Supply Chain - Water Treatment - Products & Services

Ufton Nervet WTW is a groundwater treatment site located in the Kennet Valley Water Resource Zone, to the south of Reading and supplies an ‘island zone’ of approximately 12,000 properties. Groundwater is pumped through pressure filters for iron removal after which chlorine is dosed before flows enter the contact tank, which is a single cell semi-buried tank of concrete construction where the water comes into contact with chlorine to achieve disinfection. SO2 de-chlorination occurs before high-lift booster pumps pump the water into the water supply network. Thames Water contracted MMB to design and build the proposed run-to-waste (RTW) and contact tank (CT) as part of the AMP7 Capital Delivery Alliance Lot 1- Water non-infra Thames Valley framework. The problem The existing contact tank asset has been raised on the drinking water safety plan as a resilience issue since it is not possible to take it out of service for a periodic planned maintenance inspection. This should occur so risks to water quality and long-term structural integrity can be managed, without shutting down water production to maintain customer supplies. Since the existing contact tank is semi-buried, in the event of high turbidity, there is no permanent automated means to run-to-waste pre or post-contact tank. The only option available is a manual invention and over-pumping into an adjacent ditch. The project has to overcome the following constraints: The WTW feeds an ‘island zone’ network, meaning if the site becomes inoperable the customer potable network loses water and pressure in less than eight hours because there is no means to re-zone the network to feed it from another site. Ufton Nervet WTW is a small site with limited space which is surrounded by a watercourse ditch in poor condition. Areas of the site which do not contain existing assets have low to moderate categorised trees, or modified grassland in poor condition. The site is surrounded by agricultural land which is a floodplain so any new assets would need to be kept to a minimum to avoid having an impact on the floodplain storage, but still meet the planned operational and maintenance requirements expected of any asset. The site has restricted access via a single lane road meaning delivery of larger items would be challenging, but the contact tanks need to be large enough such that if one is taken out of service those remaining provide enough contact time between chlorine and water. All these constraints mean any spare space is at a premium and careful planning is needed to phase the work to keep outages and overall programme as short as possible. [caption id="" align="alignnone" width="1200"] Existing contact tank - Courtesy of MMB[/caption] Solution It is proposed to tie-in to the existing contact tank feed with DN500 pipework and isolation valves on each side of a new tee piece, which will enable the works to continue running whilst the new contact tanks are built offline, before the existing 200m3 tank is decommissioned and demolished at the end of the project. Four pressurised contact tank vessels will be installed in the field adjacent to the site. These are elevated out of the floodplain with an access gantry provided to allow operational staff to cross from the existing site to operate the tank isolation and maintain air valves. The contact tanks will be 21m long and 2.1m in diameter to meet the 15 mega litre/day (MLD) throughput and client asset standard contact time, even with one contact tank taken out of service for inspection to enable the site to remain operational. Chlorine will be dosed via a new point of application (POA) static mixer and an aeration gas dosing system will be housed in kiosks with associated sample pumps, which will replace the current cascade aerator on the existing contact tank. A balance tank will provide the hydraulic break between the pressurised contact tanks and existing high lift booster pumps, with an internal dividing wall to allow either cell to be taken offline. Two pairs of actuated valves and turbidity instruments will allow for a manually initiated automated system pre and post the contact tanks to be de-chlorinated before running to waste. The RTW system will comprise a dichlorination chamber, flow meter chamber, sample chamber, and headwall all sized for a maximum discharge rate of 120 l/s. A new site road will provide vehicle access to the contact tanks and a perimeter security fence installed around the extended site boundary. [caption id="" align="alignnone" width="1200"] 3D model showing the four pressurised contact tank vessels - Courtesy of MMB[/caption] Ufton Nervet WTW Contact Tank: Supply chain - key participants Because the project scope is complex and requires specialist input and early supplier engagement the following multi-disciplinary teams were involved in delivering the project. Client: Thames Water Principal contractor & designer: MMB Specialist design (planning, CFD, ecology): Mott MacDonald Civils/groundworks: Hercules Site Services Ltd Topo/GRP/Point Cloud: 40Seven Ltd Ground investigations: