Supply Chain - Project Planning & Surveying - DSEAR Assessment

The Southampton and Andover Link Main Schemes (SLM/ALM) are being delivered by Southern Water Services (SWS) under the Water for Life Hampshire (WFLH) programme. The WFLH programme aims to create greater resilience to water shortages, especially during dry weather and droughts. Existing abstraction licences for the River Test and River Itchen have been significantly reduced by the Environment Agency to protect these rare and sensitive rivers. Both are designated as Sites of Special Scientific Interest (SSSI), and the River Itchen as a Special Area of Conservation (SAC). With more than 85% of the world’s chalk streams in the UK, these rivers are key examples of rare chalk stream habitat which support a wide variety of species. The proposed schemes, alongside the development of new sources of supply such as water recycling, will secure resilient water supplies for customers while helping reduce abstraction from these rivers, especially during a drought; so there is more water left in the environment when nature needs it most. Background

The Water Resources Management Plan 2019 (WRMP19), and subsequently updated for WRMP24, sets out Southern Water’s response to the water supply challenge in Hampshire. The response consists of a strategic new source of supply, new and increased bulk supplies from neighbouring water companies, demand management, and new strategic transfer pipelines across the region. SWS were required to identify the optimal infrastructure and associated operational controls required to transfer the new supply from Otterbourne Water Supply Works (WSW) to the’ existing distribution networks supplied from Testwood WSW (Southampton) and River Way WSW (Andover).

[caption id="attachment_23978" align="alignnone" width="1200"] Optimisation model components: (left) the current network and (right) the proposed new network - Courtesy of Southern Water[/caption]

The Southampton and Andover Link Main Schemes are potable water transfer schemes which are required to link up key SWS operational sites across Hampshire to ensure continued sustainable, reliable water supplies.

Principally, the proposed schemes consist collectively of approximately 41km of new trunk mains ranging in size from DN500-DN900, operating in conjunction with a number of existing strategic trunk mains, connecting key WSW’s and Water Service Reservoirs (WSR) across a number of Water Resource Zones (WRZ). Additionally, the schemes include new pumping and storage assets to support the water transfers.

Solution optimisation

Through the scheme optioneering phase, which started in early 2022, a Network Control and Optimisation (NCO) study was undertaken to align with and build on previous work undertaken in WRMP and other strategic network modelling studies.

The aim of the NCO study was to assess the resilience of the proposed new strategic transfer pipelines, often referred to as the Western or Hampshire Grid, and how different options might exhibit varying levels of resilience across business as usual (BAU) and drought operation. The study was completed with the understanding that the infrastructure architecture could not be determined unless the associated operation was also defined. The study was conducted in parallel to engineering design development to determine the preferred options for design, construction and commissioning as part of the wider Water for Life Hampshire programme, ensuring a holistic approach across the region.

The study utilised a proprietary AI software product, Optimizer, to develop optimal asset configurations and was chosen to reduce program costs and expenditures. A traditional approach would typically involve hydraulic models using an iterative “trial and error” method, but the large number of options would make it impossible to evaluate all possible outcomes.

Using Optimizer, with which the Southern Water InfoWorks network model was linked as an embedded hydraulic engine, enabled the automatic evaluation of thousands of trial solutions computing cost and performance, and incorporating operating constraints and design criteria. Optimizer produces a range of least-cost network solutions, including asset sizes and maximising the efficiency of network operational performance, considering both BAU and drought supply/demand scenarios.

The tool produces a set of plans along a Pareto front that represents the optimal-performing configuration for a budget cost, and therefore quickly identifies options to be analysed in further detail. This process enabled efficient development of the engineering design as the scheme architecture was refined quickly with focus on key assets required.

[caption id="attachment_23976" align="alignnone" width="1200"] Optimisation model components - Courtesy of Southern Water[/caption] Scheme development

Through 2022 as the scheme transitioned into concept design, various route corridor options were considered between the fixed strategic sites identified within Otterbourne, Southampton and Andover.

Options considered additional alternative Southern Water operational sites to interconnect with and how to transfer water between these sites to provide further system resilience. These options were refined initially through careful review of desktop environmental, ecological and heritage constraints information, later supplemented by data obtained through site visits, and field surveys (non-intrusive and intrusive).

Options considered the location of the pipeline easement, access routes, pipeline materials and construction methodology. A key intermediate site selected to integrate into the system was Yew Hill WSR, located to the south-west of Winchester. This provided opportunity to utilise common sections of pipeline transfer from Otterbourne to serve SLM and ALM whilst maximising existing transfer capability. This also provided opportunity to expand potable water storage capacity in a network location capable of providing numerous resilience options.

From the initial assessments, high level route corridors were established and broken down into a series of segments. The segments were then appraised in detail following a Red, Amber, Green (RAG) classification by environmental, ecological, heritage, engineering and construction specialists.

Different route options were demonstrated with different segments, with some segments having sub options within. Through a desk-based process, each discipline provided their feedback on the key constraints within each segment, and where mitigation could be required and the form it could take.

Where there were options between or within segments, a preference was stated by each discipline with clear factual reasoning. From these preferences, the route was selected depending on which constraints for each segment were most critical to avoid, whilst balancing constructability and land access constraints.

[caption id="attachment_23977" align="alignnone" width="1200"] Pipeline route refinement methodology - Courtesy of Southern Water[/caption]

Following internal SWS project delivery process, agreement on a single option to progress to outline design was made based on a combination of technical, operational and environmental considerations.

The general design and construction principles used to develop the initial pipeline route of the schemes were to minimise:

Number of major road crossings. Number of bends along the route. Overall length of the pipeline. Encroachment into urban or built-up areas. Interaction with other existing utilities. Requirement for works within flood zones. Requirement for vegetation removal. Works within areas of unsuitable ground quality such as historic landfill. Works within areas with poor ground conditions such as peat and alluvium. Interaction with environmentally sensitive areas.

The proposed pipeline routes and design were subsequently further refined taking into account environmental constraints identified through field surveys, archaeological investigation, community considerations and engineering capabilities clarified through intrusive ground investigation.

All desktop and survey data was made available to all project disciplines via the utilisation of Mott Macdonald’s Moata digital platform, specifically Moata Geospatial and Moata Land Management. This provided all teams withs access to information at every stage of the project, allowing cross-disciplinary teams to collaborate in real time.

The integration of the Moata platform was so successful that it won Best Project – Innovation at the Institution of Civil Engineers South East England Engineering Excellence Awards in 2025.

[caption id="attachment_23981" align="alignnone" width="1200"] Members of the Southern Water and Mott MacDonald teams at ICE awards - Courtesy of Institution of Civil Engineers[/caption] Southampton Link Main: Proposed scheme scope

The key components selected to form the scope for the SLM are as follows:

Extension to existing the Otterbourne WSW High Lift Pump Station (HLPS): Includes additional pumps each fitted with 315kW motors. New pipeline between Otterbourne WSW & Yew Hill WSR: A DN700 ductile iron pipeline, approximately 4.3km in length, of which approximately 0.5km requires DN1500 micro-tunnelling across three pipe-jacks. Rownhams WSR: New inlets to the existing service reservoir and flow control valve arrangement. New pipeline between Yew Hill WSR & Rownhams WSR: A DN900 ductile iron pipeline, approximately 14.6km in length, of which approximately 1.35km requires DN1500 micro-tunnelling across five pipe-jacks. Yew Hill Service Reservoir: A new 8.5Ml service reservoir at Yew Hill cross connected to the existing WSR and associated pipework. Testwood WSW: Pipework cross connections.

The scheme will provide a transfer between Hampshire Southampton East WRZ and Hampshire Winchester WRZ and a transfer between Hampshire Winchester WRZ and Hampshire Southampton West WRZ. Specifically, the scheme will transfer water from Otterbourne WSW to Yew Hill WSR and onward to Rownhams WSR and Testwood WSW.

Key design constraints for the scheme included:

The need for long pipe-jack drives to negotiate a congested alignment between Otterbourne WSW and the M3. New WSR at Yew Hill to expand storage capacity, integrating multiple existing and new supply feeds whilst maximising efficiency of design to operate in numerous flow scenarios. The need for a trenchless crossing of the Chandlers Ford to Romsey railway line. Mitigating impact (direct or indirect) to Emer Bog SAC through careful route optimisation. Modified control of existing pipelines and operational sites to reverse flows. [caption id="attachment_23980" align="alignnone" width="1200"] Yew Hill WSR CFD 3D model : Velocity vector plot - Courtesy of WRc via MGjv[/caption] Andover Link Main: Proposed scheme scope

The key components selected to form the scope for the ALM are as follows (NB: At the time of writing (July 2025) scheme refinements are ongoing and some of the following may be subject to change):

Olivers Battery Water Booster Station: Upgrades to the mechanical, electrical, instrumentation, control and automation (MEICA) works at the existing booster station. Micheldever Road WSR: New inlets to the existing service reservoir and flow control valve arrangement. New pipeline between Crab Wood WSR & Micheldever Road WSR: A new DN500 pipeline (diameter and pipe material TBC), approximately 22km in length. New network WBS within Andover: Duty and location TBC.

The scheme will provide a transfer between Hampshire Winchester Water Resource Zones and Hampshire Andover Water Resource Zones, specifically the scheme will transfer water from Yew Hill WSR to Crab Wood WSR and onward to Micheldever Road WSR and the Andover distribution network.

Key design constraints for the scheme included:

Extensive archaeological mitigation requirements. Interaction with Ministry of Defence operational land. Trenchless crossings of River Dever SSSI and River Test SSSI. Multiple crossings of the A303 including utilisation of trenchless installation. [caption id="attachment_23987" align="alignnone" width="1200"] (left) SLM & ALM location plan, (middle) SLM alignment overview and (right) ALM alignment overview - Courtesy of Southern Water[/caption] Site investigations and scheme consenting

In 2022, MGjv was appointed as Principal Contractor and Principal Designer to undertake Early Contractor Engagement (ECE) support across both schemes; assisting with development of the concept design. As scheme development moved into 2023, MGjv coordinated and undertook extensive site investigation works to verify ground conditions. The scope of the investigation comprised trial pitting, cable percussion boreholes, rotary core boreholes, downhole geophysical testing, surface geophysical surveying, laboratory testing and the preparation of factual reporting.

In parallel, numerous excavations at different locations along the two proposed pipeline routes were undertaken to explore the potential for buried archaeological remains. Initially, an extensive programme of archaeological trial trenching was completed which informed the requirement for subsequent selected strip, map and sample works.

