Supply Chain - Storage Tanks - Water Towers

Storm overflows are a critical component of sewer networks, acting as relief points within the network and preventing systems from being overloaded and causing flooding. In the UK, this legacy Victorian sewer infrastructure is under growing pressures from climate change and increasing urban development. As stated in the UK Government’s ‘Storm Overflows Discharge Reduction Plan’ (SORP) (Defra, 2023), reducing storm overflows and improving water quality is a core part of the largest infrastructure investment in UK history. To address this, Wessex Water Services Limited (WWSL) is integrating Nature-based Solutions (NbS) as key interventions into their asset base through their commitment to restoring the environment. Background

Mott MacDonald (MM) has been working closely with WWSL to assess several of their storm overflow sites for installation of constructed treatment wetlands. MM is designing both traditional and innovative wetland approaches to deliver schemes at different scales and approaches, whilst maximising sustainability through retrofitting existing and decommissioned infrastructure.

The focus of this case study is to outline the regulatory drivers, the overall design approach taken by MM and detail how the design has gone beyond simply seeking to limit environmental impact.

[caption id="attachment_15838" align="alignnone" width="1200"] Example of a separated storm overflow and final effluent discharge point - Courtesy of Mott MacDonald (David Naismith)[/caption] Regulatory drivers

Under the Environment Act 2021 (Parliament of United Kingdom), all water companies in England are legally required to progressively reduce the adverse impacts of discharges from storm overflows. Under the SORP (2023), all water companies are required to achieve the following three specific targets:

By 2035, water companies will have improved all storm overflows discharging near every designated bathing water and improved 75% of storm overflows discharging into or near ‘high priority sites’. By 2045, water companies will have improved all remaining storm overflows discharging into or near ‘high priority sites’. By 2050, no storm overflows will be permitted to operate outside of unusually heavy rainfall or to cause any adverse ecological harm.

These targets need to be achieved in addition to all legal duties stipulated under the Urban Waste Water Treatment Regulations (England and Wales) (1994) and the Water Industry Act (1991).

Storm overflow operation is influenced by rainwater and/or groundwater contributions. Where groundwater is the key contributor causing the overflow to operate, often for prolonged periods of time, NbS can provide treatment to ensure no adverse ecological harm. This aligns with the requirements set out in the relevant legislation.

Suitable regulation is and will be key to ensuring wetlands are appropriate and adequately designed to address needs. Wessex Water has been working with Defra and the Environment Agency to develop a permitting approach suitable for use at their sites with groundwater influenced storm overflow wetlands. It is anticipated that through using existing wetland sites as research and case study systems, under Operating Techniques Agreements (OTAs), suitable permitting can be developed for future use.

To date, there is a requirement to satisfy the requirements of the Urban Wastewater Treatment Regulations (England and Wales) (1994), specifically Schedule 3 Table 1, which sets out effluent quality requirements with respect to BOD5 and demonstrate that the Best Technical Knowledge Not Entailing Excessive Cost (BTKNEEC) tests have been satisfied.

[caption id="attachment_15846" align="alignnone" width="1200"] Example of a wetland with established vegetation - Courtesy of Mott MacDonald (David Naismith)[/caption] Design approach - phased delivery

Since 2022, Mott MacDonald has assisted Wessex Water to review their most frequently spilling groundwater induced storm overflows and assess the suitability of each for the installation of constructed treatment wetlands. Overflows that are governed by groundwater infiltration into the sewerage system in the upstream catchment typically exhibit a lower peak flow and overflow for a longer duration. Initial screening was undertaken to derive a candidate list of sites - where installation of treatment wetlands may be a feasible option to reduce untreated discharges to the environment and prevent subsequent ecological degradation of the receiving waterbody. This screening primarily consisted of the review of all available data sets (e.g., storm overflow water quality, quantity, and spill frequency data) and undertaking initial site visits.

It is recognised that the use of treatment wetlands systems in Europe to treat storm overflows has occurred, but their use in the UK is limited. The integration of non-traditional and unfamiliar technology within the UK water industry comes with associated risks and opportunities. Wessex Water has used a phased delivery approach which allows for a gradual implementation, facilitating easier planning and control of delivery. Key blockers are identified at the initial stages of delivery, allowing for issues to be solved with a minimised impact and will make the process smoother in the long run. A staggered approach has allowed for the growth of expertise and capacity, development of efficiencies and best practice and lessons learnt to be implemented from earlier phases.

[caption id="attachment_15840" align="alignnone" width="1200"] Soft engineered bank, pond and marginal planting - Courtesy of Mott MacDonald (David Naismith)[/caption] Overview of constructed wetlands solutions

There is good evidence of the use of constructed wetlands (CWs) for treating storm overflows in Europe and the USA, with the most recent information available for systems in Germany, Italy, France and the USA. At present there is little published literature on the use of CWs for CSOs/SOs for the UK.

One of the first storm overflow filters was built in Germany in 1989, these were referred to as Retention Soil Filters (RSF) as they were constructed with a soil and compost filter media. Following early experience with these systems, the filter media was changed to technically mixed sands to prevent clogging (Meyer et al., 2013).

The German Association for Water, Wastewater and Waste (Deutsche Vereinigung fur Wasserwirtchaft, Abwasser und Abfall, DWA), released national guidelines on design and operation in 2005, based on the improved RSF design with sands and gravels as the filter media. These guidelines were updated in 2018 (DWA, 2018; Nivala et al., 2018) based on the experiences since the first issue. Further development of the design of storm wetlands in France and Italy began in the late 2000s, with national guidance being produced.

Treatment process

A typical storm overflow wetland is installed between the overflow point from the storm tank and the existing storm outfall. Irrigation flow can be taken from the final effluent stream or a potable water source. The figure below illustrates a flow diagram for an example site with Vertical Flow (VF) wetlands installed. It should be noted that at some sites, storm overflow and final effluent share a common outfall to an adjacent watercourse.

[caption id="attachment_15832" align="alignnone" width="1200"] Example treatment process of a vertical flow wetland used to treat storm overflow - Courtesy of Mott MacDonald (David Naismith)[/caption]

The typical performance for CSO/SO wetlands is provided in the table below.

The pollutant reductions ranges are derived from a review of literature and cover a range of system configurations but provide a general indication of the water quality improvements that can be expected.

Parameter Typical Reduction Range Parameter Typical Reduction Range Total suspended solids 50-95% Nitrate 45-50% Biological oxygen demand (BOD) 60-90% Total phosphorus 40-90% Chemical oxygen demand (COD) 80-90% E. Coli 1.2-2.3 log10 Ammonia 40-90% Enterococci 0.9-2.2 log10 Typical Performance of CSO/SO Wetlands Wetland types

Selection of the type of treatment wetland to be implemented has been very site specific, as each site has offered unique challenges and opportunities, though with some commonality. Typical constraints have been land area available, topography (especially levels of existing chambers where flows have to be intercepted), ecological aspects, and existing services.

The design has sought to select the most suitable wetland type for each site. The following wetland types are being designed by MML and are elaborated upon in the following sections:

Free water surface (FWS) wetlands. Vertical flow (VF) wetlands. Floating treatment wetlands (FTW). Swales and bioswales. [caption id="attachment_15839" align="alignnone" width="1200"] Example of a free water surface wetland - Mott MacDonald (David Naismith)[/caption] Free water surface (FWS) wetlands

This type of wetland most closely resembles natural wetlands and take the form of a marsh habitat. They consist of soil media in the base, a permanent flooded water depth of at least 300-500mm and are usually densely planted with mixed native species of submerged, emergent, and marginal aquatics. These wetlands are typically used for secondary and tertiary treatment and are effective at reducing BOD, COD, oxidised nitrogen, total phosphorus, and suspended solids concentrations.

FWS wetlands are good for high flow sites as attenuation capacity can be built in, they are continuous flow so do not require measured volumes or inflow control like VF wetlands. They do require a larger surface area and land-take than VF wetlands so are only suitable on sites where land is available, and the soils and topography are favourable. They can be incorporated into the landscape and designed to reflect more natural wetland features, so can appear less engineered than VF wetlands with less visual impact.

Vertical flow (VF) wetlands

VF wetlands consist of a sand and gravel filter with wetland plant species (typically Common Reed ‘Phragmites australis’) present on the surface. Influent is delivered in measured volumes to the surface of the wetland where it floods the top sand layer to a design depth. The influent then filters vertically down through the sand and gravel layers receiving treatment before being collected in the base of the wetland and directed to the next downstream stage. These wetlands usually operate in a minimum configuration of two cells that are alternately fed with influent, with each cell having a rest period between feedings. These wetlands are particularly effective at reducing biological oxygen demand (BOD), chemical oxygen demand (COD), and ammonia concentrations.

VF wetlands provide high performance for area footprint but do require wastewater to be delivered in measured volumes, therefore pumping or gravity siphons are required. They were selected where space was limited, and available flow data indicated they would be suitable.

[caption id="attachment_15842" align="alignnone" width="1200"] Example of a vertical flow wetland - Mott MacDonald (David Naismith)[/caption] Floating treatment wetlands (FTW)

This type consists of module units that comprise a floatation and substrate support system, planting substrate, and plants. They are typically installed on open water areas with multiple anchoring points to the bed and/or banks to hold them in position. They have the advantage of being able to accommodate relatively large fluctuations in water level while providing water quality improvement and ecological benefit. They can be used to improve the performance of settlement ponds by promoting greater suspended solids removal.

The modules are fabricated off site with media installation and planting undertaken on site. The modular construction, ability to build different configurations and shapes, and low infrastructure requirements make FTWs an effective solution for retrofitting to existing ponds, lagoons and tanks.

Swales & bioswales

Traditionally used for sustainable drainage systems (SuDS) applications, dry and wet swales are shallow ditch like features with dense vegetation. Bioswales are deeper features with a saturated, anaerobic zone in the base. Swales have been considered here in specific situations where spill volumes could be low, space is limited and irrigation between events is a challenge, as they are more resilient to dry periods. Adopted from the Catchment Sensitive Farming (CSF) approach, they are proposed on an experimental basis for network pump stations and low volume spilling sites to improve water quality and reduce impact on the receptor. However, they are likely to have lower water quality improvement potential than the other wetland types.

[caption id="attachment_15836" align="alignnone" width="1200"] (left) Example of a floating treatment wetland - Courtesy of Biomatrix Water and (right) example of a swale - Courtesy of Mott MacDonald (David Naismith)[/caption] Wider benefits during solution development

An appropriate balance between grey and green infrastructure has been sought during design development at existing Wessex Water WRCs (water recycling centres) and SPSs (sewage pumping stations). The design approach of the schemes has focused on wider benefits alongside reducing construction, carbon, and energy requirements. The team has taken a collaborative approach to design working with multiple stakeholders and disciplines, including operational and specialist technical teams, statutory agencies, contractors, and suppliers. This included early engagement, where possible, to mitigate risks and maximise opportunities.

Retrofit & reuse

Where possible, the design has investigated the use of existing but decommissioned or under-used infrastructure for the installation of wetland systems. This has included the conversion of disused sludge or filter beds into vertical flow (VF) wetlands and re-use of redundant storm tanks or oxidation ditches into floating treatment wetland (FTW) settlement tanks. If existing infrastructure can be re-purposed where possible, this will reduce materials and construction costs and potentially reduce carbon impacts. The other advantage is to utilise space within sites more effectively, reducing the potential land take of a system and the need to purchase further land outside of the works.

The design process has also sought to maximise reusing material, such as biofilter media, to encourage responsible material consumption, reducing the required transport and volume of material sent to landfill.

