Supply Chain - Project Planning & Surveying - Geospatial Surveys

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.

St Augustines Road is a busy thoroughfare in Chesterfield linking the town to Matlock and the south-eastern edge of the Peak District. Lying within the Yorkshire Water (YW) waste catchment area, the road is steep in its nature with gradients often exceeding 7%. Due to the local hydraulic catchment and topography, during heavy rainfall events flooding occurred at the road’s intersection with Derby Road (A6). The flooding lifted manhole covers from their frames which caused significant damage to the highway. It also caused internal and external damage to the surrounding properties. To combat this, mitigation was carried out by Yorkshire Water and Chesterfield Borough Council (CBC), including the implementation of mitigation measures such as non-return air bricks and flood gates, however, this had limited success. CBC also commissioned the construction of a detention basin to the rear of the flooding properties; but again with limited success. Hydraulic study As a result of the mitigation’s limited success, a hydraulic study was commissioned by Yorkshire Water. This confirmed the root cause of the flooding was hydraulic overloading of both the foul and surface water sewers. A notional solution was developed by Yorkshire Water which included the upsizing of these sewers, with some form of temporary storage for the foul system to retain flows in a rainfall event. Later iterations of the hydraulic model revealed that improvements to the surface water network would in fact also reduce the frequency of flooding on the foul water network due to interactions between the two systems during storm conditions. In light of this information, in May 2021 Yorkshire Water secured funding to implement a series of significant improvements on St Augustines Road. Preferred solution The preferred solution included the construction of a new outfall into the River Rother and the transfer of all flows from the surface water sewer in Derby Road. This would provide a much greater flooding resilience in the existing system. The existing 225mm surface water sewer was to be upsized to Ø750mm along its 320m length. It would then be diverted via a tunnel underneath Derby Road into the wetland area immediately adjacent into the River Rother. Here, a new outfall would be constructed to discharge the surface water sewer into the river network. [caption id="" align="alignnone" width="1200"] (left) The preferred option and (right) flooding on St Augustines Road - Courtesy of Galliford Try[/caption] Constraints and engineering challenges The preferred solution progressed to detailed design with several technical challenges to be overcome. Several of these challenges were exacerbated by the need to construct the outfall into the River Rother outside of the salmonoid spawning season. An Environment Agency (EA) bespoke Flood Risk Assessment Permit, (FRAP) was required to construct the outfall and all in-channel activities were required to be undertaken before 1 October 2021 in order to mitigate the impact on any spawning salmon. A significant flow rate of up to 0.89m3/s would be discharged into the river during storm events and river scour was a concern. In order to combat the scour on the riverbed and riverbanks, there was a requirement to reduce the velocity of the flow before it interacted with the River Rother, causing excessive turbulence. To achieve this, box culverts were selected due their unique cross section and significant channel width. This slowed velocities down to near 1m/s, which is widely regarded to have negligible effects on turbulence and thus reducing scour. The headwall was also designed to allow flows to enter the River Rother at a 45° angle, as per EA Standard Rules SR2015 guidelines, further reducing the risk of scour on the opposite riverbank and riverbed. Outfall design This design however did not come without complications, such as the need to carry out the structural design, build and installation of a bespoke outfall within a few months. BSP Consulting was commissioned to carry out the structural design of the outfall which was to be precast, reducing the need for in situ concrete handling adjacent to the sensitive receptor. Off-site build (OSB) also reduced the construction programme and allowed the headwall to be manufactured concurrently within the determination period of the FRAP. [caption id="" align="alignnone" width="1200"] Outfall under construction - Courtesy of Galliford Try[/caption] Poor ground and underfoot conditions adjacent to the River Rother proved too risky and problematic for traditional mobile crane lifts, so all lifts of the precast sections were to be undertaken with a tracked excavator. This further constrained the design and restricted the maximum mass of each section to 13 tonnes. Consequently, in its final iteration the precast headwall was designed in two sections