Supply Chain - Sewerage - Contractors

September 2022 saw the successful completion of a new kilometre outfall pipeline in Arklow, Ireland. The lack of wastewater treatment facilities in Arklow resulted in untreated wastewater being discharged directly to the Avoca River. The design and construction of a new wastewater treatment plant and long sea outfall was required to improve the water quality of the Avoca River and bring benefits in terms of health, environmental integrity and facilitate economic and social development for Arklow town and its surrounds, which has been constrained by the lack of adequate wastewater treatment capacity. This paper focuses solely on the marine design/construction elements of the project as construction of the new treatment works and other associated structures are still ongoing. Background Arklow is a town in County Wicklow on the southeast coast of Ireland. There were no wastewater treatment facilities in Arklow town and as a result, untreated wastewater was being discharged directly into the Avoca River. This was not compliant with obligations under the European Union Urban Wastewater Treatment Directive. Uisce Éireann, therefore proposed a development to provide an effective wastewater collection network, treatment capacity and treated effluent outfall that would improve water quality in the Avoca River. Ward & Burke was appointed as the main contractor for delivering the Arklow Wastewater Treatment Plant (WwTP) project, with the design and construction of the associated long sea outfall sub-contracted to Van Oord Ireland Ltd. Royal HaskoningDHV was appointed by Van Oord as designer for the long sea outfall (LSO). The overall project required the design, construct and implementation of the following: A new, state of the art, wastewater treatment plant that has been designed to provide an ultimate treatment capacity for a population equivalent of up to 36,000 at the Old Wallboard Factory, North Quay, Ferrybank. Sewer pipelines (along the North and South Quays) to bring the untreated wastewater to the WwTP. A marine outfall pipeline to safely discharge the treated wastewater to the Irish Sea. Upgrade of the existing rock armour revetment adjoining the site. [caption id="" align="alignnone" width="1200"] Outfall pipe arrival from Norway by sea to the dock in Arklow for preparation and assembly - Courtesy of Van Oord Ireland[/caption] The proposed outfall pipeline was required to discharge the treated effluent from the wastewater treatment plant to receiving waters. Both marine and river outfall options were initially considered for the proposed development. However, hydrodynamic and water quality modelling demonstrated that the wastewater discharge standards required for a river outfall would be much more onerous than that of a marine outfall. For that reason, the river outfall was not considered further. Solution The detailed design of the new outfall system for the Arklow Wastewater Treatment Plant Project considered and finalised the new outfall pipe route, hydraulic design, preferred material and construction methodology, pipe weighting, backfill and diffuser arrangement. The outfall system comprised of a 630mm outer diameter pipeline (630mm OD SDR 17 PE100 pipe) and started at a connection point onshore, behind the revetment and extended offshore for approximately CH927m to the discharge location. The outfall discharge arrangement/diffuser configuration was located in approximately 13m of water depth from the Extreme Water Level (EWL) and consists of six risers (355mm O.D. SDR 17 PE100 pipe), four diffuser ports (160mm O.D. SDR 17 PE100 pipe) each with 24 return duckbill valves that horizontally discharge the treated effluent at a height of approximately 1m above the seabed level. The detailed design trench detail was developed to provide a minimum cover depth to the outfall pipeline of 1.5m following installation. This cover depth allowed for both seasonal and long-term fluctuations on the seabed levels and protection from potential damage due to dragging anchors. The trench was backfilled with selected as dug material, typically medium dense sands and gravels, that were side-cast during the trench excavation. Where the outfall crossed beneath the existing and proposed coastal revetment, the pipe wall structural thickness was checked and verified to prevent any high point loads from the revetment rock armour. [caption id="" align="alignnone" width="1200"] Outfall pipe floated along the quay wall in Arklow prior to preparation and assembly works - Courtesy of Pipelife Norge AS[/caption] The marine outfall was also designed to be stable in the ‘worst case’ design loads for current and wave loading conditions provided. It was therefore necessary to weight the pipeline with concrete collars and subsequently concrete kennels after installation (float and flood method), to provide a specific gravity of not less than 1.35 that could be achieved without any reliance on backfill material. This installation weight was provided with 1015kg (290kg/m) (in air) fixed weight concrete collars at 3.5m centres and to satisfy the permanent on bottom stability, 2292kg (654.86kg/m) (in air) concrete kennels were provided at 3.5m centres in between the fixed weight concrete collars. The collars and kennels were provided by Tracey Concrete. Constraints Arklow is a town with a population of 14,000 people and a small port which generates medium to high traffic within the port. This constituted working and delivery restrictions during the preparations of the offshore section of the outfall pipeline. In addition, the turbulent weather did not allow for preparing the outfall pipeline offshore, outside of the port vicinity. Additionally, a survey undertaken by Uisce Éireann showed an existing subsea cable in close proximity to the designed LSO route. The cable supplied power to a substation located South of the site location from the offshore Arklow Bank Wind Farm. The survey undertaken by Uisce Éireann confirmed the location of the power cable and showed that the cable route was outside the redline boundary for the works. However, the owner/operator of the subsea power cable was consulted to ensure that the new LSO route and location was compliant with the applicable exclusion zones/constraints for the subsea power cable. [caption id="" align="alignnone" width="1200"] Welding of risers for diffuser section of outfall pipe - Courtesy of Van Oord Ireland[/caption] Site investigation Site information was provided by Uisce Éireann from a ground investigation undertaken in 2017 at the proposed site location, as well as information from the Geological Survey Ireland (GSI) website borehole archive that included relevant land-based and overwater boreholes. The ground investigation indicated that the ground conditions generally comprised of a variable sequence of medium dense to coarse soils and gravel. The offshore investigation data indicated that there is a significant variation in the ground conditions between the boreholes which were spaced at approximately 150m intervals e.g., buried valleys, rock outcrops etc. Large boulders of metamorphic rock were also encountered in the boreholes. Whilst the depth of the boulders