Supply Chain - Asset Maintenance & Rehabilitation - Refurbishment

Tunstall Reservoir is located approximately 5km to the north of Wolsingham, in County Durham. It is an impounding reservoir retained by an earth filled embankment with a central clay core. The dam is approximately 25m high and 300m long. The reservoir was previously used to feed a water treatment works located at the toe of the dam; which is now decommissioned. The reservoir is now used for amenity purposes and to provide environmental compensation flows to the downstream valley. Following a Statutory Inspection under Section 10 of the Reservoirs Act, a number of measures in the interest of safety were recommended by the Inspecting Engineer in order to ensure the safety of the dam.

Section 10 of the Reservoirs Act

Following a Statutory Inspection under Section 10 of the Reservoirs Act, a number of measures in the interest of safety were recommended by the Inspecting Engineer in order to ensure the safety of the dam. These recommendations involved the following:

• Recommissioning the existing siphon that used to feed the works and was no longer in use had to be intercepted and provided with a new route in order to provide additional drawdown capacity to the reservoir.
• Repairs to the lower part of the spillway where the existing blocks were damaged.
• Filling an existing tunnel within the dam structure.

[caption id="attachment_18531" align="alignnone" width="1200"] (left) Condition of the spillway blocks prior to the works and (right) new concrete slab with stainless steel protection to the joint - Courtesy of Esh-Stantec[/caption]

Siphon re-commissioning

Various options were considered at the concept stage in order to restore the use of an existing siphon that was abandoned in the early 2000s when the treatment works were decommissioned. The preferred option involved the following:

1. A siphon discharge chamber to break the siphonic effect. This was decided given the uncertainty about the existing system and the significant difference in levels in the downstream leg. Thus, the water would flow by gravity between the chamber and the outfall. This discharge chamber also functions as a thrust block to restrain the thrust acting on the new gate valve that has been installed immediately upstream of the chamber.
2. The use of the existing settlement tanks to retain the water and aid to the settlement of suspended solids. A penstock chamber has been provided between the tank and the new discharge point to retain the water for a day before it is discharged into Waskerley Beck once the majority of the sediment has settled.
3. Routing the new pipework away from the areas of the embankment that present the most valuable Waxcap habitats. Waxcap mushrooms are rare as they are restricted to grassed areas that are not grazed, and are locally protected in Durham.

[caption id="attachment_18533" align="alignnone" width="1200"] Tunstall Reservoir dam - Courtesy of Esh-Stantec[/caption]

Spillway repairs

The original Victorian spillway structure is formed by sandstone blocks bedded in concrete. However, the Inspecting Engineer identified that the majority of the blocks in the lower part of the spillway presented signs of wear and tear and needed replacement.

The proposed solution consists of four new reinforced concrete slabs that have been placed over the existing spillway, except the most upstream slab where blocks had to be removed to tie-in with the existing structure and avoid a step. An expansion joint was necessary in the centre of the new slabs. The flexible sealant in this joint has been covered by a stainless steel plate that has been designed to protect the sealant from the predicted high velocities expected in the flows and reduce the maintenance requirements.

A number of groundwater relief drains have also been incorporated into the design in order to capture the emerging groundwater at the lower part of the spillway and both reduce the hydraulic load on the new slabs and improve the long-term reliability of both the new concrete and the remaining sandstone blocks. These discharge to a new headwall in the bank downstream of the end of the spillway.

[caption id="attachment_18535" align="alignnone" width="1200"] Tunstall Reservoir spillway - Courtesy of Esh-Stantec[/caption]

Tunnel infill works

When the dam embankment at Tunstall was completed and the filling of the reservoir began, significant leakage was observed through the eastern abutment. A concrete cut-off wall extending into the hillside was constructed in 1879 which significantly reduced the leakage rate. Nevertheless, as some leakage continued, a tunnel and shaft were constructed downstream of the cut-off wall, and an 18-inch cast iron diameter pipe was installed inside the tunnel to capture the leakage and convey it to the treatment works.

Following the Section 10 inspection of the dam in February 2021, a number of Measures in the Interest of Safety (MITIOS) were raised recommending works to address the leakage and the stability of the tunnel. One of these IOS measures recommended to fill the tunnel whilst providing some drainage, as a result of the concerns about its structural integrity and the potential risk to the integrity of the dam embankment and the spillway in the event of a collapse of the tunnel.

The project team scoped and contracted a ground investigation (GI) in Autumn 2022 to investigate the leakage paths into these tunnels.

Based on the findings of the GI and the review of the reservoir levels, it was concluded that the cut off wall is in good condition and that the main flow path goes around the concrete cut off wall. There is also a strong correlation between reservoir levels and the recorded flows, which decrease significantly when the levels are 6 m below the top water level (TWL). This was observed again during the construction works, as the water level was kept 6 m below the TWL for health and safety reasons while there was work ongoing in the tunnel and the spillway.

[caption id="attachment_18544" align="alignnone" width="1200"] (left) View in the unlined section of the tunnel (notice the beams across the soffit) and (right) view of pipe inlet and partial headwall (notice standing water on the invert) - Courtesy of Esh-Stantec and CC Informatics[/caption] Various options were considered during the Concept stage. The option of not filling the tunnel was disregarded as it would not eliminate the potential risk to the integrity of the dam embankment and spillway channel. Filling the entire extent of the tunnel was considered, however it was not preferred due to the significant constraints associated with it. These constraints include the difficult access and requirement to work in a confined space, potential land ownership issues, the presence of a SSSI immediately to the east of the abutment, and the increasing depth to the tunnel as it continues beyond the spillway. For all of these reasons, it was agreed with that filling the extent of tunnel beneath the dam and spillway would be sufficient as that would eliminate the risk to these structures.

Three possible fill materials were considered:

1. Cement grout was discounted due to concerns of potential pollution as a low viscosity mix would be likely to mix with groundwater and filter through the rock, causing a pollution incident.
2. Foamed concrete was discounted as a result of the potential constraints to place it at the furthest point inside the tunnel, and the remote location of the site and access within the site would further complicate the timely delivery of concrete.
3. Expanding geopolymer foam was selected as the preferred material as it reduced the risks associated with grout and foamed concrete; and it had successfully been used by Esh-Stantec in the delivery of other projects.

The expanding geopolymer foam was deemed to be more cost-effective than the alternatives as it offered significant savings to the installation process, because:

• It avoided the risk of pollution and therefore any mitigation works to stop grout leakage;
• Simple installation from a mobile compound, avoiding the need for complex plant and equipment;
• Geopolymer mix materials delivered to site in barrels, allowing for easy storage and transport within the site.
• Installation from the surface via boreholes every 10m along the line of the tunnel.
• Lower carbon footprint that cement based alternatives.

[caption id="attachment_18545" align="alignnone" width="1200"] (left) View of the geopolymer in the tunnel, and (right) view of the pea gravel stop end - Courtesy of Esh-Stantec and CC Informatics[/caption]

The filling was undertaken via a number of injection holes that were drilled from the surface at 10 metre intervals, and expanding geopolymer was injected via these injection points. The progress on site was as follows:

1. A pre-drilling survey took place to confirm the condition of the pipe in the tunnel ahead of the works.
2. Eleven injection holes were drilled along the dam embankment and across the spillway.
3. Prior to the injection, after the drilling had been completed, high resolution cameras were used in each injection hole and a drone survey was carried out to confirm that there was no damage caused to the pipe and that the expanding geopolymer would not enter the pipe.
4. Pea gravel was introduced through the final injection point in order to create a mound that would stop the advance of the geopolymer and prevent it from blocking the pipe. The use of the gravel mound avoided the need to carry out works inside the tunnel with the associated risks of working in the confined space.
5. Once the project team was satisfied that the drilling had not cause any damage to the pipe, the injection began, advancing at 10 metres per day on average.