and was combined with an in situ toe and infill slab/wall which completed the structural design. Design During the design stages, extensive ground investigation was carried out. This identified water bearing sand and gravel strata adjacent to the river which transitioned to mudstones and clays towards St Augustines Road. It was this change in strata which posed a significant challenge for the no-dig section of the work beneath Derby Road. This section of work was critical as it linked the outfall to the upsizing work on St Augustines Road. Discussions were held with Active Tunnelling Ltd who proposed the use of the guided auger bore technique to install the sewer in this transitional strata. Although initially designed as a 750mm diameter sewer, this was reduced to 600mm which was the maximum diameter which could be accommodated by the tunnelling contractors. Hydraulic modelling was undertaken by RES Environmental to confirm the viability of this proposal and in order to compensate for this localised throttling, the pipeline had to be upsized locally to 900mm immediately upstream of the tunnel. The alignment of the tunnel was severely limited due to proximity of existing buildings on Derby Road. BSP Consulting was again called into action as pre-condition surveys and settlement calculations were commissioned in order to understand the impact of the tunnelling works on these at-risk properties. [caption id="" align="alignnone" width="1200"] (left) Installation of drive pit on St Augustines Road, (middle) guided auger bore rig, and (right) the transition between 600mm and culverts - Courtesy of Galliford Try[/caption] Settlement calculations were undertaken using the “Guide to best practice for the installation of pipe jacks and microtunnels technique” and a predicted settlement of <3mm was deemed to be acceptable. The pre-condition surveys highlighted only minor cosmetic issues and were used as reference to the state of repair of the properties prior to construction work commencing. The majority of the civil design was undertaken in house. This element included a design coordination role combining and processing the information received from the consultants and stakeholders. An example of the numerous stakeholders which were consulted is that of the Coal Authority. Initial searches indicated the presence of historical coal workings. More detail was sought and records indicated the presence of an adit within 20m of the proposed pipeline. A coal permit was sought from the Coal Authority and the design progressed whilst this was processed. St Augustines Road (Chesterfield) Flood Alleviation: Supply chain: key participants Principal contractor & civils design: Galliford Try Temporary works & headwall design: BSP Consulting Hydraulic modelling: RES Environmental Ltd Ecological consultants: Middlemarch Environmental Traffic management: Amberon Traffic Management GRP & utility mapping: Cloud Conversion Ground investigation: Grange Geo Consulting Ltd Pipelaying & outfall construction: Arthur Civil Engineering Trenchless installation: Active Tunnelling Ltd Cofferdam design & supply: National Trench Safety UK ‘EndSafe’ safety barrier: Groundforce Shorco Cofferdam installation: Ivor King The Piling People Dewatering: Alba De-Watering Services Ltd Precast concrete: Bonna Sabla CCTV, CIPP & cleansing: CPS Drainage Solutions Handrailing & grille design: Galliford Try (Fabrications) Silt curtain: Murlac Land and Marine Environmental Solutions Pumping: Selwood Ltd Ridgistorm pipes: Polypipe Civils Pipe & flap valve supplier: Keyline Civils Specialists Landscaping & site clearance: Landscape Maintenance Services Ltd Reinstatement of traffic signals & street furniture: Swarco Aggregates & muck away: JC Balls & Sons Brickwork: Derwent Joinery & Construction Gates & fencing: SFC (Midlands) Limited Surfacing: BDS (Yorkshire) Ltd [caption id="" align="alignnone" width="1200"] Service detection - Courtesy of Galliford Try[/caption] Installation The Environment Agency granted the FRAP on 13 August 2021, and the detailed design was finalised and submitted to Yorkshire Water’s technical approval committee on 16 August 2021. Work began on site a few days later, leaving just six weeks to construct the headwall and cease all in-channel activities as per the conditions of the FRAP. Work commenced immediately on the enabling works, with particular attention paid to the temporary works. Haul road To provide drainage to the waterlogged land adjacent to the River Rother, a land drainage scheme was commissioned, designed and installed by Lincolnshire Drainage. This provided a more suitable foundation on which to install the haul road and working laydown areas. The haul road was designed by BSP Consulting and was of substantial construction given the underlying strata, at 700mm thickness with geotextile layers to improve longevity. Ground dewatering After the installation of the haul road, wellpoint dewatering was installed around