Supply Chain - Networks - Sewerage - Wastewater Pumping Stations

Upper Crescent WwPS was constructed in the 1970s, and the site contains two pumping stations:

As principal contractor and principal designer, GRAHAM Construction had overall responsibility to deliver the project on time and within budget. Enisca Brown Ltd was contracted for designing and delivering a 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.

The contract delivery team worked in a collaborative manner with NI Water and their project manager AECOM, as well as key suppliers and subcontractors to deliver a robust, effective and modern wastewater pumping station and storm water storage facility. This allows for future growth within the catchment area and protects the environment from discharges during storm events.

In 2022, GRAHAM undertook Early Contractor Involvement to further develop the scope and complete detailed design for the main construction works. Due to the age of the existing pumping stations, rigorous investigations were carried out to determine their operation and control philosophy, condition and potential for imposing health and safety risks to operatives and the contract team.

The completion of the detailed design, ahead of main contract award, ensured cost certainty for NI Water and lessened the risk of delays due to design changes on site.

The existing Upper Crescent WwPS in Comber involved a 2-Phase upgrade plan to complete all activities required:

Phase 1: Early procurement of items with long lead-in times and site preparation:

Phase 2: Construction

One of the biggest challenges was that the two adjacent pumping stations had to remain operational throughout the entire construction phase. The new Upper Crescent WwPS and 687m3 of stormwater storage required the construction of a 26m diameter x 10m deep cofferdam and the new WwPS could not be commissioned until the existing had been decommissioned.

Screw pumps: Each of the screw pumps within the Upper Crescent Storm Pumping Station was individually phased over to the new control panel in a lengthy process, which required a test period of each pump before the next pump could be phased over. Staged changeover was required due to the criticality of their operation during storm events. The pumps could not be taken out of service during storm events due to the potential of out-of-sewer flooding in low lying areas within the Comber Catchment.

Cofferdam construction: Once the programmed critical works within Phase 1 were complete, Phase 2 works could commence on the construction of the circular cofferdam. This was undertaken by specialist piling contractor Ward Piling Ltd with responsibility for:

A secondary 3-sided cofferdam was also constructed adjacent to the main cofferdam to facilitate the construction of a new inlet manhole.

Craneage: The craneage requirements for the entire project were critical in developing the construction methodology and phasing of the works. Multiple heavy and bulky lifting operations were required to construct the new Upper Crescent Wastewater Pumping Station. These included lifting 25-ton excavators into and out of the cofferdam, lifting of the 10-ton steel plate wall shuttering/formwork used to cast the circular pumping station structure, pulling of the sheet piles with vibro hammer and installation of the large precast roof beams and slabs.

A 280-ton crawler crane was selected as the suitable crane for our project needs. The imposed loading of the crawler crane also had to be considered in the design of the cofferdam, due to the loading it would place onto the cofferdam structure. Early planning of the detailed and complex construction methodology streamlined the construction process and avoided any major delays or unforeseen complexities in the construction of the new WwPS.

Concrete pours & precast roof: Due to the proximity to Comber River/Strangford Lough and the findings from the ground investigation during the ECI, it was anticipated that a high-water table would be encountered with steady flow of groundwater infiltration. However, the reality was much better than expected. The sheet pile installation was much more effective at cutting off groundwater infiltration than anticipated, significantly reducing the dewatering resources.

The main walls were then cast; the remaining 7.5m height of the structure in five wall pours (four quarter radius pours and the internal dividing wall pour). The walls were cast using custom adjustable radius steel formwork shutters. Every effort was taken to maximise the speed and ease of construction, and the larger pours reduced the number of construction joints within the wastewater retaining structure.

The roof beams were precast on site due to their size and weight; 1m deep cross sections weighing approximately 20 tonnes each. A steel platform was constructed on site, on which each of the roof beams was cast while the tank structure was under construction.

The roof slabs were set into pockets cast into the top of the tank walls, with a H-shape beam over the wet well to accommodate large access covers for the three submersible pumps and two mixer pumps. The roof deck consisted of 22 precast slabs, which were cast off site due to insufficient space on site. The largest slab weight was 14 tonnes.

