Supply Chain - Wastewater Pumping Stations

In February 2020, Storm Dennis brought flooding to the area of Glenboi during which 24 houses were flooded as the culverted watercourse system became inundated and exceedance flows made their way into the existing Glenboi Surface Water Pumping Station. The existing pumping station could not handle the exceedance flows and therefore Rhondda Cynon Taff Council sought Welsh Government funding to procure a new and improved capacity pumping station via a design and build competitive tender process. The contract was awarded on an NEC4 Option A Design and Build, and following submission of a competitive design and build tender process, envolve infrastructure was successfully appointed as the delivery partner for the >£1m project. Project scope The works comprised: Proposed underground wet well attenuation tank and pumping chamber. Fenced compound with impermeable hard standing to access the pumping station wet well with permeable hard standing beyond, accessed via pedestrian gate. Valve chamber. Connection onto existing rising main. New headwall to the newly provided existing rising main. Connection from existing highway drainage system. Kerbed bituminous pavement lay-by. Substation maintenance compound and electrical cabinet and plinth, and emergency generator plinth. Installation of electrical connection. M&E works associated with the pumps and a telemetry warning system. Early contractor involvement (ECI) and design Envolve’s ‘one-team’ integration model with Hydrock and Rhondda Cynon Taf in conjunction with the expertise of envolve’s in house design manager and construction team, formed an integral part of the collaborative delivery model. Envolve infrastructure’s sector leading ‘one-team’ approach guaranteed a collaborative partnership from the outset, facilitating an efficient and coordinated design process with Rhondda Cynon Taf. Envolve’s responsibility during the design process reviewed suitability and efficiency of the outline design, planned construction methodology & proposed constructability options to collaboratively develop the final design. Temporary works designs for the entire project were procured and managed by envolve’s in house design manager. [caption id="" align="alignnone" width="1200"] (left) Pipework within the shaft and (right) precast concrete segmental shaft rings - Courtesy of envolve infrastructure[/caption] ECI was integral to the final design solution from the outset, close collaboration with Rhondda Cynon Taf developed a more efficient and reduced cost engineering solution to meet the project objectives, providing a cost-effective and value driven solution. ECI began with a partnership with Hydrock developing the detailed design. Envolve’s ECI strategy was to further investigate and interrogate the outline design, whilst minimising risk and embodied carbon through streamlining constructability and increasing operational efficiency. The design and delivery team undertook a review of the design philosophy in tandem with Rhondda Cynon Taf’s conceptual design. A proposal was drawn up, identifying the benefits of a deeper wet well shaft in lieu of a smaller shaft with accompanying storage tank. This approach mitigated the requirement for a reinforced concrete retaining wall adjacent to the existing highway. Further investigation into the most efficient shaft construction identified the benefits of constructing a ‘wet’ cassion, in lieu of a conventional ‘dry’ construction. This construction method mitigated potential subsidence risk to 7 local residential properties and the main B4275 carriage way as there would no longer be a requirement to lower the existing high water table by our selected engineering solution. In enlarging the proposed shaft, envolve was also able to house the proposed pumping equipment within the shaft itself, significantly reducing the overall footprint of the facility. The final visual impact of the project was prioritised to provide adjacent residents with the least impactful and sustainable reinstatement on completion of the project. In lieu of a large tarmac area, a sustainable permeable hard standing was specified. On site ECI works undertook ground investigation to determine the classification of waste material for excavation arisings including sampling and laboratory testing. Envolve’s design solution successfully met Rhondda Cynon Taf’s requirement for a 250m3 storage tank with an outflow of 200 litres per second, achieved via a 6m diameter and 11m deep shaft with incorporated pumping station, all within the minimal footprint of the land available. This significant design improvement ensured the final engineering solution worked within the site boundaries, also providing Rhondda Cynon Taf with an £800k cost saving for the overall project. In summary, the outputs of our ECI expertise resulted in the following improvements to the final project design: One deeper wet well in lieu of smaller shaft. Removal of storage tank. Removal of reinforced concrete retaining wall. Mitigation of groundwater risk through ‘wet’ caisson construction. Housing of the pumping equipment within the enlarged shaft. Sustainable permeable hard standing in lieu of a tarmac. Once work commenced on site, envolve was appointed as principal contractor and principal designer. [caption id="" align="alignnone" width="1200"] (left) Birdseye view of the wet caisson shaft under construction and (right) precast concrete segmental shaft rings at the base of the shaft - Courtesy of envolve infrastructure[/caption] Glenboi FAS: Supply chain - key participants Principal designer & contractor: envolve infrastructure Detailed design: Hydrock Shaft construction: HB Tunnelling UK Confined space emergency/rescue provisions: Pulse Safety Solutions Crane Hire: Davies Crane Hire Precast concrete shaft rings: Marshalls Civils & Drainage Precast cover slab: Tracey Concrete Construction During the pre-construction phase, an access/egress plan was agreed with all stakeholders via early engagement, identifying all affected residents and stakeholders and agreeing the most efficient access/egress routes and locations for the site compound and working area. A traffic management plan was drafted and agreed with the residents, always ensuring appropriate access and egress whilst minimising the interface of construction activities with the local community. A central main compound location housed the shared project office facility, material storage and waste processing facilities. Envolve’s yard team operated a quarantine zone for deficient/damaged materials to reinforce an uncompromised approach to quality management. Envolve’s customer liaison officer (CLO) held an open day with the local community informing them of the planned works, this was an opportunity to get to know the local community and address any concerns or specific requirements they would need. Ahead of mobilisation, the CLO delivered compliment letters to all affected stakeholders, providing direct contact details for all matters relating to the project. The main construction activities were as follows: Site set up including stakeholder notice boards and branding. Service diversions, including installation of new 300mm diameter gravity surface water inlet. Excavate and cast the shaft collar, excavate and sink shaft. Cast base & mechanical installation of rising main, pumps and inlet mains. Construction of new valve chamber arrangement. Placement of cover slab with 110t mobile crane. Construction of permeable hard-standing, including tanker lay-by. External soft landscaping. [caption id="" align="alignnone" width="1200"] Birdseye view of the construction site - Courtesy of envolve infrastructure[/caption] Directly employed resource A delivery resource strategy was created from envolve’s highly experienced directly employed staff and workforce. Their in-house training team facilitated training requirements ahead of commencement. With self-delivery teams supplemented with specialist local subcontractors with whom envolve had longstanding relationships. During the project, envolve recruited local specialist resource to enhance the existing teams. Construction operations were managed by envolve’s specialist site management team supported by their in-house SHEQ department. Sustainability and carbon management In adherence to envolve’s carbon reduction strategy and net zero commitment, a permanent power supply connection was made for the main compound with a ‘green’ electricity supplier, removing the need for temporary diesel power generation for the duration of the project. Embodied carbon was an integral part of the initial design process, envolve’s design solution to construct one large ‘wet’ well shaft, mitigated the need for an additional storage tank and reinforced concrete wall, all of which combined to a significant reduction in excavation, disposal, material procurement and associated vehicular movements for the site. Further selection of the precast concrete sections from a UK-based supplier provided support for the local supply chain and reduced unnecessary transportation emissions. The benefits of specifying a permeable pavement solution for the site will help reestablish a more natural hydrologic balance and reduce runoff volume by trapping and slowly releasing precipitation into the ground instead of allowing it to flow into storm drains and out to receiving waters as effluent. [caption id="" align="alignnone" width="1200"] Completed shaft and cover slab - Courtesy of envolve infrastructure[/caption] Construction design management CDM15 regulations were discharged through the development of a detailed construction phase plan and through collaborative working. The design was approved through a detailed design process review, regular meetings and early engagement, retaining a collaborative relationship with the team. Stakeholders remained at the heart of the delivery, through conducting weekly progress meetings for the duration of the scheme covering design, construction progress, environmental and third party interfaces. Social value Through collaboration with Glenboi Primary School, envolve invited its pupils for a site visit and talk with the delivery teams to explain what the project was and how it would improve their community. 30 pupils from the school attended the safe viewing area, outside of the site boundary and within a safety zone which was especially set up for the visit by the construction team. The team spent the afternoon discussing the effects of climate change and the problems this was causing to the local environment, the purpose of the project and the benefits they will see for years to come with lots of interesting and thought provoking questions from the pupils! There was even time for the pupils to dress up in PPE and have their photo taken in one of the especially prepared small excavators! [caption id="" align="alignnone" width="1200"] School visit to site from Glenboi Primary School and the footpaths and outdoor learning facilities - Courtesy of envolve infrastructure[/caption] Following this, further support was provided to the school with the offer to complete their woodland walk and outdoor learning facility with accessible footpaths connecting the outdoor classrooms. A prestigious opening ceremony was hosted by the school for the grand opening with fantastic poems and songs performed by the pupils – there was even a special cake baked in appreciation of the relationship envolve developed with the school over the lifetime of the project. The woodland learning facility will hopefully provide years of outdoor learning opportunities for the school and its pupils. Envolve operate a successful apprenticeship programme which sees a handful of placements throughout the business each year, these roles span from Commercial through to Engineering. This project presented a unique opportunity for an Engineering placement and a person from the programme was allocated to the project for its duration as part of their development plan. Summary Through inspirational stakeholder engagement and community integration, the project not only delivered on its engineering outputs but also engaged a cohort of young people from the local primary school, highlighting the sustainability and climate objectives of the project and hopefully inspiring future careers in the engineering sector. The collaborative approach nurtured a transparent and trustworthy relationship between envolve and Rhondda Cynon Taf, demonstrating how this close working relationship directly influenced the development of an efficient and value led engineering solution which will benefit the community of Glenboi for years to come. Envolve’s anticipated programme duration of 14 weeks significantly improved on the client’s required programme completion date of May 2023.

