equipment and materials, a 5.5m diameter, 5m deep shaft and two flow controlling combined sewer inspection chambers with a pumped return, MCC cabinet, two weirs and a Hydro-Brake®. Galliford Try also had to construct two inlet and outlet inspection chambers within a very tight street with multiple existing services. They accomplished this using road closure notices and daily communication with the residents of the local area. During the works, Galliford Try had to excavate the shaft using a 14t wheeled excavator, an MGF TWD of sheets and frames, 5m away from a listed building. SWW estates team carried out a structural survey on the building before they started, and no evidence of any movement was detected associated with the works. Galliford Try mucked away 225t of spoil from the shaft while working closely with another SWW contractor during the construction phase to reduce their footprint further, they arranged joint use of their muck away process meaning reduced footprint of their working area and around half the amount of muck wagons going through Dawlish town centre. Galliford Try also required a 40t mobile crane to lift in the large pre-cast concrete shaft section which required an intricate lift plan and careful logistics. To connect the stormwater storage tank and flow control inspection chambers into the existing network Galliford Try had to accurately survey the existing sewer and optimise the inlet point inspection chamber missing two water mains, a gas main and a surface water drain. To return the flows to the existing sewer they had to precisely know at which point their tank would spill to contain the required volume of storage. The existing sewers in Brook Street were incredibly old and fragile, they had to delicately expose the existing sewer and break in without cracking the upstream and downstream section of pipework. Galliford Try managed to install the chambers using the minimum amount of new pipework. [caption id="" align="alignnone" width="1200"] (left) All weather kiosk constructed off-site, containing the alarms, telemetry, pump return and mains in-comer and (right) access cover within the Manor House Car Park into the 30m3 stormwater tank all completed day before handover - Courtesy of Galliford Try[/caption] Off-site build All four new inspection chambers were concreted from PCC sections and all sections of the shaft were also PCC, reducing installation time and costs. The kiosk was constructed off-site by Galliford Try and installed by their panel shop and then commissioned three days before the commissioning, date reducing storage and on-site presence. Challenges & risks Galliford Try used a vacuum excavator (the fastest and most economical method of excavation) to dig around existing services. Benefits include: reducing reinstatement costs, eliminating the hazard of utility strikes, and reducing the amount of manpower/equipment required. The construction challenges: Small footprint/working area. Existing services in road. Managing access for stakeholders. Temporary works - excavating deep shaft adjacent to existing buildings. Completion & carbon savings Galliford Try completed this work following on from a previous project to remove the surface water run-off from the local catchment; greatly reducing the combined sewer flow rate and reduced the time the storm tank would fill, further reducing the risk of a spill during the bathing water season. The overall scheme (including the surface water separation) would at some point become carbon negative, due to reducing the combined sewer flow to the local STW and not paying the energy bill to treat the additional storm flow now going straight into the Brook. This reduces the amount of flow being stored and pumped back into the combined sewer on time. [caption id="" align="alignnone" width="1200"] Completed car park area day before handback - Courtesy of Galliford Try[/caption] Community Whilst road closures were in place, Galliford Try helped residents by assisting with taking their bins out to the new temporary location, as well as helping the older residents bring their shopping in.

Guildford, the county town of Surrey, sits a commutable 30 miles south west of London and 70 miles from the south coast. Boasting a castle, a cathedral, a picturesque town centre and a university, it is surrounded by Green Belt countryside. The River Wey flows through the town centre and then northwards through water meadows where it provides the outfall for the STW. The Wey eventually discharges into the Thames. The current STW serves a population equivalent (PE) of around 107,000, but the town has a growing population which is expected to grow to circa 125,000 PE by 2041. Background

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.

[caption id="attachment_26867" align="alignnone" width="1200"] Figure 2: Site overview: BIM model of new Guildford STW - Courtesy of BAM Enpure JV[/caption]

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.

Previously in Water Projects

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.

Contract

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.

[caption id="attachment_26869" align="alignnone" width="1200"] Figure 3: 3D design using a model hosted by Arcadis, image from Autodesk’s Navisworks viewer - BAM Enpure JV & Arcadis[/caption] The project

The project consists of the following:

A transfer tunnel. An inlet pumping station. Inlet works screening. Primary settlement. Activated sludge treatment. Final settlement. Tertiary treatment of final effluent. Chemical dosing facilities. Storm storage tanks. Import cess and sludge facilities. A new control centre. New welfare building. Outfall into the River Wey.

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

Timeline Phase 1: Ground improvement: Started summer 2023 and completed February 2025 Phase 2: Civil engineering: Started summer 2023 with completion due in late 2025. Phase 3: Mechanical & electrical engineering: Started autumn 2024 and is due to complete summer 2026. Phase 4: Commissioning: Starts winter 2025 and is due to complete in spring 2027. [caption id="attachment_26883" align="alignnone" width="1200"] Figure 4: 3D model of the sludge processing area - Courtesy of BAM Enpure JV & Arcadis[/caption] Developing the site

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:

Rapid Impact Compaction (RIC) to improve ground strength and reduce long-term settlement of the landfill. Vertical Rigid Inclusions (VRI), a displacement concrete pile technique which provided support for roads, lighter structures pipes and ducts. Driven concrete piles bedded in the London Clay below the land fill to support large structures, tanks and pipelines.

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.

[caption id="attachment_26880" align="alignnone" width="1200"] Figures 5: (left) Spatial variation in landfill thickness 2023 and (right) historic site layout (1976) with present day boreholes overlaid - Courtesy of Arcadis[/caption]

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.