the outfall area and along the proposed culvert alignment. The dewatering was installed by Alba De-Watering Services Ltd at 1.5m centres. However, due to the underlying mudstone, each well had to be pre-augered and was then installed using the more traditional spout method to ensure that a reasonable well depth was achieved to adequately dewater the working area. A silt curtain was supplied and installed by Murlac Land and Marine Environmental Solutions prior to the channel works to minimise silt and sediment damage downstream from the works. It proved to be very effective during the cofferdam installation. [caption id="" align="alignnone" width="1200"] Cofferdam and silt curtain - Courtesy of Galliford Try[/caption] Cofferdam A cofferdam was required to retain the River Rother and this was designed and supplied by National Trench Safety UK and installed by the primary subcontractor Arthur Civil Engineering. The cofferdam was unique in design in that it utilised Larsson piles in a trapezium shape (plan) to minimise over-dig yet still accommodate the headwall and first culvert. The cofferdam was installed by Ivor King The Piling People using a 35t excavator with a Movax side grip pile driver attachment. The cofferdam was effective but 4” end suction pumps supplied by Selwood Ltd were still required to maintain the cofferdam and keep water levels low. Headwall installation Once the cofferdam was watertight, the headwall toe was cast in situ, after which the precast headwall arrived in two sections as planned. It was lifted into position by Arthur Civil Engineering using a 50t tracked excavator. An administrative issue led to the need to negotiate a 2-week FRAP extension with the EA and the headwall was completed and the cofferdam removed by 14 October in accordance with the conditions of the revised FRAP. Pipeline works Construction works on the remainder of the project continued in March 2022. A temporary one-way system was implemented to provide a safe working area to install the remainder of the pipeline with open cut works commencing on 14 March. The open cut works progressed steadily with over 100 services safely crossed. The later spring and summer months provided excellent conditions for online sewer relay with drought-like conditions, culminating in hosepipe bans for the majority of the UK. [caption id="" align="alignnone" width="1200"] Open cut pipelaying - Courtesy of Galliford Try[/caption] Prior to the tunnelling works commencing, concern was raised over the proximity of the tunnel as it crossed under a 225mm foul water sewer in Derby Road. With a clearance of just 300mm, the existing foul sewer was inspected by CPS Drainage Solutions using CCTV and a precautionary 5m cured-in-place patch liner was installed to strengthen the sewer prior to the guided auger bore operation. No-dig works commenced in early June and progressed well without incident and were completed towards the end of the summer. No settlement was detected during the installation and no visual deformations were reported from the nearby structures. Open cut works continued late into the summer with flooding benefits delivered by 5 October. Significant rainfall events have since occurred and the feedback from residents previously affected by the flooding has been positive. Off-site build Off-site build was utilised heavily without which it would not have possible to abide by the conditions set in the FRAP and achieve the tight programme when constructing the outfall into the River Rother. The headwall and culvert manhole cover slabs were precast by Galliford Try off site and the hand railing and grille were fabricated by Galliford Try (Fabrications). The flap-valve was fabricated off-site by Keyline Civils Specialists. [caption id="" align="alignnone" width="1200"] 900mm Ridgistorm pipe from Polypipe Civils ready for installation - Courtesy of Galliford Try[/caption] Public engagement & community impact Throughout the project customer engagement was a priority for Galliford Try and Yorkshire Water. Although COVID-19 curtailed some of the engagement meetings which were planned at the start of the project, regular communication with residents of St Augustines Road and surrounding area took place. A significant quantity of the communication was made to the local residents Facebook group, which provided timely and accurate updates on progress. Traditional letters were also posted as back up and for those who didn’t have access to Yorkshire Water’s online updates. Towards the end of the project volunteers from Galliford Try and Yorkshire Water spent a day helping out at the local food bank on St Augustines Road and made a donation of £500 to assist with their ongoing charitable cause. Project success The project is considered huge a success for Galliford Try and is the largest single project completed on the Infrastructure Framework for Yorkshire Water within the AMP7 period.

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.