Dunelm Geotechnical & Environmental Contact tanks: Vessco Engineering Ltd Mechanical installation (pipework): JB Fabrications Mechanical installation (metalwork): FabTek Ltd Electrical installation: IMAC Ltd MCCs/systems integration/ICA: BGEN Ltd Kiosks & security covers: Morgan Marine Ltd Static mixers/aeration system: Statiflo International Ltd Valves: AVK UK Ltd Precast concrete: FLI Precast Solutions Legato® interlocking blocks: Elite Precast Concrete Ltd Instruments: ABB Ltd Instruments: IFM Electronic Instruments: Siemens Sample pumps: Grundfos Ltd Security systems: Reliance Ltd Security fencing: Allen Fencing Ltd Flood protection measures (borehole pump buildings): Flood Control International Overcoming the constraints Computational Fluid Dynamics (CFD): CFD modelling of the proposed contact tanks at Ufton Nervet WTW was undertaken to prove the performance of the proposed design. The performance of the contact tanks is measured in terms of the standard retention time t5 (the time taken for 5% from the point of the chlorine addition to measurement at sample point No. 4 after the contact tanks). [caption id="" align="alignnone" width="1200"] CFD modelling - Courtesy of MMD CFD Team (Spain)[/caption] The purpose of the model was to provide evidence that the water has a minimum t5 retention time of 20 minutes to comply with the standard if the raw groundwater is considered unstable, or 15 minutes if considered stable. A non-reactive tracer was added to the model at the primary dosing point and measured at the outlet through time to obtain its exit age distribution. The model was run as a worst-case scenario with one of the furthest of the four tanks taken out of service; meaning only three were modelled including interconnecting pipework. The model was also based on a 15 MLD design horizon which is conservative as it is 1.5 MLD beyond the abstraction limit and capability of the existing borehole pumps. It was agreed with the client that the groundwater was considered stable such that a 15-minute t5 was the target figure, and the model showed an 18.2-minute t5 with 21m long contact tanks. This offered a saving of approximately £230k by having shorter tanks because the CFD modelling showed that 25m long tanks would have been required for a 20-minute t5. This would have made delivery of the tanks down Ufton Lane even more challenging. Even so, Autotrack analysis was completed to confirm in theory there was a route to the site, which was viable for delivery of the 21m tanks, which the tank suppliers’ delivery management company confirmed was possible during a pre-delivery survey. This was considered to be the right balance of resilience and affordability because it is unlikely the unstable groundwater events would occur at peak design horizon demand whilst one of the contact tanks is out of service. [caption id="" align="alignnone" width="1200"] Exit age distribution of tracer measured at the outlet - Courtesy of MMD CFD Team (Spain)[/caption] Use of SYNCRO to hold a digital construction rehearsal to de-risk programme: A P6 programme has been produced which lists numerous construction activities and outages limited to eight hours due to the island zone constraint, and a 3D model has been produced to illustrate the physical space each asset needs when installed. As part of MMB’s Digital Delivery Plan SYNCRO (one of the digital tools utilised by MMB) was used to hold a construction rehearsal which led to the following benefits; a better understanding of the space constraints, engaged client stakeholders for programme buy-in, improved safety and a de-risked programme. By combining the P6 programme with the 3D model and reviewing it via SYNCHRO software allowed a better understanding of the concurrent activities and the ability to spot where there could have been potential space constraints. The digital rehearsal revealed that the design was proposing to install precast pipe support plinths and the access metalwork at the same time as the contact tanks were being installed, so SYNCHRO was used to update the P6 programme live to re-sequence the work. This rehearsal simulated the contract lift of the contact tanks and illustrated just how much space was needed to have a safe working area to complete a lift of a 21m long 10t tank on a 20m radius. This again led to a change in the construction sequence of the mechanical installation of pipework and access metalwork. Focusing on safety and being prepared to challenge programme where there looked to be too much concurrent working, should ensure a right first-time approach before committing to starting on site, reducing the risk to quality or safety and having to abortively re-plan works, which may end up increasing costs. [caption id="" align="alignnone" width="1200"] MMB SYNCHRO digital rehearsal - Courtesy of MMB[/caption] The digital rehearsal review coincided with a change in a key construction assurance client team member, so the above process sought their buy-in and confidence in the construction programme and occurred at a significate project milestone (contractual solution review) where the client can make