[caption id="attachment_26872" align="alignnone" width="1200"] Figure 6: Gas protection void former being laid on stone blanket prior to tank base blinding, Connections to vents at tank perimeter - Courtesy of BAM[/caption]

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

Main contractor: Bam Nuttall Ltd Planning consultant: Adams Hendry Consulting Ltd Civil engineering design: Arcadis Group Ltd Boreholes & testing: Geo-Environmental Services Ltd Asbestos monitoring: Socotec Ltd Rapid impact compaction: Cofra Ltd (Boskalis Group) Vertical rigid inclusions: Foundation Piling Ltd Concrete piling: Aarsleff Ground Engineering Ltd Temporary works specialist: Mabey Hire Ltd Temporary works specialist: MGF Ltd Tunnels & shafts: Joseph Gallagher Ltd In situ concrete works: Kelly Formwork Ltd In situ concrete works: DJ Civils Ltd Precast concrete manufacturer: FLI Precast Solutions Precast concrete manufacturer: A-Consult Ltd Pipe supplier: Electrosteel Castings (UK) Ltd Pipe supplier: Saint Gobain PAM UK Soil processing: Remediation Waste Management Services Concrete supplier: Heidelberg Materials Gas protection: PAGeo Contracting Ltd Gas protection system installation verification: MTS Ltd [caption id="attachment_26876" align="alignnone" width="1200"] Figure 7: Sludge processing area: MCC kiosk (grey in foreground), sludge blending tanks (top left), poly dosing kiosks (top right) - Courtesy of BAM[/caption] Overview of project progress

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.

[caption id="attachment_26878" align="alignnone" width="1200"] Figure 8: Sludge processing area: (left) the bases for elevated cake silos, (middle), sludge belt presses, and (right) the poly prep & dosing kiosks - Courtesy of BAM[/caption] Guildford STW: MEICA works supply chain - key participants Main designer/contractor: Enpure Ltd CFD analysis: The Fluid Group Cake silo: Saxlund International PST scrapers & ferric dosing plant: Colloide Inlet works & PST odour covers: Power Plastics Ltd Grit remover plant: Jacopa Escalator screens: Longwood Engineering Imported sludge Strainpress: Huber Technology Sludge thickening & dewatering: Kent Stainless Ltd Odour control plant: Odour Services International Ltd FBDA grids & blowers: Xylem Water Solutions Cloth pile filters: Eliquo Hydrok Ltd Storm tank cleaning system: Sulzer Pumps Wastewater Ltd Tank logging system (WASP): JR Pridham Services Ltd Glass lined steel tanks: Balmoral Tanks Ltd Sludge tank mixing: Landia UK Ltd Tunnel

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.

[caption id="attachment_26873" align="alignnone" width="1200"] Figure 9: (top left) 3D model of the Inlet Pumping Station (IPS) - Courtesy of Arcadis, (bottom left): steel fixing to IPS internal walls - Courtesy of BAM Enpure JV, and (right): IPS shaft construction - Courtesy of BAM[/caption] Inlet pumping station

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.

Storm tanks & inlet works

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.

[caption id="attachment_26874" align="alignnone" width="1200"] Figure 10: Circular precast storm tanks and Inlet works (August 2025) - Courtesy of BAM[/caption] Primary settlement, activated sludge plant & final settlement tanks

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.

[caption id="attachment_26875" align="alignnone" width="1200"] Figure 11: From top: Activated sludge plant, primary settlement tank, and two of the four final settlement tanks - Courtesy of BAM[/caption] Final settlement tanks

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.

Tertiary treatment plant & outfall

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.

[caption id="attachment_26877" align="alignnone" width="1200"] Figure 12: Tertiary treatment plant construction (August 2025) - Courtesy of BAM[/caption] Sludge processing

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 & control

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.

Welfare building

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.

[caption id="attachment_26871" align="alignnone" width="1200"] Figure 13: Welfare building housing plant control systems - Courtesy of BAM[/caption] 3D modelling

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.

Piling & ground improvement

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.

[caption id="attachment_16135" align="alignnone" width="1200"] (left) Driving precast concrete piles and (right)Vertical Rigid Inclusion installation - Courtesy of Bam Nuttall Ltd[/caption]

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.

The year ahead

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.

The Bangor Beach Road Sewage Pumping Station (SPS) Project is part of Dŵr Cymru Welsh Water’s (DCWW) work to reduce the water quality impact of sewer overflows on the Menai Shellfish Waters. The Menai Strait is a unique marine environment between Anglesey and North Wales, with the water quality directly impacting the shellfish quality and hence the local fishing economy and importantly, the ability to sell shellfish to European markets. Bangor Beach Road SPS is located in the northeast of Bangor in the Hirael area, close to the sea front promenade, next to King George’s Field playing field. Project background & solutions options

The Bangor Beach Road SPS Project was developed after feasibility and assessments studies had been completed for the wider wastewater catchment, including extensive hydraulic and coastal water quality modelling.

These showed that the Bangor Beach Road SPS was an impacting asset and that a solution, to reduce storm overflows here, was an effective approach to improving water quality. The asset was on the National Environment Programme list to reduce its impact on the shellfish waters, placing obligation on Welsh Water to deliver the solution by April 2025.

Solution options were investigated at the SPS including increasing pass forward flow, local treatment, and flow removal, however, to deliver the outcome within the timeframe, storage was the best solution.

[caption id="attachment_24319" align="alignnone" width="1200"] Bangor Beach Road PS Project - Courtesy of Griffiths Ltd[/caption] Project drivers & goals

The aim of the project was to divert storm flow (from overflowing to the Menai) to the new storm storage tank, where it will be stored offline until flows have reduced, at which point it is returned to the network for treatment.