In late 2023, Southern Water submitted requests for EIA Screening Opinions on each scheme to the Local Planning Authorities to confirm requirements for planning consent. Final responses were received in Spring 2024. The outcome of the requests was that SLM was not deemed EIA Development and therefore retained Permitted Development (PD) Rights where applicable. In comparison, ALM was deemed EIA Development and requires a full Planning Application and Environmental Statement (ES) to be submitted for approval.

A summary of site investigation works is as follows (as of early 2024):

Southampton Link Main 41 geotechnical pits excavated. 9 sample boreholes undertaken. 313 archaeological trial trenches dug. 122 geoarchaeological trial trenches dug. 3,100m2 strip, map and sample (as of early 2024). Andover Link Main 128 geotechnical pits excavated. 29 sample boreholes undertaken. 317 archaeological trial trenches dug. 65 geoarchaeological trial trenches dug. 31,219m2 strip, map and sample (as of early 2024). [caption id="attachment_23985" align="alignnone" width="1200"] Archaeological strip map and sample investigation - Courtesy of Southern Water[/caption] Undertakings

Following confirmation of the planning requirements for both schemes in Spring 2024, MGjv was contracted to deliver the full design and delivery of the SLM as the scheme was able to progress under PD Rights for the pipeline. Separate discrete assessments were undertaken that clarified the new Yew Hill WSR, which was also confirmed as PD. The expansion of the Otterbourne WSW HLPS would be subject to a planning application.

The requirement on the ALM scheme for full planning and ES required additional design and survey/investigation works to be undertaken and so MGjv has continued in an ECE role until mid-2025 to support the application, due late 2025. The procurement strategy for the full design and delivery is currently being developed.

SLM & ALM: Supply chain - key participants Client: Southern Water Principal designer/contractor: MGjv Galliford Try Morrison Utilities Tunnel design: Arup Tunnel design: HB Tunnelling Ltd Tunnel design: Joseph Gallagher Ltd Service reservoir design & CFD modelling: COWI Service reservoir design & CFD modelling: WRc SLM open cut pipelaying works : Bartlett Contractors Ltd Moata GIS: Mott Macdonald Ecology surveys: Kingfisher Ecology Archaeology surveys: Wessex Archaeology Ltd Pipes: Saint Gobain PAM UK [caption id="attachment_23984" align="alignnone" width="1200"] Otterbourne to Yew Hill: (left) shaft sinking - Courtesy of Southern Water and (right) DN700 pipework - Courtesy of Bartlett Contractors Ltd[/caption] Summary & next steps

The Southampton and Andover Link Main Schemes will provide a new strategic supply backbone across Hampshire to maintain security of supply to customers and help protect the county’s rare and sensitive chalk streams.

The schemes will provide additional BAU resilience whilst also providing capability to mitigate important drought restrictions being placed on the River Test and River Itchen, impacting key operational sites within the region.

Further articles will follow in due course covering the detail design, construction and commissioning phases of the schemes.