Northumbrian Water’s Ovingham Raw Water Pumping Station (RWPS) is an abstraction station located on the north bank of the River Tyne in South Northumberland between the towns of Wylam and Ovingham. The station provides raw water from the River Tyne to Horsley Water Treatment Works (WTW) and the Great Southern Reservoir at Whittle Dene WTW. Treated water is then pumped to Birney Hill Reservoir and supplies the City of Newcastle upon Tyne and Tyneside with a population in excess of 800,000. Background There are two delivery mains to Horsley WTW (eastern and western mains), and the pumping station currently contains six pumps (four fixed speed Pleuger pumps and two pumps on variable speed drives). In the recent years these pumps have suffered multiple failures which puts at risk the supply of raw water to the WTW. A feasibility report completed in March 2016 stated that the root cause of historical mechanical failures of the existing pumps is a large volume of silt being carried over into the pump bays when the river is in flood. There are also operational and maintenance issues around the current high voltage inverters and drives. Northumbrian Water Group (NWG) appointed Mott MacDonald Bentley (MMB) to investigate viable options for pump replacement in 2018 and the pump options returned by suppliers were for submersible pumps, submersible borehole pumps, axially split casing pumps, and vertical turbine pumps. MMB and NWG agreed that vertical turbine pumps (VTPs) were the most appropriate pump option for the site and the pumping station was designed to the following duty requirements: Deliver 110.7 MLD (1280 l/s) with a standby pump available. Deliver 154.7 MLD (1791 l/s) with all pumps running, including the standby pumps. Be capable of a minimum station flow of 40 MLD (462 l/s). Be capable of feeding Horsley and Whittle Dene simultaneously. Provide the full range of flows between these figures, whether the river is at LWL, HWL, or anywhere in between, and irrespective of whether delivering up the east main, the west main or both. Be most efficient at 106 MLD (1226 l/s). Following a tender process Bedford Pumps Ltd were chosen to supply the new VTPs. [caption id="" align="alignnone" width="1200"] Ovingham RWPS - Courtesy of MMB[/caption] Scope of the works The replacement of two existing variable speed pumps with a duty of 384 l/s with two Bedford Pumps VTPs c/w 680kW IP 68 motors capable of pumping 452 l/s and minimum solids handling capacity of 25mm to improve the pumping and solids handling capability of the station. The installation of two floor-mounted high efficiency 3.3kV 680kW drives air cooled variable speed drives and a new PLC control system. Associated heating, ventilation and air conditioning (HVAC), steel support beams, platforms and electrical/instrumentation works. Ovingham RWPS: Supply chain - key participants Client: Northumbrian Water Construction delivery partners: MMB Hydraulic modelling: Mott MacDonald Topographic surveys: Atlantic Geomatics Geotechnical & environment Investigation: Dunelm Geotechnical & Environmental Ltd Vertical turbine pumps: Bedford Pumps Ltd Electrical installation: Intelect (UK) Ltd Local control panels: Blackburn Starling Ltd Systems integration: IDEC Technical Services VSD design & installation: Quantum Controls VSD construction: Schneider Electric Metalwork: JHT Fabrications Kiosks: Morgan Marine Surge system integration: Quantum Engineering Developments Ltd HV Cabling: Integrated Utility Services Pump refurbishment: Fluid Sealing & Engineering Ltd [caption id="" align="alignnone" width="1200"] Hydraulic model schematic extract from Ovingham RWPS Refurbishment Technical Note - Courtesy of MMB[/caption] Detailed design and engineering challenges Hydraulic analysis: A hydraulic model of the delivery mains (eastern and western mains) was built in Deltares WANDA v4.5 to calculate the steady state and transient pressures for a number of different operating scenarios. The maximum operation flows are 165 MLD (eastern main) and 180 MLD (western main). The subsequent technical note recommended the following: Ten existing air valves should be refurbished and four new air valves should be installed to the eastern and western main (completed). The 35.98m3 surge vessel on the eastern main should be replaced (future works). A surge vessel should be installed on the western main (completed). Fast acting double plate non-return valves should be installed on the pump outlet pipes (future works). CFD modelling: Computational fluid dynamics (CFD) was carried out to assess the most suitable wet well location to install the VTPs to minimise potential adverse hydraulic effects that could be induced by the joint operation of the VTP and Pleuger pumps. The modelling report recommended that the VTPs should be installed in wet wells No. 3 and 4. [caption id="" align="alignnone" width="1200"] Extract from Ovingham RWPS CFD modelling report - Courtesy of MMB[/caption] Cooling water: The motors installed on the new pumps needed to be IP68 due to the high likelihood that the RWPS would flood up to roof level, therefore fan-cooled motors were not suitable. The motors were supplied with a helical design cooling water jacket which was extensively tested in the motor supplier’s works. A