The Ards Peninsula is a scenic area in County Down, situated on the north-east coast of Northern Ireland. It separates Strangford Lough from the north channel of the Irish Sea and its coastal towns and villages are popular with day trippers and caravanners alike. By 2020, the wastewater treatment works serving the villages of Carrowdore and Ballywalter were operating at full capacity. NI Water investment was required to ensure that these areas could meet future EU and Northern Ireland Environment Agency (NIEA) standards. The area of Ballywhiskin only had primary settlement, which was not deemed sufficient, and the caravan parks and small settlements in the Ballywalter area were served by septic tanks, which again only offered primary settlement of wastewater before discharge to nearby watercourses. The beaches in the area represent significant tourist amenity and an extensive treatment scheme was essential to meet future bathing water quality standards in line with NIEA standards. What the scheme involved The two-year Ards North Wastewater Improvement Scheme involved the rationalisation of the Carrowdore, Ballywhiskin and Ballywalter catchments so that all wastewater flows from these areas could be transferred to a new state-of-the-art wastewater treatment works (WwTW) constructed on a greenfield site off the Ganaway Road in Ballywalter. In addition to these catchments, the new treatment works has been designed to treat wastewater flows from nearby caravan parks and small settlements, which previously had no treatment facilities. The scheme was split into two contracts; one for the design and construction of new pumping stations, pipelines and a modern wastewater treatment works, which was awarded to BSG Civil Engineering, and another for the design and installation of a new long sea outfall, which was awarded to Farrans. Project management/technical support for both contracts was provided by Tetra Tech. This article focuses on the work carried out to construct the new WwTW, pumping stations and pipelines by BSG Civil Engineering to serve the combined catchments and cope with seasonal fluctuations in population to protect the tourism potential of the area for many years to come. [caption id="" align="alignnone" width="1200"] Bulk excavation - Courtesy of BSG Civil Engineering Ltd[/caption] Early contractor involvement/design and build contract BSG Civil Engineering was appointed by NI Water as the main contractor in November 2018 under an NEC 3 Early Contractor Involvement (ECI) contract. BSG provided multi-disciplinary design, project and supply chain management and all civil engineering, process and MIECA works for the contract from start to completion. The ECI phase allowed BSG to align resources and integrate objectives with NI Water and their project management team from Tetra Tech at an early stage to benefit delivery. This proactive approach led to enhanced collaboration, innovation, value, efficiency and reduced whole life costs for the project. Primary drivers The purpose and drivers for this project were as follows: Achieve compliance with current and future EU directives on effluent discharge standards. Meet Registered Discharge Standards set by the Northern Ireland Environment Agency (NIEA). Provide a flexible design to cater for future flows and the significant summer/winter fluctuations. Minimise impacts to community and environment. Support local development, tourism and economic growth. Deliver best value for money construction making use of existing assets. [caption id="" align="alignnone" width="1200"] Ards North WwTW - Inlet works overview - Courtesy of BSG Civil Engineering Ltd[/caption] Scope of works The main elements of work included: Installation of 14km of pumping main between WwTW & new/upgraded pumping stations via directional drilling and open cut methods. 2km of gravity sewer installed between pumping stations. 6mm inlet screening and storm storage for 2 hours/3x DWF) Grit treatment and removal. 3 (No.) 131m3 primary settlement tanks with automatic desludge and scum removal. Return activated sludge (RAS)/surplus activated sludge (SAS) pumping station. Anti-septicity treatment at source at the pumping stations. 3 (No.) 12m diameter final settlement tanks with automatic desludge and scum removal. Sludge holding tank. Sludge thickening and processing. Two-stage odour control plant. 330KVA standby power generation. 52.28 kwP roof mounted solar PV array, complete with dual 22kWh EV charging points. Process flows, levels, and quality monitoring; ancillary processes to support the main process units and intelligent motor control centre (MCC) with telemetry. Programmable logic controller (PLC) and human machine interface (HMI) control system. Installation of new long sea outfall pipe (detailed in a separate article). Design criteria for the Ards North WwTW Due to the large number of caravans in the area expected to be served by the new Ards North WwTW, the plant needed to be designed to deal with significant variations in flow and load to ensure satisfactory treatment could be achieved throughout the year. This meant that the works had to cope with a summer population equivalent (PE) of 8508 and a PE of 4809 in winter months. Inlet works & flow control/balancing Flows up to Formula A from the outlying stations can arrive at WwTW simultaneously. The inlet balancing chamber balances out flows going forward to the inlet screening plant. The inlet screening plant consists of two duty/standby incline screens and a cross conveyor. Each screen has a manual inlet penstock installed to enable isolation for maintenance purposes, or for bypass through the static 6mm bar screen. [caption id="" align="alignnone" width="1200"] Inlet works side view - Courtesy of BSG Civil Engineering Ltd[/caption] Screened raw sewage continues to the grit removal plant. The grit settles in a sump underneath the grit paddle. Any grit that settles in this sump is periodically aerated using the grit blower and then removed. From here the grit is transported out of the grit plant by the grit classifier and is deposited into the grit skip. From here it is removed off site for disposal. After the wastewater has passed through the grit removal plant, flow continues to the FFT pumping station. Here influent is collected, and FFT of 48.2 l/s (summer) & 29.6 l/s (winter) is pumped to the PST flow splitting chamber. Ards North Wastewater Improvement Scheme: Supply chain - key participants Client: NI Water Project management: Tetra Tech Principal designer/contractor: BSG Civil Engineering Ltd Structural, hydraulic & process design: Doran Consulting MEICA design: BSG Civil Engineering Ltd Temporary works design: MEA Ltd Electrical installations: AW Control Systems Dewatering: Causeway Geotech Aeration equipment: Xylem Water Solutions Aeration blowers: Aerzen Machines Sludge thickeners: Huber Technology MCC: LMP Controls Inlet screening: M and N Electrical and Mechanical Services | Hydro International Grit treatment: Jacopa Storm screening: Eliquo Hydrok Ltd Actuators: Rotork Septicity dosing & booster pumps: FM Environmental Half bridge scrapers & access flooring/metalwork: Graham Steelworks & Engineering Ltd Odour control plant: John Cockerill Environment Pipes & fittings: APP Fusion Group Standby generators: PM Power Poly dosing