Guildford Borough Council (GBC) are progressing with the development of approximately 41 hectares of brownfield land located along the west bank of the River Wey as it runs through central Guildford and north through Slyfield Industrial Estate. Guildford Sewage Treatment Works (STW) lies within this land and requires relocation in order to enable the development to proceed. This relocation forms a critical part of the Slyfield Area Regeneration Project, and will allow the delivery of up to 1,550 new homes, partially on land occupied by the existing STW, to enable local housing needs to be met. The new sewage treatment works will be built to the north of Slyfield Industrial Estate on land that has been used for quarrying, and in turn used as a landfill site, and is currently largely unused. In addition to the construction of a new works, relocation of the works to this location will require the construction of a new transfer tunnel to divert existing incoming flows to the new site, and the construction of a new outfall to the River Wey. The existing STW must also be decommissioned to enable use by the Weyside Urban Village (WUV) Development. Design flows The new Guildford STW is designed for a population equivalent (PE) of 125,300, with room to expand the site in the future. Design criteria Flow rate Dry weather flow (DWF) 322 l/s Average flow 368 l/s Flow to full treatment (FtFT) 746 l/s IPS peak capacity 2,250 l/s Location of new works The site was formerly quarried for sand and gravel during the 1960s and 1970s, with the resultant voids filled with waste materials progressively moving from west to east (i.e., towards the River Wey), which continued until the late 1980s. There is no record relating to the exact nature of the fill materials. The site was understood to have taken household and commercial wastes, but not special or difficult wastes. Following this, the site has remained vacant and undeveloped. [caption id="" align="alignnone" width="1200"] (left) Location of new sewage treatment works and tunnel route and (right) Slyfield Regeneration Project area - Courtesy of Adams Hendry[/caption] Transfer tunnel The STW transfer tunnel will consist of a 1.4km long, 1500mm internal diameter, 1780mm outer diameter tunnel, made of precast concrete pipe, which will be installed by pipejacking (microtunnelling) method. Six shafts are required to facilitate its construction and will serve as temporary launch and reception shafts. Network modelling by Arcadis verified the designed flow velocities remain self-cleansing and provide for the flow rates required. A geotechnical interpretive report has been prepared in review of the ground conditions for the scheme as whole, and to ascertain suitability for shaft sinking and tunnelling. The principal geological stratification for the site consists of Made Ground overlain principally with River Terrace Deposits, with sections of overlapping Alluvium, overlaying the solid geology of firm to very stiff clay of the London Clay Formation (LCF). The selected method of microtunnelling was chosen as it allows long pipeline sections to built, and its suitability to the ground conditions within LCF at Guildford, while limiting the exposure to personnel to underground works, against traditional methods. The microtunnelling is operated from a central control cabin at ground level, and only limited personnel access into the tunnel is required to service the microtunnel boring machine during construction. A ground movement assessment has been prepared and modelled using XDisp software by Oasys. The analysis constitutive model is based on the O’Riley & New method. The method predicts ground movements resulting from ground loss which produces strain of the soil within the influence zone, and projects the settlement in a gaussian distribution curve. Ground improvement & remediation The project team has consolidated decades of site investigation data into a unified format and 3D model. The process involves first combining data within OpenGround software and applying scripted translation to a common description - for example having all London Clay called ‘London Clay’, rather than ‘LC’ or ‘Clay’. [caption id="" align="alignnone" width="1200"] RIC 1 and 2 pass areas - Courtesy of BAM Enpure Ltd JV[/caption] This combined dataset is then used in Leapfrog 3D geological modelling software, which applies intelligent interpolations, and highlights anomalies that can be quickly assessed and removed. The resultant 3D model has then been used to enhance communication in the engineering AutoDesk BIM 360 federated models, and in the proprietary Arcadis SmartAtlas GIS viewer. Rapid Impact Compaction (RIC) is a method of imparting energy to the ground using a repeated but relatively short drop-weight, where a base plate (or “puck”) is in constant contact with the ground. RIC is preferred over a larger drop-weight technique due to its more progressive and less disturbing impact on the ground it is being used on. The method is also faster and uses smaller scale setups. A challenge for the RIC method was whether the energy it imparts is sufficient to densify the ground, versus other higher energy drop-weight methods. A trial was deemed necessary to demonstrate the suitability of this method. RIC is proposed to be applied over the majority of the site with an expected densification of landfill down to approximately 4.5m. Areas where assets will not be supported on driven full depth piles will undertake a second pass of the RIC method, reducing the long-term settlement of the landfill material. The predicted reduced surface will be levelled as required by the infill of depressions with imported stone or other suitable material. Improvement of the existing ground by reinforcement through installation of Vertical Rigid Inclusions (VRI) method across the site. Supporting of level sensitive and heavier elements will be on precast driven piles founded below the landfill material. The combination of methods will be designed to achieve Thames Water’s settlement performance values over 40 years, and remain within the allowable values of 50mm and 100mm. This will reduce the need for full depth driven piling which would otherwise be required. Reduction of infiltration to the landfill materials by ensuring impermeable surfaces drain to the treatment works and are released at the outfall away from the site. Gas and leachate well monitoring is provided along the perimeter of the site to monitor any impact and provide leachate removal points if required. [caption id="" align="alignnone" width="1200"] (left) Rapid impact compaction rig and (right) pile under test - Courtesy of BAM Enpure Ltd JV[/caption] Guildford STW Relocation Project: Supply chain - key participants Client: Thames Water Principal contractor & designer: BAM Enpure Ltd JV Client designer: Jacobs Civil designer: Arcadis Planning consultant: Adams Hendry Consulting Ltd Process & M&E: Enpure Ltd CFD analysis: The Fluid Group Physical modelling: Hydrotec Consultants Ltd Tunnel design: Joseph Gallagher Ltd Temporary works/shoring: MGF Ltd Precast structures: A-Consult Ltd Precast structures: FLI Precast Solutions Rapid impact compaction: Cofra Ltd Piling: Aarsleff Ground Engineering Ltd XDisp software: Oasys Controlled modulus columns: Vibro Menard Ltd Inlet works and PST odour covers: Power Plastics Ltd Inlet pumps: Grundfos Imported sludge Strainpress: Huber Technology Escalator screens: Longwood Engineering Company Ltd Grit removal plant: Jacopa PST scrapers: Colloide Engineering FST scrapers: Purac AB Odour control plant: Odour Services International Ltd FBDA grids and blowers: Xylem Water Solutions Sludge thickening & dewatering: Kent Stainless Ltd Cake Silo: Saxlund International Cloth pile filters: Eliquo Hydrok Ltd Polymer batching & dosing: Richard Alan Engineering Ferric plant: Colloide Engineering Tank logging system (WASP): JR Pridham Services Ltd Glass lined steel tanks: Balmoral Tanks Ltd Sludge tank mixing: Landia UK Ltd Pumps, mixers & flocculators: NOV Welfare building: M-AR Limited Guildford STW - the new sewage treatment works Inlet pumping station The new STW is being designed to maintain inflow from the external catchment ranging from dry weather to 1 in 100-year storm (plus climate change allowance) with future-proofing beyond the 2041 design horizon. [caption id="" align="alignnone" width="1200"] (left) inlet pumping station physical model and (right) inlet pump testing physical model - Courtesy of Hydrotec Consultants Ltd[/caption] The pump design has been developed to fulfil the project brief load requirements (future peak IPS capacity 2585l/s) and some flexibility either side of the requirements is available due to the standard capacity equipment design offered from the supply chain. The proposed arrangement now consists of a wet well 12.5m diameter, approximately 20m deep. A common inlet will be provided to dissipate any entrained air, and two selectable pumped sections with double isolation will be provided by wall mounted penstocks on full height walls. The pumping well will be constructed in two halves, hydraulically connected in normal operational mode however each half will be able to be isolated (using motorised penstocks) in accordance with specification requirements surrounding double isolation, to allow person entry into half of the wet well at a time. Each half of the wet well will have three pumps installed giving a capability to provide full flow to treatment from two pumps with a standby permanently installed. The pumping station was first modelled by computational fluid dynamics (CFD) to demonstrate the assumed flow patterns that will occur. The pumping station was then physically modelled to comply with the specification and process design requirements particularly with respect to distribution, mixing, settlement, turbulence, dispersion, and freeboard for the full range of flows that each structure is expected to receive. [caption id="" align="alignnone" width="1200"] Storm overflow physical models - Courtesy of Hydrotec Consultants Ltd[/caption] Inlet works The inlet works is being designed to receive all pumped flows from the inlet pumping station (including future peak IPS capacity 2585 l/s), inlet works drainage and screening liquor return flows. Flows will enter the inlet works and then separate across the four escalator screens inclined at an angle of 45°. Each screen will be provided with a local proprietary control panel. Each panel will incorporate a differential ultrasonic level control. An emergency bypass will be provided upstream of the screens to accommodate all four screens blinding at the same time. Three 1200mm wide duty screens will be required to screen flows from low flow up to 2585 l/s, screening 6mm in two directions. The inlet works and grit treatment plant will be covered with odour covers which will be connected to the inlet works and PST odour plant. The inlet works has been classified as a Zone 2 Area under the odour covers and all equipment beneath the odour covers will be ATEX rated. Storm tanks Storm flows from the inlet work storm separation chamber will flow into two storm tanks via a 1400mm above-ground pipe. Within the 1400mm pipe between the storm separation chamber and the storm tanks there will be a partial pipe MCERTs certified flow meter to measure the total flow into the storm tanks. During normal operation the blind tank will fill first, then the spill tank will fill. In the event that both tanks are full to capacity (and still in storm flows) the spill tank will overflow via a weir and the storm tank will discharge to river. [caption id="" align="alignnone" width="1200"] Elevated inlet works - Courtesy of BAM Enpure Ltd JV[/caption] The storm tanks contents will automatically return to the inlet pumping station via 700mm gravity pipe when the flow being pumped to the inlet works drops below a predetermined set point. The return flows will be controlled to approximately 0.5 DWF via an automated valve controlled by an electromagnetic flow meter located in the gravity main, returning to the common inlet well of the inlet pumping station. Storm tank cleaning will be a pumped system with the two pumps located external to the storm tanks. Storm tank cleaning will be initiated during the latter part of the storm tanks draining back to the inlet pumping station and will not operate when the tanks are filling. The pump discharge pipe work will include connections for flushing with washwater. Ferric storage & dosing Two 45m3 ferric storage tanks will be located in a concrete bund with the dosing skid packages and control system located within an adjacent kiosk. The bund will be capable of containing 110% of the one of the storage tanks plus 10% allowance for rainwater. A drive-in bunded area for chemical deliveries will be provided and an underground chemical interceptor will contain any local spillages, complete with a Castell interlocked 3-way valve to allow the bunded drainage area either to drain into the interceptor (during a chemical delivery) or to drain into the site drainage (normal operation). Chemical dosing points will be provided upstream of the PSTs, on the common outlet channel of the ASP, and upstream of the tertiary treatment plant. The dosing points will utilise sparge systems to ensure adequate distribution of chemicals into the channels. Odour control plant The odour plant is a 2-stage system. Stage 2 filters will discharge into an 18-metre-high odour stack. The plant has been designed to achieve a minimum removal efficiency of 98% of H2S and 99% removal of odour, based upon a total system duty of 8432 m3/hr (of which 4813 m3/hr is from the inlet works and 3619 m3/hr from the primary settlement tanks). Service water A potable water main supplies a service water break tank via a ballcock (float valve). The service water break tank has a working volume of approximately 30m3 which gives a nominal retention of approximately three hours at average throughput. Service water booster pumps draw water from the tank and transfer it to the service water main network where it feeds the polymer make-up system for all thickeners and dewatering belt presses. Primary settlement distribution chamber The distribution chamber has been CFD modelled to calculate the flow split to each downstream primary settlement tank from first principles, and assess whether the proposed design would deliver an equal flow split (+/-5%) for seven future flow scenarios. This required the inlet bellmouth to be turned down to improve flow splitting. [caption id="" align="alignnone" width="1200"] PST distribution chamber CFD models: (left) with four PSTs in service and (right) with six PSTs in service - Courtesy of The Fluid Group[/caption] Primary settlement Primary settlement consists of four 47.15m long by 10m wide tanks, with a depth ranging between 6.24m at the hopper end and 5.3m at the outlet length (equating to 1 in 50 floor slope). Each PST tank has three sludge hoppers at the inlet end. The outlet of the PST discharges into a common 1000mm wide outlet channel. From this outlet channel the 1000mm outlet pipe from the drop box combines with the 700mm RAS lines into an above-ground 1200mm pipe. Retractable odour covers will be provided across the PST tanks to allow for future inspection, cleaning and maintenance. The odour covers will be connected via ducting to the inlet works/primary settlement tank odour plant. All mechanical equipment installed below the covers will be constructed from 316 stainless steel or high performance plastics. The primary settlement tanks have been classified as a Zone 2 Area, and all electrical equipment beneath the odour covers will be ATEX rated. The design of the PST Tanks is based upon a maximum inflow of 3022m3/hr to all four in-service tanks, and a peak flow to each tank of 1007m3/hr with one PST out of service. In normal operation all four PST tanks will be in service. Within each PST tank a chain and flight scraper system will be provided which will utilise high-tech non-metallic materials as the main materials of construction. Scum from the primary tanks will gravitate via a rotating surface skimmer pipe to the above-ground primary settlement scum tank. The primary scum return pumps are progressive cavity pumps, operating in a duty standby configuration. The pumps are fixed speed pumps operating between a high and low level in the scum tank. The PST sludge hoppers will desludge based upon a SCADA-adjustable interval and duration. The primary desludge pumps are progressive cavity pumps, operating in a duty/standby configuration. The pumps are variable speed pumps operating to maintain a SCADA-adjustable flow set point. Once the effluent has flowed through each PST it will enter into a common 1000mm wide outlet channel. From this outlet channel flows transfer to the ASP distribution chamber via a drop box and 1000mm above-ground pipe. [caption id="" align="alignnone" width="1200"] ASP overview - Courtesy of BAM Enpure Ltd JV[/caption] Activated sludge plant The ASP plant will have a distribution chamber using the same general arrangement as the primary settlement distribution chamber. The activated sludge treatment tank consists of four ASP lanes. Each ASP lane has a selector tank followed by an anoxic zone and then the three aerobic zones. The main aeration lane will be fitted with aeration pipework and fine bubble diffusers. The aeration vessel is 80m long and 6.1m wide with a water depth of 7.05m. The total instantaneous maximum air demand of the ASP is 10,438 m3/h. The first third of the aerated fraction of each lane will contain 50% of the aeration capacity, the middle third 30%, and the final third 20%. Each aeration lane will have three passes, arranged as channels of 6.15m width. The air for the diffuser grids will be supplied from three ASP air blowers operating on a duty/assist/standby basis. The aeration system will be controlled by an ammonia based real time control (RTC) system utilising a feed forward ammonia load input and a feedback ammonia concentration. Once the effluent has flowed through each ASP lane it enters into a common 1000mm wide outlet channel. From this outlet channel flows transfer to the FST distribution chamber via a drop box and 1200mm above-ground pipe. [caption id="" align="alignnone" width="1200"] Anoxic and aeration zones flows - Courtesy of BAM Enpure Ltd JV[/caption] Final settlement tanks The FST plant will have a distribution chamber using the same general arrangement as the primary settlement distribution chamber. The four FSTs will consist of 32m diameter flat bottomed circular tanks with a side wall depth of 6.15m. The FST will separate solids from the flow via settlement, producing a clarified effluent which overflows a peripheral weir into a launder channel, before gravitating to the tertiary treatment distribution chamber via a 1000mm below-ground pipe. The combined clarified outlet flow from the four tanks will be monitored by a common flow meter, as well as suspended solids and phosphorus monitoring instrumentation, all provided on the common line to tertiary treatment. The design of the FSTs is based upon a maximum inflow to each tank of 1741m3/hr with one FST tank out of service. In normal operation all four FST tanks will be in service. Each tank will have a 700mm inlet pipe, which will flow into a central diffuser drum before entering the FST tank. Each tank features a 600mm outlet pipe fed via a peripheral launder channel, as well as a 400mm RAS gravity outlet pipe. Each of the four tanks features a full bridge rotating scraper system which will run continuously in normal operation. [caption id="" align="alignnone" width="1200"] 32m final settlement tanks & sludge return (RAS pumping station) - Courtesy of BAM Enpure Ltd JV[/caption] Sludge return (RAS/SAS pumping station) Sludge from each pair of FSTs will enter one of two RAS/SAS desludge chambers. The two chambers will be located side by side and will share a set of three duty/duty/standby RAS transfer pumps, which will recycle the settled sludge from both RAS/SAS desludge chambers to the activated sludge plant distribution chamber feed line. The variable speed centrifugal RAS transfer pumps will be capable of pumping 2200m3/hr at a maximum head of 8.9mhd. The pumps will operate between high and low level in the duty RAS/SAS desludging chamber, with both chambers provisioned. A pair of duty/standby SAS pumps is provided, which will facilitate wastage of surplus sludge, with each pump drawing from a single RAS/SAS desludge chamber. The fixed speed centrifugal pumps will transfer sludge to the SAS buffer tank. Control of the SAS pumps will be carried out either on a timer or based on the level in the SAS buffer tank, with the common discharge line featuring flow monitoring. Tertiary treatment Clarified effluent flow from the FSTs will pass to the tertiary ferric mixing and flocculation (post-precipitation) stage, where the option will exist to dose ferric sulphate solution into the flow in order to encourage flocculation of remaining solids. This stage will be split into two parallel streams, with flow from the FSTs initially entering via a single bellmouth inlet into a common inlet channel, before passing via twin overflow weirs into two rapid mix chambers, and subsequently overflowing into two flocculation chambers. The design of the rapid mixer chambers will ensure complete mixing (>95% CoV) of chemical in less than 4 seconds. Flow from the flocculation chambers will weir into a common outlet channel leading to a flow distribution chamber feeding the tertiary treatment stage. The distribution chamber has been CFD modelled to calculate the flow split to each downstream cloth pile filter from first principles, and assess whether the proposed design would deliver an equal flow split (+/-5%) for seven future flow scenarios. The tertiary treatment stage will comprise six cloth pile filters, which will operate with all filters in service - however the peak flow will be able to be treated with only five filters in service. The filters will be sized to accommodate a peak flow of 840 l/s, producing a final effluent of 20 mg/l TSS (95%ile) and 0.2mg/l TP (average). Bypass pipework is to be provided adjacent to the cloth pile filter structure, by which clarified effluent from the FSTs may bypass the tertiary ferric dosing/flocculation and cloth pile filter stage. Each of the six cloth pile filters will feature a central rotor drum onto which filter discs are attached. The rotor and discs will be fully submerged within the tank, with the discs supporting the physical cloth filter media. Flow entering the filters will flow from outside the discs through the cloth into the discs’ interior, with solids collecting on the external surface of the cloth pile, creating a headloss. As this headloss increases, the water level in the tank will rise and at a pre-set water level (as detected by an ultrasonic level sensor) a cleaning cycle will be initiated. [caption id="" align="alignnone" width="1200"] Tertiary treatment flocculation chambers: Eliquo Hydrok Mecana cloth pile filters - Courtesy of BAM Enpure Ltd JV[/caption] Filtered final effluent (FFE) from the inside of the filter disc and rotor drum assembly will pass forward through the unit via a low-level aperture to an outlet chamber, from which flow will weir into the common final effluent outfall chamber. An emergency overflow weir is to be provided, allowing unfiltered effluent from the filter tank (external to the discs) to weir over into the outlet chamber. Backwash liquors from the backwash pumps will exit the filters via a common manifold, draining by gravity to the grit plant liquor PS. Eight backwash pumps will be provided per machine, giving a total of 48 pumps across all six machines. The pumps will be submersible units placed within the tank, with each pump being dedicated to three filter discs. The backwash flow rate is rated for 10 l/s (subject to the installed pipework design/headloss). Each of the six filter tanks will see some solids settlement occurring (and potential accumulation of other debris), which will create a build-up of sludge in the bottom of the tank. This sludge will be periodically removed by a set of two duty/standby sludge pumps per machine (i.e. 12 sludge pumps installed in total). The discharge from each sludge pump will be connected to the common backwash manifold, leading to the grit plant liquor pumping station. Final effluent discharge Flows leaving the cloth pile filters will pass out from the main filter chamber via a low level aperture into a small outlet chamber, from which flows will weir over into the common outfall channel. The final effluent (FE) will flow under gravity through an FE flow measurement flume, with an ultrasonic instrument for measurement of final effluent flows discharged to outfall. The FE outfall channel will feature a pipe leading to the FE washwater system, with a further line branching off this pipe servings as the suction line for FE Meteorburst Analyser. On exiting the FE outfall channel, flows will enter a dedicated FE outfall main, which will drain by gravity, discharging to the river north of the STW site. [caption id="" align="alignnone" width="1200"] New Guildford STW: 3D model night-time overview - Courtesy of BAM Enpure Ltd JV[/caption] Guildford STW - Sludge Treatment Plant Sludge thickening equipment Primary sludge from the PSTs will be pumped via the primary sludge pumps to the primary sludge buffer tank, which will have a volume of 120m3 and will be sized to provide 4-hours of intermediate storage prior to thickening. A set of two duty/standby primary sludge thickener feed pumps will be provided to transfer sludge (at up to 7.0%DS) from the primary sludge buffer tank to the primary sludge gravity belt thickeners. Two primary sludge gravity belt thickeners (GBTs) will operate in a duty/standby configuration in normal operation, although the streams will be able to run as duty/assist if required. Each machine will be able to handle up to 51m3/h (771 kgDS/h) of primary sludge, at up to 7%DS achieving a solids capture rate of 95%. Surplus activated sludge (SAS) from the FSTs will be pumped via the SAS pumps to the surplus activated sludge (SAS) buffer tank, which will have a volume of 67m3 and has been sized to provide 4-hours of intermediate storage prior to thickening. A set of two duty/standby SAS thickener feed pumps will be provided, which will transfer sludge (at up to 2.0% DS) from the SAS buffer tank to the SAS gravity belt thickeners. Two SAS gravity belt thickeners (GBTs) will operate in a duty/standby configuration in normal operation but will be able to run as duty/assist if required. Each machine is sized to handle up to 55m3/h (332kgDS/h) of SAS, at up to 2%DS, achieving a solids capture rate of 95%. Sludge balancing/blending tanks Thickened primary sludge, surplus activated sludge, and screened sludge imports will be pumped to two thickened sludge blending tanks. The tanks will have a combined volume of 2150m3 (1075m3 each), and will be sized to provide a combined total of 4-days retention time prior to dewatering of the blended sludge. The tanks will operate in a duty/standby configuration, with either tank being available for selection as the duty unit for either filling or emptying. [caption id="" align="alignnone" width="1200"] Thickened sludge blending tanks - Courtesy of BAM Enpure Ltd JV[/caption] Each tank will feature separate inlet connections for the three types of sludge being received, with actuated valves and crossover lines allowing all sludges to be directed to either of the two tanks. The tanks will also feature outlet actuated valves, which will allow either tank to be isolated from the sludge belt press feed pumps downstream, thereby ensuring the pumps only draw from a single tank at any given time. A set of three duty/duty/standby sludge belt press feed pumps will be provided, which will transfer blended thickened and imported sludge from the thickened sludge blending tanks to the sludge belt presses. The pumps will be variable speed progressive cavity units, with a peak capacity of 30m3/h (i.e. 15m3/h per pump) at a maximum head of 48.5m, based on sludge of up to 7.0%DS. Dewatered cake leaving each belt press will enter a discharge cake hopper leading to the suction end of a sludge cake pump. Three pumps will be provided, with a single pump dedicated to a single machine; each pump will operate in conjunction with the associated belt press upstream. The pumps will be variable speed progressive cavity units, with a peak capacity of 7.4m3/h of sludge (up to 30%DS). The pumps will transfer the cake via individual discharge lines to the sludge cake silos, with manual discharge crossover facilities allowing sludge from the pumps to be directed to either of the two silos as required. Cake silo storage & discharge Dewatered sludge cake will be pumped to two truck-loading cake silos, with a combined storage capacity of 600m3, sized to provide 7-days of storage at average cake production. Each silo will feature a discharge screw conveyor (with a sliding frame ‘anti-bridging’ device) which will discharge the cake through a hydraulically operated slide gate valve. Odour control plant The odour plant will be a 2-stage system. Stage 2 filters will discharge into an 18-metre-high odour stack. The plant has been designed to achieve a minimum removal efficiency of 98% of H2S and 99% removal of odour, based upon a total system duty of 6629m3/hr, extracted from the various tanks and thickening/dewatering machines in the sludge plant area. New STW outfall Outfall route The outfall route from the new works site location was assessed thoroughly in the ITN 2 stage of the project’s life and from exiting towards the middle of the works site, proceeds north towards the River Wey. The route deviates initially to minimise any impact on significant trees that exist within the floodplain, and any impact on the band of vegetation around the perimeter of the site. Final effluent & stormwater pipeline The final effluent pipeline will be a 750mm diameter pipe. This will be situated above ground from the final effluent channel to the edge of the site, and will be supported by piles when within the treatment works site. The pipeline then proceeds below ground through the embankment (to be reinstated using clay stanks) and under the adjacent ditch via an inverted siphon arrangement. A jetting/access point will be provided just before the pipeline dives below ground, giving the facility to clean this arrangement and flush from a more direct point than the pipes exit from the final effluent channel. Air relief may also be provided at this point, subject to detailed design. The storm overflow pipeline will be a 1050mm diameter pipe. This will be situated below ground from the storm tanks to a sampling manhole at the edge of the site; supported by piles when within the treatment works site. The pipeline will then proceed from the manhole through the embankment (to be reinstated using clay stanks) and under the adjacent ditch via an inverted siphon arrangement. The sampling manhole will provide an ability to clean this arrangement. [caption id="" align="alignnone" width="1200"] (left) Outfall route plan - Courtesy of Bam Enpure Ltd JV, and (right) outfall low flow scenario CFD model - Courtesy of Arcadis[/caption] Outfall structure The outfall structure will consist of a reinforced concrete headwall, set back from the river channel, to be founded in the river terrace deposits and flared to direct flows downstream and minimise the impact of upstream debris from collecting. The headwall will have duckbill valves on the discharging pipes, and erosion control products utilised in the surrounding area to tie the headwall into the natural riverbank and bed. The erosion mattress employed following the headwall structure will provide a secondary point at which turbulent flows can dissipate energy without eroding the natural bed of the river. Where the headwall ties into the natural riverbank, the hard/soft interaction between headwall and natural soil will be reduced by the installation of Rock Rolls erosion control and willow stakes at the base, and the installation of a natural hydro-seeded CocoBN blanket or equivalent (to be seeded with local seed varieties) which will retain the slope shape until vegetation establishes and provides an effective natural erosion control. This will also provide a gradual slope to access down to the river. Programme The project obtained planning permission in October 2022, with construction works starting on site in July 2023. Detailed design of the civil, mechanical and electrical works are due for completion by December 2023. Construction of the works will be complete by August 2025, with commissioning due to commence in from April 2025 through to December 2025. Flows from the existing works will be diverted to the new works from December 2025 (10% flow) in a 7-stage commissioning process with 100% flows diverted to the new STW by March 2026. Following 100% flow diversion the existing STW will be de-commissioned ready for handover to Guildford Borough Council.