[caption id="attachment_18534" align="alignnone" width="1200"] Overview of the siphon diversion route in preparation for the works - Courtesy of Esh-Stantec[/caption]

Tunstall Reservoir MITIOS: Supply chain - key participants

• Principal designer & contractor: Esh-Stantec
  • Esh Group
  • Stantec UK
• Geopolymer injection subcontractor: Geobear Ltd
• High resolution cameras & drone survey: CC Informatics
• Confined space entry specialist: MRS Training & Rescue
• Ground investigation: Ian Farmer Associates
• Topographical survey & laser scan of tunnel: Academy Geomatics Ltd
• Pipework modifications: UTS Engineering
• Steel fabrications: JHT Fabrications Ltd

Conclusion

The contract has been delivered by Esh-Stantec and the recommendations in the interest of safety made by the Inspecting Engineer have now been addressed. The siphon will provide additional drawdown capacity to the reservoir in the event of an emergency, the damaged part of the spillway has been repaired to a satisfactory standard, and the potential risk of collapse of the tunnel has been removed.

Anglian Water’s Toplers Hill Water Tower is situated just off the A1, south of Biggleswade, Bedfordshire, on a site which includes both the water tower and a water reservoir. The tower was constructed in June 1934 and its condition has started to deteriorate with age. Following Anglian Water’s internal inspection of the water tower, areas of concern were identified regarding the roof, internal coatings and some of the access ladders, which would require replacement or refurbishment before the tower could be returned back to service without compromising water quality to customers.

Issues

The deterioration of the water tower was clearly identifiable, with there being several leaks in the roof of the tank and any sampling of the water would be insufficient to pass due to the interior surface corrosion. Also, the instrumentation and roof interface point were not sealed, with a noticeable build-up of debris/silt/carbon and corrosion across the walls. Another issue was the broken ladder which would cause a health and safety access issue moving forward.

The option of replacing the water tower with cellular units was considered, however, due to minimal site spacing, it was discounted and the solution was to modify the existing asset.

Due to the consequence of the tank’s condition, there was a risk of low-pressure events. Toplers Hill Water Tower also provides standby storage to the adjacent Toplers Hill Reservoir, which cannot be removed from service until the water tower has been returned back to service; therefore highlighting the importance of the solution being delivered in a timely manner.

It was evident that the roof needed replacing, which required considerations for the crane’s lifting ability, the crane’s positioning, lay down areas, the weather conditions and teamwork. It was also apparent that there would be the need to reposition a number of telecommunications aerials atop the tower to ensure the site team were not at risk of radiofrequency (RF) radiation whilst working the tower.

[caption id="attachment_13576" align="alignnone" width="1200"] Toplers Hill Water Tower - Courtesy of @one Alliance[/caption]

Solution and construction

Anglian Water’s @one Alliance was tasked with developing a solution to the issues and the construction phase started in 2022.

Scaffolding: The team required safe access up the tower and around and inside the tank, so extensive scaffolding was put in place to allow this. The scaffolding works comprised the following:

• An external scaffold tower supporting an electrically-powered hoist to the top of the water tank.
• Full external access scaffolding surrounding the tank.
• Full birdcage scaffolding inside the tank with several boarded levels to the sides of the tank. The birdcage scaffold would need to be altered throughout the installation whilst repairs were taking place to enable safe access to all internal faces of the tank.

Crane pad and lay down area: Whilst the scaffold was being installed, Claret Civil Engineering designed a crane pad to facilitate the old roof removal and new roof installation. A separate levelled roof dismantling/assembly area was created nearby and covered with track matting.

Tank internals: With the scaffolding installed, the internal walls and higher levels of pipework and support brackets were prepared by OnSite Central Ltd. This included lead paint removal by high pressure water jetting, abrasive grit blasting, and re-coating the tank interior with Acothane DW; a DWI approved, solvent free polyurethane coating for potable water tank lining. The new tank coating was tested for integrity and strength as it was installed then cleaned, disinfected and sampled ready for return to service.

Roof replacement: The leaking tank roof was removed by crane by Hayes GFS Ltd and dismantled this on site. This was replaced with a new glass lined steel structure provided by Permastore and installed by Hayes. The top section of the walls had been identified as heavily corroded, so was cut away and prepared to receive the new roof arrangement. Using a crane from Cadman Cranes Ltd, the new tank roof was lifted into position onto the existing structure.

[caption id="attachment_13580" align="alignnone" width="1200"] New roof ready to be lifted - Courtesy of @one Alliance[/caption]

Water tower access: The external tank ladder with two shorter ladder runs and an integral access platform for the existing side access hatch were replaced.

Instrumentation: Whilst the existing level instruments and cabling were re-used where practicable, a new ultrasonic level transducer and associated cable runs were also installed. The old and new instruments were mounted to purpose-made apertures in the replacement roof to monitor the ultrasonic levels within the water storage tank.

Toplers Hill Water Tower: Supply chain - key participants

• Client: Anglian Water
• Design & project delivery: @one Alliance
• Refurbishment of tank internals & re-coating: OnSite Central Ltd
• Old roof removal/new roof installation: Hayes GFS Ltd
• Civils works: Claret Civil Engineering
• Glass-lined steel roof: Permastore Ltd
• Polyurethane coating: Acothane UK Ltd
• Crane hire: Cadman Cranes Ltd

Project challenges

Due to poor weather conditions, the crane lift date was delayed by several weeks. In addition, a last minute revision to the lifting plan caused delays to the lifting activities.

Having to apply the Acothane DW throughout both the winter and summer months, temperature and humidity extremes were experienced which was challenging during the preparation, application and curing of the coating.

Other challenges included nesting birds, tight site access, and several incidents of theft and on-site vandalism.

[caption id="attachment_13575" align="alignnone" width="1200"] The new roof being lifted into place - Courtesy of @one Alliance[/caption]

Health & Safety

The @one Alliance, prides itself of ‘Deliberately Delivering Differently’ and with this scheme, several H&S opportunities presented themselves as it developed. Early on it was noted that there was some concrete spalling on the external tower wall, which was a concern as small clumps of falling concrete could occur at any time. The team decided to carry out some loose concrete removal at the start of the site phase to removed this hazard.

Another anticipated H&S improvement was the use of a remote-controlled robotic paint stripper and shot blaster to prepare the internal walls for the new coating. This meant that operatives did not have to be inside the tank to manually shotblast the exiting coating, but unfortunately, the team discovered that the device could not traverse the bolt heads or tank boiler plate joints well so was ineffective.

The team also found that the internal tank birdcage scaffolding could be rationalised down to one lower level deck for tank wall access and work could be undertaken from mobile tower scaffolds. This not only reduced H&S concerns, it also saved time in having to install and strip additional scaffolding which equated to a saving of approximately £40,000.

Project status

As the date of writing (July 2024), the team are finalising the last activities of the tank refurbishment.

Once the telecommunications aerials are repositioned to their original orientation the scaffolding will be fully removed and the water tower will be handed back to Anglian Water. It will then be returned to service and the year-long warranty period will start.

Llyn y Fan Fach is a reservoir at the head of the Afon Sawdde, located within the Bannau Brycheiniog National Park. Constructed between 1914 and 1919 by conscientious objectors it raised the original lake by approximately 3m. The spillway for the reservoir is via a 6.1m ogee weir in the centre of the main dam. This discharges into a masonry and concrete stilling basin and spillway channel before flowing freely into the Afon Sawdde. The reservoir was previously used to supply water to a treatment works downstream but is now used to provide compensation flows to a fish farm that was created at the same location as the treatment works.

Inspection

Alongside routine maintenance, a Section 10 Inspection under the Reservoirs Act 1975 was undertaken on 15 October 2019. The inspection report stipulated the following Measures in the Interest of Safety (MITIOS):

• Arrest the structural cracking and eliminate leakage into the draw-off shaft. This will be in the form of a new structural liner to the valve shaft and sealing of the existing structure.
• The spillway apron and vehicle crossing will be reconstructed to safely convey the safety check flood.

The initial preferred option was discontinuance and returning the area back to its original state, however, the spillway structure was given a Grade II listed status in 2021 for special historical interest with its use of conscientious objectors for construction during WW1. Therefore, discontinuance was no longer a suitable solution and refurbishment was progressed through to design.