generally exceeded 3m below bed level, the presence of boulders at shallower depths could not be discounted and posed a risk for the construction of the outfall. The requirement for further site investigations were identified and these included magnetometry, sub-bottom profiling and unexploded ordinance (UXO) surveys to determine the mitigation measures required to be undertaken prior to the proposed works and construction of the pipeline. Arklow LSO : Supply chain - key participants Arklow WwT Project delivery contractor: Ward & Burke Long sea outfall design/build: Van Oord Ireland Ltd Van Oord designer: Royal HaskoningDHV HDPE pipe: Pipelife Norge AS Concrete collars & kennels: Tracey Concrete Tideflex S35 valves: MeasurIT Technologies [caption id="" align="alignnone" width="1200"] Excavation of trench at the onshore connection point using the backhoe dredger ‘Razende Bol’ - Courtesy of Van Oord Ireland[/caption] Marine works A total length of 927m of polyethylene pipe (630mm OD SDR 17 PE100) was manufactured by Pipelife Norge AS, in three lengths of 309m which were then towed from Norway by sea to the dock in Arklow, Ireland for preparation and assembly. Along the quay wall, concrete collars, each weighing 1 tonne were installed around the pipe strings at 3.5m centre to centre distances. The collars were lifted from land with special lifting equipment and the two halves of the collar were connected from the water using small workboats. Flanges were fitted with the assistance of a marine tug boat and the on board crane. During these operations the HDPE pipe was lifted out of the water. The lifting operations of the pipeline where analysed in detail to predict stresses in the material and the bending radius of the pipe. Using this analysis the lifting operations could be adjusted to prevent buckling or damaging the HDPE pipe. For the installation of six riser feet on the pipe, a spreader beam was used to lift the pipe 1m out of the water. The usage of the spreader beam followed from the analysis done for the lifting. Excavation of the trench was carried out using land-based excavators on the revetment and Van Oord’s backhoe dredger ‘Razende Bol’ for the marine trench. A minimum cover of 1.5m above the crown of the pipe was required for the outfall pipeline through its entire route. The excavated trench material was cast adjacent to the trench for re-use as backfill material upon completion of installation. [caption id="" align="alignnone" width="1200"] (left) Outfall pipe during sinking operation and (right) outfall pipe aligned prior to sinking operation - Courtesy of Van Oord Ireland[/caption] Installation After pipe preparations were completed and the trench was excavated, the pipe installation commenced. The three separate pipe sections were connected with flange connections next to the quay wall in Arklow in order to create one long pipe length of 927m. Bend restrictors to prevent over-bending at the flange-flange interface were also installed. The finished pipeline was manoeuvred out of the port using two tugs and multiple small work boats. The pipe was anchored overnight just outside the Arklow port. Before the sinking operation, the pipes were aligned and brought into the onshore connections point where pumps were set-up to flood and sink the pipe. The pipes were pulled into the shore using a pre-installed pull wire and an onshore drum winch. The polyethylene pipelines were installed using the ‘float and flood’ method starting from the fixed onshore end. During the sinking operation, the offshore end of the pipes were connected to a multicat which was moored alongside the backhoe dredger ‘Razende Bol’ for proper positioning. The controlled pumping of seawater into the onshore pipe end, initiated the sinking process which caused the pipe to form an S-curve of approximately 20m long between the seabed and seawater surface. Two tug boats (shoal busters) were used in order to position the pipe correctly at the location of sinking. As a contingency measure and to ensure the installation process was well controlled, a foam pig was pre-installed in order to create a seal between the pipe section filled with air and the section filled with water, in case the pipe had to be re-floated due to inclement weather. Once the pipe sections were completely installed in the trench, the profile was checked by a multibeam survey to verify the final pipe position. Post pipe installation, the foam pig was removed from the pipe. A Type II pressure test of 2.25 bar was performed in accordance with the procedure set out in IGN 4-01-03, to 1.5 x the maximum internal working pressure. [caption id="" align="alignnone" width="1200"] Outfall pipe concrete collars being fitted in water with special lifting equipment - Courtesy of Van Oord Ireland[/caption] Once the outfall pipeline had been sunk to the sea bottom and pressure tested, concrete kennels, each weighing 1 tonne were placed in between the concrete collars at 3.5m centre to centre spacings to provide additional permanent weighting. Additionally, six diffusers were installed from the backhoe dredger platform by divers. Each diffuser comprised of a flanged PE pipe, fittings and a riser with a four-port crosshead, each with a flange allowing for Tideflex S35 valves to be fitted directly. Included as part of the diffuser installation, was a removable access flange at the top of the riser to enable access inside the riser. After completing the diffuser and kennel installation, the pipe was backfilled over its full length to provide 1.5m cover. Rock armour protection was further provided extending approximately 7m around the diffuser section from its centre to protect the area around the diffuser from scour. Also provided was a steel protection frame for the diffuser, fitted with sacrificial anodes to allow a 50yr design life for protection from dropped objects, anchors, trawlers and fishing nets. Finally, on the offshore end a marker buoy and on the onshore end a Saint Andrews Cross were installed to mark the pipeline location. Due to the turbulent weather at the site location, including hold points in the working method, so that each installation step could be paused at planned intervals, allowed Van Oord to work around the weather. Additionally, working with local contractors who helped to adjust and adapt work methods and techniques within the limited amount of space, allowed the team to prepare and install the outfall system using specialised equipment and marine vessels, with minimal disruption to the environment and public. In particular, a bespoke rigging system was designed and fabricated using a local yard to assist with the efficient installation of the collars whilst working from the water. [caption id="" align="alignnone" width="1200"] Outfall pipe during sinking operation - Courtesy of Van Oord Ireland[/caption] Conclusions The successful completion of this project will allow treated effluent to be safely discharged from the new Arklow WwTP once operational and bring benefits in terms of health, environmental integrity and facilitate economic and social development for Arklow town and its surrounds, which had been constrained by the lack of adequate wastewater treatment capacity.