plant: ProMinent Fluid Controls (UK) Ltd Micro-strainers: Whitewater Care Photovoltaic solar farm: Solmatix Renewables Ltd DO/MLSS & turbidity instrumentations: Hach Lange Flow meters & ultrasonics: Siemens Tipping buckets: CSO Group Ltd Precast concrete supplies: FP McCann Stormwater storage When incoming flows exceed FFT, the FFT pumping station will start to fill and eventually overflow to the blind storm tank. Once the blind storm tank has reached maximum capacity, flow will backup, allowing the level within the FFT pumping station to increase further. A higher-level overflow pipe allows flows to pass to the online storm tank. Once maximum capacity is reached here, flows will pass to the Ganaway Burn via the 6mm overflow screen and flow meter. Storm return will occur when the FFT pumping station is at a suitable low level. The storm tanks will return flow to the FFT pumping station in sequence i.e. blind tank first. Both tanks are fitted with automated penstocks which will open to return the contents of each storm tank to the FFT pumping station. Both storm tanks are fitted with tipping bucket cleaning systems from CSO Group Ltd, which help prevent build-up on the tank floor to achieve that ‘brushed floor effect’ when empty. The tipping bucket will operate when each of the storm tanks has reached the empty level. [caption id="" align="alignnone" width="1200"] (left) Ards North WwTW - Courtesy of NI Water, and (right) storm tanks tipping bucket installation - Courtesy of BSG Civil Engineering Ltd[/caption] Primary treatment The PST flow splitting chamber receives flows from the FFT pumping station and return liquors pumping station. Flow from the PST flow splitting chamber passes to three primary settlement tanks. These tanks are hopper bottomed and are desludged using automated valves to the primary sludge pumping station. Wastewater continues through to the PST collection manhole which mixes with RAS upstream of the ASP distribution chamber to feed the three ASP lanes. Sludge and scum drawn from the three PSTs arrives in the primary sludge pumping station. This station consists of two submersible pumps in duty/standby arrangement and is used to transfer sludge and scum removed from the PSTs to the thin sludge tank. Activated sludge plant The ASP lanes are identical in design and equipment. Each lane comprises an anoxic zone and an aeration zone. Each anoxic zone is equipped with a mixer. Each aeration zone is equipped with an aeration grid, air control actuator, air flow meter transmitter, two dissolved oxygen probes and an MLSS probe. Each aeration zone is fitted with mixers and aeration grids with fine bubble disc diffusers, which are attached to a central manifold which then connects to the ASP blowers. The influent entering these zones is controlled to maintain a set dissolved oxygen and MLSS level. The dissolved oxygen demand is supplied via the ASP blowers, configured in a duty/assist/standby arrangement. The blowers’ manifold is monitored by a pressure transmitter, a temperature transmitter and an air flow meter transmitter. [caption id="" align="alignnone" width="1200"] Aeration plant air manifold control valves and instrumentation - Courtesy of BSG Civil Engineering Ltd[/caption] Final treatment Flow from the ASP Lanes gravitates to the FST flow split chamber, fitted with adjustable weirs where the flow is split evenly to the three final settlement tanks. Each tank is identical and is equipped with a half bridge scraper, sludge blanket detector, ladder position switch and a proximity switch. Scum travels to the scum collection chamber and furthermore to the FST scum pumping station. The station is equipped with a duty/standby pump set which pumps its contents to the thin sludge tank. The tanks desludge is controlled via flow meters through actuated hydrostatic valves located in separate chambers that adjoin the RAS/SAS pumping station. Each tank’s settled effluent hydraulically discharges into the tank’s outlet launder channel to the final effluent/washwater pumping station. Final effluent Final effluent flows into the final effluent/washwater pumping station and on to the final effluent sample chamber. Here, the final effluent is monitored for turbidity and temperature levels and is also the dedicated location for the auto sampler. The final effluent/washwater pumping station contains two submersible fixed speed final effluent/washwater pumps in a duty/standby arrangement. These are used for supplying the washwater tank with the necessary effluent for washing the screens, sludge thickeners, etc. Final effluent is returned through a packaged plant automatic backwash strainer system located inside the control building. The automatic backwash strainer system, situated inside the sludge thickening building, is a filter that is used to remove particles from the final effluent returned from the final effluent/washwater pumping station. Final effluent flows from the sample chamber which is connected to the long sea outfall pipe. Sludge pumping, treatment & storage The RAS/SAS pumping station is equipped with two sets of pumps. RAS pumps and SAS pumps, a level ultrasonic and high-level floats are used to control both sets of pumps. The duty pump returns the desludge from all FSTs back to the PST collection manhole, continuing to the aeration distribution channel. The SAS pumps, also arranged in a duty/standby configuration, periodically pump forward sludge to the thin sludge tank. The frequency is operative set to maintain a desirable MLSS level within the ASP lanes. [caption id="" align="alignnone" width="1200"] RAS/SAS pumping station - Courtesy of BSG Civil Engineering Ltd[/caption] The thin sludge tank is equipped with an external mixer for the blending of the tank’s contents to feed the sludge thickening plant. A level ultrasonic with low and high-level floats are used in the control of the mixer. Mixed sludge from the thin sludge tank is pumped to the sludge thickening plant via the two thickeners feed pumps. These pumps are progressive cavity pumps and are arranged in duty/standby configuration. The pumps are VSD controlled to allow the flow to the thickening plant to be controlled. There are two sludge thickeners, with an individual throughput of 8.3 m3/hr @ 1.3% DS with a discharge of no more than 6%, based on a 5-hour day, 7-days per week operation at 100% of the maximum design load. The thickeners are arranged in a duty/standby configuration with two actuated isolation valves installed on the feed pipework allow this to be fully automated. If one thickener was to develop a fault, the standby thickener can resume operations without manual intervention. Polyelectrolyte is made up on site to be added to the sludge fed to the sludge thickening plant. The addition of this chemical aids flocculation and makes thickening easier. This plant is a liquid polymer set. The liquid poly is delivered within IBCs for the makeup process. The set mixes the poly from the IBC with water to a preset concentration rate and is then transferred to the poly storage tank. The duty poly dosing pump doses to the thickener’s sludge feed pipework from here. Thickened sludge from the sludge thickening plant is transferred to the thick sludge tank. Here thickened sludge is stored for removal off site. A collection