Forming part of Southern Water’s (SW) Hampshire supply region, the Isle of Wight (IoW) is located just off the south coast of England and is divided into two water distribution zones (WDZ), namely IoW North and IoW South. The IoW South comprises major towns of Ryde, Sandown, Shanklin and Ventnor with multiple villages and more remote rural areas forming the wider distribution network. The water sources and distribution systems have been brought together, with their origins being from former smaller localised systems developed in the late 19th century, which were added to in the 20th century as the IoW population grew, to form an integrated system. Today, there are five existing small and medium sized water supply works (WSW) with a combined daily output of 18 ML supplying customers via several small water service reservoirs (WSR). The water distribution network totals approximately 547 km of mains, serving a population of approximately 45,000 people. Project driver The Cooks Castle WSR has been identified for replacement based on asset condition and the associated security of supply risks to customers. This project aims to provide a long term solution for storage requirements and enhance the network associated with the removal/replacement of this existing WSR. To validate the need and determine the optimum size, top water level and location of any new WSR, a solution needed to be developed considering a wider, integrated view of water sources, network storage and water distribution now and into the future. The business planning objectives were broadly defined as: Create a more resilient water supply network for future generations (Southern Water Network 2030 rationalisation). Maintain levels of service to customers and mitigate water quality risks. Ensure future growth and proposed new sources can be integrated (Water Resource Management Plan - WRMP) and reduce dependency on the bulk transfer from the mainland via the Cross Solent Mains. Increase operational flexibility through optimisation of existing/new assets. Improve security of supply to customers (zonal storage provided in line with Southern Water Asset Class Policy). Decommission surplus assets to reduce cost of maintenance. [caption id="" align="alignnone" width="1200"] Figure 2: The planning process developed - Courtesy of Southern Water[/caption] Optimisation The Optimatics’ OptimizerTM tool was used, allowing the team to analyse up to 35,0000 plans (the group of assets the Optimizer chose to test) in a single optimisation run (see Figure 1 - top of page). OptimizerTM was allowed to generate plans incorporating both new asset options and removing or retaining existing assets. New options tested included a total of approximately 80km of strategic mains in varying diameters, over 20 WSR configurations in five different locations, decommissioning of existing WSRs and associated rezoning, rationalisation of WSWs and provision of new pumping stations. The OptimizerTM evaluated plans using input ‘design criteria’ which were formulated and aligned with the project planning objectives and Southern Water standards. More complex ‘rule-based adjusters’ were formulated to allow automation of controls and prevent Optimizer from selecting options which conflicted with one another, e.g. to prevent Optimizer’s ability to select multiple sizes of WSR at the same location. The evaluation of these design criteria by the OptimizerTM produced a cost and performance evaluation for each plan. The best performing plans were then compared with each other on a Pareto curve - see Figure 3. [caption id="" align="alignnone" width="1200"] Figure 3: Typical Pareto curve showing best performing plans - Courtesy of Southern Water[/caption] Incorporating environmental performance into the optimisation was a particular challenge. The team approached this by taking the results from a high level environmental feasibility assessment and factoring in WSR and pipe costs proportionally to reflect better and worse performing options. This then carried through into the overall cost/performance results for that plan. In the example, the Pareto curve shows about 216 OptimizerTM plans (from 30,000) from which 10 plans have been identified as feasible options. The OptimizerTM tool is very powerful at testing several configurations (plans) based on the given inputs, design criteria and formulations. Review and validation are critical parts of the process, and this involves the team checking outputs (individual plan performance), tweaking inputs (adjusting costs/penalties/formulations) and refining the optimisation until several tangible plans are derived. Figure 4 shows typical age of water results for several WSRs with shortlisted plan 7639, 8142 & 8041 compared against the existing system performance. This demonstrates how the optimised plans can significantly reduce the age of water meeting one of the projects key objectives. [caption id="" align="alignnone" width="1200"] Figure 4: Age of water optimisation - Courtesy of Southern Water[/caption] Defining outputs: the optimal integrated solution Taking a short list of tangible plans from the optimisation is a starting point which allowed the team to define the pathway to the final integrated solution. Not all factors can be simply incorporated into OptimizerTM therefore these external factors need consideration alongside the optimisation outputs to form the final integrated solution. One important factor was implementation of solutions over several AMP cycles and ensuring that staged development did not detrimentally impact on customer levels of service. Similarly, consideration of outage scenarios, e.g. WSW shutdowns and mains bursts were considered outside of the optimisation, then retrospectively tested against the shortlisted network configurations. The solution The final integrated solution comprised: Network connections to a single rationalised WSW using three input water sources (currently two separate WSW with two sources). This aligns with WRMP and improves IoW drought resilience. Removal of seven existing WSRs reducing asset risk through deterioration, maintenance costs and age of water issues. Provision of one new strategic WSR providing wider security of supply to several district metered areas (DMAs) compared to current configuration. Trunk mains reinforcements and new installation/upgrading of network pumping stations to support strategic transfers from proposed WSWs to WSRs and customers. Increased operational efficiency and lower OPEX by considering rezoning, triad periods and exploiting opportunities to modify the current network via simple valving operations.