[caption id="attachment_11928" align="alignnone" width="1200"] Spillway prior to works - Courtesy of Arup[/caption]

Tower works design

To address the tower cracking and leakages several options were explored including concrete liners, conventional crack repairs, and partial rebuild of the tower. To assist with the design, an investigation was undertaken to determine the most likely driver of the cracking. This investigation reviewed the locations and history of the cracking and hypothesised that, due to thermal effects, a volumetric change of the dam walls that connect to the valve tower is inducing tension stresses in the shaft walls causing cracking exacerbated by environmental actions. An Finite Element model was developed to verify the tension stress areas that would be expected due to this action.

Owing to the size of the dam walls and the nature of the action it could not be effectively restrained, therefore the solution needed to accept these cracks as movement joints, prevent water ingress and protect the cracks from environmental actions that contribute to accelerated deterioration. The proposal consisted of the following three components:

1. A glass reinforced plastic (GRP) liner that is flexible enough to accept the thermal strains of the existing dam wall elastically, whilst being strong enough to resist the hydrostatic loading from the reservoir. The GRP liner is also designed to withstand the environmental conditions within the tower as it is the primary means of preventing water ingress to the shaft. Arup worked closely with the supplier, iLine Technologies Ltd, to guide their design and verify it met the requirements.
2. The existing cracking to be raked and filled with a flexible sealant. The sealant allows the cracks to continue to move. It is shrouded from UV radiation and temperature effects by a new façade to extend its working life.
3. A new reinforced concrete wall on the upstream face of the tower to structurally replace the cracked valve tower wall. This wall is made of two leaves cantilevering from the dam walls with a movement joint down the middle. This structure will also insulate the cracks and their repairs from environmental effects as well as being the first line of water ingress defence with a waterbar around its perimeter and waterproofing admix.

[caption id="attachment_11926" align="alignnone" width="1200"] (left) External lining construction - Courtesy of Arup, and (right) Installation of GRP lining from iLine Technologies Ltd - Courtesy of Morgan Sindall[/caption]

Spillway works design

The proposal was to fully replace the lower spillway with a precast structure capable of passing the 1,000 year (design) and 10,000 year (safety) flood events for the Category B dam. The wall heights were designed to contain the flows including full USBR freeboard. In order to maintain cultural heritage of the existing spillway, the spillway was lined with stonework.

Llyn y Fan Fach Reservoir: Supply chain - key participants

• Main contractor/designer: Morgan Sindall Infrastructure
• Consultant designer: Arup
• Mechanical contractor: Whitland Engineering Ltd
• GRP liner: iLine Technologies Ltd
• Precast concrete: FLI Precast Solutions Ltd
• Formwork: Cordek Ltd (using Filcor 90)
• Shuttering support: PERI UK
• Concrete repair: Beton Bauen Ltd
• Underwater survey/repairs: Edwards Diving Services
• Over pumping: Pump Supplies
• Valves: Glenfield Invicta

Delivery

Constructing this scheme was going to be challenging due to the site constraints including remoteness, narrow access roads, SSSI areas, National Park status, listed structures, bridge weight limits and popularity of the location with members of the public. From the main site office to the working area there was a 240m altitude difference over the 2.4km access road.

Due to the site location, opportunities for off-site fabrications were maximised to minimise the challenge of getting fresh concrete to the working area. Due to the distance from the concrete batcher, narrow access roads and having to offload concrete for transportation to the dam, it would take nearly two hours to get concrete to the work-face.

A significant constraint was the low clearance and low capacity bridges on approach to the site. This restricted the size of plant that could be transported and in turn, the size of components that could be handled. Therefore a large number of precast concrete units were required to make up the spillway structure with a considered and minimised use of in situ stitches. Another example where this constraint influenced delivery was that the tower required GRP sections with a 2.7m internal diameter being transported over a 2.4m wide bridge. The rings were therefore formed in half sections and assembled in situ.

[caption id="attachment_11925" align="alignnone" width="1200"] (left) Lined tower - Courtesy of HR Wallingford, and (right) Completed external lining - Courtesy of Morgan Sindall[/caption]

The use of prefabricated products gave the additional advantage of reducing site risks from concrete washout, excess materials, reduced potential quality issues, minimised working at height and reduced amount of plant to be transported to the working area. This also helped to reduce the overall programme had conventional methods been used and had a positive effect on minimising the construction impact and carbon footprint on the project.

The site team utilised Filcor 90 expanded polystyrene shuttering from Cordek Ltd to make the external repairs to the drawdown tower and dam face. This innovative shuttering solution used the output from 3D surveys to fabricate the intricate curvature of the existing tower and corbel detail and then mold the shuttering off site, allowing delivery to site in manageable sections. Given the location of the dam, the at times poor weather conditions the site team faced, traditional timber shuttering would not have been able to form the shape of the tower.

[caption id="attachment_11921" align="alignnone" width="1200"] 3D external formwork - Courtesy of Morgan Sindall[/caption]

Demolition and reconstruction of the spillway was the most critical aspect of the project due to the inherent risks on the dam structure from scouring if it were to spill during construction. Water levels in the reservoir were lowered to provide a minimum storage capacity for a 1 in 150 year storm event as was stipulated by the Welsh Water Dam Safety Team and QCE.

To ensure that water levels were managed in the reservoir throughout the scheme, a temporary storm pumping system was established using 12” electric pumps. The pumps were located on floating pontoons on the reservoir to keep them off the reservoir bed to avoid silt issues. Due to the criticality of the works, a Dam Safety Construction Management Plan was developed to control any increased risk to the safety of the dam during construction. Duty and standby pumps and generators were installed with auto changeover facility and telemetry systems that would automatically call out personnel in the event of an issue.

Under normal operating procedures, water from the reservoir was drawn off using a submerged siphon pipe which passed through the draw off tower, tunnel and down the mountain. The first valve on the siphon pipe located in the tower had to be replaced requiring our specialist diving contractor to install a temporary blanking plate within the reservoir to stop flows in the pipeline.

An additional temporary over pumping set up was installed to maintain the required flows down the mountain to supply the local fish farm. Isolating flows enabled the removal of the existing valve and replacement with two new units and pipes and subsequent re-commissioning of the siphon pipe. Remote operated vehicles were used to minimise manned diving and also to prove isolations before anyone entered the water. All diving works were closely managed with the site management and client representatives by operating under “gold command” which provides detailed planning and scrutiny of all activities to always ensure the safety of personnel.

A biodiversity enhancement scheme was undertaken to help improve the local environment and offset the impact of the works which saw the planting of over 200 new trees and the installation of a dipper box by the main watercourse.

[caption id="attachment_11927" align="alignnone" width="1200"] Spillway construction and lining - Courtesy of Morgan Sindall[/caption]

Summary

The scheme was completed in two phases from July 2022 until late December 2022 and from May 2023 to September 2023 and delivered successfully on time. Completion of the scheme has now provided Welsh Water with an asset that they can operate for many years to come and has enabled them to close off their statutory obligation under the Reservoirs Act 1975.

Throughout the scheme there were no reported accidents or injuries and a great safe working and positive intervention reporting culture was clear to see. “How Are We Doing?” feedback was obtained through the project from Welsh Water and received excellent comments. The scheme has also now been signed off as achieving Perfect Delivery by Welsh Water which is a testament to the hard work and professionalism shown throughout all stages of the project.

Porthcawl in South Wales boasts a rich maritime heritage and attracts over a million visitors a year. The seaside location is a draw for visitors and residents, but rising sea levels and increasing storm intensity coupled with ageing infrastructure, have increased the town’s risk of coastal flooding. As well as threatening properties, this has constrained development opportunities in the area. This project reduces threat of coastal flood and erosion risk to around 700 properties, while supporting tourism and providing greater opportunities for amenity and regeneration. Works include a complex renovation of the Grade II listed Western Breakwater, enhancement of the Eastern Promenade, and protection improvements at Rhych Point and relict dunes.