a go/no-go decision on whether the project goes ahead into detailed design and construction. The review received positive feedback from the client that the session proved to be a valuable and more engaging way to bring them up to speed with the scheme and the construction programme. The project will revisit SYNCHO to plan in more detail at other key milestones like works outages, or whilst on site as a more visual way of completing 5-week-look-ahead planning sessions. MMB has a Digital Delivery Network which is a community of people who can support projects with tools like SYNCHRO and others which can be found on the MMB Digital Delivery Hub. The benefits of this digital rehearsal were more cost/risk mitigation rather than direct cost reduction on a project. The estimated consequence of not having realised the space constraints and programme concurrent working is 10-weeks lost time meaning £148k cost increase ‘saved’ (avoided). It is difficult to estimate the cost saved/benefit of having a happy engaged client stakeholder like a construction assurance engineer. This is assumed as saving/mitigated a potential two-week delay resulting in a approximately £30k saving. Providing maintainable assets vs keeping flood plain impact negligible: The existing site not only feeds an ‘island zone’ network; it also becomes an island during flood events and is surrounded by drainage ditches. Relocating the entire site would be uneconomical and too intrusive so expanding the treatment works into the adjacent field is the best whole life cost solution even if that field is a flood plain. This meant any new assets needed to have as small a footprint as possible to ensure it had negligible impact on the flood plain, and yet still needed to be assessable for the planned maintenance and main driver for the scheme; to be able to take one contact tank out of service for quality and structural inspections. [caption id="" align="alignnone" width="1200"] Flood plain location of contact tanks - Courtesy of MMB[/caption] The solution is to install the steel contact tanks on slim 2m tall concrete plinths, with the inlet/outlet stainless steel pipework supported off steel pipe supports founded on Legato blocks or strip foundations. Precast units were selected where practical and economical to speed up the install to reduce the risk of needing to poor concrete into a floodplain as part of the 10-month long construction programme. The outlet pipework was looped back to join the inlet pipework such that all the isolation and air valves can be operated from the same common access platform, which is 21m long by 6m wide and stands 2.8m above ground level, which saved approximately £400k in metalwork and civil plinths The platform then bridges over the ditch between the treatment works and adjacent field to provide operational access. To ensure all the new assets didn’t have a negative impact on the floodplain a flood model and flood risk assessment was completed based on the volume of new assets to be installed in the field, which showed negligible impact to the flood plain. The contact tanks can be accessed at ground level outside of flood events via a new Grasscrete access road, which removed the need for road drainage which saved £37k. Foundations would have the existing underlying alluvium layer of soft organic clay replaced to target the medium dense gravels layer with stone to allow for better drainage during periods of rainfall and reduce the risk of settlement. The alternative to the elevated assets would have been to bund the entire area which would have had significant cost, carbon and floodplain offset impact which was calculated using the Mott MacDonald Moata Carbon Portal. [caption id="" align="alignnone" width="1200"] Ufton Nervet WTW 3D models - Courtesy of MMB[/caption] Biodiversity net gain (BNG): Approximately 2m of the existing ditch will be disturbed to install the new headwall, so another section approximately 10m long will be enhanced from poor to moderate condition equating in a 13.3% BNG in river units. The 0.1ha of agricultural grassland will be enhanced from poor to moderate condition to achieve a net gain of 10% to account for that lost from installing the new assets. Approximately 88 urban trees are proposed to be planted and maintained to moderate condition along the 180m boundary fence line to achieve a net gain of approximately 40%. To achieve a net gain of 10% would mean only 22 small trees needing to be planted, but this would of only provided a visual screening along 25% of the fence line. Therefore a hedgerow will also be planted along approximately 125m of the inside of the fence line to provide further visual screening and offer at least a 27% net gain in BNG hedgerow units. Conclusion The project started in January 2022 so has been delivered through the COVID pandemic with a team remote-working via MS Teams but making use of Mott MacDonald’s practice network has enabled colleagues from across the UK, Spain, and India to work together for the first time. The project is anticipated to start on site in April 2023 and to be completed by January 2024.