The commissioning of the new pumping main required a temporary shutdown of the WwPS to disconnect the existing pumping station and connect the new pumping station to the pumping main. This critical activity required meticulous planning and detailed coordination between the contract team and NI Water.

The work was programmed for forecasted dry days to ensure flows were reduced during the operation. Regular commissioning meetings were held with NI Water and the contract team in advance of the proposed works. Detailed discussions concerned the proposed works, programme and specific requirements in a systematic approach to confirm with relevant stakeholders that all eventualities had been considered before the works were progressed.

The final connection to the rising main was programmed to take place at night, during an 8-hour period when incoming flows would be at a minimum. The works would also be very weather dependant, as wet weather would dramatically reduce the amount of time available to complete the connection. The additional stormwater in the combined network could potentially overwhelm the on-site storage more rapidly than the team could complete the connection.

Once the pumping main connection was completed, the new Upper Crescent Wastewater Pumping Station became operational and a 28-day trial period to verify the station’s functionality/reliability to the client commenced. During the 28-day trial, the existing wastewater pumping station was methodically demolished, down to the basement levels ensuring that the new WwPS was not affected.

The excavation was backfilled with engineered fill to ground level in preparation for final hardstanding construction and landscaping, which was completed during the final weeks of construction.

Upper Crescent WwPS is located at the end of a cul-de-sac and corner of a public park. Ahead of construction commencing on site and throughout the work, a number of public relations activities were employed to inform the many stakeholders about the project and in particular the piling activities, removal of spoil from site and turn of flows when commissioning the new pumping station. These included: regular briefings to local elected representatives; one-to-one meetings with stakeholders; letter drops; house calls; school visits to the site; press releases and social media announcements.

During the project’s construction phase, GRAHAM needed some additional lands to enable the construction of the new Upper Crescent WwPS, as the pumping station would occupy most available lands within the existing site. The construction team where therefore required to obtain a section of the neighbouring Muckers Park owned by Ards and North Down Borough Council to form a temporary site compound and provide additional land for a crane platform. The crane platform required a diversion of footpath used by the local Park Run.

Early engagement with Comber Park Run enabled successful diversion of footpaths for the weekly race and patrons of the park. The diversion had to be artificially lengthened, to ensure that the length of the park run circuit was not shortened. During the construction of the new WwPS, GRAHAM provided refreshments for a number of park runs, distributing NI Water reusable water bottles and provided a cake for the Park Run’s 10th Anniversary.

On completion of the WwPS, the park was reinstated to its original configuration and handed back to the Ards and North Down Borough Council. Upper Crescent WwPS was operational from 27th February 2025 with site-wide testing and commissioning of the plant successfully undertaken for handover to NI Water in June 2025.

The location chosen is on the north-east extent of the existing Slyfield Industrial Estate and is on an area previously used as a landfill site. In August 2023 Water Projects published a case study which provided insight into the extensive pre-construction design for civil and process engineering elements of the project. This article delves into the construction of the project and provides an update on the significant progress made to date on site.

The site for the new STW is approximately 70,000m2 and was previously used as a landfill site. It had originally been used as sand and gravel quarries and then subsequently used as landfill from the 1960s to the 1980s.

The landfill material is generally domestic and light industrial. It consists of black bag waste, timber, plastics, fabrics but contains fragments of asbestos and other materials.

The site was capped off with a granular layer in the early 1980s and has laid dormant ever since. The landfill depth varies across the site from between 2m and 6m thick. This then overlies an alluvium layer, sands and gravels and London Clay. The depth of the London Clay is approximately 10m below existing ground level.

Typically, major structures within a sewage treatment works are built below or partially below ground level to maximise gravitational energy. The new Guildford STW differs in that the strategy is to deliberately design and build above ground as far as practicable.

This is to minimise the disturbance to, and removal of the existing landfill thereby reducing the impact on the environment and the cost of disposal.

After a period of Early Contractor Involvement, Thames Water awarded a contract to BAM-Enpure Joint Venture (BEJV) in 2021 to design, build and commission this significant new works and once operational, to de-commission the existing works.