Building a business case for investment

Bridgend County Borough Council (BCBC) commissioned Arup to develop a business case for investment to reduce coastal flood risk to Sandy Bay, a wide and popular beach in Porthcawl. Analysis revealed that the condition of Porthcawl’s historic Western Breakwater was key to managing coastal risk throughout the bay. As a result, it was agreed with Welsh Government, to include the structure in the project.

The bay is surrounded by more than 100 acres of land identified for regionally significant regeneration. A phased approach was developed so works within the council’s control could be funded without the delay and risk of awaiting future development.

As part of the evidence for the business case, flood inundation modelling, informed by asset condition assessments and wave modelling, showed that 110 homes and 70 businesses were at risk of flooding. However, if the Western Breakwater were to fail, this increased to more than 530 homes and 175 businesses.

[caption id="attachment_14768" align="alignnone" width="1200"] (left) Flood inundation modelling and (right) site location plan - Courtesy of Arup[/caption]

Innovative investigations & restoration of a historic breakwater

Porthcawl’s 182m-long Western Breakwater is 200 years old and Grade II heritage listed. It forms a crucial part of the coastal infrastructure that protects the harbour and Sandy Bay from extreme wave impacts, but a challenging programme of repairs and strengthening measures was needed to maintain its structural integrity.

To protect its legacy, Arup consulted closely with Cadw, the Welsh Government’s historic environment service, as well as BCBC’s heritage specialists, enabling consents to be obtained without programme delay.

The challenge with the Western Breakwater was understanding the existing structural form (as the breakwater had undergone numerous modifications over its lifetime) and the likely failure scenarios associated with that structure. It was essential for the team to uncover its chronological development since its construction in the 1820s and to identify the nature and extent of its defects.

Arup combined historical research with drone, lidar, geophysical and geotechnical survey data to understand its structural weaknesses. Surveys used non-destructive techniques such as ground-penetrating radar, supplemented by trial pits and horizontal cores. Using the information gathered, the team devised a plan to help maintain the breakwater’s original character while reducing flood risk and improving its structural integrity.

The design included repairs to masonry and concrete, raising parapets, installation of a precast concrete cut-off wall and new rock armour. The design thus reduced the risk of voids and the impact of waves. Stone was sourced from the local quarry used in the original construction to replace a failed seaward sloping wall, and the voids were grouted to prevent water leakage and corrosion. A cut-off wall was constructed to provide a protective layer to reduce scour risk and future washout of fine material.

To strengthen the slender parapets without damaging the heritage-listed historic masonry, Cintec reinforcing anchors were added. This is a system that uses grout contained in a fabric sock mesh, combined with steel anchors. It helped to preserve the breakwater’s original character, as well as minimising carbon impacts and overall project costs.

By repairing the existing breakwater, rather than building a new one, the project reduced embodied carbon, and using locally quarried materials reduced transport impacts. The choice of prefabricated mass concrete blocks instead of reinforced concrete for the cutoff wall reduces future maintenance needs for the Western Breakwater. During construction it also reduced the health and safety risks of deep-water working, as the blocks acted as permanent shuttering.

Early engagement with Knights Brown contractors providing early supplier engagement was key; it ensured that the team’s designs could be safely implemented during periods of low tide and in challenging coastal working conditions.

[caption id="attachment_14767" align="alignnone" width="1200"] Western Breakwater Point Cloud model - Courtesy of Arup[/caption]

Placemaking public realm enhancements

As well as repairing and improving the listed breakwater, the project extended to the Eastern Promenade, located on the west side of the popular Sandy Bay beach. Initially, a secondary wall to stop waves overtopping the promenade was planned, but Arup’s placemaking design sought to ensure the promenade would be attractive for visitors and residents in years to come, and overtopping studies showed that the wall could be replaced with multifunctional planters. This added more green space, integrated terraced seating and minimised service diversions and disruption to the public.

The team also improved cycling and walking routes, ensuring the promenade was more functional and appealing for visitors and locals.

Preserving the dunes

Where previous proposals would have seen the sand dune habitat protected by concrete terraced defences, ABPmer’s study for Arup into coastal processes showed that the dunes could be preserved and restored using nature-based solutions, minimising costs and carbon emissions. For the restoration of the dunes to create a natural buffer, the team proposed 285m of low-level fencing to encourage the build-up of new dunes. These simple measures, combined with a growth and stability monitoring plan, will help maintain the coastal pathway. This approach has enhanced coastal resilience and revitalised the beach ecosystem, benefiting both residents and tourists.

Supporting marine biodiversity

To help support marine biodiversity, the team worked with CubeX Industries Ltd/BlueCube Marine and Swansea University to test innovative modular textured panels used to form an artificial reef and rock pools.

The hexagonal panels featured 13 distinct patterns made from ultra-high-performance concrete, with three different concrete mixes tested, including one incorporating local crushed cockle shells and ash. These were affixed in a beehive arrangement on the horizontal toe of the breakwater, to evaluate pattern colonisation by fauna and seaweeds under varying submergence times and wave exposures. The panels aimed to mimic natural habitats and foster marine life such as the protected honeycomb worm. [caption id="attachment_14773" align="alignnone" width="1200"] Settlers of Porthcawl - Courtesy of BlueCube Marine[/caption]

The project, known locally as the Settlers of Porthcawl, gained community support for eco-engineering interventions. Through questionnaires, the team established the public’s preferences for patterns imitating natural textures, and for a mixture of designs on the seawall. The project gained popularity among local schools and hosted over 200 students to teach them about climate change, biodiversity and sea-level rise.

Monitoring for a year revealed colonisation disparities across the sites due to wave exposure. This emphasised the significance of submergence and exposure. It was found that the most successful patterns to help foster colonisation were those with protruding ledges and rough microstructures, as opposed to smooth designs.

Project details

• Programme overview: Welsh Government
• Client: Bridgend County Borough Council
• Project cost: £6m
• Design start: October 2016
• Construction period: April 2021 - June 2023

Porthcawl Coastal Scheme: Supply chain - key participants

• Designer: Arup
• Construction supervisor: WSP
• Marine specialist: ABPmer
• Geophysical survey specialists: TerraDat (UK) Ltd
• Land surveys: Azimuth Land Surveys
• Archaeology: Glamorgan-Gwent Archaeological Trust
• Surveys: Tetra Tech
• Maritime structural engineering sub-consultant: Steve Hold Consulting
• Main contractor: Knights Brown
• Groundworks: McCarthy Contractors Bridgend Ltd
• Concrete repairs & grout: Beton Bauen Ltd
• Scaffolding: PSS Scaffolding Ltd
• Fabrication: Total Fabrication
• Precast: Macrete (Ireland) Ltd
• Green infrastructure pilot: Swansea University
• Architectural concrete: CubeX Industries Ltd
• Artificial reef & rockpools: BlueCube Marine
• Handrailing: Broxap Ltd
• Cintec anchors: Celtest Company Ltd
• Masonry: Dawson Stone Masonry Ltd
• Surfacing: Asphalt Surfacing Ltd

[caption id="attachment_14769" align="alignnone" width="1200"] Western Breakwater construction works - Courtesy of Knights Brown[/caption]

Challenging, collaborative construction

Knights Brown was appointed principal contractor under a NEC3 Engineering and Construction Option A contract, reflecting a commitment to cost acuity and risk mitigation.

In the high-risk environment, reducing construction risks meant minimising drilling, concreting and grout injection times to suit three-hour tide windows. Design and construction teams worked collaboratively on site, for example to minimize grout loss due to residual post-survey uncertainty around structural void volumes and locations. Cradle solutions extended working times. Precast standardised mass concrete blocks and redesigned Cintec anchor applications all supported installation.

Extensive consultation with users of the infrastructure and development of a phasing plan (including measures such as avoiding construction at Rhych Point during peak tourist season and phasing construction to retain public access to Eastern Promenade) was crucial to mitigate negative impacts during construction. This enabled community and sporting groups to access the promenade and maintained RNLI lifeboat access to the slipway. Project information boards and use of local media raised awareness of the scheme and kept users informed of progress.