[caption id="attachment_15864" align="alignnone" width="1200"] (top left) Decommissioned filter beds being considered for retrofit, (top right) filter media being considered for reuse, (bottom left) decommissioned oxidation ditch being considered for retrofit - All courtesy of Wessex Water, and (bottom right) planting within an existing floating wetland - Courtesy of Mott MacDonald[/caption] Sustainability

The design has considered the whole life cycle of the wetland and mitigated the risk of potential degradation of habitat during dry periods when selecting the type of wetland to be installed at a site and irrigation required. To reduce energy consumption, designs have been exploring the use of renewable energy using solar pumps for irrigation of wetlands during dry summer periods. Where topography and site constraints have allowed, the designs have sought to install gravity systems to avoid pumping and have adopted greener engineering solutions to provide additional value and sustainability benefits.

Where possible, the designs include viewing platforms and interpretation boards for recreational users of adjacent land to use to view and learn about the proposed wetland and surrounding area. The incorporation of these elements provide opportunities to educate on the importance of water management and biodiversity and also directly benefit people’s wellbeing through the creation of interactive spaces.

The design process has considered how multiple benefits for local wildlife and enhancements to existing habitat could be achieved. The use of soft engineered banks to retain wetlands has been prioritised where land and site-specific constraints allow. This, in addition to planting of mixed native species with attention to locally important species, has the potential to support the local ecosystems and enhance biodiversity. Where excavation has been unavoidable, enhancements such as: utilising excavated chalk to enrich surrounding chalk grassland; creation of butterfly and invertebrate mounds; and strategic planting have been included in the design. For example, at Maiden Newton WRC, the design includes scrub planting for the enhancement of local reptile habitat and hedge planting and management, using traditional hedge laying techniques, to both screen the existing WRC works and provide ecological, landscape, and heritage educational opportunities

[caption id="attachment_15843" align="alignnone" width="1200"] Soft engineered bank, pond and with established vegetation - Courtesy of Mott MacDonald (David Naismith)[/caption] Conclusion/summary

Working towards achieving targets set out in the SORP, Wessex Water is trialling NbS schemes across the region which shall inform the long term NbS strategy. The systems will be monitored for performance but also for ease of operation and maintenance. This monitoring will feed into capturing performance trends, lessons to be learnt and efficient maintenance operations. The information captured can then be fed back into various elements of the business to inform the development of NbS for this application.

From this, there is potential to educate and inform the national narrative and provide the evidence for other water companies to take up these solutions. Promoting the wider benefits (biodiversity, carbon, energy reduction, research, and education), resilience to climate change impacts and landscape fit, backed up with evidence, should increase the uptake of NbS within the water industry.

At time of writing (August 2024), Mott MacDonald has commenced design on a total of 11 sites whose construction phase is programmed to occur in AMP8 (2025-2030) and AMP9 (2030-2035).

The list below provides a high-level overview of the types of wetlands being designed for the sites*.

Gurney Slade SPS: Swale with engineered soil. Bradford on Tone WRC: Vertical flow wetland. Hatch Beauchamp WRC: Bioswale (deep swale with engineered soils and a saturated, anaerobic zone). Maiden Newton WRC: Combination of vertical flow & free water surface wetlands. Wookey WRC: Re-purposing of decommissioned filter beds and retrofit with a vertical flow-style wetland using existing filter bed media. Cheddar WRC: Re-purposing of decommissioned oxidation ditch and retrofit with floating treatment wetland. North Cadbury WRC: Vertical flow wetland and/or bio-bed or bioswale. Sydling St Nicholas WRC: Potential short term swale solution and long term vertical flow wetland. Chew Stoke WRC: Re-purposing of decommissioned primary settlement tanks and creation of a free water surface wetland. Hullavington WRC: Vertical flow wetland. Great Badminton WRC: Free water surface wetland.

* Subject to change upon receipt of surveys and/or review of guidance pertaining to permitting and monitoring requirements for storm overflow treatment wetlands, anticipated to be released by the Environment Agency in 2024.

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.

The Burnley Integrated Catchment Scheme is one of United Utilities (UU) largest AMP7 projects. The project is being delivered through our Construction Delivery Partner (CDP) Framework by Advance-plus, a joint venture between MWH Treatment, J Murphy & Sons (JMS) and Stantec. The project commenced in 2020 and through previous years articles we have been able to share the project journey we have been on from concept, through solution and design development, and construction updates. In this year’s article we are pleased to provide an insight on the significant progress made over the last twelve months, and a look forward to the December 2024 regulatory outputs. Project requirements & the integrated catchment solution scope

The integrated solution scheme requirement is River Water Quality Improvement for the Water Framework Directive (WFD) driver identified in the Water Industry National Environmental Programme (WINEP) to achieve a ‘good status’ in the defined reaches of Pendle Water and the River Calder. To meet this, the treatment capability at Burnley Wastewater Treatment Works (WwTW) is to be enhanced to achieve compliance with the new treated effluent permit standards, coupled with management of storm discharges in the defined reaches, to achieve a compliance with the WFD 99%ile wet weather intermittent standards. There are eight regulatory drivers attached to this WFD element of the scheme.

The project also includes a further two regulatory drivers for U_MON3 spill monitoring and U_MON4 flow monitoring.

Through complex river water quality and network modelling, the lowest whole life cost integrated catchment solution was determined and developed.

Four sites make up the integrated catchment solution which are all inter-dependent in delivering the regulatory outputs.

[caption id="attachment_18284" align="alignnone" width="1200"] Activated sludge plant, interstage pumping station and blower building - Courtesy of United Utilities & Advance-plus[/caption] Burnley WwTW

Burnley WwTW serves a domestic population equivalent (PE) of 107,115 plus trade load. The site is undergoing a significant upgrade with the scope comprising design, construction, and commissioning of:

New 12,000m3 detention tank with associated pumping station. New additional (4th) primary settlement tank (PST). New 1300 l/s interstage pumping station. New activated sludge plant (ASP) with BioMag process. The BioMag System enhances conventional biological wastewater treatment by using magnetite (Fe3O4) to ballast floc allowing an increase in mixed liquor suspended solids (MLSS) in the ASP and enhanced performance in the final settlement tanks (FSTs). Refurbishment of the four existing final settlement tanks (FSTs). New surplus activated sludge (SAS) thickening process. New ferric and caustic dosing plants. Associated motor control centres (MCCs), SCADA upgrade, and power upgrade. U_MON3 Event Duration Monitoring (EDM) on spills to storm tanks. U_MON4 flow monitoring.

2024 has seen the project progress at pace, transitioning through the typical construction sequence of civils, mechanical and electrical installation and now into commissioning.

[caption id="attachment_18278" align="alignnone" width="1200"] BioMAg Magdrums - Courtesy of United Utilities & Advance-plus[/caption]

Storm tanks & interconnecting pipework

A critical element of the works has been modifications to the existing storm tanks and installation of interconnecting pipework to provide the flow path and link into the detention tank feed pumping station.

Safe access into the storm tanks to core the interconnecting walls and install the pipework is only possible during dry weather, low flow periods and requires robust planning and risk management with the operations staff. The wet and unpredictable weather during the first half of 2024 proved challenging and hindered progress in this area but is now complete and ready to go into service when required.

Primary settlement tank (PST)

The new PST was built by A-Consult Ltd using the precast concrete panel method of construction. The design comprises a fixed bridge, rotating scraper arrangement to accommodate installation of a cover to provide odour mitigation. The mechanical installation has been undertaken by EPS Water and Corporate Engineering supplied and installed the cover. The odour extraction fans, ductwork and vent stack have also been installed and put into operation. Commissioning of the PST is complete.

Interstage Pumping Station

To transfer flows to the new ASP, via a new distribution chamber, an interstage pumping station (ISPS) has been constructed, comprising a two-compartment design to facilitate future maintenance activities. The mechanical installation, by FSE, of the pumps and pipework is now also complete along with associated access steelwork. The new pumps have been supplied by Xylem Water Solutions who have supported the designers in providing the most efficient arrangement. The pumping station installation is complete and commissioned.

Activated sludge plant

In constructing the new ASP, STAM Construction Ltd have installed 650 tonnes of rebar and poured 4500m3 of concrete. The overall size of the ASP is 48m x 48m x 6.6m deep, has a capacity of 14,500m3 and comprises four lanes. For the last few months, mechanical installation of the air blowers, air pipework manifolds, internal pipework, aeration grids, diffusers (by Suprafilt Ltd) and access platforms and walkways (by Tushingham Steel Fabricators) has been taking place and now complete. The electrical installation followed swiftly behind, along with testing and commissioning.

[caption id="attachment_18281" align="alignnone" width="1200"] Burnley WwTW: ASP plant - Courtesy of United Utilities & Advance-plus[/caption]

BioMag

Evoqua Water Technologies’ BioMag process involves dosing magnetite which acts as a ballast, which coupled with chemical dosing provides efficient solids removal from the process. Adopting the BioMag technology has meant the footprint of the ASP is smaller than a conventional ASP process and the four existing FSTs provided sufficient capacity and could be utilised with refurbishment without the need to build additional units. This has contributed significantly to the lowest whole life cost solution.

The BioMag comprises equipment including four Magdrums, two shear mills, process tanks, magnetite silo and pumps which have all been mechanically installed by Alpha Plus Ltd. The electrical installation, by PICOW Engineering Group, is complete and Evoqua Water Technologies have now commenced their commissioning.

To meet the desired performance with the introduction of the BioMag process and dosing of magnetite, and to provide asset life longevity, the four existing FSTs have undergone significant refurbishment work. The scope included civils refurbishment of the tank walls which involves cutting approximately 300mm from the top of the walls before installing new reinforcement and re-casting concrete to the required coping levels. Cutting works is being undertaken by Holemasters and FRC works self-delivered by JMS.

The mechanical and electrical work was undertaken by Jacopa and comprised refurbishment of the bridge, scraper assemblies, and other ancillary equipment.

[caption id="attachment_18277" align="alignnone" width="1200"] Detention tank and pumping station - Courtesy of United Utilities & Advance-plus[/caption]

Detention tank

Construction of the new detention tank has been completed by A-Consult Ltd and comprised 64 precast concrete panels, standing 10.4m high. Works included the mechanical installation of the internal and external pipework and fluidic mixing system by Fluid Sealing & Engineering (FSE). The feed pumping station has also been constructed and the pumps and pipework installed. The electrical installation by PICOW Engineering Group is just completed with commissioning due to be undertaken in October 2024.

Sludge thickening

The new sludge thickening plant, via a new storage tank, accepts sludges from the treatment process, and through two Huber Technology drum thickeners with poly dosing, thickens the sludge to 5.5% dry solids before sending it to the existing sludge treatment centre via new transfer pumps.

The plant also includes a new pumping station to return filtrate from the thickening process back to the front end of the treatment process. The installation is fully complete and commissioned, awaiting sludge to be generated through process commissioning of the new process.

[caption id="attachment_18279" align="alignnone" width="1200"] Sludge thickening area- Courtesy of United Utilities & Advance-plus[/caption]

Chemical dosing

The new ferric and caustic dosing plants comprise storage tanks, dosing rigs and dosing pipelines, all of which have been delivered and installed on site by NPS Engineering Group. A new chemical delivery and offloading facility has also been constructed with final tie-ins to the existing site road network ongoing. The electrical installation is also now complete in this area with dry testing and commissioning in progress.

Electrical works

A new, uprated HV cable has been installed from the off-site substation to the wastewater treatment works, a length of approximately 900m, passing through a number of fields and third party land. To meet permit requirements, a new automated standby generator has also been installed to provide resilience to the interstage pumping station and ASP in the event of mains power failure. The generator has undergone successful G99 testing and now in operation.

To control all the new assets a number of new motor control centres (MCCs), housed within kiosks, are required around the site, along with a new site wide SCADA system. All MCCs have been provided and installed by Technical Control Systems Ltd. The electrical installation of the associated assets and field instruments etc is complete in all process areas. The new SCADA system and associated fibre network are now operational providing full control and visibility of all new and existing assets.