BEJV is a non-integrated joint venture, formed specifically to combine the excellence of experienced civil engineering contractor Bam Nuttall Ltd and the process engineering/MEICA specialism of Enpure Ltd to deliver a turnkey solution for Thames Water. The workscope split is as follows:

Decommissioning of the existing STW will also be undertaken by BEJV, in addition to working collaboratively with TWUL operational and networks teams to integrate existing TWUL operational assets into the new sewage treatment works.

BEJV undertook a series of site trials in 2021/2022. The purpose of this was to investigate the proposed ground improvement techniques further in order to validate proposals and inform detailed design. There are a combination of techniques which interface with each other in a complex manner.

The trials also gave important information about potential effects to both leachate levels and ground gas within the existing landfill to ensure there would be no impact on environment, ecology and human health.

The three techniques tested, and subsequently used within the works were as follows.

1. Rapid impact compaction (RIC): RIC was undertaken to remove the risk of long-term settlement to the landfill. Whilst the main structures would be supported on piles, this was to remove the risk of long term ground settlement underneath and around the structures. RIC is a method of imparting energy to the ground using a repeated but relatively short drop-weight, where a base plate is in constant contact with the ground. It is undertaken on a pre-determined grid pattern. At Guildford a 9T hammer was chosen, fitted to a 35T base machine and working on a 2.5m x 2.5m grid. Each ‘pass’ of the technique used 40 blows at each point.

Within the trial areas the technique was tested with 1, 2 or 3 passes (ie, 40, 80 or 120 blows per location). Cone penetrometer tests were used to measure the extent of deep level ground compaction before and after the trials. The continuous monitoring from the boreholes demonstrated that at each ‘thump’ of the ground there was no discernible change in leachate levels or ground gas volumes, and that there was no dispersal of leachate happening throughout the landfill.

From the trials it was determined that all areas of the site that are being built on should receive either 1 or 2 passes of RIC for the permanent works.

3. Vertical rigid inclusions (VRI): VRIs are mass concrete piles which are used for lightly-loaded structures and areas such as roads and hardstandings. They are a displacement pile, with the surrounding soil pushed sideways by an auger. As the auger is withdrawn the resulting void is filled with concrete up to ground level. They therefore work by increasing the density of the ground. A granular layer is then installed above to remove any ‘hard spots’. Again, this technique does not bring landfill material to the surface. It was trialled in two areas and found to be suitable for use, without causing any effects to leachate levels or ground gases. It is therefore being used as part of the permanent works over the whole site wherever there are not piled structures.

The trials of all three techniques, together with the subsequent site testing proved that the design principles were correct, and gave information on how to refine the solutions further. It also demonstrated that the techniques would not cause any adverse environmental effects.

Enabling works took place during Spring 2023 and consisted of site clearance, setting up the site offices and welfare and establishing fencing. The whole site was then covered with a 100mm thick layer of imported granular material to provide further protection against the risk of asbestos within the existing capping layer.

A series of 20 further boreholes were installed around the perimeter of the site to enable daily monitoring of both leachate and ground gas within the landfill and to ensure that none was being mobilised by our works. Mobile monitoring stations for noise, dust, vibration and asbestos were all set up, which are monitored continuously throughout the works. Over half a million data points have already been captured.

The permanent works started in earnest in Summer 2023 and in August, rapid impact compaction was conducted over the site, with a combination of one or two passes, as informed by the results of the previous site trials. In total the ground was hit 360,000 times! Precast piles were then driven for the major structures and pipelines. These were all 250mm square piles and varied in length from 16m to 20m. A total number of 3,422 piles have been driven using three piling rigs.

Vertical rigid inclusion installation is currently underway, with a total of 1,700 out of 9,000 already completed. The works are sequenced to avoid clashes with other work areas, on what is a congested site. Following installation, each work area is left for the piles to cure for the following seven days, thus effectively sterilising large areas of the site at a time. This therefore requires detailed collaborative planning on all work fronts to ensure that the site can remain operational.

Of the 59 concrete structures, some are simple reinforced bases, however ‘the big 5’ are significant structures:

Due to the repetitive nature of their construction, BEJV chose to construct the PST and the ASP using precast concrete techniques, which are then stitched together on site. The four FSTs and two storm tanks are also being constructed using precast panels which are then post-tensioned.