The Ards North Long Sea Outfall, constructed at Ballyferris on the east coast of the Ards Peninsula, has an asset design life of 60 years and can convey flows of up to 4200 m3/day of treated effluent from the Ards North WwTW to the pre-determined deep water discharge point in the Irish Sea. Legislative compliance was demonstrated by computational and hydrodynamic effluent dispersion modelling and the termination point for the outfall was at a pre-agreed location 500m offshore. The treated effluent is dispersed and diluted through a multiple port diffuser in 4m depth of seawater. Ards North WwTW The Ards North WwTW catchment is seasonal with significant summer peaks in flow generated by holiday parks. In addition, the initial contract documents required a long sea outfall to be designed for storm tank overflows. This resulted in a significant range of design flows and challenges to achieve an asset standard compliant hydraulic design. Flows ranged from: Minimum flow rate (Winter DWF): 13 l/s FFT Ards North WwTW: 48.22 l/s Maximum flow rate (Formula A at WwTW): 74 l/s Given the range of flows, the exemplar design included a pressurised outfall fed from a header tank and final effluent pumping station. [caption id="" align="alignnone" width="1200"] Tow and sink operation - Courtesy of NI Water[/caption] Exemplar design Farrans Construction along with RPS Consulting Engineers were appointed to develop the exemplar design for construction. The completed design evolved during the design period with initial designs providing capacity for the full range of flows. On award, RPS completed a pipeline route assessment using Civil 3D ground models to review the option of providing a gravity solution capable of delivering the full range of design flows through the outfall to the diffuser against 1:100-year storm conditions with an appropriate allowance for sea level rise to 2030. RPS Water Environment & Marine completed an assessment of the tidal range and sea level rise to develop a maximum tidal discharge level. Admiralty Tide Tables for the secondary ports of Donaghadee and Portavogie were used, and linear interpolation of the Highest Astronomical Tide (HAT) and Mean Low Water Spring  (MLWS) levels provided tidal levels. Sea level rise due to climate change was assessed using derived data through UKCIP18, providing a tidal range of +3.64 to -1.91m AOD Belfast which was adopted for the design process. Hydraulic analysis Ground modelling and initial hydraulic analysis confirmed that any gravity solution would require significant depths of excavation on the land-based section, and it was concluded that a pressurised system using a header tank was the preferred solution reducing the depth of dig, associated costs, health and safety risks during construction, and whole life operation and maintenance of the asset. Potential pipeline routes were identified and appraised to establish the best option considering lands access, road opening, future maintenance to fittings and furniture, ground conditions and depth of dig. The preferred option was a route across agricultural land, local roads before passing through a caravan holiday park to the high-water mark where the land and marine-based sections of the outfall would join. [caption id="" align="alignnone" width="1200"] Aligning pipeline over pre-dredged trench - Courtesy of NI Water[/caption] A range of pipeline diameters and materials were considered to achieve optimum velocities, a balance between pipe diameter and TWL in the proposed header tank. PE pipes were selected for the outfall with varying SR ratings used to offer material cost savings using only higher rated pipes for the marine sections to take account of installation (towing and sinking) stresses on the system. Specialist hydraulic modelling was then completed by Hydraulic Analysis Limited (HAL) to provide confidence in the performance of the system against all combinations of design flows and tidal levels. The analysis confirmed the pipe diameter selection, siting of air and scour valves and provided specific specifications for pipeline gradients, bends and air valves installation to ensure stable free surface flow conditions were achieved within the mains gravity driven sections. Renegotiated WOC During the detailed design stage, a renegotiation of the Water Order Consent (WOC) allowed for discharge of storm flows from the Ards North WwTW direct to an adjacent watercourse. This significantly reduced the maximum design flow for the long sea outfall and on reassessment allowed the removal of the effluent pumping station and header tank offering significant operational savings for NI Water. [caption id="" align="alignnone" width="1200"] Barge mobilisation from Bangor Marina - Courtesy of Farrans[/caption] The final solution was therefore to discharge treated effluent directly from the sample chamber to a gravity outfall which acts in part as a pressurised system. This amendment to the design approach was verified by HAL and removal of the pumping station and header tank was agreed by all prior to finalising the construction details including: Design of pipeline bedding and surround for both land and marine-based works. Land-based pipelines were designed as traditional open-cut installations with bedding and surround specified to meet the requirements of BS EN 1295-1:2019 Structural Design of Buried Pipelines. Air, scour and hatchbox chamber details for the land-based section. Given the variation in summer and winter dry weather flows, the inclusion of hatch boxes was provided for maintenance and to aid cleaning of the outfall. Marine section bedding and surround. The marine section was considered as two sections namely: Inter-tidal zone where the pipeline was bedded in suitable granular bedding and surround and installed with collars and kennels for flotation resistance and stability. The pipeline was protected with 2 layers of rock armour. Offshore zone where the pipeline was installed in a deeper pre-dredged trench with an imported granular bed and surround and restrained against flotation using kennels at 3m centres. This section of the pipeline was