Wooler Water Treatment Works (WTW) is fed by four boreholes and supplies up to 160m3/hour of potable water to Wooler and surrounding areas, including several tourist and semi-residential holiday parks serving over 5,000 people. Seasonal fluctuation in demand can increase turbidity and increase iron and manganese concentrations in the borehole water, particularly when flows are high, interrupted or varied. The existing treatment facility was reaching the end of its asset life and did not have the treatment stages to remove the turbidity, causing flows to run to waste. Frequent power outages and varied seasonal populations led to regular manual operator intervention and a growing reliance on tankering from other sites to ensure the supply zone remained primed. Background/drivers In 2016, Northumbrian Water (NWG) awarded Mott MacDonald Bentley (MMB) an Investigate and Define contract to review potential solutions to improve treatment at Murton and Wooler WTWs. Following this, in April 2018, NWG issued MMB a NEC3 ECC Option C Design and Construction (D&C) contract to deliver the design, construction, testing and commissioning of the new treatment facilities. Design for Wooler commenced in June 2018, with construction works commencing in May 2020. The main build was completed in April 2021 and water brought into supply following testing and commissioning. The previous treatment site was set to run to waste until turbidity in the borehole water was suitable to be treated further. NWG experienced turbidity spikes on pump start-up and flowrate changes, exacerbated by frequent power outages. This resulted in time consuming, costly operator intervention, and wastage of borehole water to the environment. Disruptions in supply needed quick operator intervention to ensure no impact to the customer, often necessitating tankering to maintain supply. The rural setting of the WTW meant during winter, operators faced increased risk in accessing the site. The new WTW incorporates four large pressure filter vessels which are effective in removing turbidity, iron and manganese at higher levels. The reduction in run to waste occurrences provides a more sustainable use of water abstracted from the aquifer whilst improving water supply security to the Wooler area. Within the investigation phase MMB and NWG decided to relocate the works to a more urban setting to reduce the risk on operators and minimise risk of weather events affecting power supply and communications to the site, both of which are critical to maintaining supply to the local community. This is especially critical at Wooler, as the area benefits from a transient tourist population which puts additional strain on the water supply system. [caption id="" align="alignnone" width="1200"] Clockwise from top left - Dechlorination plant, wastewater tanks, chlorine contact tank and treatment building - Courtesy of MMB[/caption] Design development The design phase commenced during the latter phases of construction works at the nearby sister site, enabling the design team to capture positive and negative lessons from the construction and client operations team. Over 100 lessons were collated and assigned owners to incorporate into the Wooler design. The results were evident in the programming and sequencing of the project, which halved the workforce on site when compared to Murton. Several design efficiencies were identified that further reduced the construction duration, including, designing out thrust block requirement, simplification of a complex dechlorination system and pre-washing filter media prior to delivery to reduce commissioning and significantly reducing commissioning water wastage. The MMB project team successfully challenged client asset standards which would have required an additional filter, and as such specified filtration by four sand pressure filters. The filters consist of an anthracite cap, sand, and manganese dioxide (MnO2) media. The sand and anthracite layers capture larger solids particles during periods of poorer water quality whilst the MnO2 acts as a catalytic media and further promotes manganese and iron deposition onto the filter media. By removing iron and manganese over a single stage, the project team designed out a secondary treatment stage, saving on TOTEX, carbon and minimising site footprint. The filtration method selected also provides a higher level of robustness, reliability and low operational costs compared with other technologies. The notional solution proposed maintaining use of the borehole pumps to generate sufficient pressure to drive flow through the new treatment plant to the existing service reservoir served by the site. [caption id="" align="alignnone" width="1200"] Multiple supply chain interfaces were modelled to proactively reduce snagging - Courtesy of MMB[/caption] The additional pressure required would require replacement of the borehole pumps and over 4km of mains in serviceable condition. Instead, the pressure head was broken within the site, reducing operation and maintenance risks, and improving site control and resilience through installation of high efficiency booster pumps to supply the network. Pumping of waste flows was minimised through agreeing discharges into the local sewer and surface water network, with dechlorination included for treatment of non-compliant flows. Pumping of drainage flows was also avoided through minimising site access roads, maximising green space and incorporation of SuDS trench and lagoon within the site footprint. Digital delivery was preferred from the onset, and the site location was GPR and laser scanned to produce an accurate 3D model of the current land and subterranean utility infrastructure. This model was developed further with key suppliers and multidisciplinary designers to progress to a full site-wide model of the civil, electrical, mechanical and process elements. The pressure filter, chemical dosing and metalwork suppliers uploaded models of their discrete works packages into the selected Common