Community benefits emphasised local employment and training opportunities, including five new-entry apprenticeships, engagement with local supply chain and support of local initiatives for young people not in education, employment or training. A bespoke schools engagement programme based on ‘The Tale of the Sea Monster’ educated and raised awareness of the need for improvements in a child-friendly, engaging way.

Construction was hit by several large and powerful storms; evidenced by modelling to be impacted by climate change. In response to damage from a May 2021 storm, repairs employed hydro-demolition of concrete around reinforcement bars, repairing the corroded bars and spraying concrete to repair panels. The resilience of these repairs was proven in December 2021 when Storm Barra halted construction work but caused no damage to repairs.

[caption id="attachment_14776" align="alignnone" width="1200"] Western Breakwater during Storm Diana - Courtesy of Keith Jones[/caption]

Conclusion

Despite the impact of the COVID-19 pandemic, as well as multiple severe storms, the Porthcawl Sandy Bay Coastal Scheme was completed in the agreed time-frame and within budget in Summer 2023.

Beyond its primary objective of reducing flood risk, the scheme has delivered substantial economic benefits to the local community and the wider region. By safeguarding critical infrastructure, residential properties and commercial assets, the scheme protects livelihoods and preserves the vitality of the coastal economy. Moreover, the enhanced recreational opportunities and improved coastal aesthetics will attract tourists and investors, stimulating economic growth and enhancing the town’s resilience to future shocks.

Janine Nightingale, Director of Communities, Bridgend County Borough Council commented:

“... [the scheme] forms a vital part of the infrastructure for defending the town against flooding and will also help to secure future development in the area.”

The scheme was highly commended for the Environmental Project of the Year and shortlisted for the National Infrastructure Commission’s Design Principles Project of the Year at the British Construction Industry Awards 2023.

The Saltcoats Rising Main project involved upgrading just over a kilometre of existing pipe on the most burst-prone section of the rising main, which stretches between the towns of Saltcoats and Stevenston in North Ayrshire. The rising main was originally installed in 1992, and it runs approximately 3km from Saltcoats WwPS towards Stevenston WwTW. The existing main is a 700mm diameter ductile iron (DI) pipe, ranging from two to five metres in depth, conveying a flow of around 500 l/s.

Background

The driver for this fast-tracked project was that the main had burst on various occasions, with four bursts before Caledonia Water Alliance’s (CWA) involvement and a further burst during the design phase.

The failure on the pipe became evident along the invert, with noticeable ‘channelling’ discovered after taking cut-outs during the repair works. There is a bathing water nearby and bursts were causing the pumping station to spill and have a direct impact on the water, prompting Scottish Water to seek permanent solutions to improve the pressure main’s functionality instead of continually responding to leaks.

[caption id="attachment_13076" align="alignnone" width="1200"] (left) Aerial view of the project and (right) rising main failure - Courtesy of Caledonia Water Alliance[/caption]

Project scope

• Lining of the first 1km of existing 700mm diameter DI rising main from Saltcoats WwPS.
• Installation of cured in place pipe (CIPP) lining by hot curing.
• Installation of one air valve and one scour valve. The scour valve to be relocated off carriageway for future ease of access and maintenance.
• Excavation of five lining pits to enable lining in both directions.
• Two  bypass installations to enable over pumping of all flows during lining works.
• Planned shutdown to install valve arrangement for bypass.
• Installation of approximately 1km in length of overland 700mm steel pipes.

Site investigation

Given the environmental impact of bursts to the nearby bathing waters, the project started moving quickly and CWA were engaged to review potential solutions. While reviewing the requirements for a potential offline replacement, it became apparent that this would take some time and require multiple third-party approvals before any work could take place.

It would also involve finding a suitable location for a new pipe, which would involve executing the works through an existing golf course and through the only access road in and out of a busy caravan park. To limit the impact of the works and reach the site quicker, Scottish Water agreed to use a trenchless solution and re-line the existing rising main. Scottish Water instructed Caledonia Water Alliance to focus on the first 1km of the main, as this would cover the section of previous bursts to date.

This would make the scope more achievable in lieu of the bathing season approaching, given the location of the remainder of the pipe.

[caption id="attachment_13074" align="alignnone" width="1200"] Pipe delivery - Courtesy of Caledonia Water Alliance[/caption]

Project summary

• Project name: Saltcoats Rising Main
• Project cost: £4m
• Start date - design: 1 November 2022
• Start date - construction: 31 March 2023
• Completion date: 27 October 2023

Planning

With the agreed solution of lining the pipe now in place, the focus turned to getting on site as quickly as possible. This meant fast-tracking numerous stages, such as ground investigation and detailed design, and instead progressing with a high-level detail of the proposal, with various assumptions in place. The main issue which arose was how to manage the flows.

Caledonia Water Alliance proposed different options to SEPA, ultimately suggesting that they could turn the pumps off and tanker/spill the flows while working on lining the pipe. This would have been the quickest solution but would involve the rising main being offline for several months, which SEPA, as a regulator, could not accept.

SEPA did however appreciate why Caledonia Water Alliance were asking the question. Caledonia Water Alliance had anticipated this being the case with the only other option to bypass the flows with an overland pipe while working on the existing main. However, this posed issues - mainly around laying 1km of 700mm diameter pipe over a golf course and how they could cross a busy road. Given the services within the road and the time constraints, Caledonia Water Alliance could not bury it, even partially.

[caption id="attachment_13070" align="alignnone" width="1200"] Assembly of overhead pipe bridge - Courtesy of Caledonia Water Alliance[/caption]

This led to the proposal of an up-and-over bridge crossing. Caledonia Water Alliance was initially reluctant, given the visual impact this would have but, realistically, had no other choice. In the end, this worked out well, through extensive communications with the local residents, businesses, and caravan park, all agreeing the work was necessary to rehabilitate the rising main. The next challenge was to get the 1km bypass installed and operational before the bathing season beginning on the 31 May 2023.

From receiving the project at the end of October 2022 and starting on site in March 2023, Caledonia Water Alliance was able to collaborate with Environmental Techniques Ltd to design a cured-in-place liner with pit locations; working alongside their specialist subcontractor Selwood, to develop the overland bypass pipe.

As above, Caledonia Water Alliance went to site with some assumptions of the rising main location and depth, so they knew there would be changes as the project developed on site.

Saltcoats Rising Main: Supply chain - key participants

• Project delivery: Caledonia Water Alliance
• Trenchless rehabilitation & liner design: Environmental Techniques Ltd
• Civils subcontractor: Jacks1 Civil Engineering
• Underpressure connections: Swan Pipelines
• Scaffolding: AHL Scaffolding
• Temporary works/shoring: Groundforce
• Water supply: Enviroclean
• Liner supply: Insituform
• Bypass pipework: Selwood

[caption id="attachment_13073" align="alignnone" width="1200"] Bypass pit showing pipework cut out and a new ‘T’ piece and valve arrangement - Courtesy of Caledonia Water Alliance[/caption]

Temporary bypass

The first part of the work, after establishing the site, was to install the temporary bypass. The bypass utilised a 700mm diameter flanged steel pipe, bolted together. This was strung out from a bypass pit adjacent to Saltcoats Pumping Station, approximately 1km downstream.

This required a tremendous effort to deliver a large quantity of pipework, drop it in place and bolt it together whilst working on both bypass pits at either end of the 1km section of pipe. The team completed the works on the bypass on time before the bathing season. With this now operational, CWA ensured the safety of the first 1km of the main from potential bursts.

Liner installation

The liner chosen was a cured-in-place pipe liner (CIPP) as this would provide the structural capacity of the host pipe. CIPP lining has been extensively used throughout the UK to repair failing sewer pipes, prevent infiltration and to add structural strength where required.

Designing CIPP liners for pressurised pipe systems presents unique challenges that differ significantly from their application in gravity-fed sewers. In pressurised systems, the liner must withstand not only external forces such as soil, groundwater, and traffic loads but also the continuous internal pressure exerted by the fluid within the pipe.