Meeting drivers

To satisfy the U_MON3 driver, an ultrasonic level device detects any spills into the storm tanks. This was verified and certified to allow the U_MON3 driver to be satisfied in May 2024.

To cater for the increase in flow to full treatment (FTFT) of 275 l/s (taking FTFT to 1295 l/s), a second channel has been constructed, complete with flume and flow monitoring. In conjunction with the existing flume, the system will be verified and certified to U_MON4 standards.

[caption id="attachment_18285" align="alignnone" width="1200"] Burnley STW: Chemical dosing area - Courtesy of United Utilities & Advance-plus[/caption] Burnley process commissioning & start-up

Planning for commissioning commenced in the design phase anticipating the complexity of managing a smooth transfer from the existing process to the new, without compromising compliance. The design and build have included things such as pipework, sacrificial valves, connection points, and isolation points etc to facilitate effective commissioning. Monthly process commissioning workshops have been held throughout the last year, involving the project teams and operational staff, to jointly develop the start-up plan and methodology. Lots of hard work has gone into developing this robust plan taking into consideration all aspects of process risk and appropriate mitigation and contingency measures.

It is envisaged to take around 8-10 weeks to start-up, establish and stabilise the biological treatment, and migrate from the existing to the new process, passing through a structured Agreement to Operate (ATO) process, comprising nine interim stages. A period of optimisation will follow before entering into the 56 days completion test period.

iATO 1A: Commence flow to PST4, ISPS and ASP lanes 1&2, with MLSS build up. iATO 1B: Pass forward flows from ASP Lanes 1 & 2 to FSTs. iATO 2: Turn all flows to new ASP. iATO 3: ASP Lanes 3 & 4. iATO 4: SAS thickening. iATO 5: Magnetite loading. iATO 6: Primary ferric and caustic dosing. iATO 7: Increase flows to new FTFT of 1295 l/s and detention tank. iATO 8: Secondary ferric & liquid poly dosing.

At the time of writing (September 2024), the project has hit the major milestone of interim ATO 1A which is the initial turning of a portion of incoming flows into PST4, interstage pumping station and lanes 1&2 of the ASP plant. The team is now in the process of establishing the biology in those two lanes, and using a mixture of crude effluent and surplus activated sludge (SAS) from the existing process, building up the mixed liquor suspended solids concentration towards the target of 2500 mg/l, which is the gateway to stage iATO 1B.

It is expected that the new process to be fully operational and optimised with completion testing commencing in December 2024.

[caption id="attachment_18283" align="alignnone" width="1200"] Interstage pumping station and BioMag & blower buildings - Courtesy of United Utilities & Advance-plus[/caption] Burnley WwTW Catchment Strategy: Supply chain - key participants Client: United Utilities Construction Delivery Partner: Advance-plus JV MWH Treatment (Advance-plus jv) J Murphy & Sons (Advance-plus jv) Stantec UK (Advance-plus jv) Civil design detention tank: COWI UK Ltd Physical modelling: Hydrotec Consultants Ltd Dewatering design: OGI Groundwater Specialists Ltd Dewatering: Alba Dewatering Services Ltd Concrete construction: STAM Construction Ltd Detention tank shaft: Joseph Gallagher Ltd Pump station shaft: EJ Kelly Sheet piling: Sheet Piling (UK) Ltd PCC driven piling: Van Elle Concrete cutting: Holemasters Temporary works/shoring: MGF Ltd Precast post tensioned tanks: A-Consult Ltd Precast roof sections: Macrete (Ireland) Ltd Precast shaft segments: FP McCann Blower building: Saredon Steel Buildings Ltd BioMag building: Gallaway Construction Ltd Access metalwork: Tushingham Steel Fabricators BioMag process: Evoqua Water Technologies (Xylem Water Solutions) BioMag mechanical installation: Alpha Plus Ltd Civils & pipework: SGC Civil engineering Ltd Pumping station mechanical installation: Fluid Sealing & Engineering (FSE) Transformers: Winder Power Electrical installation: PICOW Engineering Group MCCs: Technical Control Systems Ltd Systems integration: Tata Consultancy Services SAS glass coated steel tank: Stortec Engineering Ltd Dosing systems: NPS Engineering Group PST fixed scraper bridge: EPS Water Epoxy coated carbon steel pipework & wall starters: Freeflow Pipesystems Ltd SAS drum thickeners: Huber Technology Odour control system: Air-Water Treatments Ltd PST odour covers: Corporate Engineering Ductile iron pipework: Saint Gobain PAM UK Ductile iron pipework: Electrosteel Castings (UK) Ltd FST scraper bridge refurbishment: Jacopa Ltd Blowers: Sulzer Pumps Wastewater Ltd Aeration system: Suprafilt Ltd SAS tank air mixing system: Utile Engineering Submersible pumps: Xylem Water Solutions Valves: AVK UK Ltd Standby generators: DTGen Kiosks: Industrial GRP Ventilation: Air Technology Systems Ltd Lindred Road CSO (PEN0056)

Work at this existing combined sewer overflow (CSO) site comprised the construction of an online 1,950m3 detention tank which will hold storm waters during times of heavy rainfall, reducing discharges to the watercourse. New pumps within the tank return the effluent to the sewer for onward treatment at Burnley WwTW. A new motor control centre and power supply were installed for this facility.

The detention tank which is of segmental shaft construction, 15m diameter x 20m deep, and located within the very busy and congested Lomeshaye Industrial Estate in Nelson, has been constructed by Joseph Gallagher Ltd. This was a highly challenging build within a car park of one of the local businesses and an enormous amount of planning and stakeholder management was required.

[caption id="attachment_18286" align="alignnone" width="1200"] Lindred Road detention tank during construction - Courtesy of United Utilities & Advance-plus[/caption]

Work started on site in July 2022, with the first phase involving the diversion of numerous services, including gas, fibre, BT, water and power, to clear the area for the tank construction. Enabling works to provide safe access routes, segregation, and procurement of alternative car parking for the impacted business employees was also required before the main construction work could commence in earnest.

Ground was broken in August 2022 with the tank construction continuing through to December 2022 when full depth was reached. Construction of the pump sumps, inlet channel and complex benching arrangement followed.

The spring months of 2023 saw the mechanical works inside the tank take place with the installation of the pumps, pipework and access ladders and platforms. Once the internal works were complete, the roof beams were installed and the roof slabs placed on in May the same year.

The subsequent months saw the installation of the inlet and outlet pipework for the tank, including associated manholes and chambers. To facilitate the connection of the 1200mm inlet pipe into the existing CSO chamber, a complex timber heading arrangement needed to be constructed in order to access beneath, and protect a myriad of services crossing the vicinity.

The civils and pipework were undertaken by SGC Civil Engineering Ltd and the mechanical works by FSE. The new site power supply was energised in October 2023 allowing testing and commissioning to follow.

The new detention tank went into operation in December 2023 with all works on site complete in March 2024, and is now providing great environmental benefit through significantly reduced discharges.

[caption id="attachment_18282" align="alignnone" width="1200"] Burnley WwTW: Odour control cover for PST4 from Corporate Engineering - Courtesy of United Utilities & Advance-plus[/caption] Altham Outfall Fennyfold CSO (BUR0026)

This existing CSO site is located in Padiham, near Burnley, and is part of the sewer network that transfers flows to Hyndburn WwTW for treatment. The solution here was to construct a new chamber over the downstream sewer, and install a new real time controlled actuated penstock valve that regulates and optimises flows passed forward to Hyndburn, whilst reducing spills from the existing CSO. A new control kiosk was also provided.

This new facility is situated within an environmental and stakeholder sensitive area, adjacent to a number of allotments, and the River Calder. The parcel of land required for the new kiosk and chamber had to be procured and a new access track for both construction and future operation and maintenance was laid. To facilitate the main construction activity, a complex temporary works arrangement was required, with large scale over-pumping, to carry out the works on the live sewer. Works included installing temporary isolation rails and plates during overnight and low flow conditions.

The civils and mechanical works were undertaken during spring 2024, with the new mains power supply being energised in June. Testing and commissioning ensued, with the new real time controlled system going into full automatic operation in August.

Reinstatement and landscaping took place during summer and the works are now complete at this site.

There was lots of positive engagement with the local community of allotment holders throughout the works, including a tree planting day with the local school arranged.

Hyndburn WwTW

To cater for the change in flows being presented at Hyndburn WwTW through the inlet sewer from the BUR26 catchment, the solution modelling identified works would be required on the site storm tank return system to ensure that the river water quality objectives would be achieved.

The initial solution model indicated the existing storm tank return pumping station needed to be replaced with a new facility with an increased pumping capability which would have cost in the region of £2.4m.

Through value engineering workshops, pushing the boundaries with several iterations of water quality solution modelling, and positive discussion and engagement with the EA, we successfully designed out the need to build a new storm tank return pumping station. Instead, the works simply comprised optimisation of the existing facility to return the storm tank contents sooner once a storm event has subsided.

[caption id="attachment_18276" align="alignnone" width="1200"] Detention tank on water test - Courtesy of United Utilities & Advance-plus[/caption] On course for success….

With the works at Lindred Road CSO, Altham Outfall Fennyfold CSO and Hyndburn WwTW now complete and in full operation, and Burnley WwTW in the thick of process commissioning, the United Utilites/Advance-plus team are on course to successfully deliver the catchment solution project and meet the eight Water Framework Directive regulatory outputs ahead of the 22 December 2024 regulatory date.

At Burnley, the U_MON3 output is complete with the U_MON4 verification and certification is due to take place in October.

Getting to this stage, and on course to successfully deliver, this major and highly complex scheme, has not just happened by chance. It has been years of hard work, dedication, and an intense focus on health, safety and wellbeing being at the forefront.

A proud landmark moment of reaching 500,000 hours worked across the project RIDDOR free was achieved in May this year.

It is testament to true collaboration between the United Utilities and Advance-plus project teams and wider stakeholders which has seen us overcome many challenges and get to where we are today as we head into the home straight.

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.

Ballyronan is a small village situated in County Londonderry, within the Mid-Ulster District Council area located on the western shore of Lough Neagh. The towns of Magherafelt and Cookstown are both approximately 4 miles to the north-west, and 11 miles to the south-west respectively. The existing Ballyronan Wastewater Treatment Works (WwTW) was constructed to cater for a design population equivalent (PE) of 571, but in 2021, it was calculated that the existing works was dealing with a PE of 1,020 and that a future PE of 1,520 was anticipated. Existing works

The existing works comprised of an inlet chamber, a rectangular hopper-bottomed primary settlement tank, two percolating filters, a hopper-bottomed humus tank and a sludge holding tank. There was also a brick building which housed the control panel and NIE supply for the WwTW. Interstage pumping was also required to lift the primary settled flows to the biological filters.

The existing works was required to comply with a discharge consent of 40 mg/l BOD, 60 mg/l total suspended solids, and 7.5 mg/l ammonia.

[caption id="attachment_16703" align="alignnone" width="1200"] (left) Existing site on western shores of Lough Neagh, (top right) existing PSTs, and (bottom right) existing percolating filters - Courtesy of NI Water[/caption] Project drivers

Though the treatment process was generally in compliance with the current standard, the Northern Ireland Environment Agency (NIEA) had indicated that a new, more stringent consent would be imposed for future flows discharging to Lough Neagh. In addition, the existing works was operating beyond its capacity, many of the structures were nearing the end of their design life, and regular operator intervention was required to maintain compliance.

Since the existing works was not capable of fulfilling the requirements of NI Water’s long-term strategy to enhance wastewater services, and was expensive to operate and maintain, a new treatment works was deemed essential to ensure compliance with the stricter consents throughout the design horizon.