backfilled with as-dug excavated rock. The outfall was completed with a collar and kennel arrangement and a 4-port crosshead diffuser, fabricated from 400mm OD PE pipework and fitted with four 150mm diameter Tideflex non-return valves. The diffuser arrangement is protected by a galvanised steel frame with sacrificial anodes. Design for construction complied with the requirements of the NI Water Asset Standards and Specifications, CESWI, Relevant CIRIA Guidance and other Industry accepted standards. [caption id="" align="alignnone" width="1200"] The outfall was installed off the coast at Ballyferris adjacent to a caravan park - Courtesy of NI Water[/caption] Undertakings Farrans Construction was appointed as principal designer and contractor for the works, including an early contractor involvement stage consisting of scope and design development, stakeholder engagements, statutory approvals and ground investigations. Farrans appointed Marine Specialists Ltd, a specialist subcontractor, to assist in completing these works. Ards North LSO: Supply chain - key participants Client: NI Water Principal designer/contractor: Farrans Construction Project management/technical support: Tetra Tech Exemplar design: RPS Consulting Engineers Hydraulic modelling: Hydraulic Analysis Ltd Specialist marine subcontractor: Marine Specialists Ltd PE pipe & fittings: Associated Pipeline Products Precast concrete collars: Ardmore Precast [caption id="" align="alignnone" width="1200"] (left) Onshore pipeline assembly - Courtesy of Farrans, and (right) installation of concrete kennels - Courtesy of NI Water[/caption] Installation The primary method of installation was by open-cut trench and rock breaking technique with contingency arrangements in place for encountering ‘unbreakable’ materials, consisting of a drill, blast, dig methodology. The works were completed in the following phases: Phase 1: Works comprised shore-based operations to prove the trench to depth along the intertidal zone, consisting of rock breaking, excavation and temporary backfilling of the trench. This phase was designed to mitigate the risk of delay due to adverse weather conditions and capitalised on large spring tides by utilising land-based equipment during the winter months. It would also minimise the disruption to the public by reducing the duration of pipeline installation and final connection on the beach. Phase 2: This involved the marine-based operations, rock breaking and excavation of the trench proven to depth with the use of a barge-based 60t 360° track excavator with a 14m reach, Topcon 3D GPS system, 4t breaker and ripper tooth. The excavator operated from a pontoon barge 26.8m x 12.2m with a deck capacity of 360t. Phase 3:  This phase included a combination of both shore and marine-based operations. The trenching extended seaward in accordance with the limiting conditions for weather, visibility, sea state, wind and gusts. The position, alignment and depth of the trench were confirmed by the 3D GPS systems and regular bathymetric surveys. The pipeline The pipe lengths (supplied by Associated Pipeline Products) were butt fusion welded, prefabricated to a string length of 500m, fitted with concrete collars (ballast weights) and tested. At the ends of the pipe string, a pupped stub was welded complete with stainless steel backing rings. A blank flange was bolted to the stub/backing ring to allow for the entrapment of air within the pipeline allowing the pipeline to float when placed in the water. Shore-based excavation work was completed at low tide to re-excavate the trench along the intertidal zone previously proven in phase 1 of the works in preparation for pipe tow-and-sink operation. Once the trench was proven to depth and prepared for pipeline installation, the pipe string was gradually moved toward the water using land-based excavators. [caption id="" align="alignnone" width="1200"] Re-excavating the proven trench - Courtesy of Farrans[/caption] At high tide, the pipe was floated, towed and positioned above the pre-dredged trench. Connection was made to the pre-installed land section of the outfall and the pipe was filled with water allowing a gradual sinking and pipe placement along the trench. Backfilling operations commenced once the pipe was surveyed and verified. Professionally qualified divers installed the prefabricated diffuser head. Live underwater video surveys were conducted to monitor the installation of all equipment. The execution of these activities adhered to stringent health and safety protocols, strict environmental considerations, and project timelines, ensuring the successful completion of the project on time and within budget. Community liaison Safety was at the heart of the project and protecting the public while works were ongoing on the beach, in close proximity to a holiday park was paramount. NI Water and Farrans undertook a range of initiatives to ensure that local holidaymakers, residents and the wider public were aware of the planned installation, including leaflet drops, beach signage, posters and importantly a children’s safety art competition. [caption id="" align="alignnone" width="1200"] NI Water and Farrans held a joint safety initiative for children in caravan parks - Courtesy of NI Water[/caption] Successful delivery The installation of the long sea outfall pipe was a complex and challenging element of the wider £18m Ards North Wastewater Improvement Project and required extensive planning, communications and collaboration with a wide range of stakeholders. With a wealth of expertise and experience on board and as a result of meticulous planning, strong teamwork and robust health and safety measures, the new long sea outfall was successfully installed in summer 2022, well in advance of commissioning of the new WwTW in spring 2023. This critical piece of infrastructure, along with the new Ards North WwTW and both new and upgraded pumping stations in the catchment, will support long-term economic growth in local development and tourism and will benefit all those living, working, visiting or investing in this scenic part of the Ards Peninsula.