Additionally, the liner must also be able to withstand negative internal pressures, or vacuum conditions, which can cause the liner to experience inward forces, particularly near joints and bends. The design had to account for these vacuum scenarios to ensure that the liner remains stable and securely bonded to the host pipe, preserving the structural integrity of the pipe under varying pressure conditions.

[caption id="attachment_15903" align="alignnone" width="1200"] Liner installation - Courtesy of Caledonia Water Alliance[/caption]

The liner was designed with the operating and supplied test pressures of the existing rising main. The number of known bends, as well as the potential for more unknown bends, meant that the hot water curing was a more suitable process for this project as the liner would invert itself under the pressure of the curing water, navigating around the bends automatically.

A scaffold tower was installed at the installation pits to secure the end of the liner and to ensure enough vertical height to allow the water pressure to invert the liner through the length of pipe required. The hot cure process utilises a hot water boiler to raise the temperature of the curing water which begins the process of hardening the resin.

The liner provides a 60-year design life, similar to installing a new pipework, but with significantly less digging requirements and waste production.

[caption id="attachment_15902" align="alignnone" width="1200"] Drone image showing the scaffold tower and the liner installation operation underway - Courtesy of Paul Milligan, Caledonia Water Alliance[/caption]

No-dig technique

The decision to use trenchless relining methods was primarily driven by the need to minimise the number of excavations, significantly reducing disruption and environmental impact. In Saltcoats, this approach required only five lining pits and two bypass pits along the existing rising main, demonstrating the efficiency of trenchless technology compared to traditional dig-and-replace methods. One of the key benefits of trenchless relining is the reduced need for extensive excavation, which minimises surface disruption to roads, traffic, and the surrounding environment. This is particularly in Saltcoats to minimise disruption to the local communities, golf course and caravan park. By using trenchless techniques, the project can be completed faster with less noise, dust, and inconvenience to residents and visitors to these areas.

For the bypass pits, existing pipe sections were cut out, and new T-piece and valve arrangements were installed. This allowed for the connection of temporary bypass pipes, enabling the flow to be managed through valve operation without interrupting service. The trenchless approach also reduces the risk of encountering unforeseen underground utilities, which can lead to costly delays and repairs.

Overall, trenchless relining offers a safer, more efficient, and less invasive solution for repairing and upgrading pipeline infrastructure.

Conclusion/update

The project was completed successfully on site and within the proposed programme, despite coming across some major obstacles on site. Once the lining was completed, it was inspected, tested, and finally put into commission by transferring the flows back into the newly rehabilitated main.

[caption id="attachment_13071" align="alignnone" width="1200"] CCTV output pre and post lining - Courtesy of Caledonia Water Alliance[/caption]

Following successful commissioning, the rising main was run for a period of 48 hours without any defects. After this time, Caledonia Water Alliance was able to start dismantling the bypass pipe, removing it from site and reinstating the area.

Undertaking the Saltcoats Rising Main Rehabilitation Project was a significant effort by all involved to first install and have the bypass pipe operational before the bathing season, and then to have the existing main rehabilitated and working within the timescales which Caledonia Water Alliance provided Scottish Water at the start of the works.

This was particularly impressive given the fast-track nature of the works and getting a large-scale project to site quickly. There is now a Phase 2 and 3 proposed for the remainder of the rising main to Stevenston WwTW to rehabilitate it over its entirety. These will be looked at over the next 2 to 3 years.

Leominster WwTW is a medium sized biofilter sludge works, treating a population equivalent of approximately 11,000. Welsh Water have invested £12.1m to deliver the process enhancements at the works as part of Welsh Waters’s commitment to deliver on improved water quality in the Wye River basin catchment. Other enhancement works were completed on existing sites including Eign, Rotherwas and Kingston & Madeley WwTWs. As part of the National Environmental Programme (NEP) commitments to meet the obligations of the Water Framework Directive in AMP7, new permit limits were put in place for 31 March 2025. The project exceeded this milestone by one year, achieving the tightened permit and Welsh Water’s annual commitment for river reach improvement.

Existing works

In advance of the improvement scheme, the works comprised an inlet works, primary settlement tank (PST), seven mineral media biofilters, two humus settlement tanks (HSTs), ferric dosing, two storm tanks and sludge storage.

The works treated mainly domestic sewage from the catchment of Leominster, Herefordshire.

The planned improvement works

The upgraded Leominster WwTW is designed to cater for increased treatment flows equating to a design horizon population equivalent of 16,685 (46% growth) and a tightening of the phosphorus permit from 1mg/l to 0.5mg/l. The new works design included for the integration of the following process improvements into the existing treatment works infrastructure:

• Four new tertiary nitrifying sand filters (including a tertiary lift pumping station and backwash returns system).
• New ferric sulphate dosing system for primary, secondary, and tertiary dosing points of application (including a new dosing equipment kiosk and safety shower).
• New sodium bicarbonate dosing system to supply additional alkalinity to the process for pH correction (including a chemical storage silo and dosing system).
• Inlet works refurbishment, upgrading the two existing escalator screens with two new 6mm screens, screenings trough, screenings transfer to two new compactors.
• New passive bypass screen with improved operation and maintenance access provision.
• New access platform around the screens to reduce the need for operator access into confined space areas.
• New potable water booster pumping station.
• New final effluent sampling system.
• New low voltage distribution board and inlet works MCC.
• New tertiary treatment MCC.

Scope of works

As part of Welsh Water Capital Delivery Alliance (CDA), Morgan Sindall, in partnership with designers, Arcadis, was appointed as the main contractor by Welsh Water. The scope of works for the project included the investigation, assessment, design, procurement, construction, and commissioning of existing and new treatment facilities; thus providing capacity to treat increased sewage loadings to meet discharge permit standards agreed with the Environment Agency (EA).

[caption id="attachment_15336" align="alignnone" width="1200"] (top left) Construction of tertiary treatment system December 2022, (top right) construction of tertiary treatment system May 2023, (bottom left) Construction of tertiary treatment system July 2023, and (bottom right) Construction of tertiary treatment system November 2023 - Courtesy of Morgan Sindall Infrastructure[/caption]

Innovative solution selection

Welsh Water, Arcadis and Morgan Sindall collaboratively assessed multiple options as part of the optioneering phase of the outline design, which included optioneering workshops for shortlisting, and risk and value assessments to select the most cost-effective solution based on whole life cost and risk. A schedule of innovative solutions included:

• New nitrifying sand filter to combine the need for tertiary solids removal, to achieve the tightened phosphorus permit, and increase nitrification capacity to relieve pressure on the works to meet the existing ammonia permit.  Removed need for additional secondary treatment.
• Re-use of the inlet structure for the new 6mm screens, improving access and removing need to go in confined space during routine maintenance procedures.
• Re-use of the existing ferric sulphate storage tanks.
• Assessment of innovative alternative chemical to ferric sulphate (rare earth minerals).
• Use of BIM 3D modelling to ensure integration of mechanical design and location for the alkalinity silo and tertiary plant and avoid clashes with existing underground pipework.
• Gravity fed sampling system for final effluent monitoring.
• Design for Manufacture and Assembly (DfMA) MCC kiosk (used in the development of Welsh Water standard design).
• Re-assessed the need to refurbish existing sludge holding tanks through modification of sludge imports.
• Re-use of old Dortmund style rectangular/pyramidal standby PSTs.
• Re-purposing and re-establishment of area of works with abandoned process treatment assets– reducing the need for land purchase.
• Utilise existing static mixers on secondary ferric sulphate dosing.
• Ferric sulphate dosing flexibility (primary, secondary and tertiary).

Project initiation and whole supply chain early engagement

The overall delivery programme for the treatment upgrade scheme at Leominster presented the Welsh Water CDA team a challenge to meet the NEP regulatory output dates for end of March 2025 and ODI date for 31 March 2024. To efficiently meet this milestone, the team developed a joint collaborative plan to work to with the key project stakeholders, including members from Welsh Water asset and operations teams and key supply chain members.