Data Environment (CDE) BIM360. The packages were incorporated into the overall site model, produced in Revit. This enabled the MMB design team to accurately model surrounding road structures, interconnecting pipework, services and road infrastructure in both Revit and Civil 3D. The 3D model is earmarked for use as a digital twin, to improve asset management and aid with efficiency of the everyday site operation. The site was designed such that all key instrumentation is above ground, but transfer pipework between treatment stages is below ground, giving full access to all valves and dosing points. Through development of the 3D model, operators were able to fully review the site in advance of a spade being struck, leading to changes to further mitigate operational and site hazards. Rethinking of the operating pressures has reduced operator risk within the building and the new process utilises more resilient process units than previously, incorporating a sophisticated control philosophy which minimises unintended shutdowns and enables restart at the push of a button, rather than a complex series of manual valve operations. [caption id="" align="alignnone" width="1200"] Treatment process units being installed after off-site manufacture and testing - Courtesy of MMB[/caption] Off-site manufacture opportunities were identified to minimise personnel operating on a relatively small site. Chemical dosing facilities were manufactured and tested within kiosks and delivered to site as plug-and-play elements of the process, improving quality control through factory testing and commissioning. Vertical pressure filter units, associated pipework, and metalwork access gantry were all pre-assembled and tested prior to final offload and assembly on site. This approach was taken for the complex manifold pipework weaving between and connecting the site process plant. The 3D model was utilised by stainless steel pipework fabricators to design and detail the pipework for accurate off-site manufacture, eradicating cutting on site. Building on lessons learned from Murton, the contact tank design was changed from in-situ build to a semi pre-cast assembly, reducing the on-site build programme of the structure and reducing the trades and temporary works required. Covid19 hampered the ability to carry out informal meetings, though the digital delivery of the project meant that communication was not impacted during the critical latter stages of the design. The 3D model was utilised to facilitate key coordination meetings including ALM and HAZOP reviews, helping both MMB and NWG communicate proposals to non-technical colleagues. Enabling NWG to utilise the same model during design aided with design acceptances and operational reviews of proposed site processes. Fire and hazard reviews were carried out utilising third person perspective within the model. The integrated use of BIM360 brought more of the supply chain into the collaborative solution development allowing all stakeholders to visualise the final product in a way not possible with traditional 2D drawings. This allowed for greater clash detection prior to construction enabling designs to be tweaked at low cost in the office, reducing standing time on site. Key interfaces between each mechanical supplier were digitally inspected in advance of installation, reducing the likelihood of common avoidable defects in major treatment projects. [caption id="" align="alignnone" width="1200"] Complex subterranean service network required careful clash detection - Courtesy of MMB[/caption] Wooler WTW: Supply chain - key participants Design & build: MMB Hydraulic modelling: Mott MacDonald Ground investigation: Dunelm Geotechnical & Environmental Sheet piling: Van Elle Precast concrete: FLI Precast Solutions Blockwork: Gallaway Construction Structural steelwork design & build: Glendale Engineering (Milfield) Ltd Metalwork: JHT Fabrications Ltd Electrical/cabling: Dongard Mechanical & Electrical Ltd Scaffolding: Ingleford Scaffolding Ltd Shoring/temporary works: MGF Ltd Pressure vessels: ACWA Services Surge vessels: Quantum Engineering Developments Ltd Chemical dosing design & supply: Sheers Ltd Pumps: Grundfos Static mixers: Statiflo Intenational Major valves: AVK UK Ltd Steel pipework fabrication: JBF Group MCC: CEMA Ltd Systems integration: IDEC Technical Services Generator: WB Power Services Ltd Security systems: 2020 Vision Systems Ltd Roller shutter doors: Ascot Doors Ltd Security doors: Bradbury Group Construction Working within a D&C environment, constructability is considered at every stage. The Wooler construction team were identified early in the project, with regular reviews held to discuss the design, its buildability and associated temporary works requirements. These reviews, along with similar client meetings, were held to invite challenge and give the whole project team an opportunity to influence the design; reducing and controlling risk when total mitigation was not possible. Excavators with in-built GPS and intelligent machine control utilised the digital terrain model to excavate within 6mm accuracy, reducing over dig but also bringing wider programme and health and safety benefits. The programme was sequenced using the 3D model, with the order of build determined by service and structure depth. All below ground structures and pipework were set out utilising the model which, alongside excavation accuracy, ensured pipes were laid accurately with no clashes or diversions incurred despite the complex subterranean service network required. [caption id="" align="alignnone" width="1200"] (left) Precise installation of below ground infrastructure and slab penetrations prior to main slab pour and (right) treatment building slab cast prior to superstructure installation - Courtesy of MMB[/caption] The accuracy minimised soil disposal resulting from over dig and designing out thrust blocks through modifications to the pipework specification further reduced excavation. Under licensed exemptions, 1000t of excavated