The Exmouth Offshore Project is a key element of the wider Exmouth programme of works to deliver no more than 10 significant (>50m3) spills per annum from the aggregation of Maer Road Sewage Pumping Station (SPS) Combined Sewer Overflow (CSO) and Phear Park SPS CSO. The output from the programme will reduce spill frequencies for better environmental conditions as a long-term solution with a positive impact on the bathing waters. The works were undertaken in Sandy Bay Devon Cliff Holiday Park in Exmouth and was delivered around Sandy Bay’s winter maintenance window, compressing 15,000 working hours within just 13 weeks. Overrunning the programme would have directly impacted Sandy Bay’s tourist season, with significant revenue loss (approximately £2m/day). The works were located only 4 meters from a Blue Flag beach. Introduction & background

The Exmouth Offshore Project required the installation of an 804m long, 900mm diameter, gravity long sea outfall, to achieve an increased flow rate of 991 litres per second.

The works took place in Sandy Bay Devon Cliff Holiday Park (Exmouth), one of the UK’s largest caravan sites, with over 2200 units and 10,000 visitors per week in the summer season and were only permitted during the Sandy Bay winter maintenance period.

South West Water contracted Galliford Try as principal designer and contractor for the project.

[caption id="attachment_17044" align="alignnone" width="1200"] (left) Pipe string along coastal path and (right) Pushing pipe lower car park and compound - Courtesy of South West Water[/caption] Construction

To meet this challenging programme, specialist horizontal directional drilling (HDD) contractor Peter McCormack & Sons mobilised one of the largest and most powerful drilling rigs ever used in the UK, to complete the largest forward reaming (48”) operation in the country.

The works required 18 months of planning and the programme challenge included expediting the specialist reamers, 1.2m in diameter manufactured in America and imported to precise programme requirements. The methodology and accurate planning minimised programme risk by minimising the use of marine spread.

This relied on forward reaming (pushing the pipe from land), which is an unconventional method for the length and diameter of pipe of this scale, but reduced the reliance on marine support in winter sea conditions reducing weather risk.

Early marine trenching support was mobilised to clear boulders at the exit point at seabed over two days. Survey marine vessel continued throughout the project to confirm HDD exit point.

818m of HDPE pipe was welded on land, stretching in a single length at strategically high ground to slide the pipe. This allowed to fully pressure test the pipe to give complete confidence in the weld quality. The project team considered both the safety of the public accessing the coastal footpath adjacent to the works and maintenance operations within the holiday park with accurate interface management. In addition to this, the project team worked closely with landowners to agree a route for the welded pipeline to be positioned, in readiness for the pipe push with regular communications with landowners.

[caption id="attachment_17047" align="alignnone" width="1200"] (top left) 500t drill rig compound and entry point and (bottom) pipe pushing operation at sunrise - Courtesy of South West Water[/caption]

The works naturally attracted attention, and allowed the team the opportunity to explain the work that were undertaking and the long-term benefits South West Water outfall would provide to wider Exmouth storm overflow project.