[caption id="attachment_15328" align="alignnone" width="1200"] Construction of tertiary treatment system February 2024 - Courtesy of Morgan Sindall Infrastructure[/caption]

The development of up-front outline design specifications and subsequent letting of Early Contractor Involvement (ECI) contracts with the supply chain allowed for all parties to truly work collaboratively in setting out and advancing the design strategy in an efficient manner. The ECI contracts enabled the supply chain and Arcadis to work together in an open and transparent manner through driving greater design efficiencies through sharing of ideas, skills, industry experiences, true value engineering opportunities, developing design and construction innovations, all resulting in a positive influence to the final scheme solution.

The successful working relationship was maintained through regular joint online progress meetings and workshops, where design efficiencies were discussed and implemented, and where any potential blockers were removed, to benefit design and construction. Other joint stakeholder meetings which assisted the advancement of the delivery programme included HAZOP’s, Access, Lifting and Maintenance (ALM) reviews, DSEAR meetings, referencing lesson learnt from previous schemes, progressing DfMA opportunities, production of outline commissioning plans early, and holding regular buildability review meetings as the design progressed. Having a common project management system, where all members of the joint delivery team shared information, was hugely beneficial, in addition to the open access to the scheme’s federated 3D BIM model.

Leominster WwTW: Supply chain - key participants

• Client: Welsh Water
• Principal contractor & civils: Morgan Sindall Infrastructure
• Designer & environmental consultants: Arcadis
• CFA piling rig: Foundation Piling Ltd
• Shaft installation: B&W Tunnelling Ltd
• Sheet piled interlocked cofferdam: Berryrange Ltd
• Mechanical installation: Industrial Pipework Services Ltd
• Electrical installation: PCS Ltd
• Earthing specialist subcontractor: BEST Services Ltd
• Tertiary nitrifying sand treatment: Brightwork BV
• Tertiary nitrifying sand treatment: Nijhuis Industries UK & Ireland
• Ferric dosing system: Colloide
• Alkalinity dosing system: Rospen Industries Ltd
• MCC & ICA controls: GPS Group
• Kiosks: Morgan Marine
• PLC network: Mitsubishi
• Below ground access chambers: Cubis Systems
• Pumps: Xylem Water Solutions
• Inlet screens and screening handling: SPIRAC Ltd
• Potable water booster system: Dutypoint Ltd
• Static mixer: Statiflo Ltd
• Temporary pump specialist: Hydrainer Pumps

[caption id="attachment_15329" align="alignnone" width="1200"] Fully constructed tertiary treatment system integrated into existing treatment works - Courtesy of Morgan Sindall Infrastructure[/caption]

Sustainable and efficient design and construction

The new tertiary treatment plant and associated pipework, utilities and control kiosks were installed in an area within the boundary of the existing treatment site, where disused sludge drying beds were previously located. Re-purposing this area led to a more sustainable solution as it avoided the associated expenditure, programme, and environmental requirements that land purchase would have involved.

Due to this area of the existing treatment site being near the final effluent pipework, it enabled the flow diversion to the new tertiary lift pumping station to be achieved via a short length of below ground gravity pipe at a shallow depth. This is also a more sustainable design as it avoided the increased excavation and carbon footprint requirements that additional manholes, longer/deeper pipe lengths and a pumped solution would have required.

Other examples included surveying existing duct runs and draw pits to review capacity and reuse, where possible, as well as refurbishing the existing ferric dosing system and containment bund, instead of installing new plant, thus providing efficiencies and cost savings to Welsh Water.

Another element of efficient design and construction was the civil bases associated with the three new MCC kiosks for the new plant and equipment being installed.

As the two larger kiosks were to be DfMA and hence delivered to site with the panels already installed within the kiosk, a support frame for the kiosk and floor was also provided. Due to the panels requiring man access below them for installation of cables, the support frame included for vertical legs and steps for access into the kiosk that was installed on a simple concrete flat slab with mesh reinforcement. This was a more sustainable solution as it minimised the excavation requirements and reduced the total volume of concrete and steel when compared with sitting the kiosk at ground level on a below ground concrete trench and base slab with more steel reinforcement. The solution led to a quicker installation and better from a Health & Safety perspective as the extent of confined space working was reduced due to the absence of a trench.

[caption id="attachment_15331" align="alignnone" width="1200"] Example of a Cubis Systems modular chamber and (inset) chamber being assembled at Leominster- Courtesy of Cubis Systems & Morgan Sindall[/caption] For the smaller alkalinity MCC kiosk (not DfMA), it was decided that the kiosk would sit at ground level but as it still required access under the panel for installation, a below ground trench was required. To make the construction process more efficient, the trench comprised of innovative and sustainable HDPE recycled plastic modular units from Cubis Systems, that were put together on site and built around with minimal concrete surround and base slab and backfill to support the kiosk. As well as the material of the modular solution being more sustainable, it also led to a reduced carbon footprint in delivery due to it being very light weight. This also made it a safer and quicker installation as the manual handling involved was minimal.

Cubis Systems products were also used for the draw pit construction where the rapid stack modular units were utilised to form the main structure saving man hours with additional safety benefits.

The existing layout of the inlet works presented increased risks to operations with the main components below ground level and within a confined space. The new design involved raising the working platform to ground level, around the new screens and creating a better working environment and removing the need for operations to enter the previous confined space areas.

Design efficiencies

Working together with Welsh Water and the framework MCC subcontractor (GPS Group), the team were instrumental in the development of the standardised design for manufacture and assembly (DfMA) design for MCC kiosks within the Welsh Water business. The Leominster team delivered this standard product in the form of a new low voltage distribution board kiosk and a new tertiary filter MCC kiosk at the site.

The DfMA GRP kiosks are mounted on a raised steel frame floor to support the MCC and the access covers while giving ample space beneath the structure for cable connections and testing.

This kiosk design reduced health and safety risks associated with installation and commissioning and led to considerable reduction in installation time on site, as the kiosks were delivered to site, off loaded, and fixed down, all within a few hours. [caption id="attachment_15332" align="alignnone" width="1200"] Installation of DfMA low voltage distribution board MCC kiosk - Courtesy of Morgan Sindall Infrastructure[/caption]

The early engagement, with the electrical installation subcontractor, PCS Ltd, through an agreed Early Contractor Involvement contract arrangement, ensured that cable design and routes were agreed early in the design, to the new plant and equipment.

The standard designs for lighting, junction boxes and emergency stops were used where possible. In addition, the Welsh Water Capital Delivery Alliance team worked collaboratively with PCS Ltd and BEST Services Ltd, an earthing specialist subcontractor, to fully understand the earthing requirements for the site. Regular design review meetings were held to develop a workable earthing design, considering the impact of this deliverable with numerous site constraints.

Conversion of the existing Siemens PLCs to remote I/O, allowed for integration of all existing signals into the new schemes Mitsubishi PLC network. This minimised the number of telemetry outstations on the site, bringing all control associated with these MCCs into the new PLC network.

Hydraulic integration of new process scope into existing works

The new project scope required integrated into the existing treatment works hydraulic design and included the incorporation of two new SPIRAC Ltd escalator screens and storm bypass static screen within the existing civil structure, and the installation of new flow control weirs into the existing biofilter and humus tank distribution chambers.

[caption id="attachment_15337" align="alignnone" width="1200"] New Fineguard inlet screens from SPIRAC Ltd with improved safe access for operators – Courtesy of Morgan Sindall Infrastructure[/caption]

The new weir design was needed to achieve an appropriate flow distribution across the two sets of existing biofilters and the three existing humus tanks. To ensure seamless integration and maintain safe flow throughout the facility during the implementation of these changes, a comprehensive hydraulic assessment was conducted to verify the incorporation of new process assets within the treatment stream without negatively impacting on the existing asset structures.

To maximise the reuse of the existing works pipeline infrastructure and flow hydraulics, the team positioned the new tertiary treatment filters within the site layout to optimise the existing final effluent pipework arrangement by rerouting the flows from the existing humus tanks to the new tertiary treatment lift pumping station and then reintegrated the treated effluent from the tertiary filters back, by gravity, into the existing pipework to the final effluent lift pump station.