West Hallington Reservoir is a Northumbrian Water Group (NWG) asset situated 1km to the northeast of the village of Colwell in the Tynedale district of Northumberland. The reservoir was constructed between 1884 and 1890 for Newcastle & Gateshead Water Company for the purpose of municipal water supply. The reservoir was built adjacent to the earlier East Hallington Reservoir and operates as a non-impounding structure. It has a maximum depth of 12.1m, a capacity of 3.3Mm3 and a surface area of 50 hectares at the Full Supply Level (FSL) of 155.1m AOD. Scope of works An inspection carried out under Section 10 of the Reservoirs Act 1975, identified that the reservoir had insufficient drawdown capability, and thus needed to be increased such that the reservoir level can be drawn down by 4.8m in 8 days. Mott MacDonald Bentley (MMB) developed a design solution which utilises two 700mm diameter siphons on the west embankment to operate at a combined flow rate of 3.2m3/s. The new siphon pipeline, alongside a temporary pump arrangement and the existing scour pipes, will meet the required drawdown capacity. The siphon flows will be conveyed across a stretch of adjacent field which NWG has purchased. The flows will then either percolate to ground or gravitate to the Coal Burn and eventually to the River North Tyne. Detailed design and engineering challenges Hydraulic analysis MMB has designed and constructed over 25 siphons for various water companies in the UK. The siphon arrangement was analysed using an in-house design spreadsheet, and demonstrated that the siphon would break when the water level dropped 3m below top water level which was deemed acceptable. The siphon location was moved to the west embankment due to concerns about stability and leakage through the south embankment (the original proposed location of the siphon) and because it was easier to access this area of the site. [caption id="" align="alignnone" width="1200"] Summary chart from the reservoir drawdown hydraulic analysis - Courtesy of MMB[/caption] Pipes and thrust restraint Hoops stresses within the DN700 mild steel siphon pipes were checked and a DWI Regulation 31 coating specified. The stainless steel pipe supports were analysed for bending and shear and concrete thrust blocks were designed for the system test pressures. The pipe wall thickness was reduced from 10mm to 8mm as an efficiency. The pipework arrangement drawing was uploaded into the federated model in BIM360 to check for clashes and when installed on site was found to fit perfectly. Ground investigation and geotechnical analysis Following the original construction of West Hallington Reservoir (between 1884 and 1890) the Resident Engineer Charles Henzell wrote a report to the Institution of Civil Engineers describing the works and detailing a number of challenges which included: Areas of soft book leaf marl overlaying harder boulder clays on the route of the embankment needed to be excavated. Embankments sinking or slipping and the toe of the slope reinforced with concrete walls, sheet piles and additional stepped embankments. Springs in the vicinity of the works. [caption id="" align="alignnone" width="1200"] (left) Cable percussive borehole rig on the crest of the embankment and (right) scaffold decked area required for rotary bore works on the slope - Courtesy of MMB[/caption] A desk study and intrusive in situ ground investigation (cable percussive and rotary bored boreholes, standard penetration tests (SPTs), piezo installation, lab testing) were carried out to classify and determine the thickness of the superficial and solid geology along with groundwater levels, identify any contaminated or aggressive ground and determine the engineering properties of the native soils. Slope stability and ground bearing pressure checks were carried out to ensure large plant would not compromise the stability of the embankments. The clay core and embankment material of the Pennine-type dam was found to be very silty and exhibit poor engineering qualities and so was disposed of, and a source of good quality puddle clay and Series 600-2C material was found locally at a brick factory in Birtley, Gateshead. This was installed in compliance with the test and inspection plan (T&IP) to a good standard. Thankfully the three springs in the west embankment mentioned in the Henzell report were not encountered. [caption id="" align="alignnone" width="1200"] Extreme weather conditions during the construction stages: (left) winter 2022 and (right) flooding from Storm Babet (October 2023) - Courtesy of MMB[/caption] Temporary works A borehole at the toe of the embankment on the dry side indicated the presence of water-bearing sands and gravels and so interlocking sheet piles were specified that punched through the sands and gravels into the underlying clays and so cut off groundwater flows into the excavation. A Portadam supplied and installed by OnSite Central was employed to provide a dry area to construct the intake bay. The Portadam was erected in the wet by operatives wearing buoyancy suits, and then pumped out and an excellent seal was achieved. The Portadam also allowed plant access around the pipework whilst the stone pitching was reinstated. Flood risk assessment A flood risk assessment (FRA) was carried out to support the planning permission and, as due diligence, to ensure MMB would not flood a property by accident. The assessment looked at the extent of flooding during operation of the siphon along with fluvial, surface water, groundwater and finally reservoir flood risk due to an uncontrolled release (which of course the siphon is designed to help prevent). The FRA concluded that:

The maximum modelled flood extent from a drawdown of Hallington Reservoir is in agreement with the flow path identified by the Environment Agency in the long-term flood risk map and no communities are shown to be at risk due to the proposed drawdown. As periodic testing of the reservoir drawdown will occur during dry periods, it is not considered that a drawdown of West Hallington Reservoir at this location would increase flood risk elsewhere.