The project compressed 15,000 working hours within 13 weeks which equates to 10 months of normal working hours. This could only be achieved by running a continuous 24x7 drilling operation. Despite the intensive nature of this challenge, the team completed the HDD works ahead of programme, on budget with zero harm to the team, zero pollution incident, and minimal impact to the public. This pipe is a wider part of Exmouth stream of works including storm overflows to achieve long term goal.

Exmouth Outfall: Supply chain - key participants Client: South West Water Principal contractor: Galliford Try Design: Pell Frischmann Design of outfall route & drilling specialist/sub-contractor: Peter McCormack & Sons Ltd Topographic, GPR & boreholes: AGS Ground Solutions Unexploded ordnance survey report: 1st Line Defence 900MM PE pipe supplier: Egeplast international GmbH (Germany) HDD 500t kit & drilling tools: American Augers (USA) Pipe pusher: VanLeewen Trenchless Technology (Netherlands) Welding plant supplier: Ritmo remedy 1000FA (Italy) Concrete: Aggregate Industries Welding plant operator: Pipe Force Martin Woodcock Fiberglass systems: Pipex px Crane hire: Spence Crane Hire Ltd Plant hire: Plantforce Rentals Ltd Plant: Sunbelt Rentals Ltd Aggregate: Steve Wills Haulage [caption id="attachment_17043" align="alignnone" width="1200"] 500 T drilling rig - Courtesy of Galliford Try[/caption] Teamwork and Inclusion

Working collaboratively towards a common agenda, multiple partners were involved including the pipe supplier, drillers, pipe pushers, pipe welders, crane operators, mud pump operators, water tank suppliers, fuel suppliers etc.

A mutually inclusive team worked. Collaborative teamwork environment with no risk-taking policy with a culture of everyone working on site and delivery people have same respect with different roles and responsibilities.

Cultural Behaviour Safety videos were shared on regular basis to remind site team safety, culture, and respect aspect. Site team was well trained and fully skilled to follow safety rules religiously. No one was either bigger or lower than anyone which was demonstrated by actions through a mutually inclusive respectful culture. Shift change and intermittent toolbox talks were carried out. Several graduates and other interested people were taken to site for their learning. One of the UK’s Water Plcs were visited the site for their learning.

[caption id="attachment_17046" align="alignnone" width="1200"] (left) Drill pipe and pilot drill bit and (right) outfall pipe, roller and guide - Courtesy of Galliford Try[/caption] Health & Safety considerations

Accurate and realistic RAMS were produced. Uninterrupted CCTV monitoring was placed. Each shift had a team of 25 highly skilled and well-trained site team with zero risk taking policy. Specific H&S steps:

Strict one-way system with separate entry and exit points for plant and construction vehicles. Separate entry and exist of South West Water Operators to make existing pumping station in safe operation. Detailed interface management plan of each operational activity including regular on site maintenance of drilling rigs. An hourly check of whole plant, Noise barriers and vibration control equipment for public safety and wellbeing with fully secured fence - large visible metal sign boards and multiple laminated signs in and around the Sandy Bay for public awareness. On duty several field marshals to navigate foot path users. Same drilling team was kept. Compressed programme 15,000 working hours within 13 weeks. Injury free 15,000 working hours into 13 weeks. No near miss. No pollution incident.

Noise barriers and vibration control equipment was installed for the safety and benefits of local community and footpath users. This was checked daily by the site team and the environmental manager to ensure there were zero environmental and H&S incidents.

Protecting the Blue Flag beach

To protect the Blue Flag beach, the entire working area was surrounded by flood barrier to prevent drilling fluids from escaping the site to avoid any risk of pollution of sea. All drilling fluids were recycled by using a recycling centrifuge system. This sustainable innovation allowed the drilling arisings to be fully dewatered, allowing transportation of the inert material without the risk of silt on the road network, causing unnecessary nuisance to the travelling public. This initiative minimised water use and mitigated 364 lorry movements through Exmouth, saving 92T eCO2.

[caption id="attachment_17042" align="alignnone" width="1200"] 900mm diameter pipe welder - Courtesy of Galliford Try[/caption] Conclusion

Despite the intensive nature of this challenge, by running a continuous horizontal directional drilling operation over a 24/7 operating pattern, the works were completed on budget and ahead of the programme. There were no time delays, no environmental impacts to the blue flag beach (just 4m from the site), and any impacts to the Holiday Park were minimal.

South West Water have showcased this project through the media and LinkedIn focusing on the engineering challenges the team faced and promoting both construction and the wider environmental benefits of this scheme.

The team have produced a presentation given by Galliford Try’s team to over 250 employees nationally to share the best practice and learnings from this project across their entire business.

South West Water are extremely pleased with progress of these works to meet their commitments with the Environment Agency.  Relationships with the Holiday Park management are extremely good, and the owners are grateful for the efforts the team and SWW have made to complete these works with minimal disruption to their business.