The provision of a new fully automated rotating biological contactor (RBC) WwTW would provide effective and robust wastewater treatment services for the future catchment area, catering for economic growth (having a design population equivalent of 1,520), and improving the local environment by adhering to a tighter discharge consent of 20 mg/l BOD, 30 mg/l total suspended solids, and 7.5 mg/l ammonia.

Project team

As principal contractor, GEDA Construction had overall responsibility to deliver the project on time and within budget. Water Solutions Ireland were responsible for designing and delivering a full turnkey MEICA, process design and build solution for the new works.

McAdam provided civil, structural, and geotechnical design services, including the initial enabling and investigatory works carried out at the Early Contractor Involvement (ECI) stage, as well as the detailed design for construction.

[caption id="attachment_16706" align="alignnone" width="1200"] Early excavation works with compound set up - Courtesy of NI Water[/caption] The contract delivery team worked in a collaborative manner with NI Water, project managers RPS, and key suppliers and subcontractors to deliver a robust, effective and modern treatment solution which allows for future growth in the catchment area and protects the environment by adhering to a tighter discharge consent. Ballyronan WwTW: Supply chain - key participants Project managers: RPS Civil contractor: GEDA Construction MEICA & process designer/contractor: Water Solutions Ireland Civil, structural & geotechnical design: McAdam Electrical design: SBE Design PLC software & commissioning: Ashdale Engineering MCC: R&R Engineering Mechanical storm screen: Jacopa Ltd Static storm screen: Eliquo Hydrok Ltd 6mm inlet screening: M&N Electrical & Mechanical (Hydro International Ltd's UK Wastewater Services Division) Rotating biological contactors & primary/final settlement tanks: KEE Process Ltd Pumps & mixers: Xylem Water Solutions Instrumentation: Park Electrical Systems Flow measurement: Siris Environmental Ltd Flow measurement: AMPM Flow & Energy Services Ltd Penstocks, valves & actuators: Flow Technology Services Storm tank cleaning tipping bucket: CSO Group Ltd GRP kiosks & site-wide metalwork: Victoria Engineering 10mm bar screen, skip rails & trolleys: Graham Steelwork Engineering Potable & FE service water boosters: Dutypoint Ltd Lifting equipment: Columbus McKinnon Co Ltd Access covers: JP Corry Site security fencing & gates: NK Fencing Concrete & precast products: FP McCann Pipes & fittings: APP Welfare unit: Sean Jordan Engineering [caption id="attachment_16704" align="alignnone" width="1200"] Excavation of FSTs to depth of 5m - Courtesy of NI Water[/caption] Project description & scope

The RBC treatment process at Ballyronan WwTW was to be constructed within the same footprint of the existing site. The new treatment works was designed and built to include the following individual process stages for robust and effective treatment of incoming flows:

A preliminary treatment process stage comprising of 6mm mechanical inlet screening and forward flow control equivalent to Formula ‘A’. Any flows greater than Formula ‘A’ are treated via a mechanical storm screen. A new interstage pumping station for passing forward flows equivalent to FFT to the downstream treatment processes. A new storm storage and management facility, providing a total storage capacity of 81m3 for both storm and emergency flows. The storm tank is also equipped with a tipping bucket system for efficient cleaning of the storm tank floor from CSO Group Ltd. The interstage pumps transfer FFT to two primary settlement tanks each of 6m diameter. The primary sludge from the primary settlement tanks is drawn off by the primary sludge pumping station for transferring to the new concrete sludge holding tank. Primary settled flows then gravitate to the biological treatment process; three RBCs from KEE Process Ltd. Following treatment in the three RBCs, the treated effluent gravitates to the two final settlement tanks each of 6m diameter. The sludge from the final settlement tanks is drawn off by the humus sludge pumping station, which can either be transferred directly to the new concrete sludge holding tank or to the primary tanks for co-settling with the primary sludge, before being stored in the new concrete sludge holding tank prior to transporting off-site. Following final settlement, the treated effluent gravitates through a final effluent washwater transfer pumping station, prior to discharge at the final effluent outfall location. [caption id="attachment_16698" align="alignnone" width="1200"] Bottom section of FSTs installed - Courtesy of GEDA Construction[/caption]

The new Ballyronan WwTW includes a new concrete sludge storage tank sufficiently sized for 10 days’ storage prior to being tankered off site.

The site-wide drainage system is segregated between storm and dirty drainage, with any dirty drainage directed to the new return liquors pumping station which transfers additional flows back to the head of the works for treatment.

The old brick building was demolished, and the new works was provided with a new GRP kiosk housing a dedicated main works MCC which controls all mechanical and electrical plant equipment and instrumentation.

As the new works had to be built within the confines of the existing site boundary, a complex construction phasing plan was developed to bring the new treatment works online in four separate stages. GEDA Construction, Water Solutions Ireland and McAdam worked closely with NI Water Operations to ensure effluent compliance was maintained throughout the individual construction phases.

Early contractor involvement

GEDA Construction was awarded an NEC 4 (Option A) Early Contractor Involvement (ECI) contract in February 2021 for a replacement treatment works at Ballyronan WwTW. To assist with the development of a turnkey design and build solution for a replacement treatment works, GEDA appointed Water Solutions Ireland as the MEICA & Process Contractor and McAdam Design as the Civil Designer to deliver both the ECI contract and construction contract.

An extensive ECI process was undertaken for the replacement treatment works at Ballyronan WwTW, which included ongoing collaboration with NI Water for design outputs and workshops such as HAZOP and Value Management. The ECI phase allowed GEDA Construction, Water Solutions Ireland and McAdam to gain an early understanding of the key drivers for the project and achieve buy-in from all stakeholders within NI Water and their project management team from RPS to benefit delivery.

The collaborative approach between the Contractor and NI Water in the ECI contract was an exemplary reflection of NI Water values, purpose and vision. As a result, the ECI led to enhanced value, robustness and operational efficiency for the overall construction project.

[caption id="attachment_16697" align="alignnone" width="1200"] Make up of the FSTs from KEE Process - Courtesy of GEDA Construction[/caption] MEICA & process design

GEDA Construction, in conjunction with Water Solutions Ireland and McAdam, undertook an optioneering exercise to investigate the ideal treatment solution for Ballyronan WwTW under a back-to-back NEC 4 (Option A) ECI contract. This optioneering exercise included the process design requirements of a new treatment works and the potential option of employing temporary treatment facilities to replace the existing works during construction. A full turnkey MEICA design was provided, including steelwork structural drawings and ICA documentation such as PLC architecture and Functional Design Specification for the new process.

Civil design

McAdam was appointed under a bespoke Professional Services Contract to GEDA Construction for all civil engineering design requirements for the ECI and was also engaged by GEDA for the construction contract.  The ECI contract allowed McAdam to develop a turnkey civil design including a detailed construction sequencing plan which included the use of both temporary pipework and permanent pipework for the new structures to enable phasing.

An offline build solution was presented to NI Water as an option during the ECI phase for ease of construction and ongoing process management during construction. However, in agreement with all stakeholders, the preferred design for the replacement WwTW was constructing the new treatment works in a phased manner within the existing site footprint whilst the existing works remained operational. This approach satisfied the long-term operation and maintenance requirements for the new works and negated the need for NI Water to purchase additional land.

Main challenges for design/construction

Existing site: The key challenge around the design and construction of the new Ballyronan WwTW was building a new treatment works in its entirety within the same site boundary as the existing WwTW.

[caption id="attachment_16699" align="alignnone" width="1200"] Installation of RBCs - Courtesy of GEDA Construction[/caption]

Interface between new and old works during construction: The construction of the new treatment works at Ballyronan required a continuous interface between the new and old works during construction. The new WwTW was constructed and commissioned in four individual phases.

Phase 1: Relocation of existing MCC and temporary diversion of NIE connection. The existing brick building housing the MCC was then demolished which provided the required footprint to construct two new final settlement tanks and humus sludge pumping station.

Once the new final settlement process was constructed and commissioned, a temporary diversion of flows from the outlet of the existing percolating filter beds was put in place via a temporary pumping station. This made the existing humus tank redundant and available for demolition.

Phase 2: The new interstage PS and storm tank was constructed. The existing humus tank was demolished which created space on site for constructing the three RBCs. Following construction and commissioning of the new interstage PS, storm tank and RBC process, primary settled flows were diverted to the new RBC flow splitting chamber for seeding.

At the initial stages of turning flows between the two biological treatment processes, any effluent from the RBCs was re-diverted for re-treatment through the existing filter beds to ensure effluent compliance. The effluent from the filter beds was then pumped via a temporary pumping station to the new final settlement tanks before gravitating to the effluent discharge location.

Both the effluent from the new RBCs and the existing filter beds was rigorously tested, and once the RBCs were fully seeded and proved to be treating incoming flows to the required standard, NI Water granted approval to demolish the two existing filter beds. The construction of a section of the site-wide dirty drainage and the new return liquors pumping station also took place in this phase.

Phase 3: The existing two filter beds were demolished in Phase 3 which then created sufficient space on site for constructing the two PSTs. The new inlet works comprising Formula ‘A’ flow control was constructed in the final phase, as was the new concrete sludge holding tank.

[caption id="attachment_16700" align="alignnone" width="1200"] Construction of inlet works, sludge tank & storm tank - Courtesy of NI Water[/caption]

Phase 4: The final phase involved the construction of the two new primary settlement tanks (PSTs) and completing a successful turn of flows from the interstage PS to the new PSTs. Once this was completed, Water Solutions Ireland and GEDA Construction were granted approval to respectively decommission and demolish the existing primary settlement tanks.

The new MCC panel and kiosk were also installed in this final stage, with the entire site transferred across and commissioned as a whole. Other works included:

The construction of the new final effluent outfall configuration which included a new outfall pipe and headwall. FE washwater transfer PS FCOM flow measurement chamber FE washwater booster and potable washwater booster.

At the end of Phase 4, the incoming flows were fully treated by the new RBC works at Ballyronan WwTW.

Turn of flows

As the new works was brought online in four individual phases, a complex turn of flows plan was carefully developed to ensure effluent compliance for NI Water.

GEDA Construction and Water Solutions Ireland managed the individual turn of flow processes between the existing works and new treatment works. A rigorous on-site and external sampling regime was undertaken to regularly monitor the performance of the existing and new works. This sampling regime proved critical in allowing the site team to advise NI Water when the new RBC treatment process was fully functional and treating effluent to the required standard.

[caption id="attachment_16701" align="alignnone" width="1200"] Completed Ballyronan WwTW - Courtesy of GEDA[/caption]

As a result, NI Water granted approval for the decommissioning of the existing filter beds. From this, the existing biological filter beds could be demolished to allow further construction to progress.

The turn of flows process, particularly from the old filter beds to the new RBCs, had to be carefully managed both hydraulically and biologically to ensure the treatment process was optimised and effluent compliance was maintained at all times.

The various turn of flow processes required both temporary gravity-fed lines and temporary over pumping lines to demolish existing structures. For example, GEDA Construction had to lay a temporary sewer to divert flows from the existing primary tanks to the new interstage pumping station in Phase 2.

Both GEDA and Water Solutions Ireland had to construct and fit-out a temporary pumping station to direct flows from the outlet of the existing percolating filter beds to the new final settlement tanks.

Commissioning

Construction work on the new Ballyronan WwTW was completed early September 2024 with site-wide testing and commissioning of the plant successfully undertaken for handover to NI Water in October 2024.

Speaking about the economic and environmental benefits of the project, Senior Project Manager, Sean Milligan commented:

“NI Water’s substantial investment of around £5m has provided a robust wastewater treatment solution for the Ballyronan area that will support local development and help improve water quality in Lough Neagh.”

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.