tanker removes the tank’s contents off site by coupling to the tank’s Bauer Coupler connector. [caption id="" align="alignnone" width="1200"] PST No 1 & control building - Courtesy of BSG Civil Engineering Ltd[/caption] The tank is equipped with a decant valve arrangement to facilitate settlement of the tank’s contents. The tank is also equipped with a level ultrasonic, low and high-level floats for level status and control of an externally fitted mixer for tank agitation. The return liquors pumping station receives liquors from the following areas: inlet works drains, thin sludge tank decants and overflow, thick sludge tank decants and overflow, sludge thickening plant bund, FE and washwater drains and odour control plant drains. The station comprises of two fixed speed pumps, which are arranged in duty/standby arrangement. These return liquors to the activated PST splitting chamber. Washwater pumping The final effluent washwater & potable water booster sets are positioned within the sludge building. A ’dual washwater tank’ system is in place to feed both sets of pumps. The GRP dual washwater tank is designed with a lower compartment which holds 6m3 and an upper compartment which holds 1m3. The lower compartment is designed to contain the final effluent delivered via the final effluent/washwater pumping station, which in turn feeds the final effluent booster set which boosts the pressure as required for the washwater of the inlet screens, sludge thickeners, odour control, and the storm tank tipping buckets. The upper compartment is designed to contain potable water which in turn feeds the potable water booster set, which boosts the pressure as required for the nine retractable hose reels around the site for wash down, poly makeup plant water and poly carrier water. [caption id="" align="alignnone" width="1200"] Low level structures RC concrete installation - Courtesy of BSG Civil Engineering Ltd[/caption] Odour control plant The 2-stage odour control unit (bio & carbon filter) is connected to the various strategic areas. The odour control unit comprises of two odour fans, which are arranged in duty/standby arrangement. Actuated valve, flow meters, pressure transmitters and temperature transmitters are used to control the odour control system. Only odour omitted from the sludge thickening building (due to their extreme odorous compounds) will bypass the biofilter and go directly to carbon filter for treatment. Outlying pumping stations Existing treatment facilities at Ballywhiskin and Carrowdore were decommissioned and replaced with new pumping stations, while a completely new pumping facility was constructed at Sandycove Caravan Park where no NI Water asset previously existed. The last of the outlying WwPS to be upgraded was Ballywalter Fowler Terminal Pumping Station (TPS). This facility was completely refurbished with larger capacity pumps, a new MCC and additional storm storage capacity. Fowler Way TPS pumps to Sandycove WwPS which in turn pumps to the new Ards North WwTW, while the pumping stations at Ballywhiskin and Carrowdore pump directly to Ards North. [caption id="" align="alignnone" width="1200"] (left) Ballywhiskin TPS - Courtesy of NI Water, and (right) Carrowdore WwPS - Courtesy of BSG Civil Engineering Ltd[/caption] Civil construction challenges There were various challenges throughout the construction phase of the works that had to be overcome to ensure that the contract programme was achieved. As the project spanned over a 20km distance, there were varying ground conditions to deal with from very loose running sand in the gravity pipeline sections at Sandycove; soft, deep peat at Carrowdore WwPS; extremely hard rock at Ballywhisken to stiff clays with loose gravels at the WwTW site. This led to a variety of temporary works systems having to be designed and employed to deliver the works safely. Groundwater levels also varied across the scheme with various dewatering techniques used to maintain dry working spaces. Artesian water pressure and groundwater under tidal influence presented difficulties during the construction of these works. Overhead services also presented a construction issue at the WwTW site. As a result, carefully planned construction sequencing and specialised plant were employed. 13.5km of pumping main was installed along roads within this rural area. In order to keep to programme, pipe installation had to be carried out using a minimum of two separate teams at all times. Due to the limited options for suitable diversionary routes in the area, the pipe installation programme had to be carefully managed and continually communicated to the roads authority to ensure both pipe installation squads had consecutive sequencing of works throughout the pipeline installation phase of the scheme. [caption id="" align="alignnone" width="1200"] (left) Sandycove WwPS and (right) Ballywalter Fowler Way TPS - Courtesy of NI Water[/caption] Sustainability To boost the sustainability of the treatment facility, 138 solar PV panels from Solmatix Renewables Ltd were fitted to the roof of the new control building which will produce over 45,000 kWh per annum. This renewable energy could save NI Water up to £300k over 25 years. Charging points for NI Water’s growing fleet of electric vehicles have also been installed at the new treatment works. Communications & PR NI Water and its project management team developed a proactive comms and PR strategy for the Ards North Wastewater Improvement Scheme which included circulation of project brochure, issuing of regular press releases, letters to residents, briefings for elected representatives, circulation of progress updates, safety events with children, and face-to-face meetings with landowners. Myriad stakeholders were kept up to date with progress and informed in advance of pipelaying works and associated traffic management arrangements. Following completion of the project, a site tour of the new WwTW was organised to give local elected representatives the opportunity to view the modern facility first hand. Feedback from the visit was extremely positive. [caption id="" align="alignnone" width="1200"] NI Water, TetraTech, BSG Civil Engineering Ltd and Farrans along with local elected representatives to mark completion of the £18m Ards North Wastewater Improvement Scheme - Courtesy of NI Water[/caption] Conclusion A collaborative, forward-thinking approach between NI Water, BSG Civil Engineering and Tetra Tech has produced whole-life cost, programme and carbon savings in the delivery of this project. Phased flows were brought into the new Ards North WwTW between the months of November 2022 and January 2023. During this time, a process optimisation phase took place before the plant was rigorously tested and commissioned under varying flow and load scenarios. The plant was then put through a period of intensive detailed process sampling achieving highly performing results during separate 14 and 28-day sampling periods during Spring 2023. The project was successfully completed and handed over to NI Water ahead of the 2023 summer tourist season. The new Ards North WwTW is ensuring that high-quality effluent is being discharged out to sea, helping to improve the bathing water quality along this part of the Ards Peninsula in line with the project objectives.