Synchro 4D MMB chose SYNCHRO 4D from Bentley Systems during the latter stages of the design process. SYNCHRO 4D is software that enables MSP/P6Programme to be linked with a Revit model and to run a construction simulation. [caption id="" align="alignnone" width="1200"] A screen dump from the SYNCHRO 4D simulation - Courtesy of MMB[/caption] The simulation highlighted a number of pinch points when materials must be delivered or when water levels must be lowered or raised and helped drive efficiencies. SYNCHRO 4D was also useful for explaining the construction process to the client, to site operatives and to visitors. Solar power The mechanical equipment associated with the siphon is housed within a high security kiosk. Due to the remote site location, the cost of a permanent power supply for the kiosk building services was prohibitive. A solar powered solution has been installed utilising roof mounted PV cells, DC/AC converter and battery storage. This sustainable solution provides sufficient energy for lighting and heating within the kiosk with negligible running costs. West Hallington Reservoir: Supply chain - key participants Construction delivery partners: Mott MacDonald Bentley Feasibility study & ARPE: Stantec UK Ecological surveys: OS Ecology Ltd Temporary water barrier (Portadam): OnSite Central Ltd Large diameter pipes: Powerrun Pipe-Mech Ltd Electrical/instrumentation installation: Intelect (UK) Ltd Large diameter valves: AVK UK Ltd Large diameter valves: Glenfield Invicta Valve actuators: Varley Hydraulics Ltd Stonemasons: Stuart Marley Ltd Steelwork fabrication: AJ Engineering & Construction Services Ltd Steel fixing: D&N Reinforcements Ltd Kiosks: Technocover Ltd Bespoke steel access cover: EJ Solar panels: Green Leaf Engineering [caption id="attachment_9915" align="alignnone" width="1200"] Solar panel display - Courtesy of MMB[/caption] Construction: Problems, successes and lessons learned? Intake bay The intake bay was located along the Small Burn which originally ran across the middle of the reservoir and was diverted into the adjacent Coal Burn in the 1880s via a DN375 clay gravity drain. The ground around the intake bay was found to be poor and was excavated down to competent sub-grade and reinstated with 340 tonnes of gabion stone and 60 tonnes of Type 1 capping material. As this area is normally under a 5m depth of water it was inaccessible during the ground investigation stage. Pressure testing As the DN700 pipes are fabricated from coated mild steel, a Type 1 pressure test (water loss method) was required. All bolts had been tightened using Hytorc© equipment and the torque readings recorded in the T&IP, but achieving a pass proved difficult due to sunny weather. A temperature rise on the above -ground pipework led to a pressure loss of more than 0.2 bar in the water filled pipe voiding the test on a number of occasions. Eventually cloud cover enabled a valid test; one of the only times a site team has prayed for the sun to go in! [caption id="" align="alignnone" width="1200"] Siphon intake bay constructed within a Portadam barrier supplied and installed by OnSite Central - Courtesy of MMB[/caption] Stone pitching Reinstatement of the original stone pitching (to resist wave action) took seven weeks longer than planned; mainly down to availability of stone masons. Productivity increased as the works progressed and the three man gang went from replacing 3 to 5m2 per day. The stone pitching was reinstated to a good standard, but it was felt that the detailing around one of the pipe supports would be built differently next time. The 2,500m perimeter of the reservoir had been faced with stone pitching down to original ground level; installation of which in the 1880s without an excavator and selector grab must have been a job and a half! Ecology Prior to the construction works, NWG employed OS Ecology to undertake trapping for white clawed crayfish, a native species that is in decline due to the introduced North American signal crayfish. No white clawed crayfish were found within West Hallington Reservoir but three were trapped within the adjacent East Hallington Reservoir. A pied wagtail nest was spotted by eagle-eyed site workers next to the engine of an excavator. The excavator was withdrawn from service until the eggs had hatched and the fledglings left the nest. [caption id="" align="alignnone" width="1200"] Reinstatement of the stone pitching - Courtesy of MMB[/caption] Testing, commissioning & conclusions The siphon is designed to operate above a water level of 152.5m AOD and to self prime above a level of 154.1m AOD (TWL = 155.1m AOD) and so the All Reservoirs Panel Engineer (ARPE) requested that during the testing and commissioning stage, MMB should demonstrate the following: That the siphon can be primed between the water levels 152.5m AOD and 154.1m AOD. That the siphon can self-prime above a water level of 154.1m AOD. That the Full Supply Level of 155.1m AOD can be achieved. The water level rate was restricted to 300mm/week and any seepage through the clay core will be monitored in future via a flow measurement chamber. During operation of the siphon, receiving watercourses and culverts were monitored at a number of locations to ensure scour or carriageway flooding were recorded and the test halted if required. The works were completed within budget (final NEC3 contract value £3.3m, £60k gain pot) and on time. The original compliance date of 31 September 2023 was extended to incorporate obtaining the Section 166 agreement and a new date of 30 June 2024 was agreed with the ARPE. [caption id="" align="alignnone" width="1200"] DN700 siphon pipework during installation - Courtesy of MMB[/caption] Leaving a legacy Northumbrian Water is very keen on creating community projects and “leaving a legacy”. MMB widened the access from the main road and provided three passing places as the access route is used by both residents and members of the fishing club. Looking ahead Northumbrian Water are investigating another 10 reservoir sites that potentially require siphons, and so Mott MacDonald Bentley hope to use the good practice and experience learned at West Hallington Reservoir on other schemes in the future. A Northumbrian Water Engineering Briefing Note for siphon design and construction is also underway, which captures all the learning and good practise and will sit alongside the newly published CIRIA 813 Siphons in Dams: Design, Installation, Operation, Management and Testing.

The River Lyd Pumping Station is consented to abstract up to 40 Mld from its intake source at Lifton, Devon during November through to March, pumping raw water approximately 7km to Roadford Reservoir. The pumping station was last used on a full operational basis during the mid-1990s and the original equipment had remained in a shutdown and non-operational state up until the point of the upgrade works. The existing electrical switchgear was deemed to be life-expired and beyond the state of any possible refurbishment. The primary driver for the scheme and the scope of works was to upgrade and re-commission the pumping station for operational use at full output design capacity. During the course of the capital works project, a temporary works scheme was implemented in order to maximise operational use of the available pump sets while the capital build was in progress. Background The pumping station is configured with six Pleuger-type QN borehole pumpsets supplied by Flowserve Ltd and which had been previously refurbished by the manufacturer in the intervening period, and the pumps were maintained in storage at Roadford Reservoir. Four pumps are sized at 5 Mld and two at 10 Mld, providing for a combination of flows up to 40 Mld. The discharge from the common pump manifold is to the 900mm diameter rising main to Roadford Reservoir operating with a system pressure at 11 bar. At the works, two surge anticipation valves protect the pipeline in the event of failures and resulting critical surge conditions. Downstream of the common pump discharge manifold, and within the section of pipework that forms the washout connection at the river headwall, are two pressure transducers which have been installed to provide high pressure alarms and initiate pump stop in the event of an adverse operating condition and to afford protection to both pumps and also the rising main. From the common discharge, manifold flows leave the site through the existing 900mm rising main and are measured by a new Siemens electromagnetic flow meter installed as part of the refurbishment works. Eel screens Prior to the upgrade and re-commissioning works of the pumping station, a separate contract was undertaken by Galliford Try in 2021 to replace the river eel screens. The scope of works in this respect was to make the connections between each of the eel screens designed and manufactured by Andritz Ltd and a new air-burst cleaning system. The air-burst compressed air system is a self contained package plant designed and built by Quantum Engineering Developments Ltd with its own local control panel and PLC which control the cyclical cleaning of each of the eel screens. Local alarms are initiated at the LCP and key alarms are relayed back to the main plant MCC as required. Duty/standby screw type air compressors are installed, supplying a single air receiver with operating pressure at 9 bar. There are six air lines that connect with its respective screen and the control of air is via electro-pneumatically operated valves installed at the air compressor skid. Flexible 50Nb air hoses are installed in ducts and connect each piped outlet with a connection to the eel screen. Within the pump chamber a piped manifold of manual isolating valves and air hoses has been installed to provide for the connection to each eel screen. [caption id="" align="alignnone" width="1200"] Airburst package plant - Courtesy of Galliford Try[/caption] HV & LV electrical works The scope of HV electrical works required the re-establishment of the HV supply to the site and these works have been undertaken by National Grid to provide a new 1250 kVA supply to their existing substation on the site and inclusive of new interconnecting HV cabling from their primary substation. A new transformer of required capacity has been designed and manufactured by Wilson Power Solutions Ltd under supply to Enerveo who have completed the site HV installation. The LV side of the transformer is connected to a new form 4A Type 3 MCC which has been designed and manufactured by Galliford Try. The build incorporates the six soft starts for each of the existing 190kW and 110kW pumpsets. The incomer is rated at 2000A and busbar 2500A. Phase failure, surge protection, and transformer protection are incorporated within the build. There are common controls section, distribution board feeders, 110V and 24V supplies. Plant control and surveillance is managed by a Schneider Electric PLC and HMI which are built within the C&I section. Water quality monitoring A containerised suite of raw water quality instruments has been installed in accordance with the requirements set out in South West Water’s Technical Standard for Intake Protection & Raw Water Monitoring. The respective quality parameters measured are colour, turbidity, ph/temperature, dissolved oxygen, and ammonia. The sample is drawn from the River Lyd by a pair of duty/standby Grundfos JP sample pumps and which are connected to the river headwall by means of dedicated ducted 25Nb flexible sample pipes. Actuated GF ball valves within the piped discharge local to the pumps allow for the sequencing of the duty/standby changeover, air scour sequence and back wash of the sample lines during the changeover cycle. Flow monitoring to the instruments is by means of inductive type flow meters. The control, monitoring, alarm initiation and operator interface is via a local control panel complete with HMI and PLC. River Lyd Pumping Station: Supply chain: key participants Principal contractor & designer: Galliford Try Pumpsets: Flowserve Ltd Flow meters: Siemens PLCs & HMIs & switchgear: Schneider Electric Eel screens: Andritz Ltd Air-burst compressed air system: Quantum Engineering Developments Ltd Generators: Aggreko UK HV transformer: Wilson Power Solutions Ltd HV installation: Enerveo JP sample pumps: Grundfos Software development & automation: Galliford Try Rising main: Kier Group Instrumentation: IFM Electronic Instrumentation: Partech Instruments Capital works delivery Before any works could be undertaken, significant tree and overgrown vegetation clearance had to be carried out at the entrance to the pumping station and along the lengths of the access paths and tracks that connect with the top of the site and the existing HV substation. GPR, topographical and ecological surveys were undertaken to establish conditions. There then followed a programme of dismantling works to remove the original GRP kiosk housing the 1990s MCC and transformer. The programme of civil works provided for the construction of reinforced concrete bases for the new 1250kVA transformer and air-burst package plant respectively. Installed on these bases are new GRP enclosures that provide the necessary protection for this equipment. A third GRP kiosk has been installed as the enclosure for the new MCC which utilised the original constructed base slab and trench albeit extended for the larger switchgear build. Elevated concrete piers have been constructed for the container housing the raw water quality instruments and with due consideration to the known risk of flooding at the site. The new enclosures required the submission and approval of a planning application. New ducts and drawpits have been installed to provide for the routing of pipework, HV and LV cables. The scope of mechanical installation works principally involved the re-installation of the refurbished Pleuger pumpsets and the associated pipework connections to the existing delivery manifold and rising main; the installation of the new airburst eel screening compressor skid and its hook up requiring a new air distribution system within the pumping chamber to supply each of the individual eel screens. The scope of the electrical installation works has been principally the uprating of the original 1000kVA supply to 1250kVA. This has required two new HV supply cables to be installed from the primary substation to the River Lyd site. A new HV transformer from Wilson Power Solutions Ltd and switchgear from Schneider  Electric has been installed to make the HV connection. The new Form 4 MCC has been designed and built as the replacement switchgear incorporating the most up to date electronic components and compliance with SWW Technical Standards. The software development and automation works has been carried out by Galliford Try. [caption id="" align="alignnone" width="1200"] (left) River water sampling container on flood prevention supports, (middle) Aggreko UK duty, primary assist and secondary assist generators, and (right) Generator flood prevention as design by the design team - Courtesy of Galliford Try[/caption] Temporary works During the period of the capital works build, and with continued falling level in Roadford Reservoir, Galliford Try was asked to put in place a temporary system of operation for the six installed pump sets using standby generators and temporary switchgear. Working with Kier Group, Galliford Try took charge of the works at the pumping station and Kier Group the rising main to Roadford Reservoir, responsible for checking, filling, flushing and pressure testing the pipeline; mindful that the system was last used in 1996. The original remit was to have the temporary plant installed and connected to allow the existing six pumps to operate by the 1 November 2022. All parties achieved their objectives, however South West Water was unable to obtain approval from the Environment Agency (abstraction permit) in the same timescale. This did however provide more time to allow Galliford Try’s capital works team to incorporate process elements of their capital build into the temporary works (flow meter replacement, air-burst compressed air system, telemetry and online operational water quality instruments). This has provided South West Water and the Environment Agency with a more robust pumping arrangement and water quality monitoring regime. Although the pumps and temporary works operation is scheduled to the end of March 2023, there is the possibility of an extension until the end of May 2023 which is being discussed between South West Water and the Environment Agency. Completion At the time of writing (April 2023) the capital works completion has been achieved insofar as it can be until such time as the temporary works operation has finished and the equipment removed off site. Following on from this, final landscaping will be completed along with those works required to complete all permanent connections to enable the pumping station to come back into operation from the beginning of November 2023.