The solution included:

Retrofitting the existing sewage pumping station. Provision of new storm pumps to deliver up to 1,000 l/s to a new 4,300m3 below-ground stormwater storage tank (under the adjacent playing field). Associated mechanical and electrical equipment. Reinstatement of the playing field facilities. Project scope & undertakings

The project forms part of wider catchment interventions including sewer improvements, tidal ingress removal, infiltration removal and future increases in treatment capacity at the receiving wastewater treatment works. The project comprises of two key elements:

Retrofitting of the existing SPS with new storm pumps. A new below-ground (off-line) storm storage tank.

Welsh Water contracted the project as separate civil (stormwater storage tank) and mechanical and electrical (sewage pumping station) elements, with Arup acting as Welsh Water civil design consultant, Griffiths Ltd as civil contractor and Eric Wright Water as MECIA design consultant and contractor.

Bangor Beach Road SPS: Supply chain - key participants Civil design inc. geotechnical, coastal & pipelines: ARUP Civil contractor: Griffiths Ltd M&E design & contractor: Eric Wright Water Storm tank design & construction: FP McCann Ltd Storm pumps: Xylem Water Solutions Pipework supply: Saint Gobain PAM UK Pipework & mechanical installation: Mectec Engineering NW Ltd Sewage pumping station retrofit

The existing SPS takes wastewater from the Bangor catchment and pumps it up to Treborth WwTW for treatment. During storm conditions, when the flows to treatment are exceeded, storm flows had historically been screened and then pumped via a long sea outfall to the Menai.

[caption id="attachment_24318" align="alignnone" width="1200"] (left & bottom right) New storm pump 4 & 5 and (top right) the existing SPS retrofit - Courtesy of Eric Wright Water[/caption]

The SPS was constructed on an area of largely made ground, set out from the sea front. During the optioneering stages, the location was considered costly and complicated to add new wet wells or pumping stations. This drove the design team to investigate options for retrofitting the existing SPS, which would have the additional benefit of less carbon and cost than constructing a new asset.

The existing SPS has three wet wells, which served the flow to treatment and overflows to the long sea and short sea outfalls. One of the overflow wells was re-purposed to locate the new pumps which serve the new storm tank. Design reviews including suppliers ensured that the existing wet wells were of sufficient dimension and could achieve the designed flow conditions with the new pumps.

Eric Wright’s mechanical and electrical works within the SPS also included mechanical pipework, valves, controls and power for the storm pumps and ensuring the integration of existing controls. This was complicated because of the multiple weirs and screens within the existing asset and the multiple overflow routes. This was a collaborative approach supported by hydraulic modelling (by Arup) and surge analysis and system checks by specialist consultants.

Stormwater storage tank

The new stormwater storage tank is a 4,300m3 below-ground prefabricated concrete tank, located below the King Georges playing field adjacent to the SPS. The required volume of storage was determined from earlier modelling, which showed that this size would retain storm flows for all but the largest storm events; reducing overflow to 10 times per year on average, which would achieve the required water quality improvement.

[caption id="attachment_24321" align="alignnone" width="1200"] The new below-ground stormwater storage tank under construction - Courtesy of Griffiths Ltd[/caption] The storm tank was designed and delivered by FP McCann, and is a rectangular arrangement made from precast concrete walls and roof, with a cast in situ base. The tank is approximately 28m by 48 m and ranges from 3 to 4m deep. The tank has a slight longitudinal fall and is divided into lanes by internal walls to aide flow distribution and reduce siltation risks. Access points were provided at each end of the tank lanes. The design had to accommodate constraints on access points due to the playing field above the tank - no manhole covers could be situated within the football pitch area. Rising main

The 900mm diameter rising main pipe between the sewage pumping station and the stormwater storage tank posed various design challenges. The pipeline needed to exit the pumping station, aligning to existing connection points, traverse the SPS revetment in the marine zone, cross a flood bund (by others) and promenade (by others) to the storm tank. With the added complication of two designers undertaking the above and below-ground sections respectively and third parties working on other construction projects within the vicinity.

[caption id="attachment_24317" align="alignnone" width="1200"] New external pipework to storm tank - Courtesy of Eric Wright Water[/caption] King George’s Field playing field reinstatement

Coordination of the tank works, and construction of the associated pipework and civil elements were undertaken by Alun Griffiths. Arup, as Welsh Water’s designers, and Alun Griffiths worked extensively with landowners of the playing field to provide a reinstatement design for the football pitch; providing a valuable community asset to a high quality standard. The final design included a pitch drainage system, tree planting and tied into surrounding improvements to the promenade (by others).

Innovations, cost savings & carbon reduction

Carbon savings for this project were realised from the decision to retrofit the existing facility and not building a new storm pumping station, and by choosing to re-purpose the wet well within the existing SPS. This also reduced time on site and hence is assumed to reduce the health and safety risks.

Eric Wright worked with the pump suppliers and engaged specialist hydraulic advice to ensure the system would operate as designed. Although retrofitting was difficult and attention needed to be paid to the condition of existing equipment, especially at interfaces, this approach reduced carbon, the need for land purchase, and provided a resilient asset for the long term.

[caption id="attachment_24316" align="alignnone" width="1200"] Pipework in the sewage pumping station connecting with the stormwater storage tank - Courtesy of Eric Wright Water[/caption]

For the new stormwater storage tank, precast concrete proved suitable for the given ground conditions and the sewage application and offered savings in time, in design and on site.

The location of the tank also posed a risk to Welsh Water Operations, with no easy access for inspections. CCTV was therefore included to monitor conditions within the tank without the need to enter the tank and help plan maintenance. The internal arrangement of the tank was designed with the aim to reduce the need for maintenance and entry to the tank for cleaning. It was laid out in profiled lanes with an inlet manifold to flush flows down each lane.