Lower Woodburn Wastewater Pumping Station (WwPS) serves the Greenisland Drainage Catchment and is located close to the town of Carrickfergus on the foreshore of Belfast Lough. The storm outfall from the WwPS flows directly into the lough. Although recognised that discharges have minimal impact on the Belfast Lough Shellfish Water Protected Area (SWPA), there is localised impact and a need to protect and preserve amenity on the accessible shoreline. Upgrading of the WwPS was needed to comply with the Environmental Regulator’s (NIEA) consent requirements. Living with Water Programme

As part of Belfast’s strategic ‘Living with Water Programme’ (LwWP), NI Water has invested £1.8m to upgrade Lower Woodburn WwPS by increasing the volume of storm emergency overflow storage and installing a static screen. The solution also facilitates proposed housing (315 units) and hospitality/recreational developments that discharge directly to the WwPS and delivers storm separation of 17.8 hectares of impermeable ground. The project delivers against the LwWP goals:

PROTECT against Flooding. ENHANCE the Environment. GROW the Economy. [caption id="attachment_12584" align="alignnone" width="1200"] Lower Woodburn WwPS site pre-construction - Courtesy of DAWSON-WAM Ltd[/caption] Project delivery

Delivery partners for this project were appointed through existing NI Water frameworks. Tetra Tech was appointed to provide professional services, (including project management, cost management and site supervision) and to act as NEC Project Manager. The Murphy/ DAWSON-WAM Ltd JV (MDW) was appointed as main contractor.