The inlet works and TTP are complex, bespoke structures with very little repetition and so are more suited to traditional in situ concrete construction. The inlet works is a particularly complex structure, and is the tallest structure on site at 13m above ground level and being formed of five separate elements.

As of August 2024, the inlet works concrete structure is half complete and the TTP structure underway. The PST precast walls are mostly in place and stitched together, with roof beams now being installed. Works have also started on the ASP walls.

Pipework to the FSTs is underway, which will then allow the construction of the bases to follow on. To date (August 2024), 4,000m3 out 14,000m3 of concrete has been poured, and 205 out of 454 precast wall elements installed.

The flows to the existing STW enter at the southern end of the works. A new transfer tunnel has therefore been constructed to intercept this and transport the flows to the new STW. This tunnel is 1.4km long, 1.5m internal diameter and flows by gravity. It is formed at an invert depth of 10.6m to 15.7m below existing ground level, entirely within the London Clay.

To construct the tunnel a series of six shafts were sunk. The largest of these is 12.5m diameter and forms the inlet shaft in the new STW. The raw sewage will then be pumped from this to the inlet works, from where it will then flow by gravity through the new STW. The remaining five shafts were used to launch or receive the tunnel boring machine (TBM) and pipe-jack, as well as being used for auxiliary connections to sewers in the existing network which don’t get picked up by the main connection.

The tunnel was constructed using the pipe-jacked method using a tunnel boring machine. This was named ‘Daphne’ in a competition by Bisley Church of England School. Daphne Jackson was the first female physics professor in the UK and taught and researched in Guildford. The tunnel consists of four straight sections, one curved section and one short hand-dug section to connect to the existing network.

Current progress is that all of the shafts have been sunk, the main tunnel is complete and fit out the shafts has commenced.

The outlet for the new STW consists of a 750mm diameter pipe from the TTP and a 1050mm diameter pipe which acts as a storm overflow during extreme weather events. These pipes are laid across a floodplain to the River Wey, a distance of approximately 330m before discharging via a bespoke headwall into the River Wey. This has been designed in conjunction with Environment Agency to minimise erosion in what is classified as a salmon river.

Due to Environment Agency and Local Authority permitting requirements as well as practical requirements of working on a floodplain with underlying running sand, these works are practically restricted to a short duration in the summer. This is being undertaken during Summer 2024 and the works are on target for completion within this period.

The majority of underground assets in the new works are being constructed within the existing landfill. This brings plenty of challenges in both design and construction. Assets must be designed to withstand both differential settlement and potential degradation from existing contaminants in the land fill material.

A variety of ductile iron, carbon steel, and concrete pipes are being used with various protection methods. The work is being self- delivered by the BAM workforce and the installation of below-ground pipework is underway with a focus on where it interfaces with the new structures. This requires extensive temporary works solutions to provide a safe working environment for the workforce within the band of landfill material.

Steel sheet piles are being used to provide temporary ground support and excavated landfill material is being sorted in a material handling area on site. This is being done to reduce the amount of hazardous material being sent off site, halving the amount of excavation and disposal required using traditional open cut methods.

As well as the main connection taking flows form the existing works to the new, there are three other existing assets which are to be integrated into the new system, at various points along the length of the new tunnel. This involves extensive research and planning in an open and collaborative approach with TWUL networks teams.

Bowers Farm Main was successfully diverted in November 2023, and has been constructed such that the final connection and commissioning to the new system will be a more straightforward operation. Planning works are currently underway on both Stokes Road syphons and Abbotswood syphons in order to construct similar scenarios for future connection and commissioning.

The main connection to the existing Guildford Main at the head of the new scheme entails connecting into an existing 10m deep concrete and brick built chamber, which carries live flows 24/7. The site team have undertaken several successful drawdowns in conjunction with TWUL to ascertain the dimensions and condition of the chamber in order to plan the final breakthrough works in great detail. This design work is currently underway and the new tunnel hand drive has been stopped a few metres short of the final breakthrough and shored up, prior to the final connection to the existing network.

Construction works of the ‘Big Build’ are continuing at pace and the BEJV Team are now focusing on ensuring a safe, effective and efficient integration of civils and MEICA elements. This will start in late 2024 and continue throughout 2025.