The football pitch above the tank was a general use playing field before the project. Welsh Water has reinstated this community asset, with the design including pitch drainage and additional trees in the surrounding area. Welsh Water worked extensively with the local council (landowner of the field) to ensure the solution was in keeping with their recent improvements to facilities in the area and provided a long-term community benefit. [caption id="attachment_24314" align="alignnone" width="1200"] CCTV image inside new storm tank during commissioning - Courtesy of Eric Wright Water[/caption] Conclusion/summary

The retrofit of the Bangor Beach Road Sewage Pumping Station and the stormwater storage tanks retrofit were commissioned in March 2025; achieving the NEP regulatory date. This provides Welsh Water with a new asset and will contribute to water quality improvements in the Menai.

Limited storms have occurred since completion, but the improved SPS and tank have been shown to operate as designed. At the time of writing (July 2025), the team are on site finalising the reinstatement and completing a small element of coastal protection.

Welsh Water will continue to make improvements within the catchment, with planned schemes to increase storm treatment capacity at the receiving WwTW and further targeted sewer improvements to reduce infiltration and reduce risks of saline intrusion. Locations across the catchment feasible for RainScape (including SuDs) have been identified for future catchment resilience.

The topography in and around the city of Hull makes the city extremely susceptible to flooding. Derringham is a residential suburb to the west of the city, which was heavily impacted by the 2007 floods. Significant flood alleviation works are therefore required in the area to manage stormwater to prevent an event on this scale from having such an impact when it inevitably occurs again in the future. The Derringham Aqua Greens Project has been delivered by the Living With Water Partnership, Stantec and Mott MacDonald Bentley (MMB) to provide flood alleviation in the heavily residential area. The Living With Water Partnership

The Living With Water (LWW) Partnership was formed following the 2007 floods when 16,000 properties in Hull and East Riding were flooded. It became clear that no single agency accepted any responsibility outside of their own term of reference, but that each had a part to play in maintaining the waterways in the city of Hull which contributed to the floods. The partnership brings together Yorkshire Water, Hull City Council, East Riding of Yorkshire Council, Environment Agency and University of Hull to enable them to collaboratively deliver flood alleviation schemes in the city. The first of its kind in the UK, the partnership aims to reduce flood risk in high-risk areas, while combining blue-green principles to deliver sustainable, low carbon solutions, encouraging knowledge share between all parties, building community resilience, improving local areas by providing biodiversity net gain.

[caption id="attachment_21743" align="alignnone" width="1200"] Location plan of the aqua green sites within the Derringham area - Courtesy of Mott MacDonald Bentley[/caption] The partnership has proved paramount throughout the design and construction phases as collaboration between all parties has been needed throughout. This included having the expertise of Yorkshire Water on the technical elements of drainage design, discussions with Hull City Council on how highways will be reinstated, proposed planting arrangements and gaining access to council owned green spaces and collaboration with the University of Hull to incorporate the requirements for testing & monitoring equipment within the design from the start. Project scope

The principles of the project are to allow exceedance flows from heavy rainfall, for which there is no capacity in the sewer network or nearby watercourses, to flow above ground via existing road accesses between properties, into detention basins retrofitted into existing green spaces in the area. The stormwater can be retained away from properties and returned to the sewer network once there is available capacity and the network is no longer surcharged.

The road access, or ‘10fts’, between properties are lowered to create a channel for stormwater to flow from the highway into the Aqua Green. A headwall and return sewer are installed from the low point of the Aqua Green, connecting into the existing sewer network in the main highway. Flows leave the Aqua Green under gravity, meaning that no mechanical or electrical elements are required for the operation of the solution. The lowering of the 10fts meant that property protection measures were required to the properties adjacent to the 10ft to prevent the solution resulting in them to be at greater risk of flooding. Existing boundary fences were replaced with new fence panels installed on concrete gravel boards to provide a waterproof barrier between the 10ft and the property.

Across the three Aqua Greens, over 1800m3 of storage has been proved. With a traditional grey infrastructure project, providing the same storage would have had a much higher embedded carbon measure, could not have been constructed in the small areas that were available and would have required some form of M&E installation with associated ongoing maintenance and running costs.

[caption id="attachment_21751" align="alignnone" width="1200"] Property protection on properties adjacent to the 10fts and (inset) position of manholes within narrow 10ft - Courtesy of Mott MacDonald Bentley[/caption] Derringham Aqua Greens: Supply chain - key participants Client: Yorkshire Water Principal designer & contractor: Mott Macdonald Bentley Outline design: Stantec UK Academic partner: University of Hull Local Authority: Hull City Council GCL liner & underdrainage: SIG Construction Accessories Headwall: Marshalls Water Management Hinged pole for testing & monitoring: Fabrikat (Nottingham) Pipework: John Davidson (Pipes) Ltd Flap valve: Affco Flow Control (UK) Ltd Surfacing: Calder CAD Ltd Landscaping: Craven Forestry Limited Aqua Greens design

The concept design was carried out by Stantec, who produced a full hydraulic model of the whole area to determine where the highest flood levels are seen, to identify the green spaces that would provide the most benefit if they were developed. A total of 11 green spaces in the area were investigated, with cost benefit analysis carried out to establish which of those spaces would provide the most benefit for the community. Three sites were selected to be developed in the first Work Package (WP1) with a further three sites to be developed in Work Package 2 (WP2).

[caption id="attachment_21746" align="alignnone" width="1200"] Installation of the liner and underdrainage layer - Courtesy of Mott MacDonald Bentley[/caption] One of the main aims of the detailed design phase was to produce standard details that could be implemented at all Aqua Green sites, to streamline both the design and construction phases. As the return sewers and associated chambers were to be laid in the 10ft between two properties, a standard 1200mm precast concrete manhole could not be installed as there was not space to do so. A 1200mm x 750mm standard product was therefore developed and agreed with Yorkshire Water as it was a much safer and simpler install.