Building on earlier work done to investigate catchment-wide solutions for Carrickfergus as part of the LwWP, MDW was engaged to develop the design and build solution under an Early Contractor Involvement (ECI) NEC contract. The design was reviewed and approved in collaboration with NI Water, and budgetary approval was granted for construction works under an NEC-ECC Main Option A contract in summer 2023.

Delivery was a collaborative effort between client, consultant and contractor teams to improve water quality and environmental conditions in the receiving Belfast Lough. The works comprised addition of surface water storage in a new concrete cofferdam constructed alongside, and connected to, the existing pumping station wet well. The constrained nature of the site lead to the need for access to neighboring lands from which to operate construction plant and machinery.

The scope was further developed during construction to improve the overall solution performance by installing a non-return valve on the storage overflow to enhance separation between storage and the marine environment and to improve the design life of the pre-existing pumping station.

Change was addressed using the provisions of the NEC contract and was managed within the overall budget for construction works. The new storage tank was integrated from an ICA perspective by linking to NI Water’s telemetry system for effective monitoring of storage levels and overflow incidents.

Throughout construction, regular site inspections were undertaken by Tetra Tech’s Site Supervisor and Health & Safety Manager to affect joint inspections with NI Water’s and MDW’s H&S Managers. This made sure of a combined approach to H&S management; issues were addressed face to face in real time and resulted in an excellent H&S performance throughout, with no accidents or incidents.

[caption id="attachment_12583" align="alignnone" width="1200"] 3D models of new storm storage tank - Courtesy of RPS[/caption] Early contractor involvement (ECI)

The ECI process proved its worth as extensive design and build challenges were overcome and a buildable solution was developed that satisfied the construction brief and costs criteria. This led to Murphy/DAWSON-WAM Ltd being appointed as principal contractor for the design and build of Lower Woodburn WwPS upgrade in August 2023. Contract works involved the design, supply, installation, testing and commissioning of an additional 317m3 of additional gravity storm storage on the existing site.

Certain elements of the project proved extremely challenging, none less than the design and construction of the additional storage tank on an existing site footprint that was extremely compact. Construction was further restricted as access to the site was from the busy A2 road, (the main road corridor from Belfast to Carrickfergus), immediately to the east of the site was a live petrol station with underground fuel tanks, on the west was an existing domestic occupied property and the access to the property and to the local strand, straddled the site on the east and south side. This was further complicated by the fact the existing pumping station had to be kept operational during the entire construction process.

The extensive ECI (which included site investigations, topographical surveys, network modeling, liaison with key stakeholders and utility providers, design development and costs approval), was completed post contract award. MDW appointed RPS as their civil design partner and through collaboration with NI Water and Tetra Tech, overcame the buildability challenges of this compact site.

The ground investigation report undertaken on the footprint of the only available space on the site identified glacial till overlying bedrock which varied from 6 to 8m below ground level. Early tank storage design calculations indicated that a tank depth of approximately 6.1m deep below ground level would maximise the footprint available within NI Water’s site, and enabled a gravity return into the existing pumping station.

[caption id="attachment_12588" align="alignnone" width="1200"] (left) CFA cased auger secant piling cofferdam installation and (right) excavation of storm tank exposing secant piles - Courtesy of DAWSON-WAM Ltd[/caption] Temporary works

Several temporary works solutions were considered to facilitate the tank construction including the use of a steel sheet pile cofferdam. This solution was omitted for several reasons but predominately because of the vibration risk to the surrounding properties and being unable to achieve sufficient embedment into the mudstone bedrock.

For the solution, DAWSON-WAM Ltd developed a secant piled cofferdam design which deployed a hard/hard continuous flight auger with reinforcement cages in every male pile (second pile). Utilising a double auger drive motor, it was capable of coring into the mudstone while maintaining pile verticality.

Working with piling design partner, Cassidy Geotechnical Ltd, a 450mm diameter secant piled cofferdam with 9m long piles was developed as the most viable solution. This was further valued engineered by incorporating the piles as part of the permanent works and introducing a single face, in situ, internal reinforced concrete lining to form the internal wall of the tank. Through design analysis, it was identified in the temporary condition the secant piled cofferdam would require propping during excavation, but this was omitted by collaboration between the piling designer and contractor by introducing a reinforced capping beam that was poured prior to excavation which reduced the deflection enough during excavation to eliminate the requirement of the temporary prop. The capping beam would also provide support the permanent in-site reinforced roof structure.

Pre-construction structural surveys were undertaken on all the surrounding properties and vibration monitors were installed at two locations adjacent to the site during piling operations. The secant method proved a success as the piles were installed to the designed length without triggering any vibration limits and when excavated provided a watertight cofferdam.

[caption id="attachment_12586" align="alignnone" width="1200"] Aerial view of site during storm tank reinforced concrete base slab construction - Courtesy of DAWSON-WAM Ltd[/caption] Lower Woodburn WwPS: Supply chain - key participants Main contractor: Murphy/DAWSON-WAM Ltd JV Project management & professional services: Tetra Tech Civils design: RPS Secant piling design: Cassidy Geotechnical Ltd Civils contractor: DAWSON-WAM Ltd MEICA: J Murphy & Sons Shuttering contractor: Form Builders Mixer: Xylem Water Solutions Static screen: Eliquo Hydrok Ltd Washwater booster pumpset: Dutypoint Ltd Combisafe fall protection: Honeywell Construction Due to the storage requirements of the tank, and given the small site footprint, there was not adequate space on the site to undertake the construction works safely. Therefore, a detailed construction phasing plan was developed by the contractor at the ECI stage which incorporated keeping the existing pumping station in service during construction. This plan identified that by temporarily incorporating the existing access lane (leading to the beach and neighbouring property) as part of the site, construction could be undertaken. An agreement was reached with the owners of the house - who had just recently purchased the property – to delay their relocation to the dwelling until works had been completed, and the council agreed to temporarily close access to the strand to aid construction. [caption id="attachment_12587" align="alignnone" width="1200"] Single sided reinforced concrete wall pours against secant piles to form internal tank walls - Courtesy of DAWSON-WAM Ltd[/caption]

Consultations were carried out through NI Water’s internal communications team and members of the project management team, and included public drop-in meetings and approximately 100 letter drops.