Potters Way, located in the Fengate area of Peterborough, is a recent housing development next to the A1139. The development was built on the grounds of the former Fengate Water Recycling Centre (WRC) which closed in 1988 following the construction of the Flag Fen WRC. In early December 2018, Anglian Water became aware of the collapse of a section of 1500mm diameter concrete sewer pipe in Potters Way when a small hole was found after a customer used a ride-on lawn mower over the area. Temporary repair works were undertaken by the Integrated Operational Solutions (IOS) Alliance - a partnership between Anglian Water, Kier, Barhale and Morrison Utility Services - while a permanent fix could be designed and implemented. Background By the end of December, the IOS Alliance had installed a temporary repair using a vacuum excavator to safely clear the collapsed pipe before using half-pipe and canvas to seal the collapse. The area was also fenced off to prevent pedestrian access and ensure site safety. During this period, Anglian Water received several complaints from customers over the odour created by the collapse. Following meetings with the residents, Anglian Water’s Water Recycling Networks (WRN) team further sealed the excavation and installed carbon filters to the air valves. At the same time, the team repaired holes found in the rising main pipework at the nearby tower. The site was then handed over to the Anglian Water @one Alliance to implement their repair solution with @one partner company Barhale engaged as principal contractor. [caption id="" align="alignnone" width="1200"] Installation of the overhead diversion - Courtesy of @one Alliance[/caption] Finding a solution One of the challenges presented in finding a solution for this project was the high flow rate of the pipework, with modelling of Potters Way showing flow rates of 3,700 litres per second in the event of a 1 in 30-year storm. Downstream of Potters Way, this rises to 4,000 litres per second. To make the matter even more complicated, the pipe featured several significant bends along the affected route that increased the difficulty of finding an adequate solution. An extensive survey of 2.8km of sewer identified 1.79km of concrete sewer pipework ranging in diameter from 1050mm to 1950mm had a condition grade of either 4 or 5. All these pipes were identified as having been subjected to a hydrogen sulphide (H2S) attack which had caused the significant deterioration. The @one Alliance set out to repair an area of the network by covering a key 500m of pipework which serves the majority of Peterborough. Potters Way Sewer Rehabilitation: Supply chain Project delivery: Anglian Water @one Alliance Temporary repairs: Integrated Operational Solutions (IOS) Alliance Principal contractor: Barhale Over pumping: Vanderkamp UK GRP pipe lining: Amiblu Norway AS Lining & manhole repair: OnSite Central Ltd Specialist CCTV Survey: Bright Innovations Group Foam concrete: GS Foam Concrete Diamond cutting: SCS Ltd Cover slabs: FP McCann Ltd Temporary works/shoring: Groundforce Pipe rehabilitation The @one Alliance solutions team opted for a multi-stage solution due to the complex nature of the pipework and the compact area the teams would be working in. In order to repair the sewer, it was decided that a mix of CIPP (cured in place pipe) and GRP (glass reinforced plastic) lining would be used. The majority of the rehabilitation was completed using CIPP lining which allows the lining to be inserted into the shell of the existing, damaged pipework where it is then pressurised and cured in place with ultraviolet (UV) lights. The CIPP relining was split into eight sections covering approximately 360m of the repaired pipeline. At 1375mm in diameter, this installation was the largest diameter CIPP liner that the @one Alliance had ever installed. Six of the eight lengths of CIPP were installed under the A1139. Over pumping In order to fit the CIPP liners, the team utilised an over pumping set up capable of 250 litres per second (l/s). By using bungs at split manholes on the nearby Bourges Boulevard, the team could redirect the flow and use the pumping set up to divert the rest of the flow. The over pumping solution was provided by Vanderkamp UK who had remote monitoring capabilities from the Netherlands and provided the site teams with a mobile app allowing them to see real time data giving them advanced warning of increased flows which would require the removal of the bungs. Without this passive flow management, the over pumping setup would have needed to be able to cope with an excess of 2,000 l/s. The set up was made up of two pipe bridges 350mm in diameter and 5.5m high to allow clearance for high-sided vehicles. GRP lining Alongside the CIPP lining, the team also used GRP lining on a 48m section of 1500mm diameter sewer executing the rehabilitation in live flow conditions of approximately 850 litres per second; the first time the @one Alliance had installed GRP lining in live flow conditions. [caption id="" align="alignnone" width="1200"] (left) Live flow conditions and (right) inserting a new section of Amiblu Norway AS GRP pipe - Courtesy of @one Alliance[/caption] Operating in live flow removed the necessity to install an additional over pumping solution that would have dealt with 95% of Peterborough’s sewage as it combined into one flow towards Flag Fen WRC. In order to commence the GRP lining, the crown of the pipe was removed on a bend and concrete platforms were constructed on either side ensuring a safe working area. A pipe pusher attachment was then used to insert segments upstream and downstream from the bend location. Finally, a prefabricated GRP bend section was installed and connected to straight sections. To safely cut the existing mains the team needed to excavate an area of 6m x 4.5m with a depth of 3.5m. While having to excavate in an urban area is an option the team would have liked to have avoided, the next best solution to the live flow repair would have included installing a temporary pumping station that would have taken up all of Potters Way’s parking and grass area requiring 10 pumps and a 10m x 7m x 7m temporary wet well to complete the required repair. This would have been a major inconvenience for residents and would have seen an increase in the overall cost of the project of 200%.

Amiblu relining pipes to protect sewer networks from H2S attacks - Courtesy of Amiblu Norway AS

Manhole rehabilitation As part of the pre-work checks, it was identified that eleven manholes along the section of pipework required rehabilitation of various levels with the most severely affected requiring structural repair as a result of H2S attacks. Core samples were taken from one manhole which identified that in some places, more than 150mm of concrete had been lost to H2S attacks with no rebar remaining in any of the samples. To repair the manhole, the team used a concrete spray to bring the walls back to their original 250mm thickness, once this had cured a primary and finishing layer were added to ensure full protection against H2S attacks in the future. A new cover slab was also installed after the original was removed to provide access to the manhole, made of precast concrete the slab was also treated for H2S protection. [caption id="" align="alignnone" width="1200"] (left) H2S attack on a manhole and (right) inside a relined section of pipe - Courtesy of @one Alliance[/caption] Challenges Weather provided a significant challenge for the implementation of the solution as the site experienced an unusually heavy rainfall. Flow rate analysis for Flag Fen WRC shows that in the previous five years the average rainfall for the area fell between 35mm and 60mm. August 2020 saw average rainfall of 137mm. Because of the heavy rainfall several weather warnings were issued placing all CIPP lining activities on hold. The impact of the weather was so severe the flow of water increased from its usual 850l/s to 4,000 l/s in just 10 minutes. In order to reduce the risk of flooding outside the Magistrates Court the bungs were deflated, and the flow reverted. Due to the innovative combination of flow diversion and overpumping used in the CIPP lining the impact of the delay was significantly reduced compared to if the team had used the temporary pumping station solution. Rising mains issues During the repair of the sewer the @one Alliance became aware of complaints from the residents regarding the twin rising mains on Potters Way which used to feed into the old Peterborough STW and was diverted into the new gravity sewer discharging into Flag Fen WRC. The primary complaint from customers was the odour produced by the rising mains. The old Peterborough STW was sold for development and the rising mains tower was marked for removal. In early 2022 the @one Alliance returned to Potters Way removing the rising mains and installing a pumping station kiosk removing the odour and significantly reducing the visible profile in the area. Result Anglian Water invested £2.8m into the Potters Way project which will now allow customers across Peterborough to continue to use their taps and flush their toilets without second thought. The relining of the sewer network has ensured the network in the Potters Way area is now protected from H2S attacks for the next 50 years. Colin Handley, Construction Manager said:

“There was fantastic team collaboration between our Tier 2 Supply Chain Partners, the Principal Contractor (Barhale) and the @one Alliance, making it one team delivering the programme. The teams worked tirelessly to monitor the smells and reduce odours, whilst working in open excavations. They purchased additional fans and diverted rising mains to lower H2S and to allow the teams to work safely.”