The overall project programme meant that long term groundwater monitoring could not be carried out prior to the design process for WP1. For design calculations, groundwater therefore had to be assumed to be at ground level, which resulted in flotation of the liner and as a result, an additional drainage later needed to be installed below the liner to prevent flotation.

During the construction of WP1, it was observed that the Aqua Greens were retaining water before the liner was installed and that the as clay of very good quality. For WP2, permeability testing and longer-term groundwater monitoring were able to be carried out. This determined that the natural clays were of higher impermeability than the geosynthetic liner and that the groundwater was not as high as was believed during the design phase for WP1. It was therefore discussed and agreed with all relevant parties that the additional geosynthetic liner did not need to be included on site. This saved a total of two weeks on the programme for WP2, approximately 60 tonnes of carbon, material costs of approximately £60,000 and removed the risk of delays associated with the liner install in wet weather.

Construction for WP1 was from October 2023 to December 2024, with works still progressing on the WP2 sites. Sole access to the green spaces via 10ft wide access tracks introduced some difficulties to the construction. Only small plant could be used and the 5m wide liner had to be cut to 2.5m for delivery to the greens. Limited space on site also meant that excavated materials could not be stored at the greens and had to be stockpiled at the site compound, requiring a significant number of dumper loads of materials to be moved on the local road network. The nature of the project and works commencing in winter meant the Aqua Greens frequently flooded during the construction, with water regularly needing to be pumped to the drainage network before further progress could be made.

[caption id="attachment_21741" align="alignnone" width="1200"] Retention of water in Aqua Greens seen during construction prior to the installation of the liner - Courtesy of Mott MacDonald Bentley[/caption] Community engagement

Due to the location of the Aqua Greens in such close proximity to residential properties, significant community engagement was needed throughout the project, during both design and construction phases, to ensure that the community were kept up to date with what the project would deliver, how the construction works would impact them and ultimately how the SUDs solution would operate and be maintained into the future. Over 30 engagement sessions have been held with the community to date, from the start of the design development to the end of the construction phase. This has been coupled with regular letters and updates on the LWW website, providing the residents with an opportunity to raise any concerns about the works as well as to help to convey the importance of flood alleviation in the area.

To aid conversations with the local community about the Aqua Green developments, computerised visualisations were produced which showed how the Aqua Greens would look upon completion. While the existing greenspaces were mainly neutral grassland before works commenced, the solution was to plant wildflower seeds in the greenspaces upon completion, to increase biodiversity of the area. To provide habitat for wildlife, wildflower areas are maintained less frequently than grassland spaces and this therefore needs to be portrayed to the residents.

[caption id="attachment_21753" align="alignnone" width="1200"] (left) Visualisation image used to aid communication with the public and (right) installation of community noticeboard on site - Courtesy of Mott MacDonald Bentley[/caption]

The visualisations also helped the MMB team to discuss the proposals with the residents to see if there was anything additional, they would like to see of change as part of the design. Some residents said that they particularly liked the shrubs at the back of one of the green spaces as they provided them some security for their garden, so these were retained as part of the design. Others suggested that the proposed parking areas would not be used and that they did not want to encourage parking on the green spaces, so these were reduced in width to just passing places on the narrow roads.

Continued engagement with the community has been needed throughout the construction phase to answer any queries that the residents had about the works and rectify any problems they had been experiencing. Upon completion of the Aqua Greens, permanent notice boards have been installed at each of the sites to inform the residents of the benefits of the Aqua Green.

Continued testing & monitoring

The University of Hull have installed testing and monitoring equipment at all three of the Aqua Green sites in WP1 to understand how these Aqua Greens perform. The testing and monitoring equipment included soil moisture probes located above and below the liner; conductivity, temperature, and depth (CTD) probes in the return sewer and a weather station at a local school. The aim is that this data will be analysed and used to improve the design to enhance these assets for future installations. The weather station data is also accessible by the local school so that the data can be used for educating the students about the weather and flood risk of their local area and how we can safely live with water.

The intention is that further testing and monitoring equipment will be included on the WP2 sites so that a comparison can be made between the lined and unlined solutions to see if one of them is more effective at providing the required storage or improving the quality of the water that enters the sewer network.

[caption id="attachment_21745" align="alignnone" width="1200"] Installation of community noticeboard on site – Courtesy of Mott MacDonald Bentley[/caption] Summary

Since the installation of the first three Aqua Greens was complete, the benefits provided by the Aqua Greens has been visibly clear during periods of heavy rainfall, with quantitative data expected from the testing and monitoring installations within the next few months. These large-scale SuDS basins have provided flood protection to hundreds of properties in an area which otherwise would be at very high risk. Providing the protection via blue-green methods rather than traditional grey infrastructure has resulted in a solution with a much lower carbon impact, while also providing the areas with an improved biodiversity, making it a much more sustainable solution. The blueprint of this project, along with that of the Living With Water partnership, can be applied to other areas across the UK where properties are at high risk to deliver more types of these projects in the future.

Campbeltown has experienced flooding over many years, which has affected residential properties, businesses, roads, and community life in general. In June 2022, construction started on a 24-month, £16m scheme, (co-funded 80% by the Scottish Government and 20% by Argyll and Bute Council) under the Flood Risk Management (Scotland) Act 2009 where the council is responsible for developing sustainable flood management solutions. DAWSON-WAM Ltd was appointed as principal contractor, with AECOM employed by the council to provide design and project management support throughout the contract. Flooding sources

The existing sewer network system in the Burnside and Meadows areas could not cope with increasing amounts of surface water. The sewer network combined surface water with sewage water from households. When the system was overwhelmed during periods of heavy rain, fouled water backed up out of the system and flooded streets and premises.