The Severn Estuary is renowned for its tidal range of 12-14 meters, the second largest in the world, and as such poses significant challenges for civil and marine works. In late 2024, a critical infrastructure upgrade project was completed near Nash, Newport, replacing a long sea outfall pipeline originally constructed in 1960 to extend its operational life. The project involved installing a 1.4km 560mmØ high-density polyethylene (HDPE) outfall pipe to replace the deteriorated concrete-coated steel pipe. Situated within one of the UK’s most ecologically sensitive regions and a Site of Special Scientific Interest (SSSI) in the Severn Estuary, the project not only secured infrastructure integrity but also adhered to stringent environmental protection measures. Project challenges and environmental safeguards

Kaymac Marine & Civil Engineering Ltd was appointed as the principal designer and contractor for the £8.4m outfall replacement project.

The Severn Estuary is designated as a Site of Special Scientific Interest (SSSI), which protects its tidal flats, salt marshes, and diverse wildlife, which required the project team to introduce and adhere to comprehensive environmental safeguards.

[caption id="attachment_19920" align="alignnone" width="1200"] The in-land RC chamber connecting the new and existing pipe (during construction) - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption]

Sediment control measures such as careful selection of plant and equipment, implemented in collaboration with National Resources Wales (NRW), minimised water quality impacts during the excavation and pipe-laying activities.

Kaymac Marine & Civil Engineering Ltd drew upon its deep industry expertise and practical experience to drive the design direction and successfully secure all necessary permits and permissions for the project. Working closely with the local council and NRW, Kaymac led the process of obtaining the required Marine License, Environmental Permits, and Planning Permissions, ensuring full compliance with all regulatory requirements.

Through comprehensive site investigations and advanced geophysical and bathymetric surveys, Kaymac Marine & Civil Engineering Ltd identified critical site-specific characteristics that directly influenced the project’s design. This informed approach allowed the team to craft tailored solutions that addressed regulatory concerns while optimising project outcomes.

Kaymac’s practical experience played a crucial role in addressing the expectations of the environmental regulators. By proactively collaborating with NRW and other stakeholders, the team was able to satisfy stringent environmental requirements, demonstrating how the proposed designs minimised ecological impacts while maintaining structural and operational integrity.

[caption id="attachment_19919" align="alignnone" width="1200"] New valves within the inland chamber - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption]

This expertise and experience, coupled with a solutions-focused mindset, not only streamlined the approval process but also ensured that the final design adhered to both regulatory standards and the project’s overarching goals.

To maintain quality standards and to ensure the works could be undertaken within the licencing timeframes, Kaymac Marine & Civil Engineering Ltd engaged suppliers early on, securing essential equipment and materials; whilst conducting regular necessary quality visits and inspections to ensure technical and Quality compliance.

Severn Estuary LSO Replacement: Supply chain - key participants Principal Designer & Contractor: Kaymac Marine & Civil Engineering Ltd Designer: Pebble Engineering Ltd Specialist design: Morek Engineering Ltd Specialist design: H2NA Ltd HDPE pipe: Pipelife Norge AS Precast concrete collars: Poundfield Precast Precast concrete mattresses: Subsea Protection Systems Duckbill check valves: Measurit Technologies Valves: Scott Parnell Landside temporary works & shoring MGF Ltd Huennebeck Construction materials Scott Parnell Neal Soils Wright Readymix Stone Supplies IPP Floating plant Jenkins Marine Kraken Marine Services P&D Environmental Construction plant hire Land & Water Plant Hire Flannery Plant Weldex RW Christopher Crane Hire Ltd United Rentals Atlas Winch & Hoist Services Ltd A1 Surveys MTK Breakers LGS Gap Hire Services HV Fusion Severn Environmental Services ABP Newport & Barry [caption id="attachment_19913" align="alignnone" width="1200"] Trench excavation prior to the first section of pipe installation - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption] Detailed design & planning

A comprehensive understanding of the physical forces that dominate the ocean environment, their origins, and the likelihood and intensity of these forces over the lifespan of an outfall is critical to its effective design, regardless of the construction materials used.

These forces can compromise the outfall’s integrity either directly or indirectly, such as through seabed erosion or by destabilising its foundation. Additionally, sediment transport can obstruct diffuser orifices, potentially leading to system failure. These factors were considered and mitigated during the planning and design phases to ensure the long-term functionality for this particular environment.

Kaymac Marine & Civil Engineering Ltd appointed Pebble Engineering Ltd as designers and worked collaboratively to develop the construction methods and subsequently the detailed design of the outfall.

Both the construction method and the detailed design needed to align and complement each other, with regard to compliance of the aforementioned environmental and planning regulations, the seabed conditions present on site and the anticipated physical conditions (such as sea, wind, wave, tidal and current) of the works location.

Delivery & preparation of HDPE pipe

The new high-density polyethylene (HDPE) long sea outfall pipe, measuring 1.4km in length and 560mm in diameter, was manufactured by Pipelife Norge AS in Norway and was towed 1,134 nautical miles to Newport in 11 sections under a single trip.