soils were diverted to local agricultural projects and 1000t of compound stone was re-purposed for an off-site access road. Similarly, 1000t of clay arisings from a nearby project were utilised within the Wooler site. Utilising CLIP (Collaborative Lean Improvement Programming) planning and careful sequencing halved the number of people working on site, compared to the sister project at Murton WTW, minimising the number of long journeys associated with rural working. Local suppliers and local staff were embedded within the delivery team, further reducing the embodied carbon impact. Accurate modelling of the proposal in advance of construction minimised material wastage in cut to suit elements of pipework, steelwork, and reinforcement. MMB utilised the local supply chain as much as possible. Major successes were brought about through engaging with a heavy steel fabricator based within a quarter of a mile of the site and an electrical installation contractor based in Northumberland, rather than usual supply chain partners. Utilising more local suppliers meant that the level of service and quality provided was high, with benefits of carbon reductions and reduced transport of major steel elements along busy rural single carriageways. Through inviting NWG, stakeholders and supply chain to CLIP planning sessions, MMB identified programme savings for all parties through sequencing of site tasks and identifying mutually beneficial opportunities, such as sharing plant to reduce vehicles on site. For example, bringing electrical and major steel subcontractors together identified opportunities for cable containment hangers to be installed within the fabrication works at no additional cost, reducing work at height risk and task time for cable installation teams. Construction sequencing, temporary works and site aesthetic were all modified to minimise impact on the local community. Installation of the permanent access point to the site was prioritised in the programme to minimise traffic management on Berwick Road, a main artery for the village. Moving treatment processes inside the main building negated the requirement for additional security fencing and the building itself was designed to resemble agricultural buildings in the area. The permanent site footprint was minimised as much as possible but in doing so, a larger temporary compound area was necessary. The project team worked with local landowners to identify the best location for the temporary works to reduce this impact, and temporary laydown areas were returned for use as soon as sequencing allowed. [caption id="" align="alignnone" width="1200"] Precast contact tank during construction - Courtesy of MMB[/caption] Health & Safety MMB’s positive safety culture was evidenced throughout construction, where in over 75,000 hours worked, over 5,500 proactive health and safety and environmental incidents were reported, resulting in no lost-time or reportable injuries. An added complication to this project has been the Covid19 pandemic, during which the site remained operational and avoided closure. The project was sequenced to minimise the number of people working on the site at any time and method statements were developed to ensure as much work as possible could be completed whilst maintaining strict social distancing. Conclusion Wooler WTW was built as part of a two-project batch. The two sites were built sequentially, which enabled MMB to derive multiple lessons from the Murton project and deliver a new greenfield treatment works within the client’s budget and with minimal impact to the local community. MMB’s long-term collaborative relationship with NWG, combined with the use of trusted local suppliers, off-site build techniques and regular planning sessions enabled multiple sequencing and material efficiencies to be realised, further driving down the carbon impact of the project. Through digital delivery, a significant number of supplier interfaces were carefully managed, avoiding the delays and defects commonly associated with multidisciplinary projects.

Stithians is a village in Cornwall that lies in the middle of the triangle bounded by Redruth, Helston, and Falmouth. Stithians Reservoir (the largest inland lake in west Cornwall) is the raw water source that supplies a maximum of 27.7 ML/day to Stithians WTW, which in turn supplies a population equivalent of 276,741 in west and south Cornwall. The reservoir, formed in 1965, has an area of 1.08 km2 and a gross capacity of 5,415 ML. Stithians dam is recognised as the windiest inland water in the south-west due to the featureless surroundings and its geographic elevation. Project summary Galliford Try was contracted by South West Water to design and build a new Granular Activated Carbon (GAC) water treatment plant to target a 25% reduction in THMs (a group of volatile and potentially toxic chemicals formed during water treatment with disinfectants, such as chlorine), manganese removal, and improvements to taste and odour. The scheme was designed to maximise off-site build opportunities as this reduces error and waste and aligns with Galliford Try’s net zero carbon strategy, eliminating possible dangerous in situ site construction issues, thereby improving safety during construction. [caption id="" align="alignnone" width="1200"] Stithians WTW and Stithians Reservoir dam prior to the commencement of the works - Courtesy of Galliford Try[/caption] Design The new plant will be fed from the existing rapid gravity filters and pumped up to the new GAC contactors via the new interstage pumps and pipework. The design has utilised the site’s topography by siting the GAC contactors at the top of the hill, so the clean and waste flows can gravitate back down the hill, through the downstream processes (UV, contact tank, sludge plant) and then be transferred into the network via the existing pumps and main network pipelines. Galliford Try ensured that the design utilised the steep incline through the site. Over time, these subtle efficiencies will have