On the outskirts of the town is the Millknowe Burn which, due to several steep catchments, is the most dominant flood source in Campbeltown. Flows from the Balgreggan Burn also caused overtopping during extreme events at the Dalaruan culvert intake and resulted in overland flows and flooding in the town.

[caption id="attachment_18234" align="alignnone" width="1200"] Google Earth image showing Campbeltown FPS site locations[/caption] Scope of works

The scope of the scheme was to reduce the risk of flooding from the Millknowe and Balgreggan Burns and from localised surface water in Campbeltown. The project was rolled out over four working areas:

Millknowe flood storage reservoir. Dalaruan culvert. The Meadown SuDS. Burnside Square. Millknowe Flood Storage Reservoir

Millknowe Field is located beside the watercourse channel, which acts as a catchment area for rainwater. It floods onto nearby roads and streets; particularly the main A83 trunk road which provides the primary access into the town. There are two block of flats beside the field, built essentially on the same floodplain that is prone to flooding during heavy rainfall when the watercourse and culvert cannot cope with the flow of water.

Snipefield Industrial Estate is located on the northern side of the watercourse channel, which is home to many local businesses. This was also prone to flooding from the field during heavy rainfall events.

The scope of works at Millknowe included:

Construction of a flood storage reservoir in Millknowe field to provide temporary flood water storage within the watercourse channel during high rainfall events. Realignment of the watercourse channel along a new sheet piled wall. Installation of over 500m of new back of wall drainage ranging in diameter from 225mm to 600mm and new outfalls with flap valves through the new flood wall. [caption id="attachment_18237" align="alignnone" width="1200"] Installation of AZ sheet piled wall with TM22 piling rig to form reservoir - Courtesy of DAWSON-WAM Ltd[/caption]

Flood storage reservoir

The reservoir was constructed in line with the Reservoir (Scotland) Act 2011 and comprised a 125m long AZ19-700 sheet piled wall encased in a 2.6m (average height) earth embankment dam and concrete spillway. A 325m AZ20-700 sheet piled flood wall formed the enclosed dam structure and provided flood protection to Snipefield Industrial Estate. The sheet piles were driven into cohesive soils and ranged between 6m to 9.5m in length. A new concrete culvert passing through the dam with headwall and orifice plate was constructed to throttle the flows. The exposed piles were capped off with a precast concrete coping.

To facilitate the installation of the 450m of steel sheet pile wall, a 6m wide x 600mm deep stone temporary piling platform was installed to support the 90T ABI TM22 piling rig.

Where space allowed, the piling platform was constructed in Snipefield Industrial Estate to the north of the watercourse. This minimised the length of the watercourse that was required to be culverted and reduced the impact on agricultural soils and the watercourse, and reduced the amount of imported stone required.

DAWSON WAM’s in-house heavy-duty steel mats were utilised which further reduced the amount of imported material for the piling platform. Three temporary bridge culvert crossings were constructed using the mats which allowed full access along the length of the wall during construction.

[caption id="attachment_18243" align="alignnone" width="1200"] Temporary bridge crossing watercourse using DAWSON-WAM Ltd’s heavy duty steel mats - Courtesy of DAWSON-WAM Ltd[/caption]

The sheet piles were purchased from Arcelor Mittal in Luxembourg, and were stored in DAWSON-WAM Ltd’s yard in Bedfordshire. The piles clutches were sealed using Biguma SV and were delivered to site in a just-in-time basis throughout the project.

DAWSON-WAM Ltd used an ABI TM22 piling rig to complete the piling installation works. This rig with its powerful 36VV vibro hammer  is the most powerful leader rig mounted vibro in the UK and Europe. Interchangeable attachments were mobilised, including the preaugering with advanced cased CFA and the HydroPress system, which allowed increased production and mitigated risks where unforeseen ground conditions were encountered.

Service crossings

The new sheet piled wall installation required to perpendicularly cross a 225mm asbestos cement Scottish watermain and a high voltage (HV) Scottish Power cable. These two services were critical to the town infrastructure and any disruption or shutdowns would have caused a extensive disruption to the town’s residents.

Traditionally these services would have to be diverted through the wall in a phased approach, resulting in inefficiencies and several shutdowns on the services. Through DAWSON-WAM Ltd’s in-house expertise and utilising its specialist vibrationless HydroPress piling equipment, installation of the piles adjacent to the utilities was successfully achieved without diverting the services. This involved early liaison and working closely with the designer and utility providers, undertaking trial pits to ascertain the ground conditions, installation of vibration monitors on the services to highlight vibration levels during install and agreeing a short shut down of the services during pile install.

Earth embankment

The earth embankment at Millknowe consisted of an up to 4m high 125m long embankment with a 21m in situ reinforced concrete spillway. The embankment footprint was excavated removing 3000t of topsoil, 6000T of peat and associated soft soils to form the earth embankment foundation on alluvial or raised beach deposits with a Cu value greater than 40Kpa.

To consolidate the formation level prior to construction, trial pits were excavated along the footprint of the structure and with the aid of a shear vein test, the employer-appointed Reservoir Construction Engineer witnessed and approved the formation levels on site.

2,600t of locally sourced Class 6C compacted in accordance with CESWI 7th Edition in a 500mm deep layer formed the foundation of the embankment. The main body of the embankment was constructed using 5,800t of compacted Class 1A granular fill, with the maximum embankment height of 4m with sloped of 1V:3H. Class 6N granular material was used to segregate the Class 6C and Class 1A material around the piles.