Ballina WwTP is located in the existing urban area of Ballina Town, roughly 100m from the border between County Tipperary and County Clare. The facility is an asset of Uisce Éireann (formerly Irish Water) and it is currently operated by Tipperary County Council (TCC) on behalf of Uisce Éireann under an existing Service Level Agreement. It serves both the Ballina and the Killaloe agglomerations and was officially opened in August 1996. It was initially designed to treat flows generated from population equivalent (PE) of 4,000. Project need

The current population associated with the WwTP has been assessed at 5,400 PE, which is more than the current design capacity (4,000 PE). This population is estimated to increase to 8,000 PE in the +10 year design horizon and to 8,400 PE in the +25 year design horizon. Therefore, it was necessary to increase the treatment capacity of the WwTP to meet the current and increasing population within the agglomeration.

The WwTP discharged treated effluent via the primary discharge point to the Grange River. The discharge limits set out by the EPA Discharge Licence were not being met in relation to the BOD and ammonia limits.

[caption id="attachment_15770" align="alignnone" width="1200"] Construction work underway at Ballina - Courtesy of Shay Murtagh Precast[/caption]

The WwTP was an extended aeration activated sludge plant. There was no excess influent management system in place and as such, all flows entering the plant were passed forward to the process tanks. All flows entering the WwTP received the following levels of treatment:

Preliminary treatment in the form of screening and grit removal. Secondary treatment in the form of two oxidation ditches and two final settlement tanks. Tertiary treatment in the form of a ferric dosing system to aid in phosphorus removal.

The waste sludge generated at the WwTP was stored and thickened on site within a picket fence thickener (PFT). As the existing dewatering facilities on site were no longer in operation, the waste sludge produced on site (approximately 90 tonnes/week) was pumped from the PFT to a tanker and removed from site.

[caption id="attachment_15774" align="alignnone" width="1200"] New inlet works under construction - Courtesy of Ward & Burke[/caption] Scope of works

Ward & Burke was appointed by Uisce Éireann in December 2022 as the Main Contractor to upgrade the existing plant, providing design, civil engineering, plant operations and MEICA works for the contract.

The purpose of the contract was to upgrade the Ballina WwTP to provide sufficient treatment capacity for the target design horizon and to meet the required effluent discharge limits set out in the EPA Discharge Licence. The works included the design, supply, installation, testing, commissioning and handover of the upgraded plant. The existing WwTP remained operational during the construction works with minimum interruptions to the operation of the existing process stream.

The works included for the provision of operation and maintenance (O&M) of the existing Ballina WwTP during the design build and O&M of the upgraded plant for 365 days following commissioning.

The scope of Ward & Burke’s design and build works included:

Construction of a new below-ground forward feed pump station and stormwater overflow (SWO), to lift incoming wastewater to new inlet works and allow excess flows towards the new storm tank. Construction of a new above-ground inlet works structure comprising: Duty/standby 6mm fine screens. 19mm bypass screen. Grit removal unit. Grit classifier. Screening handling unit. Storm overflow and flow splitting chamber to split flows between the new and existing streams. Construction of a new below-ground stormwater storage tank along with associated pumps, meters and pipework. Decommissioning of the existing inlet screens and grit removal works. Construction of a new below ground circular aeration tank. Installation of new duty and stand-by blower units for the proposed diffuser aeration system. Construction of a new below ground final settlement tank. [caption id="attachment_15773" align="alignnone" width="1200"] New final settlement tank under construction - Courtesy of Ward & Burke[/caption] Scope of works (continued) Construction of a new below-ground return activated sludge/waste activated sludge (RAS/WAS) pump sump and associated duty/standby pump set to facilitate sludge handling from the proposed new process stream. Construction of a new above ground picket fence thickener. Relocation of the existing outfall to a new treated effluent outfall to the Lough Derg which also incorporates the overflow from the new stormwater storage tank. Additional motor control centre (MCC) to facilitate the new stream. SCADA upgrade resulting from additional works elements and decommissioned existing elements. Ancillary works associated with the telemetry and control of the new process stream in combination with the existing infrastructure. Connection of the new stream to the existing infrastructure to facilitate testing and commissioning while the existing infrastructure remains live. Provision and installation of permanent and appropriate energy monitoring equipment to facilitate energy monitoring and verification of the design and operation of the works. [caption id="attachment_15772" align="alignnone" width="1200"] New storm water tank under construction - Courtesy of Ward & Burke[/caption] Ballina WwTP: Supply chain - key participants Civil/process design & project delivery: Ward & Burke Employers representative: RPS Resident engineer: Nicolas O’Dwyer Precast tanks: Shay Murtagh Precast Precast chambers: Tracey Concrete Ductile iron pipe and fittings: Fusion Pipeline Products Odour control: John Cockerill Environmental Grit removal & storm/inlet screens: Jacopa Aeration blowers: Aerzen Machines Diffused aeration system: SSI Aeration PVC pipe: Total Pipeline Specialists (TPS) MCC: Ward & Burke Construction Ltd Access covers: EJ Ireland Pumps, mixers, fine bubble diffusers: Sulzer Pumps Wastewater Ltd Flow meters: Siemens Ultrasonic meters: Pulsar Measurement Flow switches: IFM Electronics Penstocks: Talis Valves: Valve & Actuator Solutions Ltd Actuators: Auma Actuators Ltd Kiosks: Gleeson Steel & Engineering FST scrapers & site-wide metalwork: Keltec FST scrapers & site-wide metalwork: D&E Welding FE service water boosters: Campion Pumps Lifting equipment: T Allen Engineering Services Ltd Civil engineering works The major civil elements of work on the Ballina WwTP project and the outline construction methods are shown in the following table: Work element Construction Methodology Work element Construction Methodology Storm tank Below-ground precast concrete tank Forward feed PS Below ground in situ caisson Aeration tank Below-ground precast concrete tank RAS/WAS PS Below ground precast chamber FST Below-ground precast concrete tank Wash water PS Below ground precast chamber PFT Above-ground precast concrete tank 450mmØ outfall Float/sink outfall pipe in pre-dredged trench Process technologies/innovations 6mm MEVA step screens have been installed on this project which exclude the need for process washwater resulting in a carbon footprint saving. An air lift grit removal system has been employed which consists of stainless-steel coarse bubble diffuser system along with a stainless-steel grit lift pipes. This system ensures there is no moving parts submerged in the tank allowing all maintenance required to be carried out without the need to enter the tank. A fine bubble diffused aeration system has been supplied by SSI Aeration. The 9” fine bubble diffusers have got one of the best oxygen transfer efficiencies on the market. A final effluent washwater system has been designed to utilise the final effluent from the plant as wash water on inlet works launders, grit classifier and Washpactor. This means treated potable water is not required to be used, thus ensuring a better carbon footprint. The system consists of a buffer tank and a set of booster pumps and associated valving and pipework. Key challenges

Some of the key challenges on the Ballina WsTP project included:

The project took place on a live treatment plant, which had to remain fully operational during construction. The works, including the construction of the outfall, took place in, and adjacent to, a major watercourse (the River Shannon) as well as the Grange river, with historical liability to flooding. The project scope required the construction of large underground structures up to 5m below ground in silts and gravels with potentially variable groundwater behaviour due to the presence of the Shannon, Mill and Grange Rivers. [caption id="attachment_15775" align="alignnone" width="1200"] New outfall under construction - Courtesy of Ward & Burke[/caption] Conclusion/summary

The design and build project to upgrade the Ballina WwTP is due to be commissioned in October 2024; after 550 days. The upgrade will bring benefits to Killaloe and Ballina including ending the discharge of poorly treated effluent, improving water quality in the receiving waters, and enhancing local amenities and a platform for social and economic development.

The project also accounted for forecast future population growth of the surrounding areas and ensuring compliance with the Urban Wastewater Treatment Directive and EPA Wastewater Discharge Licencing.

Finham STW serves a population equivalent (PE) of approximately 500,000 in the Coventry area, treating 115 ML of wastewater per day. In 2021, as part of efforts to support economic recovery from the COVID-19 pandemic, the UK government launched the Green Recovery program - an initiative aimed at accelerating environmental improvements, creating green jobs, and fostering sustainable growth through targeted investment in infrastructure and nature-based solution. As part of Severn Trent’s Green Recovery program, the Finham Sewage Treatment Works (STW) Storm Tank project in Coventry represented a critical intervention to improve river water quality in the River Avon catchment. Project background

The Finham STW Storm Tank Project formed part of Severn Trent’s Bathing Rivers Initiative, targeting storm overflow spills reduction. The goal of the Bathing Rivers Initiative was to reduce storm overflow discharges from combined sewer overflows (CSOs) to improve river water quality for bathers and the wider environment by the 31 March 2025.

The construction of a new 4,880m3 storm tank at Finham STW, in addition to a new shaft tank at Unicorn Lane CSO, will significantly reduce spills in the catchment with flows stored at Finham before being passed for treatment once the storm event has ended.

Few projects illustrate the value of adaptability, collaboration, problem solving and technical excellence as clearly as Finham. The ability to pivot from an unfeasible initial design (due to ground conditions) to a fully operational rectangular tank within a compressed time-frame is a testament to the strength of the delivery team and the robustness of the project governance.

[caption id="attachment_25246" align="alignnone" width="1200"] Start of the piling operation – Courtesy of Keller Ltd[/caption] Technical design & construction

The initial design proposed a 15m deep shaft supported by a dewatering strategy using 32 recharge wells. However, in May 2024 a significant sub-artesian groundwater head and local aquifer saturation rendered the dewatering strategy unviable. This refers to a condition in a confined aquifer where groundwater is under pressure but does not rise to the surface.

Although not as forceful as artesian conditions, sub-artesian pressure can still cause water to seep into excavations, requiring active dewatering measures. This can lead to delays due to the need for additional pumping systems, potential soil instability, and adjustments to foundation designs. Furthermore, managing groundwater in such conditions may necessitate dewatering permits and other checks, all of which can contribute to project delays.

This led to a cease works order and a fundamental redesign of the solution, with the Finham Storm Tank project team pivoting to a rectangular tank design, developed through collaborative design sprints. The redesign addressed piling layout, inlet/outlet arrangements, cleaning and return systems, revised formation levels, and rebar schedules. This agile approach enabled the team to maintain momentum and deliver a revised solution aligned with program constraints.

To address the dewatering challenges associated with the construction of the new storm tank at Finham STW, specific design modifications were implemented to accommodate the site’s complex ground conditions. The subsurface profile, comprising 4–5m of made ground and firm clays overlying strong sandstone and mudstone, necessitated a robust foundation solution. A rotary bored piling system using 750/650mm diameter piles was adopted, capable of withstanding tension loads of up to 1000kN.

This method allowed for deep foundation installation with minimal vibration and disturbance, thereby reducing the risk of triggering groundwater ingress. By limiting the extent and depth of excavation, the design significantly reduced the need for extensive dewatering. The low-vibration, cast in-situ piling technique was particularly effective in maintaining the stability of surrounding soils and managing the sub-artesian groundwater pressure.

[caption id="attachment_25250" align="alignnone" width="1200"] Rebar in place for one of the ten concrete pours for the tank base - Courtesy of Joseph Gallagher Ltd[/caption]

Additionally, early contractor involvement facilitated proactive planning of site logistics and working platforms, ensuring groundwater risks were identified and managed from the outset. This collaborative approach enabled the team to optimise construction sequencing and minimise delays related to water management.

The design was further refined through a review of reinforcement requirements, which led to a reduction in steel usage. This not only lowered the environmental impact and construction costs but also simplified the build process, reducing the time the site was vulnerable to wet weather and other impacts of winter. Collectively, these measures enabled the storm tank to be constructed efficiently and safely, despite the presence of challenging sub-surface water conditions.

Construction delivery

Construction activities included excavation to formation level, piling, sealing of dewatering wells, diversion of existing services, and reinforced concrete works for the base slab and side walls.