The water network in the western end of the Thames Valley Supply Area is dominated by local borehole water sources. Over time, population growth coupled with general environmental drivers to reduce reliance on groundwater sources in sensitive chalk stream areas, Thames Water has sought to improve supply resilience and deployable output by linking local sources via trunk mains. This allows movement of water from one area to another as well as to reliably supply the intermediary supply zones. Typically, water from Oxford that is produced at Farmoor Water Treatment Works is transferred via a series of trunk mains to maintain resilient customer supplies to approximately 90,000 people in Swindon and the surrounding supply areas. Background The existing Faringdon Water Booster Station (WBS) to Blunsdon Reservoir transmission system comprises a 700mm diameter asbestos cement pipe and a 900mm diameter glass reinforced plastic (GRP) pipe built in 1987 and 2001 respectively. This transmission system is approximately 15.8km long and has various interconnections between the pipes to provide resilience in service. The Faringdon WBS to Blunsdon Reservoir 900mm GRP main represents one leg of this network. Due to the high frequency of failures, which had a significant impact on Thames Water’s ability to transfer treated water into the Swindon area, work began in AMP6 to replace the highest risk section in the Highworth area and 2.8km was completed, including a crossing of the River Cole. Following the successful replacement in AMP6, and an increased deterioration of the existing 900mm GRP main, the remaining balance of scope (13.7km) was approved for delivery in AMP7. To mitigate the frequency of bursts and the impact of the deteriorating asset on customer supplies, temporary emergency abstraction licences at Baunton WTW and Latton WTW were secured with the Environment Agency to allow the existing GRP main to be operated at a lower duty. Project summary The principal drivers for the project are: To reduce the supply interruption risk to customers in Swindon and the Cotswold area. In a reasonable worst-case scenario, without the current mitigations it could equate to over 14 million minutes. To minimise the risk of customer complaints associated with low pressure and/or no supply. In a reasonable worst-case scenario, without the current mitigations this could equate to over 90,000 properties. To eliminate reliance on groundwater sources under emergency licences to cover the loss of flow during a burst. To reduce reliance on groundwater sources that draw from chalk streams and the River Kennet during high demand and drought conditions. To increase trunk main capacity and transfer rates to accommodate increasing flows for future population growth (principally in the immediate Swindon area). To eliminate the frequent and expensive repair costs of the existing GRP main sections. To restore Thames Water’s trunk main network resilience and bulk transfer capability in this area, which is fundamentally impaired when the Faringdon to Blunsdon main is operating at a reduced duty rating. [caption id="" align="alignnone" width="1200"] Google Maps image showing pipeline route[/caption] Planning and design Pipeline route: Initial design work was completed during AMP6 by Stantec UK as part of the Phase 1 delivery. The proposed route closely follows the existing 700mm asbestos cement and 900mm GRP mains, and there are several advantages to following this existing route: This represents the most direct route between Faringdon WBS and Blunsdon Reservoir thus minimising the overall length of pipework required. It is mainly through farmland and minimises the need to work in residential areas. It minimises impact on landowners. Ease of access for Thames Water through use of existing way leaves Existing information from previous investigations can be utilised. The AMP7 project was awarded to Kier Infrastructure and Overseas Ltd when detailed design of the pipeline route was reviewed and refined, taking account of ecological constraints, requirements from landowners and planned developments along the route. Archaeological mitigation: A programme of archaeological mitigation was undertaken by Wessex Archaeology following consultation with the relevant county archaeological advisors. A mitigation strategy comprised excavation, recording and the strip, map, and sampling. The archaeological excavations formed part of a staged approach consisting of an archaeological desk-based assessment, geophysical surveys, and archaeological evaluations. Through collaboration with the approving authorities, Thames Water adopted targeted route changes to avoid known areas of high archaeological interest. Generally, a small number of finds were found with possibly the most significant being a crouched burial in the Blunsdon section of the pipeline. [caption id="" align="alignnone" width="1200"] Archaeological investigations and (right) crouched burial - Courtesy of Kier Infrastructure and Overseas Ltd[/caption] Pipe material: As part of the design deliverables a technical note was prepared comparing ductile iron, carbon steel and HDPE as the three commercially feasible materials for this diameter range. The recommendation was to adopt HDPE PE100 as the preferred pipe material, using 1200mm OD SDR17 from Aliaxis UK. Pipework used in cross connections, existing utility crossovers, shafts and other special cases was designed using ductile iron supplied by Saint Gobain PAM UK, with mechanically restrained VE joints as required. Furthermore, for the tunnel sections, steel pipework with the E-Joint system was utilised supplied by Noksel España. To ensure asset design life, steel pipework was maximised for the critical tunnel sections with pipe wall thickness specified at 10mm, which was greater than Thames Water’s asset standard of 6mm. Based on the pH levels of the water the pipe would be conveying, a far superior asset design life of 100+ years could be theoretically achieved. Environmental impact assessment (EIA): During the initial stages of the project, several desktop and detailed environment, archaeological and third-party assessments and reports were compiled. This highlighted areas where further surveys and investigations were later completed ahead of an Environmental Impact Assessment Screening Opinion being submitted to the relevant councils for review. A full EIA was requested but this was, however, successfully challenged with the Secretary of State who did not consider the environmental impact would be of a magnitude necessary to suggest a scheme of this scale would result in significant environmental effects, which would exceptionally necessitate an environmental statement. This successful challenge still obligated Thames Water to work closely with the local approving authorities to deliver a comprehensive programme of environment and archaeological mitigation works for the route. [caption id="" align="alignnone" width="1200"] Pipes laid along route - Courtesy of Kier Infrastructure and Overseas Ltd[/caption] Faringdon to Blunsdon Trunk Main Phase 2: Supply chain - key participants Project delivery: Kier Infrastructure and Overseas Ltd Designers & specialist consultants: WSP Sahara survey: Water Research Centre Ltd Archaeological investigations: Wessex Archaeology Civil Engineering Contractor: CPC Civils Civil Engineering Contractor: OCC Services Ltd Trenchless crossings: HB Tunnelling Limited Shoring/temporary works: GroundShore Ltd Tunnel boring machine: Herrenknecht Precast jacking pipes: FP McCann HDPE PE100 pipe: Aliaxis UK Ductile iron pipes: Saint Gobain PAM UK Steel pipework: Noksel España Tunnel roller spacers: FT Pipeline Systems Pipe fittings, bends, tees & collars: George Green (Keighley) Ltd Pipe fittings: Wolseley Pipe fittings: Electrosteel Castings (UK) Ltd Pipe fittings: PTS (SA) Limited Valves: AVK UK Ltd Welding: Fabricon Ltd Welding: PTS Group Butt fusion welding machine: McElroy Manufacturing Independent weld inspector: Technical Innovation Servis Ltd Temporary fencing & gates: RF Gardiners Ltd Construction The project was classified as a ‘high consequence project’ requiring an enhanced level of quality assurance. To achieve this, several measures were implemented. As part of this strategy, the delivery contractor Kier Infrastructure and Overseas Ltd was briefed to deliver the project in phases to tactically reduce Thames Water’s operational risk until the project was fully commissioned. The project brief also included decommissioning of the existing fragile 900mm GRP which will be safely decommissioned following commissioning of the new DN1200 pipeline. The contractor will make allowances to ensure that the existing 900mm GRP main can be slip-lined in the future for additional resilience. [caption id="" align="alignnone" width="1200"] (left) Drive shaft, (middle) tunnel pipe insertion and (right) the completed tunnel - Courtesy of Kier Infrastructure and Overseas Ltd[/caption] Tunnelling: Open cut techniques were the predominant pipe installation methodologies and were undertaken by CPC Civils and OCC Services Ltd. However, several trenchless crossings were required for the major roads and rivers crossed by the pipeline route. The relatively straight forward digger shield tunnel boring machine was the predominant method used for trenchless crossings, including Bydemill Brook and the A361. The crossing of the B4019 proved more challenging however, when hard rock was discovered. This was because of a last-minute change in the location of the micro-tunnel shaft to avoid a new attenuation pond being built by a developer in the immediate area. Following a review of the new geotechnical investigation completed, it was agreed that the previous digger shield tunnel boring machine was not suitable to overcome the hard rock. Instead, the more robust variable density tunnel boring machine was employed with a specialist drill head brought in from Herrenknecht in Germany to cope with the density of the rock. Although the deployment of this complex machine took four weeks to set-up, the 180m long, 1.5m diameter tunnel was constructed in no time at all and was successfully completed in just over eight weeks. The trenchless crossings were undertaken by HB Tunnelling Limited. Pipe welding: An automatic butt fusion welding machine was utilised on the project to enable the joints to be made in what was an industry first. The machine from McElroy Manufacturing was shipped from the United States for the project, and enabled butt fusion joints to made up to 1200mm in diameter; a first of its kind in Europe. The automatic nature of the machine enabled far higher quality welds to be made and on a consistent basis as the human element of checking temperatures, raising of the welding plates etc. was eliminated. [caption id="" align="alignnone" width="1200"] Pipe welding operation and (inset) McElroy Manufacturing welding machine - Courtesy of Kier Infrastructure and Overseas Ltd[/caption] Welding work was undertaken by Fabricon Ltd and PTS Group with Technical Innovation Servis Ltd employed as an independent weld inspector to provide an additional level of assurance on the quality of the butt fusion joints made on the 1200mm OD PE100 SDR17 pipework. Commissioning Due to the large volume of water involved in commissioning each section of the new pipeline and significant flow rates required to achieve water quality standards, flushing lagoons were constructed to allow the safe and controlled disposal of the flushing water. Working in the community/customer communications Following disruption to landowners over many years due to frequent bursts on the existing GRP pipe, all contractors have been fully focused on maintaining and improving relationships with all landowners. At the time of writing (May 2023), Kier Infrastructure and Overseas Ltd and CPC Civils have worked very successfully with all landowners along the new pipeline route developing great working relationships. This has been demonstrated on a few occasions particular during the funeral of one landowner who CPC Civils had developed a great relationship with, when works were stopped so all workers could pay their respects. [caption id="" align="alignnone" width="1200"] (left) Funeral cortege - Courtesy of CPC Civils, and (right) Salvation Army Christmas present appeal 2022 - Courtesy of Kier Infrastructure and Overseas Ltd[/caption] Kier have also worked well with local councils donating materials for community initiatives, with CPC Civils also donating two portable defibrillators to support local campaigns, as well as supporting a Salvation Army present appeal on the run into Christmas 2022 to support families who would otherwise be unable to afford gifts for their children. The project has also given the opportunity to work with the royal agricultural university and bring students to site to understand the ecological and environmental impact and considerations on a project of this scale, as well as visiting their workshops to build owl boxes to be installed along the route of the pipeline. Summary Design of the £45m Faringdon to Blunsdon Pipeline Project commenced in November 2020 followed by a construction start in May 2021. [caption id="" align="alignnone" width="1200"] Flushing lagoons - Courtesy of Kier Infrastructure and Overseas Ltd[/caption] Commissioning and beneficial use of the pipeline is expected in November 2023 with all site works being completed by August 2024. This will complete replacement of the 15.8km transmission system providing resilience to supplies to help meet future supply and demand requirements.