The embankment was capped with a 300mm layer of site won screened topsoil and reinforced with coir matting and seeded. Associate embankment toe drainage and a hardstand access road was provided for future maintenance access.

[caption id="attachment_18233" align="alignnone" width="1200"] Realigned burn along sheet piled wall reinforced with coir matting - Courtesy of DAWSON-WAM Ltd[/caption] Dalaruan culvert

270m of the existing Dalaruan storm water culvert required upgrading from the Millknowe flood storage reservoir intake to downstream of Dalaruan Street intake. This online upgrade would convey flows and provide additional inline storage from the Millknowe reservoir and prevent overtopping flows from the Balgreggan Burn during extreme rain events.

The exemplary design proposed the install of concrete culverts however as Dalaruan Street is straddled by terraced houses with listed boundary walls and with a congested mix of utilities of various eras, it was decided from an early stage in the contract a detailed survey be undertaken including trial digs to ascertain existing utility positions. This work proved prudent as a design change was requested to provide a more buildable solution while managing live flows and to avoid extensive service diversions.

The contractor and designer worked collaboratively, and through engaging with the supply chain and by re-modelling validation, the section of culvert was changed to a twin line using AquaSpira pipes.  This solution provided a bespoke steel reinforced twin piped culvert which had both health and safety and constructability benefits and prevented extensive costly service diversions.

In total, 110m of twin 900mm and 45m of twin 675mm pipes were installed including 115m of single 675mm pipe to form the new culvert. AquaSpira’s prefabricated manhole units were used, which proved to be considerably easier to install compared to the traditional concrete manhole rings, and benefited the management of the existing live storm flows, as well as a faster build time.

During the 6-month construction phase of the Dalaruan culverts, as the majority of the works required the closure of the Dalaruan Road, an extensive public relations exercise was undertaken prior to works commencing. Following the extensive liaison, a phased programme of work plan was developed which merged the phasing of the works and the concerns raised from the public events.

This plan was then shared prior to construction commencing and was supplemented with a full-time public liaison officer, this resulted in the successful installation of the replacement culvert in time to take the first storm flows.

[caption id="attachment_18240" align="alignnone" width="1200"] (left) Installation of twin 675mm diameter AquaSpira pipes and (right) installation of prefabricated manholes - Courtesy of DAWSON-WAM Ltd[/caption] The Meadown SuDS

The Meadows catchment area consisted of an existing, out of date, undersized combined sewer network system that during periods of heavy rainfall events caused out of sewer flooding to occur. This, combined with the existing culverts in the Witchburn and Meadows areas that could not convey sufficient volume of stormwater,  resulted in regular localised flooding events.

The solution was to provide 6500m2 of storm separation on the existing road network by installing over 1.2km of new storm pipe ranging in diameter from 150mm to 375mm and connecting over 65 existing storm gullies to the new infrastructure. This new pipe network conveyed storm flows to three new detention basins with a total capacity of 1500m3 to temporarily attenuate surface water runoff before releasing it back into the existing Witchburn Culvert system. The shallow detention basins were constructed in existing green spaces with 1:4 slopes with a 3D cellular confinement system installed on the basin slopes to improve soil stabilisation and control erosion.

Flows from the basins are retained by flow control manholes fitted with Storm Brake valves, which limit storm flows to between 4.5 l/s and 7.7 l/s into the culverts in a more forgiving manner.

Biodiversity within the detentions basins was enhanced by planting a wet meadows mix plant and a combination of birch and willow trees surrounding them. Due to the poor quality of the existing road surfacing, new full width reinstatement was undertaken to all roads that acquired new storm drainage significantly enhancing the whole road network.

[caption id="attachment_18244" align="alignnone" width="1200"] Reinstated detention basis at Meadows - Courtesy of DAWSON-WAM Ltd[/caption] Burnside Square

A new underground geocellular attenuation tank in Burnside Square was constructed to temporarily store and attenuate 540m3 of surface water runoff from 1.6km newly constructed storm separation pipework in the Witchburn and Burnside areas during high rainfall events before releasing it back into the existing culvert network.

As Burnside Square was at the heart of the town, it posed several construction risks none less than excavating near three-storey properties that dated back to the 1700s with stone foundations, while having to maintain safe access to the business and residential premises contained within.

Due to the level of disruption anticipated in this area, the contract had restricted these works to be completed during the winter months and required it to be re-opened for public use by June 2023 in time for the peak tourist season.

Following the completion of a detailed ground investigation, it identified that there was largely granular materials withing the dig area for the new attenuation structure, with a water strike just at dig level. Due to the above mentioned buildability concerns, a battered excavation solution posed many risks, therefore a secant piled box cofferdam solution was opted for which would act as both permanent and temporary works for the tank.

DAWSON-WAM Ltd utilised its in-house cased CFA piling rig to install the 300 (No.) 450mm diameter secant piled cofferdam, with its vibrationless installation method eliminating the risk of vibration on the surrounding properties, with this solution the space around the perimeter of the site was able to be maximized, resulting in sufficient space for pedestrians to access the premises safely during the construction period.

[caption id="attachment_18238" align="alignnone" width="1200"] (left) Secant pile installation using cased CFA at Burnside Square, and (right) Geocell attenuation tank at Burnside Square prior to backfilling - Courtesy of DAWSON-WAM Ltd[/caption]

Upon the excavation of the 2700T of granular material, the area was bedded with single-sized rounded stone which provided the base for Polypipe’s lightweight Polystorm-R crates. The crates were delivered in articulated lorries and were built in situ and wrapped in a welded impermeable liner and geotextile protection fleece.