Despite the significant design change, the team maintained a focused program to meet the regulatory deadline. The tank was successfully constructed and made operational before the 31 March 2025 target, demonstrating a high level of delivery discipline and adaptability.

Finham Storm Tank: Supply chain - key participants Main contractor: Kier Design consultants: Stantec UK Piling designer & contractor: Keller Ltd Dewatering: Stuart Wells Ltd FRC works: Joseph Gallagher Ltd Mechanical/pipework: Varlowe Industrial Services Tipping buckets: Jacopa MCC/panels: RSE Control Systems (Blackburn Starling) Swing jib & galvanised steel: T Allen Engineering Services Concrete & steel reinforcement: Heidelberg Materials Flow controls: AFFCO Flow Control (UK) Ltd [caption id="attachment_25248" align="alignnone" width="1200"] Slab construction and start of wall shuttering placement - Courtesy of Kier[/caption] Collaborative delivery model

The project was delivered using an Integrated Project Team (IPT) model, comprising of a multidisciplinary group of internal and external stakeholders who worked together to deliver the desired project outcomes. The IPT included Severn Trent Delivery and Commercial teams, the principal contractor, consultant designers, and subcontractors. This multi-party collaboration enabled efficient design-to-construction workflows, dynamic commercial management, real-time problem-solving, strong communication and relationship building through a spirit of trust and open discussion.

The IPT model was instrumental in managing the decision complexities of the shaft dewatering process, ensuring continuity of delivery and maintaining project progress. This collaborative framework enabled the team to align on project objectives from the outset, streamlining decision-making and ensuring that design and construction strategies were fully coordinated. The early involvement of the piling contractor, for example, allowed for the development of a detailed and practical construction methodology that was both efficient and aligned with site constraints.

The IPT model also enhanced communication and accountability across disciplines, which proved particularly valuable in managing health and safety on site. Daily shift briefings were led by the principal contractor, ensuring that all personnel were informed of the day’s activities, risks, and mitigation measures. This proactive approach to site management contributed to a strong safety culture and reduced the likelihood of delays due to miscommunication or procedural oversights.

Furthermore, the integrated team structure facilitated value engineering opportunities, such as the optimisation of reinforcement design. By working collaboratively, the team was able to identify areas where material use could be reduced without compromising structural integrity, leading to cost savings and a lower environmental impact. Overall, the IPT approach played a critical role in ensuring the storm tank was delivered on time, to specification, and with a high standard of quality.

[caption id="attachment_25245" align="alignnone" width="1200"] 180m3 concrete pour for slab No. 6 - Courtesy of Joseph Gallagher Ltd[/caption] Environmental & community impact

The Finham Storm Tank directly contributes to the Bathing Rivers Initiative, improving water quality in the River Avon by reducing storm overflow discharges. The project aligns with national environmental goals and supports the Water Framework Directive by enhancing ecological quality and enabling recreational use of urban rivers. This initiative does not just solve a problem, it redefines what is possible for working at pace in urban wastewater management, setting a precedent for future projects across the UK and beyond.

Successes & legacy

Although the solution required redesigning, the 4,880m3 storm tank was constructed to meet the highest standards of site safety and construction quality. It became operational by the regulatory deadline of 31 March 2025, fulfilling the objectives of both the Green Recovery Program and the Bathing Rivers Initiative.

The project’s success lies not only in the numbers - reduced spills, increased storage, improved water quality - but in the way it brings together engineering excellence, ecological improvement, and community engagement.

As part of the project’s ecological sensitivity strategy, plans are underway to enhance biodiversity and restore natural features impacted by construction. Biodiversity Net Gain (BNG) calculations have been completed to assess the ecological impact of the works and to ensure that the site delivers a measurable improvement in biodiversity value upon completion. Furthermore, the installation of bird boxes is being prepared to support local bird populations by providing safe nesting habitats. In addition, a tree replanting program is in development to replace vegetation removed during site works, with the aim of re-establishing green cover and contributing to long-term ecological resilience. These initiatives reflect a forward-thinking approach to environmental responsibility and align with Severn Trent’s broader commitment to sustainability.

[caption id="attachment_25249" align="alignnone" width="1200"] Final tank commissioning (March 2025) - Courtesy of Kier[/caption]

To support community engagement, the project team has made use of both traditional and digital communication methods to keep stakeholders informed and involved. Updates have been shared through a combination of newsletters and video content, offering insights into project progress, upcoming activities, and the long-term benefits of the works.

These efforts have helped maintain transparency, foster public interest, and ensure that the local community remains connected to the project throughout its delivery. As part of Severn Trent’s Bathing Rivers program, a dedicated virtual room was created to engage stakeholders and the public, providing updates, resources, and insights into river quality improvements and community involvement.

Guildford, the county town of Surrey, sits a commutable 30 miles south west of London and 70 miles from the south coast. Boasting a castle, a cathedral, a picturesque town centre and a university, it is surrounded by Green Belt countryside. The River Wey flows through the town centre and then northwards through water meadows where it provides the outfall for the STW. The Wey eventually discharges into the Thames. The current STW serves a population equivalent (PE) of around 107,000, but the town has a growing population which is expected to grow to circa 125,000 PE by 2041. Background

The town and immediate area are currently served by a sewage treatment works established at the turn of the last century and upgraded over the years. It is located beside the River Wey, to the north of the A3 trunk road and north of Guildford town centre. It lies just south of Slyfield Industrial Estate. The current STW has a capacity to cater for a population equivalent of around 120,000.

Guildford Borough Council’s Local Plan adopted in 2019 allocates a site to the west of the River Wey wrapping around the eastern side of Slyfield Industrial Estate for mixed use development. Part of the 40 Ha allocated site is currently occupied by the existing sewage treatment works.

Weyside Urban Village is a mixed-use regeneration project which will provide some 1,500 new homes, new community facilities, Gypsy and traveller pitches and 6,500m2 of additional light industrial and trade space. 11Ha of the site are allocated for waste management purposes. The plans include a new council depot, a public recycling centre and a new, relocated sewage treatment works.

In order to bring the development site forward, within the plan period to 2034, Guildford Borough Council (GBC) have entered into partnership with Thames Water Utilities Ltd (TWUL) to build the new STW as the first phase of the redevelopment. The new location is slightly further north on the eastern edge of the Industrial site and is a brownfield site, formerly a gravel quarry and subsequently a landfill tip.

[caption id="attachment_26867" align="alignnone" width="1200"] Figure 2: Site overview: BIM model of new Guildford STW - Courtesy of BAM Enpure JV[/caption]

The new sewage treatment works allows for an increase in capacity to serve a population of 125,000 allowing for predicted population growth in the town and surrounding area as well as more stringent effluent discharge standards.

The new site also includes areas within the new works for future expansion and increased treatment capacity as need arises.

Previously in Water Projects

The scheme to build a new sewage treatment works (STW) in Guildford is now mid-way through construction. This article provides an update to the project following on from previous articles published in Water Projects. In 2023, Enpure Ltd’s Project Delivery Director Shaun Christopher described in detail the process and assets being provided in the new works and in 2024, Dan Russell, BAM’s Operational Lead, gave an update on the progress of the project one year into the construction.

This article also covers some of the planning considerations and requirements for the scheme.

Contract

In 2021 TWUL awarded a contract to a BAM-Enpure Joint Venture to design, build and commission a new STW for Guildford, and once operational, to de-commission the existing works. BAM-Enpure Joint Venture (JV) is a non-integrated Joint Venture, formed specifically to combine experienced civil engineering contractor BAM with the process engineering MEICA specialism of Enpure, to deliver a turnkey solution for TWUL.

Construction began in the spring/summer of 2023 with BAM undertaking design and construction of the civils works and Enpure providing process and MEICA design and installation. BAM have employed Arcadis as their main civils designer and the JV has let a number of specialist sub-contractor design packages alongside.

[caption id="attachment_26869" align="alignnone" width="1200"] Figure 3: 3D design using a model hosted by Arcadis, image from Autodesk’s Navisworks viewer - BAM Enpure JV & Arcadis[/caption] The project

The project consists of the following:

A transfer tunnel. An inlet pumping station. Inlet works screening. Primary settlement. Activated sludge treatment. Final settlement. Tertiary treatment of final effluent. Chemical dosing facilities. Storm storage tanks. Import cess and sludge facilities. A new control centre. New welfare building. Outfall into the River Wey.

A detailed description of the process and assets being installed is set out in the previous Water Projects article published in 2023.

Timeline Phase 1: Ground improvement: Started summer 2023 and completed February 2025 Phase 2: Civil engineering: Started summer 2023 with completion due in late 2025. Phase 3: Mechanical & electrical engineering: Started autumn 2024 and is due to complete summer 2026. Phase 4: Commissioning: Starts winter 2025 and is due to complete in spring 2027. [caption id="attachment_26883" align="alignnone" width="1200"] Figure 4: 3D model of the sludge processing area - Courtesy of BAM Enpure JV & Arcadis[/caption] Developing the site

The new site comes with additional challenges in that it is brownfield site formerly used for gravel extraction and then landfilled through the 1960s, 70s and 80s, with mainly domestic and some commercial waste. The site is classified as a waste development such that the local planning authority is Surrey County Council (SCC).

The planning permission granted was subject to a number of conditions and commitments, not only relating to the siting and development of the STW itself such as visual impact, odour, noise and traffic generation, but also to the remediation and reuse of the landfill site. Plans and construction methods needed to ensure that there was no temporary or permanent environmental damage to the surrounding area as a result of the impact on or disturbance of the buried waste material and that operatives working on the new STW were protected from any ill effects of the landfill during operation of the site. The landfill also poses particular constraints and hazards during the construction phase.

The strategy for the site was to leave as much of the landfill waste in situ and build above and through the waste. A detailed remediation strategy formed part of the planning requirements. The plan set out how the construction and operation phases of the project would manage issues of ground water and ground gas, potential ground water contamination and leachates, contaminated solid material including asbestos, and short- and longer-term settlement of the landfill.

Dan Russell’s case study in Water Projects 2023 provided a detailed description of the use of a combination of ground improvement and foundation techniques, which consisted of:

Rapid Impact Compaction (RIC) to improve ground strength and reduce long-term settlement of the landfill. Vertical Rigid Inclusions (VRI), a displacement concrete pile technique which provided support for roads, lighter structures pipes and ducts. Driven concrete piles bedded in the London Clay below the land fill to support large structures, tanks and pipelines.

Figures 5 (below) show the historic gravel extraction map and depth of landfill determined by ground investigation - both images were extracted from the project’s Detailed Remediation Strategy.

[caption id="attachment_26880" align="alignnone" width="1200"] Figures 5: (left) Spatial variation in landfill thickness 2023 and (right) historic site layout (1976) with present day boreholes overlaid - Courtesy of Arcadis[/caption]

However, the impact of the waste material goes beyond its bearing capacity. The site was already being subject to long term monitoring for ground gas and groundwater quality by Thames Water to provide a baseline for the project. Additional boreholes were sunk and a Groundwater & Ground Gas Monitoring Plan was approved by the local authority. Daily and continuous automatic remote monitoring was undertaken during the ground improvement and excavation phases with trigger levels set and exceedances reported back to SCC and a requirement for quarterly summary reporting. Monitoring will continue during commissioning of the site at less frequent intervals.

Asbestos: Asbestos had been discovered in a third of samples taken during the ground investigation and so a monitoring regime was established. Air sampling around the perimeter of the site ensured any airborne particles were detected and works could be stopped if necessary. Proximity asbestos monitoring and identification of asbestos material in excavation has also been used extensively during excavation across the site. The project used Socotec to undertake asbestos monitoring and testing.