This approach reduced costs and construction time for the delivery of the project, reduced the impact of maintaining the existing works operation during the construction period and removed the need to agree a new final effluent sampling point location with the Environment Agency.

Digital delivery

To maximise the understanding and detail of the existing site arrangement and optimise the design process, a point cloud survey was undertaken, and a 3D Revit model produced. Along with existing as built drawings, asset and topographical survey information and historical as built drawings, the 3D model was developed further and then used to produce and develop a 3D model of the design proposals.

[caption id="attachment_15334" align="alignnone" width="1200"] (top left) Federated 3D model capture of sampling kiosk with tertiary filters - Courtesy of Arcadis, (bottom left) as built sampling kiosk with tertiary filters - Courtesy of Morgan Sindall Infrastructure, (top right) Federated 3D model capture of lift pumping station with tertiary filters - Courtesy of Arcadis, and (bottom right) As built tertiary filter lift pumping station pipework with duplex filter and tertiary filters - Courtesy of Morgan Sindall Infrastructure[/caption]

The 3D model was federated to include all the different design models (including those by the design subcontractors) and then used in internal meetings to agree on design proposals, by being marked up for updating. The federated model was also used to avoid underground clashes with existing pipework and produced the 2D drawings that informed the pricing and construction of the proposals and was also instrumental in getting acceptance from the stakeholders when used in project gateway approvals, HAZOP and ALM meetings.

This digital strategy for the project led to significant efficiencies in design as the federated model that contained the developed design proposals was uploaded to a BIM Docs page for the project, where all design deliverables were also kept, reviewed, and issued to the key stakeholders via the workflows and transmittals tools. The whole project team (designers, subcontractors, suppliers, stakeholders) were able to easily access and view the pertinent design information and subsequently design reviews and project decisions could be made easily which was instrumental in fostering a collaborative approach on this project.

Engineering challenges

Groundwater: As part of the overall design, a 3m diameter and 6m deep tertiary lift pumping station, was designed to lift and transfer influent flows, intercepted and diverted from an existing 450mm diameter final effluent gravity pipe, to the four new tertiary sand nitrifying filters.

During ground investigative works, it was identified that there was a high-water table present that would make construction of the shaft difficult. To fully understand the impact, pump tests were carried out to quantitate the expected groundwater influx during excavation and allow Arcadis to prepare and submit applications for abstraction and discharge (A&D) licences from the EA.

[caption id="attachment_15344" align="alignnone" width="1200"] Lift pumping station - Courtesy of Morgan Sindall Infrastructure[/caption]

However, due to the lengthy time-frame expected to obtain EA approval for an A&D licences, the team needed to reconsider the construction methodology of the lift pumping station in order to meet the consented target date of 31 March 2024.

B&W Tunnelling Ltd, who had been appointed to undertake the original caisson installation, jointly developed a solution with Morgan Sindall that would enable the pumping station to be constructed without the need to abstract any significant amount of groundwater. The agreed method was to drive interlocked sheet piles around the perimeter of the planned structure to a depth at which it will cut off any groundwater. With the groundwater under control, the caisson could then be installed under ‘dry’ conditions.

A 4.8m x 4.8m cofferdam was installed using 12m long GU27N sheet piles to penetrate the underlying mudstone formation. During construction the piles were required to stand as cantilevers. The temporary sheet piles were used for the construction period only, and were extracted once the caisson was complete. The Berryrange Ltd cofferdam allowed for safe construction of the shaft/lift pumping station and ensured the project kept on programme.

Network Rail: The location of the new tertiary plant on the site was in close proximity to the busy railway line that runs from South Wales to North Wales and Manchester. Network Rail were consulted, and mitigation measures agreed to ensure the safest method of constructing the new asset was followed.

A basic asset protection agreement (BAPA) was approved, which enabled Network Rail to review the safety documentation of lift plans (tandem lift method), method statements and temporary works design ahead of the planned work to install the filter tanks, sodium bicarbonate storage silo and associated high level stairs and working platform structures.

An appointed Network Rail Supervisor attended site to oversee the construction operations, which included the safe operation of piling rigs, multiple cranes, concrete pumps and the safe use of excavators in the vicinity of the operational railway line. This process was undertaken for over 20 separate operations through the programme period, all of which were undertaken safely and successfully.

[caption id="attachment_15335" align="alignnone" width="1200"] Installation of tertiary sand filters adjacent to railway line under agreed BAPA procedures - Courtesy of Morgan Sindall Infrastructure[/caption]

Health & Safety

As always, during wastewater upgrades or extensions, the challenge and onus on the team is to integrate the new plant and processes, safely and efficiently, into the existing treatment works infrastructure, while ensuring that the existing process is not impacted or interrupted.

To formalise these crucial planning activities, Welsh Water required Morgan Sindall to work to their Business Continuity Plan (BCP) process. This BCP process encompasses the development and joint agreement of a detailed activity plan, initially, between Morgan Sindall and Welsh Water local operations teams, followed by presentation of the safe systems of work to Welsh Water senior managers for their final acceptance and approval.

As the integration of the new assets were built in and around the existing works, construction activities were proactively reviewed and agreed with Welsh Water to ensure minimal disruption to the operational site during the periods when these improvement works were being conducted.

Instances where the BCP process was followed included:

• When temporary over pumping was needed to construct two intercepting manholes on the existing final effluent gravity pipeline.
• During over pumping of incoming sewage from the inlet works structure and during the installation of the new screening units.
• During construction of two flow meters on the feed pipes to the two sets of existing biological filters
• During the power upgrade to site and transfer of mains control to the new LVDB MCC unit from the old.

[caption id="attachment_15333" align="alignnone" width="1200"] Leominster WwTW: Tertiary sand filters - Courtesy of Morgan Sindall Infrastructure[/caption]

In the case of the installation of the biological filter feed flow meters, a gravity solution was selected due to the hydraulic sensitivity of the biofilters and fluctuating flowrates of the incoming wastewater with the weather. The construction required several shutdowns and temporary storage of incoming flows as well as the installation of a network of above ground pipelines with flow control valves and flow meters over a 200m distance across the operational site.

Enhancing communities

During summer 2023, the Leominster team approached the local country park to enquire if there was any community-based volunteering work that the team could assist with. The Park Ranger highlighted an area of which they were planning on creating a community garden.

The Morgan Sindall and Welsh Water team assisted the local country park rangers with clearing a large area of brash and vegetation at Queenswood Park to open the space up. In addition, the team assisted in providing a new stone footpath and bridge to enhance access for the public. Several bird boxes were installed to encourage and enhance local bird populations in the area.

Another example where the team have helped and supported the local community was through the provision of food parcels to the local Food Bank. Staff from Welsh Water, Morgan Sindall and the project supply chain, all donated food parcels to the local charity to distribute.

To encourage and assist with the development of future engineers, the team invited two Year 11 students to undertake work experience on the site for a week and hosted a new graduate on the site as part of the Year in Industry placement scheme.

To celebrate British Science week, the Herefordshire Women’s Institute attended site during construction. The Leominster Town Clerk and numerous local councillors were also invited to site to explain the environmental benefits of the new enhancement works to the existing treatment works.

[caption id="attachment_15338" align="alignnone" width="1200"] Fully constructed tertiary treatment system integrated into existing treatment works - Courtesy of Morgan Sindall Infrastructure[/caption]

Programme

Scheduled collaborative planning was undertaken at the design stage with all project stakeholders ensuring key deliverables were targeted and met to enable start on site. The collaborative planning sessions were also carried through to the construction phase where the main project programme was developed with all disciplines and key supply chain partners to achieve the milestones set.

Coupled with the regular planning sessions weekly site progress meetings were undertaken with all parties ensuring everyone was aware of the planned and forthcoming works with progress monitored throughout.

The main construction programme consisted of separate civil working areas ensuring the foundations and main structures were in place before mechanical and electrical supply chain partners were integrated into the programme to work alongside each safely to optimise the working time of the programme.

All parties worked together on site successfully with a standard daily safety brief to everyone ensuring all individuals were aware of the planned activities.