Due to site constraints, the establishment of an off-site construction compound also facilitated just in time delivery of the construction materials to the site, which maximized the small amount of on-site space and reduced site congestion.

MEICA installation included a single Xylem Water Solutions mixer to prevent silt build up in the tank, an Eliquo Hydrok 6mm screen was fitted on the existing 315mm emergency overflow pipe from the pumping station and a new 6 bar washwater booster pumpset was commissioned on site for maintenance of the screen.

Site finishes included a new perimeter fence, EMS area and a wildflower mix was used to finish final surfaces to enhance biodiversity.

Works programme

Construction works commenced on site in August 2023 and were completed on programme and within budget by late April 2024.

The collaborative approach of the project team effectively delivered a solution to improve the water quality of Belfast Lough, supporting NI Water’s agenda to Protect, Enhance and Grow through the delivery of the Living with Water Programme.

Section 101a of the Water Industry Act requires that sewerage providers deliver and fund first time sewerage (FTS) schemes where the current drainage for two or more properties is unsatisfactory and where a public solution is viable. Unsatisfactory drainage includes situations where environmental or amenity problems caused by uncontrolled discharges from septic tanks or cess pits result in pollution of ditches or watercourses, odours and public health problems. The FTS process starts when an application is received by the sewerage provider from residents requesting a connection to the public sewer system. On receipt of the application, engineers will assess the viability of providing a new public sewer system in the area - including environmental, technical and financial considerations. The assessment will cover the polluting properties, but may be extended to others on septic tanks in the immediate area if considered beneficial. If this assessment indicates the scheme is viable, then it will proceed to design and onto construction. Reasons for an FTS scheme in Sherston In Sherston, there were a number of properties on septic tanks, including several on a shared septic tank that could only be accessed via a field. This field was only accessible once a year, after crops were harvested, which resulted in the septic tank overflowing raw sewage into an adjacent ditch. This represented a significant risk of groundwater pollution; particularly as the area is within a groundwater source protection zone. [caption id="" align="alignnone" width="1200"] (left) Schematic showing the route of the new gravity sewer and new rising main and location of the new SPS and (right), illustration from the Wessex Water leaflet to property owners showing responsibility split - Courtesy of Wessex Water[/caption] Residents in Sherston applied for an FTS scheme due to this pollution, which led to an assessment by Wessex Water which concluded that a public FTS was viable and could be progressed to design and construction. Wessex Water carried this out using their in-house capabilities at a cost of £2m. Although only a few properties were causing environmental and public health issues, Wessex Water included as many properties as possible within the FTS scheme, taking into account the viability of doing so. As a result, 24 properties (estimated population equivalent of 60) currently on septic tanks will be able to connect to the new public sewerage system by July 2023. Wessex Water’s FTS policy is to construct the new public sewerage system up to the inside the property boundary, where it terminates within a demarcation chamber. This chamber denotes the boundary between the public and private drainage system. Design options Due to the levels of the existing sewers relative to the septic tank outlet pipework, a sewage pumping station (SPS) would be required as part of the solution to connect the new sewerage system to the existing network. [caption id="" align="alignnone" width="1200"] Penstock ready to be installed over the outgoing pipe (on the left) within a manhole chamber upstream of the wet well - Courtesy of Wessex Water[/caption] Several iterations of the design were undertaken to confirm the best route of the pumped rising main, location of the proposed new SPS and access road, as outlined below: Connection to the existing sewerage network in Easton Town (B4040) - Option discounted This solution provided the shortest route for the proposed new rising main and access track to service the new SPS. However, the rising main route would need to pass through a narrow driveway between existing houses. Due to the depth of the excavation, an open cut construction method was discounted as it would be within the zone of influence of the building foundations and consequently had the risk of undermining and causing structural damage to these buildings. Trial holes indicated shallow rock which would have further exacerbated structural damage due to vibration when breaking out the rock. Trenchless techniques were considered, however due to the rock, only micro-tunnelling would be suitable, and would require a reception pit within Easton Town road, which would cause significant disruption to the community. Micro tunnelling would have also resulted in the scheme becoming financially unviable. Connection to the existing sewerage network in Sandpits Lane (access via Sandpits Lane) - Option discounted This solution provided the next shortest route for the access track to service the new SPS, and although the rising main route was extended, it allowed for an additional gravity sewer to be laid within the same trench to connect four additional properties at minimal cost, which increased the cost viability of the scheme. Prior to submitting a planning application for this option, Wessex Water consulted with the community. Significant public objections were raised due to the visual impact of the proposed new access track and SPS, particularly from those who were already on mains drainage and would not benefit from the FTS scheme. In addition, land purchase negotiations for the access track could not be resolved. Connection to the existing sewerage network in Sandpits Lane (access via Tetbury Road) – Selected Option The sewerage network for this option was similar to Option 2, however the access track route and SPS location changed to take into account the points raised from those objecting on the grounds of visual impact and land purchase issues. This option was confirmed to be both technically and financially viable and no public objections were raised, which was valuable in securing planning permissions. Scope of works The selected solution comprised: 1073m of gravity sewer. 