a positive impact on the sites long term net operational costs. Project scope New interstage pumping station from the existing primary filters. Chlorine dosing system for manganese oxidation and lime dosing for pH correction with an in-line static mixer. GAC plant downstream of existing rapid gravity filters. Clean backwash pumps. Regeneration waste tank. UV plant downstream of new GAC plant. Chlorine contact tank. New sludge thickener to provide additional treatment capacity for site produced sludges. Modifications to existing contact tank and existing high lift pumps pipework. [caption id="" align="alignnone" width="1200"] Model extract showing the existing works on the left, the new process plant on the right, and the GAC at the top of the slope - Courtesy of Galliford Try[/caption] Preparation, planning and early engagement FLI Precast was engaged very early in the design stage and their programme was built into the main Galliford Try programme and weekly collaborative planning meetings were held with the site team as work progressed. FLI Precast and sub-contractor Freeflow Pipesystems were used to enable cast in wall couplers to be procured and sent to Ireland to allow early production of wall units to ensure a prompt start on site once the contract was signed for design to commence. The design also had to allow for three access roads which cross the construction area, all of which had to be always kept open for operations in order that they were able to receive delivery of process critical chemicals, on a regular basis. Construction Construction commenced in January 2022 with the GAC foundations being prepared for the delivery of the precast wall panels initially for the GAC and then the chlorine contact tank sitting lower down the slope. The GAC building is a critical element of the programme as the internal fit out is complicated and time consuming, comprising pipework, valves, dosing and sampling boards and electrical panels. Off-site build was chosen as the fastest way of erecting the building to contain all the pipework, control cabinets, valves and sampling panels which are contained within being installed quickly. [caption id="" align="alignnone" width="1200"] Stithians GAC steel frame prior to cladding - Courtesy Galliford Try[/caption] Off-site build was also the chosen methodology for the chlorine contact tank, the clean backwash storage tank and the rinse/regen tank, all of which were precast concrete panel system installations. The new sludge thickener tank was designed as glass coated steel, again off-site built with fast installation time. Precast concrete storage tanks were the next structures to be completed, at the same time as the underground pipework. All the structural elements have been linked together with process pipework and an extensive underground cabling network links them electrically back to the main South West Water control room. Stithians WTW: Supply chain - key participants Client: South West Water Main contractor: Galliford Try Civil engineering & process design: Arcadis Precast design & installation (GAC & chlorine contact tank): FLI Precast Solutions Ltd Wall couplers: Freeflow Pipesystems Ltd Precast design & installation (regen & clean backwash tanks): A-Consult Ltd UV disinfection: Wedeco Ltd Flow control valves/actuators: AFFCO Flow Control UK Ltd MCCs & LVDB: Galliford Try Electrical installation: Drew & Co Ltd GAC pipework & support steel: Alpha Plus Ltd GAC control valve actuators: Rotork Controls GAC steel frame & cladding: Hewaswater Engineering Ltd Standby generator: DTGen Sludge thickener: DD Engineering Ltd GAC launders & Leopold flooring: Xylem Water Solutions UK Ltd Media: Western Carbons Ltd Miscellaneous metalwork: Minear Engineering Ltd [caption id="" align="alignnone" width="1200"] Inside the GAC gallery: Upper level control valves and valve actuators from Rotork Controls - Courtesy of Galliford Try[/caption] Savings 300T of site-won material was re-purposed to construct gabion basket retaining walls, saving material being sent to landfill, and approximately 40 additional vehicle movements to and from site which equates to a saving of 51 tonnes of carbon and approximately £75k of capital cost. Local resources and materials were also utilised. Subcontract packages requiring a large site presence were all local and where local suppliers were not available, Galliford Try used off-site build solutions extensively to reduce carbon and minimise risk. Safety & environment A very experienced team of site operatives was key to service strike avoidance. Good early GPR (ground penetrating radar) scanning and existing client information was utilised by the designers. Project specific surveys incorporating Matterport scanning of existing buildings, boreholes, trial pits and topographic surveys, were also undertaken prior to the start of scheme. This allowed for the BIM model to be built containing location information for all the existing services to prevent clashes and provide the site team a comprehensive picture to help prevent service strikes, by allowing trial holes to be accurately and safely excavated. [caption id="" align="alignnone" width="1200"] UV building process pipework and support concrete for GRP kiosk - Courtesy of Galliford Try[/caption] Communication Regular letter drops were undertaken to local residents to keep them informed of busy delivery times and works progress. Client operations were involved in all monthly progress and programme meetings, alongside weekly updates of on-site activities. Status At the time of writing (July 2023) all the main civils structures have been constructed, GAC building, chlorine contact tank, UV building, chlorine contact tank, regen and clean backwash tanks, sludge thickener, and various concrete slabs for a standby generator, interstage pumps, sludge pumps and control kiosks. Cabling works are now underway along with final pipework connections, and commissioning works will take place in the coming months for completion in December 2023.