Upon arrival at ABP Newport Docks, each pipe section was stringently inspected, tested and then later prepared for installation.

The preparation works involved the installation of over 260 bespoke precast concrete ballast collars that were designed to ensure stability of the pipeline against the hydrodynamic forces of the watercourse and the natural buoyancy of the HDPE material, once it had been sunk to its installed position within the trench.

[caption id="attachment_19915" align="alignnone" width="1200"] Pipe being prepared for connection - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption] Innovative installation techniques in a tidal environment

The use of specialised low pressure bearing amphibious excavators handled intertidal trenching at low tide, while a GPS-equipped dredging vessel undertook the offshore trenching requirements. The installation spanned an approximate 28-day period, working shift patterns under challenging tidal conditions, with trenches reaching depths of approximately 1.5–2 meters.

A key milestone involved towing the first 250 meter section of the pipe from ABP Newport, navigating the currents and flows of the Severn Estuary, to the installation site, approximately three nautical miles away. This segment, equipped with 50 concrete collars, was positioned over the trench as the tide receded, sunk under the guidance of Kaymac’s divers to ensure accuracy, before being backfilled with the previously excavated spoil.

Finally, the precast articulated concrete mattresses from Subsea Protection Systems Ltd were installed by utilising a crane barge to provide additional scour protection and stability to the outfall. Such mattresses have been used successfully for decades to protect oil and gas pipelines and since the early 1990s, they have been increasingly used to protect ocean outfalls.

Throughout the project, Kaymac employed a flotation and submersion technique whereby each 250 meter long section was towed into position and the seaward end of the previously installed pipe length was recovered to the working platform, before connecting to the new length and then sinking within the new pre-excavated trench.

[caption id="attachment_19916" align="alignnone" width="1200"] First section of the pipe within the trench during low tide ahead of backfilling - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption]

Ensuring an accurate and safe sinking procedure in the Severn Estuary required considerable planning efforts from the delivery team, taking into consideration tidal movements and slack water periods. Each sinking activity was planned meticulously to ensure that a constant submersion rate could be implemented, assisted by a number of key specialist vessels being present to position and secure the pipe section in place whilst the slack water period approached.

Slack water periods in this location are relatively short and as such, the rate of pipe submersion needed to be planned and controlled by adjusting both the water inflow and air release rates. To avoid a bending radius that could become smaller than its allowable minimum and further, to prevent the pipe wall buckling, the rates needed to be carefully monitored and controlled, all whilst considering the load imposed by the ballast weights, the varying tidal water depth and the pulling forces applied to the outfall by the marine plant.

The pipe installation continued in four separate sections, totalling 1.47km, with a diffuser head separately installed through diving operations at the seaward end. A backhoe dredger was used to place the previously excavated material on to the pipe.

Following the backfilling, approximately 210 of the precast articulated concrete mattresses in total, each weighing 8.3t in air, were laid over the installed lengths of pipe from the crane barge. The backfilling and mattress installation were monitored and supervised by Kaymac’s dive teams, ensuring the accuracy and efficiency of both activities throughout the scheme.

Civil operations, plant isolations and final connection

To prevent disruption to the client during their day-to-day operations, the marine activities to install the replacement outfall were carried out alongside the existing operational outfall. Simultaneously, inland operations were undertaken by Kaymac’s skilled civils teams, who installed a temporary sheet piled cofferdam to excavate and expose the existing valve and land-based outfall arrangement.

Two short operational isolations were required; the first to replace the existing land based valve and connecting pipes, and the second to connect the new replacement outfall to the existing infrastructure. Again, these isolations were planned precisely around suitable tidal windows, to maximise working efficiency and to minimise interruption to the plant operations.

During the first isolation, the existing land-based single non-return valve was replaced with new valves and a T-piece arrangement system that would permit future inspection and maintenance requirements.

Once the land based replacement and connection works were complete, the replacement valve arrangement was housed within a newly constructed reinforced concrete chamber, built alongside the normal operations of the plant. The chamber was designed to permit safe future access around the valve arrangement and to retain a section of the existing flood defence embankment.

The second isolation took place while the land-based civil works were underway to construct the new chamber. Working at low tidal periods, a bespoke HDPE pipe section was fabricated that considered both the vertical and horizontal changes in direction to align with the newly installed outfall. This section was installed to connect the newly installed outfall to the existing pipeline ahead of removing the isolation.

[caption id="attachment_19918" align="alignnone" width="1200"] Old pipe being removed during low tide - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption] Conclusion

The long sea outfall replacement project stands as a model of responsible marine engineering within sensitive ecosystems.

By balancing complex engineering requirements with rigorous environmental protection, Kaymac Marine & Civil Engineering Ltd are proud to have played a key role in improving Newport’s existing infrastructure; blending innovative marine engineering techniques with stringent environmental safeguards to protect and enhance the unique ecology of the Severn Estuary.