Inspection chambers and a manifold pipe arrangement was formed to enable the filling, emptying, and maintenance of the tank. To prevent overloading of the tank in the temporary condition, the tank was backfilled with imported aggregate in a sequence using small plant, a 100mm layer of Bitmac then formed the foundation for the 900m2 of new block paving.

As the existing square was predominately used for car parking, the council grasped the opportunity to reinstate the area into a multi-functional space that could be utilised for community events as well as serving as daily parking.As part of the final reinstatement, over 52 new bollards and an array of new street furniture and planters were installed.

Supply chain: key participants Main contractor: DAWSON-WAM Ltd Project management & client design: AECOM Materials testing: MATtest Limited Culvert pipes/chambers & twin pipe culvert (Dalaruan Street): Aquaspira Ltd Sheet piles: Arcelor Mittal Attenuation tank installation: Hydro Water Management Solutions Ltd Precast concrete: FP McCann Civil contractors: McFadyen’s Contracts Campbeltown Landscaping: MW Groundworks Attenuation tank drainage crates: Polypipe Civils & Green Urbanisation Drainage & ducting materials: Huws Gray | Jewson Transformers: Wilson Power Solutions Ltd [caption id="attachment_18241" align="alignnone" width="1200"] Storm separation pipework installation at Witchburn - Courtesy of DAWSON-WAM Ltd[/caption] Community benefits

It was obvious from inception that, engineering challenges aside, one of the key challenges for the project team would be constructing the works within this rural town in Scotland which would not have previously witnessed a construction project on this scale.

Effective consultation with stakeholders, which included road users, local businesses, residents, the general public and affected landowners, would be key to the minimising disruption and to the project’s successful delivery.

Several pre-construction pop-up events were held locally with the residents, businesses and stakeholders. Consultations were carried out through Argyll and Bute Council’s internal communications team and monthly newsletters were issued through the portal giving updates on construction progress and programme of works and queries were managed through the site-specific e-mail and emergency contact number. Public drop-in meetings and letter drops were undertaken in advance of entering a new area of works.

A project of this size and complexity will always have a significant local impact and it was important that the project team endeavoured to engage with and, for the duration of the project, be part of the community.

[caption id="attachment_18235" align="alignnone" width="1200"] Realigned burn along sheet piled wall reinforced with coir matting - Courtesy of DAWSON-WAM Ltd[/caption]

Initiatives to promote community engagement included:

Visits from the construction engineering team to Dalintober and Drumlemble primary school, educating the children on the dangers of construction sites. Donations of PPE waterproofs to the school to help support their learning and exploration group. Donation of a ‘LEGO education spike prime Set’ to help engage STEM learning and problem-solving skills. Donation of Ukuleles to the local kids’ music group. Local charity donations including a donation to the Kintyre Sea Sports charity to purchase new equipment to aid in the training and development of the local disadvantaged children in water activities. Donation of 6T of topsoil to Campbeltown Climate Action for use in their community garden. Voluntary repairs to the Campbeltown youth football team goal posts and changing facilities access paving prior to a kid’s football tournament. Supply and installation of a bicycle rack in Burnside Square.

The most significant community benefit was the employment of a local sub-contractor to undertake much of the construction works. This provided and supported employment to the residents of Campbeltown and supported the local businesses as the money stayed in the community.

[caption id="attachment_18236" align="alignnone" width="1200"] Reinstated Burnside Square - Courtesy of DAWSON-WAM Ltd[/caption] Conclusion

In Autumn 2023 during two periods of heavy rainfall, the Millknowe Reservoir, the Meadows detention basins and the Burnside attenuation tank protected the town from flooding and reduced the load onto the wastewater network.

The successful delivery of the Campbeltown Flood Scheme was a brilliant example of collaboration between the contractor, client, designers, and the local community; ultimately resulting in the success of the project as well as providing an asset that will efficiently protect the town and its residents for years to come.

The project required the contractor to excavate within 25m of Beaumaris Castle – a UNESCO World Heritage site and one of the best examples of 13th and 14th century architecture in Europe attracting over 100,000 visitors last year. Faced with the challenge of installing 600m of 1.5m diameter polypipe in 6m sections between existing manholes, John Kelly Construction spent time researching the products available on the market, before finding that MGF’s High Clearance Trench Boxes were ideal for the job. [caption id="" align="alignnone" width="1200"] Courtesy of MGF Ltd[/caption] The 7m x 2.9m wide High Clearance Trench Boxes coupled with Top Boxes saved time and money to the contractor when compared to sheets and frames. The strength of the box allows suitability and capability of going to 5m depth and having high clearance struts on both ends of the box allows access at both sides – ideal for installing larger diameter pipes. [caption id="" align="alignnone" width="1200"] Courtesy of MGF Ltd[/caption] Paul Cowen, Technical Sales for MGF commented:

“Beaumaris’ most recent floods in 2017 was the catalyst that something needed to be done regarding the surface water drainage system. MGF became involved to supply the excavation support equipment to alleviate the threat of flooding to protect the natural beauty and tourism trade in the area”.

MGF’s stock logistics team confirmed availability of the kit at our Dartford depot and coordinated transfer to the Astley depot before delivery to site with three 40ft articulated vehicles and two 15t wagons to ensure the order was met. [caption id="" align="alignnone" width="1200"] Courtesy of MGF Ltd[/caption] John Kelly, Managing Director of John Kelly Construction, stated:

"I was very impressed with MGF as a company as they were very quick to respond to our queries, provided designs and all equipment ordered arrived on site with no delays."

Sector: Water & Utilities Client: Isle of Anglesey County Council Contractor: John Kelly Construction MGF depot: North West - Astley Products hired: High clearance trench box, top boxes & titan manhole box   For more information: MGF Ltd | +44 (0)1942 402700 | www.mgf.co.uk