Ground gas: A ground gas protection design has been necessary to reduce risk of ground gas entering occupied buildings, kiosks, tanks and chambers where operational or maintenance access is undertaken. A ground gas design protection strategy was set out by Arcadis with PAGeo Contracting Ltd providing expert advice and a detailed ground gas design, PAGeo then supplied gas dispersal matting, venting components and gas membranes. Both the strategy and the detailed design for ground gas protection have been submitted to and approved by SCC.

Independent verification of the gas protection installation has been provided by MTS Ltd as verification of the installation and subsequent reporting to SCC is a planning condition.

[caption id="attachment_26872" align="alignnone" width="1200"] Figure 6: Gas protection void former being laid on stone blanket prior to tank base blinding, Connections to vents at tank perimeter - Courtesy of BAM[/caption]

Surface drainage: On-site surface drainage has been carefully designed such that new impermeable areas are positively drained to the site drainage system to remove the risk of a spill causing environmental pollution. This surface water is then fed into the inlet pumping station for processing through the works. As the permeable area of the site has been greatly reduced this also significantly reduces leachate mobilisation.

Biodiversity: Another planning condition is the provision of Biodiversity Net Gain (BNG). In conjunction with GBC, the project provides 10% net biodiversity gain by use of on-site planting and off-site enhancement of the land directly to the north of the new STW. A Site of Natural Green Space, biodiversity enhancements to an area of farmland, and a marshy meadow along the River Wey are being provided.

The Environment Agency have also constructed a new fish pass in this area allowing fish to migrate around Old Bucks Weir.

Guildford STW: Civils works supply chain - key participants

Main contractor: Bam Nuttall Ltd Planning consultant: Adams Hendry Consulting Ltd Civil engineering design: Arcadis Group Ltd Boreholes & testing: Geo-Environmental Services Ltd Asbestos monitoring: Socotec Ltd Rapid impact compaction: Cofra Ltd (Boskalis Group) Vertical rigid inclusions: Foundation Piling Ltd Concrete piling: Aarsleff Ground Engineering Ltd Temporary works specialist: Mabey Hire Ltd Temporary works specialist: MGF Ltd Tunnels & shafts: Joseph Gallagher Ltd In situ concrete works: Kelly Formwork Ltd In situ concrete works: DJ Civils Ltd Precast concrete manufacturer: FLI Precast Solutions Precast concrete manufacturer: A-Consult Ltd Pipe supplier: Electrosteel Castings (UK) Ltd Pipe supplier: Saint Gobain PAM UK Soil processing: Remediation Waste Management Services Concrete supplier: Heidelberg Materials Gas protection: PAGeo Contracting Ltd Gas protection system installation verification: MTS Ltd [caption id="attachment_26876" align="alignnone" width="1200"] Figure 7: Sludge processing area: MCC kiosk (grey in foreground), sludge blending tanks (top left), poly dosing kiosks (top right) - Courtesy of BAM[/caption] Overview of project progress

As of summer 2025, civils works are nearing completion and MEICA fit out has started.

The installation of piled supports has been undertaken, and all major structures are complete. Installation of the below-ground pipework and buried ducting is in progress and the welfare building is watertight and available for equipment installation. Moving towards installation of MEICA equipment, the water testing of structures started in the February of 2025.

Steel staircases and high-level walkways are mostly complete. The inlet screens and grit removal system are in place. GRP tanks for sludge processing are being installed and many control kiosks are in place. Electrical supply buildings are near completion.

MEICA work commenced in February 2025, overlapping with completion of civils to maximise programme efficiencies. Designed alongside the civils elements of the site, the MEICA installation has taken place apace with the first bridges on the final settlement tanks attached, the larger glass coated steel tanks for the sludge area in place, and generators and some kiosks have been installed.

BAM has started the installation of the above-ground pipework and cable pulling in buried ducts, and the fit out of control rooms will commence shortly. Construction of MCC basements has been completed and two of the three MCC kiosk, and power supply and distribution works are nearing completion.

[caption id="attachment_26878" align="alignnone" width="1200"] Figure 8: Sludge processing area: (left) the bases for elevated cake silos, (middle), sludge belt presses, and (right) the poly prep & dosing kiosks - Courtesy of BAM[/caption] Guildford STW: MEICA works supply chain - key participants Main designer/contractor: Enpure Ltd CFD analysis: The Fluid Group Cake silo: Saxlund International PST scrapers & ferric dosing plant: Colloide Inlet works & PST odour covers: Power Plastics Ltd Grit remover plant: Jacopa Escalator screens: Longwood Engineering Imported sludge Strainpress: Huber Technology Sludge thickening & dewatering: Kent Stainless Ltd Odour control plant: Odour Services International Ltd FBDA grids & blowers: Xylem Water Solutions Cloth pile filters: Eliquo Hydrok Ltd Storm tank cleaning system: Sulzer Pumps Wastewater Ltd Tank logging system (WASP): JR Pridham Services Ltd Glass lined steel tanks: Balmoral Tanks Ltd Sludge tank mixing: Landia UK Ltd Tunnel

A 1.5m diameter gravity tunnel, 1.5km long, transfers flows from the existing works and intercepts minor sewers en route. There are six shafts along the tunnel route, some of which act as junctions between the new tunnel and the existing sewers. Shafts were sunk by Joseph Gallagher using the caisson method and the tunnel was driven between them using a full-face tunnel boring machine, (named Daphne by a local school). The tunnel and shafts were completed in 2024 and the final work remaining are the completion of the large inlet pumping station (IPS), shaft (E2) at the new works and connection of Guildford’s main sewer to the head of the tunnel, which will allow all flows to be diverted to the new tunnel.

[caption id="attachment_26873" align="alignnone" width="1200"] Figure 9: (top left) 3D model of the Inlet Pumping Station (IPS) - Courtesy of Arcadis, (bottom left): steel fixing to IPS internal walls - Courtesy of BAM Enpure JV, and (right): IPS shaft construction - Courtesy of BAM[/caption] Inlet pumping station

The new inlet pumping station (IPS) is a 12.5m diameter shaft with a depth of 17m, which houses six pumps with the capacity to lift flows of around 2,500 l/s from the tunnel entry, at the base of the shaft, to the inlet works where all flows are screened. The shaft is complete except for the internal walls and installation of penstocks which allow isolation of half the well at any time for maintenance of the pumps. This will be completed in the autumn of this year.

Storm tanks & inlet works

Two storm tanks provide a combined capacity of approximately 8 million litres to which flow can be diverted to temporarily hold sewage arriving at the new works should flows exceed the capacity of the works. Constructed onto in situ bases, the walls of the storm tanks were prefabricated, placed and post-tensioned by A Consult Ltd.

The inlet works and larger chambers were entirely cast in situ due to lack of repeatable sections and logistics. In situ concrete work for these was undertaken by Kelly Formwork. The inlet screens have been installed and walkways are in place.

[caption id="attachment_26874" align="alignnone" width="1200"] Figure 10: Circular precast storm tanks and Inlet works (August 2025) - Courtesy of BAM[/caption] Primary settlement, activated sludge plant & final settlement tanks

Screened flows from the inlet works will then pass through primary and secondary treatment tanks comprising rectangular primary settlement tanks (PSTs) and activated sludge plant (ASP) tanks. The walls for these tanks were designed and supplied by FLI Precast Solutions Ltd and installed by BAM and DJ Civils Ltd on in situ bases prepared by Kelly Formwork Ltd. These tanks are complete with pipework being fitted and the ASP has commenced water testing.

To ensure watertightness of the larger rectangular tanks, Heidelberg Materials and Sika’s concrete technology were used.

Concrete containing Sika WT-200 P was utilised for the PSTs and the ASP. Sika WT-200 P is a combined water-resisting and crystalline waterproofing admixture used to reduce the permeability of concrete, making it suitable for water retaining structures.

Gas protection has been laid under all large tanks. Materials were supplied by PAGeotechnial Ltd and verified by MSL Ltd. Void former mating laid on a bed of single grade 40mm stone provides a preferential escape path for ground gases and is connected to vents at the tanks periphery allowing ground gases to vent to atmosphere.

These tanks are not habitable spaces and only require a dispersal system to discourage any build-up of gas below the large tank bases.

[caption id="attachment_26875" align="alignnone" width="1200"] Figure 11: From top: Activated sludge plant, primary settlement tank, and two of the four final settlement tanks - Courtesy of BAM[/caption] Final settlement tanks

The four final settlement tanks were also precast, supplied, installed and post-tensioned by A-Consult Ltd onto in situ bases prepared by Kelly Formwork Ltd. The FSTs are complete with bridges and scrapers installed and are currently being water tested.

Tertiary treatment plant & outfall

Following final settlement, flows will pass through final filtration in the tertiary treatment plant before being discharged to the River Wey via new, twin outfall pipes. Civil construction is complete and MEICA installation of cloth pile filters and drums from Eliquo Hydrok Ltd is underway.

The outfall pipework has been fully installed across the water meadow and the headwall has been constructed at the discharge point into the River Wey.

[caption id="attachment_26877" align="alignnone" width="1200"] Figure 12: Tertiary treatment plant construction (August 2025) - Courtesy of BAM[/caption] Sludge processing

The project also provides a dewatering facility for imported sludge from other small treatment works. This area is nearing completion with the larger coated glass sludge blending tanks in place and the smaller buffer tanks being installed. Gas vent pipes have been installed below the extensive concrete slabs to allow venting of ground gases to the atmosphere.

The sludge belt presses from Kent Stainless Ltd for sludge dewatering and thickening have been installed adjacent to the bases for the elevated sludge cake silos. The silos from Saxlund International have been sized to provide storage of seven days’ worth of processed sludge, which can be discharged to trucks for export from site.

Power & control

Power supply and distribution infrastructure is now in place. The three MCCs have been constructed in sequence and the first two are being fitted out.

Welfare building

A new welfare building houses the automated systems for running the new plant and controlling effluent quality as well as office and mess space for Thames Water staff and operatives. The building is watertight with cladding being installed and the fit out of building fixtures and plant control equipment is in progress.

[caption id="attachment_26871" align="alignnone" width="1200"] Figure 13: Welfare building housing plant control systems - Courtesy of BAM[/caption] 3D modelling

Design has utilised a 3D model hosted by Arcadis with each designer adding in modelling information as their design capabilities have allowed. This has enabled precise integration of designers individual input and interrogation of the integrated design

The model is used extensively by engineers on site. 3D modelling has, for example, allowed duct chambers to be precast with precision positioning of cable openings, saving on in situ working and substantially reducing programme on these installations.

Piling & ground improvement

To enable the STW to be constructed on the site without the waste being removed a combination of ground improvement techniques have been employed including driven concrete piles, Rapid Impact Compaction, and Vertical Rigid Inclusions.

The Rapid Impact Compaction work undertaken by Cofra was completed in late summer of 2023. From July 2023 to the spring of 2024, to support the larger structures, tanks and main process critical pipelines, 3500 concrete piles were driven through the landfill into the clay. The design and installation of this piling operation was undertaken by Aarsleff Ground Engineering.

[caption id="attachment_16135" align="alignnone" width="1200"] (left) Driving precast concrete piles and (right)Vertical Rigid Inclusion installation - Courtesy of Bam Nuttall Ltd[/caption]

In areas where settlement criteria were less critical, but needed controlling (for example roadways and minor pipework), a Vertical Ridged Inclusion (VRI) piling technique was used. The system involves displacement drilling a column in the landfill and filling the void with concrete. This works by consolidating the soil around the pile, transferring load to lower layers, thus increasing bearing capacity and reducing settlement over time.

Since 2024 the installation of VRIs by Foundation Piling has been completed with 7500 inclusions installed across the site. During detailed design, the project was able to remove the need for a load transfer platform above the VRIs across much of the site. This was done by detailed analysis of the 3D model to target differing requirements for support and by reducing inclusion spacings, thereby reducing the expected landfill removal by 37,500m3.

The load transfer platform remains below roads, but pipework sits within the grid of VRIs.