257m of pumped rising main. A 280m long access track with post and rail fencing. A sewage pumping station to include a below-ground wet well (2.1m diameter, 5m deep), control kiosk, dosing unit (to prevent odour formation) and concrete turning area for maintenance vehicles. [caption id="" align="alignnone" width="1200"] (left) Excavation of shallow rock for rising main and (right) internal view of the wet well before sump benching - Courtesy of Wessex Water[/caption] Sherston FTS: Supply chain - key participants Designer & principal contractor: Wessex Water Civil sub-contractor: Lynwood Civil Engineering Ltd Electrical sub-contractor: HM Electrical Services 1996 Ltd Pump supplier: Grundfos Electrical kiosk supplier: BW Controls Ltd Dosing unit supplier: WES Ltd Wavin Q-Bic crates: Wavin UK Cell pave: Groundtrax Systems Ltd Wet well cover slab: Marshalls Civils & Drainage PVC pipework: Funke Gruppe DI pipework: Saint Gobain PAM UK Fittings: AVK UK Ltd Construction The SPS was located at the lowest point of the site to allow gravity fed pipework from properties connecting to the FTS scheme. The wet well was 5m deep, and constructed using a ‘bottom-up’ technique due to shallow rock in the area, which was identified during pre-construction geotechnical investigations. This involved excavating to foundation level and building up the shaft in precast 2.1 m diameter concrete rings. The 300mm-thick, 2.85 x 2.6m cover slab was made to order but cast off site. Where possible, valve chambers are constructed as precast sections to save on build time and cost. However, due to the space constraints and the proposed finished ground profile at this site, the valve chamber had to be cast in situ and dowelled into the wet well to reduce its footprint. The valve chamber was constructed relatively deep at 2.7m deep to avoid the need for air valves on the rising main, which would require ongoing future maintenance. [caption id="" align="alignnone" width="1200"] (left) Shuttering around the wet well in preparation for pouring the final layer of concrete surround and installing dowels into the valve chamber and (right) construction of wet well - Courtesy of Wessex Water[/caption] All pipework within the valve chamber was constructed in ductile iron DN80 and the rising main was constructed in MDPE pipe, SDR17, OD 110. The gravity pipework was constructed in PVCu Funke Gruppe pipe (100 mm and 150 mm internal diameter), which was selected to provide due to its light weight and construction durability compared to conventional vitrified clay pipework. Penstocks were required so that incoming sewerage flows can be controlled, to allow isolation of the wet well for cleaning and maintenance. The penstock was designed to be located within the wet well, however concerns were raised by the site team that the proposed opening for the penstock spindle would be difficult to cast in the correct location during the off-site fabrication of the cover slab. To resolve this, the cover slab design was amended to remove the penstock spindle opening, and it was moved to an upstream manhole, where the penstock could be positioned within the clear opening of the manhole cover. An overpumping connection allows for the temporary pumps to be installed and connected to the rising main via a Bauer coupling on the pipework from within the valve chamber. The valve chamber cover was designed to allow for the safe operation of the Bauer coupling by having a split walk-on grid over the coupling. This allowed the operator to place the foot on one of the closed flaps, whilst the other flap is lifted, thereby allowing them to position themselves directly over the Bauer coupling. This avoids the operator having to lean over an opening or handling the tankering hose with one hand. [caption id="" align="alignnone" width="1200"] Valve chamber cover, with split walk-on grid over the Bauer connection - Courtesy of Wessex Water[/caption] Surface water drainage A surface water drainage strategy was required due to the impermeable areas created by the sewage pumping station concrete surfaces and turning area. Pre-construction infiltration tests indicated that the ground had permeability ranging from 2.58 x10-6 to 6.59x10-6 mm/s, which was considered suitable for surface water disposal via infiltration. While it was imperative to keep the turning areas finished in concrete for durability, the straight sections of the access track were able to be constructed of permeable CellPave 50 cellular paving grid system (gravel filled) from Groundtrax Systems Ltd, laid over Type 3 poorly graded stone sub-base to minimise the surface water runoff created by the scheme. Surface water runoff from the concrete turning areas was collected via a french drain and directed into a 150m2 Wavin Q-bic crate system, which is sufficient to store a 1:100 year storm run-off based on the infiltration test results. The crate system was constructed beneath the SPS concrete turning area to optimise land use within the developed area. [caption id="" align="alignnone" width="1200"] (left) Q-bic system construction and (right) concrete slabs being cast over the crates to form the turning area - Courtesy of Wessex Water[/caption] Third party considerations The project is within the Sherston Conservation area as well as the Cotswold Area of Outstanding Natural Beauty, so it was important to provide a solution in the most environmentally sensitive way possible. Wessex Water undertook detailed environmental archaeological surveys in the early design stages to understand third party constraints and ensure these were incorporated within the design and construction process, including: Arboricultural surveys. Ecological surveys, including monitoring of stone debris removal to check for reptiles, and phased vegetation removal to check for hedgehogs. Archaeological surveys, including a geophysical survey ahead of construction and intermittent archaeological monitoring during construction, due to proximity of a Roman villa complex. As a result of the construction of the FTS scheme, permanent removal of the following was required: Three trees. Small area of dense scrub at the SPS location. An area of scrub at the edge of an arable field. [caption id="" align="alignnone" width="1200"] Public drop-in session and (inset) 3D model of the new sewage pumping station - Courtesy of Wessex Water[/caption] All temporarily affected habitats were seeded with a species-rich grassland and wildflower mix, managed to avoid cutting during the late spring and summer to benefit invertebrates and other wildlife. Off-site biodiversity enhancement measures were also undertaken in Sherston Primary School, including planting of additional trees, wildflower meadow, and providing bird nesting pockets to students. Close interaction with residents is a key feature of FTS schemes due to the work within private gardens. All residents were contacted prior to construction via face-to-face meetings and community drop-in session to give them the opportunity to ask any queries direct to the Wessex Water Project Team. A 3D model of the proposed sewage pumping station was created and used during the drop-in session to provide more clarity for the public on the proposed solution. Conclusion The Sherston FTS scheme has been project managed, designed and constructed using Wessex Water’s in-house teams at a cost of £2m. It comprises of a gravity sewerage pipework from properties which drain to the new sewage pumping station, from where it is pumped via a new rising main to the existing sewerage network. This scheme has provided 24 properties on septic tanks with a connection to the public sewerage network, which has been enthusiastically received by residents. Environmental damage from raw sewerage overflowing from septic tanks into adjacent ditches and groundwater has also been prevented as a result of this scheme. Work on site started in October 2022 and completed in July 2023.