Southern Water’s Sandown Water Supply Works is located on the south-east of the Isle of Wight and supplies drinking water to Sandown and Shanklin. The average winter demand of 7.7 Ml/d can almost double up to 13 Ml/d in the summer due to tourism. Southern Water’s Asset Strategy requires a reliable supply of 12 Ml/d of treated water from the works. A risk assessment to establish resilience of the works' infrastructure identified the ageing clear water tank and high lift pumping station as potential weaknesses which could affect supply. Southern Water awarded Trant Engineering a £10m design and construct contract, Phase 1 for the replacement of these assets. Phase 2 of the project works is for improvement of wash water discharge and flood resilience on site, and Phase 3 includes installation of new caustic soda offloading and storage facilities together with new dosing equipment installed in a new GRP kiosk. The story so far The new Phase 1 high lift pumping station will deliver up to 8 Ml/d to Shanklin Service Reservoir and up to 14 Ml/d to Brading Service Reservoir via existing ultraviolet reactors along with the power supply and motor control centre (MCC2). The contract also covers extensive pipework modifications and the installation of new supply flow meters, treated water aluminium monitoring and triple validated contact tank outlet chlorine residual monitoring. Prior to commencing on site, Trant undertook a series of surveys and investigations which identified a number of construction challenges. In addition to the requirement to keep the works in operation during the work, the site is located within an AONB, which required planning permission and environmental mitigations being satisfied for limited environmental impacts. Due to site space constraints and the need to cut down disruption to live treatment plant, Trant identified early on that the need to build the new equipment offline as far as possible and to provide a new incoming power supply, so that the new equipment could be powered up and tested independently of the existing works. [caption id="attachment_16889" align="alignnone" width="1200"] The new glass-coated steel sectional clear water tanks - Courtesy of Trant Engineering[/caption] Innovative design To reduce excavation work, Trant proposed a design using two new glass-coated steel sectional clear water tanks, 6m diameter and 7m high, constructed above ground on a brownfield area of the site. The tanks feed two sets of five, vertical multistage pumps, one set for Brading and one for Shanklin, installed above ground mounted on concrete plinths, with a surrounding steel access platform with staircase at either end. Due to the level of the outlet of the contact tank being below ground, an intermediate 're-lift' pump station was introduced to feed the clear water tanks. The re-lift pumping station used a jacketed shaft construction method to avoid heavy temporary works. Southern Water’s Senior Project Manager, Kev Fausset said:

“Trant was very pro-active in proposing innovative designs to minimise below-ground works and build off line for least disruption to live process works. That has helped to maintain supply and reduce the overall programme of works.”

[caption id="attachment_16888" align="alignnone" width="1200"] Inside one of the new glass-coated steel sectional clear water tanks - Courtesy of Trant Engineering[/caption] Looking forward Trant started on site in September 2023 and the scheme has made a great start with significant progress on the civil construction works. However, a high volume of complex works remains to be delivered on the scheme within what is a challenging programme and site environment. Tony Jacobson, Trant’s Senior Project Manager said:

“Success will be achieved through ongoing collaboration with our client, supply chain and the wider water industry. The new clearwater tanks will be installed during the summer and the new MCC and electrical work will be completed in time for the arrival of the new pumps in the last quarter of 2024. Simultaneously, we are progressing the mechanical and electrical works for Phases 2 and 3 so that the project delivers on all its objectives and provides an excellent standard of new and upgraded assets.”

    For more information: Trant Engineering Ltd | +4423 8066 5544 | www.trant.co.uk |