Following successful completion of commissioning of the new sewage treatment works in 2026, the existing works will be de-commissioned making way for the next stage of the Weyside Urban Village, providing homes and leaving a true legacy for local people and businesses.

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

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

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

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

The NIEA had identified the following five CSOs as UIDs:

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

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

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

The purpose and drivers of this project were as follows:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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:

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:

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.

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.

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.

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.

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.

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).

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.

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 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.

With the completion of the project, the following project objectives were achieved:

These project objectives are fully aligned with today’s environmental and economic priorities; promoting both care for the environment and financial responsibility. By improving nutrient removal, optimising operational costs, and significantly limiting untreated sewage discharges, the expansion enhances the protection of local waterways and supports sustainable regional growth, ultimately benefiting the community and the wider environment.

Following the expansion, Newthorpe and Heanor flows now undergo separate preliminary and primary treatment streams before combining at the secondary treatment stage. Flows from the Newthorpe catchment area enter the existing inlet facility, which retains its current configuration, with upgrades limited to mechanical equipment.

Archimedes screw pumps raise the inflow to an elevated inlet works structure housing new fine screens engineered to capture at least 80% of solids greater than 6mm in size. Downstream of these screens, a new detritor facilitates the removal of grit and inorganic materials such as sand, thereby protecting mechanical components from potential damage.

Subsequently, the sewage proceeds to primary treatment, where gravitational settling in two existing primary settlement tanks achieves initial physical separation of fine particles. The effluent from these tanks, which previously fed into secondary treatment via trickling filters and humus tanks, is now redirected to the expanded works.

Biological treatment occurs at the secondary stage, targeting reduction of specific parameters, including phosphorus, ammonia, iron, and suspended solids, to consented levels. For Newthorpe, an Enhanced Biological Phosphorus Removal (EBPR) process utilising a modified University of Cape Town (UCT) configuration is implemented.

Influent first enters an anaerobic zone, creating favourable conditions for polyphosphate-accumulating organisms (PAOs) in the absence of oxygen and nitrogen. Here, PAOs assimilate volatile fatty acids, enhancing their competitive viability during subsequent aerobic treatment.

Next, the process advances to an anoxic zone, where recirculated activated sludge (RAS) from secondary settlement is introduced. This recirculation not only distributes bacteria through the system but also conveys nitrogen oxides produced by ammonia oxidation in the aerobic phase. In the anoxic environment, these nitrogen oxides are converted to nitrogen gas, which is then released to the atmosphere.

The third stage involves the aerobic zone, wherein air is supplied to promote three key processes:

Final sedimentation occurs in the final settlement tanks (designed and built by Tank Consult Ltd) , where phosphorus-enriched sludge is removed. This sludge is either recirculated to the anoxic zone or processed further, including thickening and digestion for gas and cake production.

The tertiary stage further decreases effluent phosphorus concentrations, specifically targeting non-organic forms. Ferric sulphate is dosed upstream of the tertiary solids removal unit to coagulate particles into larger flocs, which are subsequently eliminated via physical filtration.

Newthorpe employs the FilterClear (mixed media filtration) system, developed by Bluewater Bio Ltd, which, upon commissioning, represents the largest installation of its kind in wastewater treatment.

At Heanor, the new transfer and storm pumping station is now fully operational, marking the successful completion of the project. The construction overcame significant challenges, particularly the close proximity of surrounding structures and persistent groundwater issues. To address these, a wall of secant piles, installed by Van Elle, was integrated into the permanent works, providing a crucial groundwater cut-off and ensuring the safe installation of the pumping station.

The blind tank, a 1,700m3 glass-coated steel unit from Goodwin Tanks, is now completed and in service. This tank is fed from the steel storm distribution chamber, fabricated by GT Fabrications.

Once the blind tank is full, the same distribution chamber spills into the two former primary settlement tanks (PSTs), which have been successfully re-purposed as storm tanks. This innovative approach provides increased stormwater storage capacity, contributing to a reduction in spills to the river. There remains further opportunity in the future to adapt additional structures on site, offering continued improvements in environmental performance and further minimising river spills.