number of options were considered to provide cooling water to the VTPs: Automatic changeover duplex strainers using rising main pressure. Potable water closed loop or ‘once through’ systems. Duty/standby automatic flushing filters. Duty automatic flushing filter with static filter standby. Due to the lack of spare low voltage capacity within the station and the lack of a nearby potable water supply Option 2 was ruled out. Option 3 was discounted due to lack of space but will probably be installed in the future when MMB complete the design of new eel screens at the site. Option 4 was discounted due to the amount of maintenance intervention. Option 1 was therefore designed and installed with automatic switch over between baskets on high pressure drop to enable a basket to be cleaned while the pump is in service. A pressure reducing valve was required to reduce the pressure from 10 bar down to 5 bar and this fitting has experienced pressure drops due to leaf debris passing through the inlet screens and so the layout will be modified. Electrical and instrumentation works: This element of the works included: Design, supply and installation of two off high efficiency, air cooled 3.3kV 680kW variable speed drives. This involved the de-commissioning and removal of the existing drives. Design and implementation of modifications to the existing 3.3kV Switchboard to allow the new VSDs to interface with the control circuit within the switchboard. Upgraded ventilation to the MV switch room to ensure the new VSDs operate at a suitable temperature. Bespoke local instrumentation/monitoring panels for the new pumps. Rather than adopt the standard panel offered by Bedford Pumps, bespoke panels were designed to integrate both the pump instrumentation and external instrumentation. A new PLC and remote I/O panel were installed to accommodate all of the new I/O associated with the systems being installed. Fibre optic cabling was employed to reduce long lengths of traditional cabling being installed. Systems Integration at site level and full SCADA integration at Horsley to provide the client with local and remote operation. [caption id="" align="alignnone" width="1200"] Vertical turbine pumps from Bedford Pumps - Courtesy of MMB[/caption] Heating ventilation air conditioning (HVAC): Heat gain within the building due to pumps, MCCs, screen motors etc. was modelled to ensure that during the summer the temperature within the building did not exceed 40° C when the external temperature was 30°C and during the winter the temperature within the building exceeded 5°C when the external air temperature was -5°C. Side wall mounted LPCB SR4 security rated aluminium louvres with a 30% free area were specified to the east and west of the building along with a 370W fan to extract warm air. Noise assessment: A pre-works noise survey was carried out to give a base line. The subsequent report found that plant noise breaking out of the station was low and so recommended that the design target noise levels for the replacement plant should be to achieve the same output noise level. Achieving these noise levels would ensure the adjacent properties would not be detrimentally affected. Construction Site works commenced March 2021 and ran through until October 2022. The client insisted that as the pumping station was a key operational asset it must stay operational throughout the works and so a big challenge was to complete the works whilst providing critical raw water supplies up to Horsley WTW. The pumping station which is situated in a rural location in Northumberland brought its own logistical challenges. Site staff had to consider that any plant used for lifting operations could be demobilized and moved from site prior to a flood event at short notice. Access to the pumps was via six large openings in the roof and covered by heavy concrete slabs. All lifts were done ‘blind’ and planned to precision to ensure everything ran smoothly with some complex lifts carried out. An adjacent HV building supplied power to the pumping station and required the installation of new VSDs. An environmental survey confirmed the presence of bats and so site staff ensured a qualified ecologist was on hand to make sure the bats and their roosting spots were not disturbed. The works were monitored and carried out during selective working hours. Following the successful completion of the works the ecologist confirmed the bats had not been affected. [caption id="" align="alignnone" width="1200"] Ovingham RWPS east elevation - Courtesy of MMB[/caption] Customer NWG are very keen on community projects and ‘leaving a legacy’. MMB carried out works to refurbish park benches at Wylam Village and to refurbish the sports pavilion at Ovingham as a thank you to the local community for any disruption during the works. Looking ahead MMB were asked to design and construct a new surge vessel for the western main. This work was completed in September 2022 alongside the VTP works. New travelling band screens compliant with The Eels (England and Wales) Regulations 2009 are also required and MMB are currently at the design stage with a view to starting on site May 2023. New non return valves (NRVs) and replacement of the eastern main surge vessel is also expected to start in 2023.