The motor control centre (MCC) was powered up in September 2024, and the entire site was brought into its final operational configuration by December 2024; seamlessly meeting regulatory requirements. The facility is now actively supporting the broader network, reliably transferring flows to Newthorpe STW and managing stormwater events as designed.

The 2.5km 450mm dual rising main connecting Heanor STW to Newthorpe STW, with a 250m section crossing the River Erewash and Canal Erewash using HDD by Joseph Gallagher Ltd,  is now fully completed, tested, and operational. It is successfully transferring flows as part of the live network, supporting the EBPR process and meeting all regulatory commitments.

The route of the rising main crossed several historical mine sites. MMB’s geotechnical team conducted an investigation to understand the status and position of the mine entries and any other mine-related features along the route. Additionally, a watching brief was in place to quickly identify any non-natural ground features. Thanks to this effort all the risks were mitigated, and the rising main was safely constructed.

At Newthorpe STW, the principal phases of construction have been successfully concluded. The outstanding operations now comprise ancillary works including landscaping, seeding to provide Biodiversity Net Gain project objectives. At the time of writing (August 2025) the site roads have been completed.

The motor control centre (MCC) was successfully energised in 2024. Initial commissioning focused on validating the new treatment processes, including comprehensive checks on all mechanical equipment and monitoring instruments, followed by testing of the ASP aeration system.

During the process stabilisation period, flows were directed back to the existing facility via the new TSR pumping station and a temporary pipeline. This ensured that all discharge consistently met regulatory and environmental requirements while the biological systems developed. Continuous online monitoring and regular sampling confirmed the facility’s compliance throughout this phase.

Once the ASP achieved process maturation, flows were switched to the new outfall arrangement. This handover was carefully managed to maintain both water quality and process stability. From the first day, the plant operated successfully and met all water quality standards.

The project’s success is a direct result of robust collaboration among all stakeholders. The design teams operated under an integrated “one team” model, leveraging global expertise to deliver innovative solutions. This approach ensured effective coordination and maximised the impact of technical knowledge from diverse backgrounds.

The supply chain, comprising over 65 suppliers and subcontractors, played an essential role in the project’s completion. Their contributions were instrumental to maintaining schedule and quality, demonstrating the critical importance of comprehensive supply chain engagement in advancing the water industry.

A strong partnership between MMB and Severn Trent was central to achieving project objectives. The active involvement of Severn Trent’s operational team provided invaluable practical insights that informed commissioning and handover, enhancing operational reliability.

MMB supported industry growth by integrating 11 apprentices and placement students across all disciplines. The project prioritised links with academic institutions, hosting several site visits and serving as a Loughborough University case study for final-year civil engineering students.

MMB and Severn Trent worked together during commissioning to optimise greenhouse gas emissions at the Newthorpe STW. Instrumentation was installed on site to measures nitric oxide (NO) and nitrous oxide (N2O) on the ASP, providing critical data for ongoing improvements.

Nitrous oxide was continuously monitored during the biological removal of ammonia in the nitrifying ASPs. The data collected during and after commissioning at Newthorpe provides Severn Trent with a robust baseline process emissions factor and valuable understanding of the mechanisms that produce nitrous oxide.

While large volumes of operational data are normally generated by the plant, the Comm Plus initiative now processes this information, turning it into meaningful, near real-time performance insights displayed on an accessible dashboard.

The integration of ammonia load and process emissions monitoring exceeds standard requirements and gives the Operations team a powerful tool to balance the plant’s overall environmental impact - comparing discharge water quality with atmospheric emissions - to drive ongoing optimisation and sustainability.

Newthorpe STW and Heanor Milnhay STW have been successfully merged as part of one of the major AMP7 Severn Trent projects, with Mott MacDonald Bentley serving as principal designer and contractor.

The completed expansion at Newthorpe STW now stands as one of the largest enhanced biological phosphorus removal sites in the region, serving a population equivalent of 100,000. Newthorpe STW has consistently achieved the stringent permit of 0.2 mg/l while minimising chemical use for phosphorus removal.

The scheme was delivered on schedule, with the biological maturation of the EBPR process achieved ahead of the regulatory deadline in December 2024, ensuring enhanced environmental compliance and operational excellence for the years ahead.