The year ahead

Completion of the mechanical works is expected in the first part of 2026 with installation of electrical and control systems expected to complete in the second part of 2026. Dry and wet commissioning will be undertaken sequentially across the site throughout the coming year, ensuring the new works is ready to commence process commissioning.

The final, and arguably most challenging activity, will be to connect the existing sewer network to the new tunnel, diverting flows from the existing STW to the new STW. A series of interventions will be required to intercept the various sewers, along the route of the tunnel, all the whilst ensuring the new STW is performing within strict limits and the existing STW is able to maintain its performance during the ramp down of flows.

Leamington Spa is a historic spa town with a growing population and significant development pressures. The River Leam, which flows through the town centre, is a focal point for recreation, including wild swimming, boating, and public parks. The sewerage catchment includes Leamington, Warwick, and surrounding villages, all draining to Longbridge Sewage Treatment Works (STW). Six CSOs were identified for improvement. This requirement was designed to safeguard public health and ensure compliance with the Bathing Water Directive and related water quality with the aim to reduce spill volumes and spill frequency with a variety of interventions; to give an insight into the best approach for bathing waters. Endorsed by Ofwat in 2021, the scheme is part of a broader strategy to support post-pandemic economic recovery through environmental infrastructure investment. The Leamington scheme exemplifies innovation in hydraulic modelling, and collaborative delivery within tight regulatory timeframes. Project overview

The Green Recovery Leamington Spa Sewerage Scheme is a flagship initiative under Severn Trent’s Green Recovery programme, aimed at moving a stretch of the River Leam towards bathing quality. This ambitious project addresses the performance of six critical Combined Sewer Overflows (CSOs) in Royal Leamington Spa, Warwickshire, through a suite of technically advanced designs that test a variety of complementary solutions.

Few projects manage to balance technical complexity with community benefit as seamlessly as the Leamington Spa Sewerage Scheme with live public functional spaces is technically complex but also requires attentive and agile stakeholder engagement, delivering large measurable environmental improvements.

[caption id="attachment_26765" align="alignnone" width="1200"] Surface water separation - Courtesy of Forkers Ltd[/caption]

While early guidance targeted storm overflows with direct discharges into these areas, the programme has since expanded to include overflows that pose wider environmental and public amenity impacts. This includes high amenity areas such as recreational waters and areas of interest to businesses and other organisations, even if they are not formally designated as bathing waters.

The shift reflects a more holistic approach to water quality management, prioritising interventions based on environmental sensitivity, public usage, and the potential impact of overflows. This broader targeting ensures that improvements are aligned with community expectations and environmental stewardship goals.

Hydraulic modelling & option development

The project leveraged the Longbridge Strategic Sewerage Growth model, enhanced with updated flow monitoring and surface water network refinements. Hydraulic solutions were identified early through iterative hydraulic modelling and refined through feasibility and Early Contractor Involvement (ECI) with Forkers Ltd.

By integrating advanced hydraulic modelling and real-time control, the scheme exemplifies the kind of forward-thinking infrastructure needed to meet the challenges of climate resilience and urban growth.

Preferred interventions included surface water separation, pumped and gravity storage, and network optimisation.

[caption id="attachment_26764" align="alignnone" width="1200"] Shaft storm tank precast concrete segments - Courtesy of Forkers Ltd[/caption] Leamington Spa Sewerage Scheme: Supply chain - key participants Deliver contractor: Forkers Ltd Designer: WSP Tunnelling/shafts/timber headings: Active Tunnelling Ltd Electrical/mechanical: STAL (UK) Ltd Ground support & shoring: MGF Ltd Vacuum excavation: VAC UK (Kilkern Ltd) Drainage sub-contractor: Arthur Civil Engineering Ltd Emergency temporary pumping: Selwood Precast concrete pipe & rings: Marshalls Civils & Drainage Precast concrete rings: FP McCann Ltd Plastic storage pipes: Aquaspira Ltd GEOlight® storage tank: SDS Limited Concrete & aggregates: Aggregate Industries | Cemex Plant hire: Flannery Plant Hire (Oval) Ltd Traffic management: RouteOne Traffic Management Ltd Carriageway surfacing: JMC surfacing Ltd Surface water separation (SWS)

A major surface water separation scheme was implemented between Campion Road and Milverton School, delivering significant benefits in surface water management. The project successfully disconnected impermeable areas from the combined sewer network, reducing the volume of stormwater entering the system. Additionally, it incorporated below-ground storage to help manage flood risk, enhancing the area’s resilience to heavy rainfall events and contributing to improved environmental outcomes.

[caption id="attachment_26763" align="alignnone" width="1200"] Surface water separation - Courtesy of Forkers Ltd[/caption] Pumped & gravity storage

The Lower Avenue Combined Sewer Overflow (CSO) scheme involved the installation of an 880m3 shaft tank with a return flow capacity of 30 l/s, located in the Station Approach car park. The shaft tank was designed and constructed by Active Tunnelling Ltd. At Princes Drive 19B, the scheme increased the flow into the existing storm tanks by an additional 75 l/s. Both storage systems were equipped with real-time control (RTC) logic to optimise return flows and minimise the risk of spills into the river, ensuring more efficient and environmentally responsible stormwater management.

Climate change & resilience

To ensure long-term resilience and performance under changing climate conditions, the design rainfall was uplifted by 15% to reflect projected 2050 scenarios. Spill frequency assessments were carried out using Severn Trent’s Technical Standard Rainfall Dataset, representing worst-case conditions to ensure robust system performance. All conveyance infrastructure was sized accordingly to accommodate future climate impacts, supporting sustainable and reliable operation over the asset’s lifetime.

Construction & delivery

The project was delivered under tight AMP7 deadlines, requiring early contractor involvement and agile design development. Forkers Ltd and WSP played key roles in feasibility, site investigation, and outline design.

Key construction innovations included the use of GEOlight® blocks from SDS Limited for modular storage. GEOlight® blocks offer a significant advantage in large-scale infrastructure projects due to their lightweight, corrosion-resistant design, which simplifies installation and reduces long-term maintenance costs compared to concrete or steel alternatives.

[caption id="attachment_26767" align="alignnone" width="1200"] GEOlight® modular storage tank - Courtesy of Forkers Ltd[/caption] Environmental & community benefits

Reducing the impact from CSOs has had significant social implications. Access to clean and safe recreational waters promotes public health and well-being, encouraging outdoor activities and fostering a connection with nature. This initiative does not just solve a problem, it redefines what is possible in urban water management, setting a precedent for future projects across the UK and beyond.

Spill reduction. Flood risk: No detriment demonstrated; some areas show betterment particularly through the implementation of surface water separation in the north-east, the construction of stormwater storage tanks in the south, and comprehensive improvements along the River Leam corridor aimed at enhancing water quality and resilience. Education: Engagement with Milverton School on drainage and sustainability. Broader significance & replicability

The Green Recovery Leamington Spa Sewerage Scheme stands as a testament to the power of innovative engineering and sustainable practices in addressing modern environmental challenges. This project not only resolves immediate issues related to CSOs but also sets a benchmark for future initiatives aimed at enhancing urban wastewater management.

The Leamington Spa Surface Water Separation Scheme, delivered as part of Severn Trent’s Green Recovery Programme, exemplifies a forward-thinking approach to sustainable water management.

Central to the project was the installation of a two megalitre GEOlight® attenuation tank from SDS Limited beneath a playing field adjacent to Milverton Primary School. The tank, connected to newly laid surface water sewers across several roads in Leamington Spa, significantly increases stormwater storage capacity within the network. This enhancement plays a critical role in protecting downstream sewage treatment infrastructure from overload and reducing the frequency of combined sewer overflows into the River Leam.

[caption id="attachment_26768" align="alignnone" width="1200"] Construction of the 2 megalitre attenuation tank - Courtesy of Forkers Ltd[/caption]

The project not only supports Severn Trent’s ‘Get River Positive’ commitments but also aligns with local and national planning policies. By integrating innovative technology with sustainable construction practices, the scheme delivers measurable environmental benefits. It demonstrates how targeted infrastructure investment can contribute to long-term river health, climate resilience, and community wellbeing; setting a precedent for future water management initiatives across the region.

Its success lies not only in the numbers (reduced spills, increased storage, improved water quality) but in the way it brings together engineering excellence, ecological sensitivity, and community engagement. The project’s legacy will be felt not just in the River Leam’s improved health, but in the model, it provides for sustainable, scalable, and socially conscious infrastructure.

Conclusion

The Green Recovery Leamington Spa Sewerage Scheme is a model of integrated water management, combining hydraulic engineering and community recreational benefit. It demonstrates how ambitious environmental goals can be achieved through technical excellence, collaboration, and innovation.

In a sector where impact is often measured in compliance, this scheme goes further; delivering outcomes that resonate with local communities, regulators, and the environment alike.

The project not only safeguards the River Leam for recreational use but also sets a precedent for inland bathing water schemes across the UK and beyond.

In response to recurring foul sewer flooding affecting residential properties in the Long Close and Blackcross area of Chippenham, Wiltshire, a critical infrastructure improvement project was commissioned by Wessex Water. The flooding had severely impacted ten properties, posing risks by flooding/damaging private property, and diminishing the quality of life for local residents and the surrounding environment. Investigations revealed that the root cause of the issue lay in the inadequate hydraulic capacity of an aging 225mm diameter main sewer, which was no longer capable of handling the flows from the surrounding catchment area. Project drivers and objectives

Although portions of the local sewer system were partially separated into foul and surface water networks, much of the upstream catchment remained a traditional combined system. The area also featured two Combined Sewer Overflows (CSOs), only one of which was permitted. Neither met modern environmental or operational standards.

Consequently, a comprehensive scheme was developed with dual objectives: to mitigate the risk of foul water flooding and to consolidate the two CSOs into a single, compliant discharge asset.

The primary goals of the scheme included:

Alleviation of foul water flooding to affected properties. Enhancement of the network’s hydraulic capacity. Elimination of one non-compliant CSO and upgrade of the other to ensure environmental compliance. Creation of new infrastructure for stormwater management to increase network resilience. Minimisation of construction impact on residents and the local environment.

This project forms part of Wessex Water’s broader investment programme aimed at modernising critical sewer infrastructure, enhancing operational efficiency, and protecting the environment.

[caption id="attachment_23674" align="alignnone" width="1200"] (left) Excavating down to rock formation and (right) Brokk® remote controlled unit breaking out sandstone - Courtesy of Bartlett Contractors Ltd[/caption] Long Close Flood Prevention: Supply chain - key participants Client & principal designer: Wessex Water Principal contractor: Bartlett Contractors Ltd Shaft designer: Robert Stone Associates Shaft contractor: Matt Durbin Associates Shaft jacking system: Specialist Plant Associates Demolition robot: Brokk® M&E contractor: HM Electrical Services GRP kiosk/MCC: BW Controls Ltd Security covers: Steelway Brickhouse Pumps: Xylem Water Solutions UPVC Pipes: Funke Gruppe Static screen: Eliquo Hydrok Ltd Shaft segments: FP McCann Ltd Excavation safety products: MGF Ltd Grout: Reader Cement Products Surfacing contractor: Walton Civil Engineering Proposed engineering solution

To address the identified capacity shortfalls and overflow issues, a robust and technically innovative solution was designed by Wessex Water internal design capability.

At the heart of the scheme was the construction of a 240m3 off-line stormwater storage tank. This was designed to temporarily hold excess flow during heavy rainfall events and prevent foul flooding in residential areas. Key components of the system included:

Two 11kw Flygt submersible return pumps from Xylem Water Solutions will discharge stored flows at 11.5 l/s back into the main sewer network under controlled conditions. Approximately 304m of rising main to convey flows from the tank. A gravity overflow pipeline leading to an existing surface water sewer, designed to act only when the tank reaches capacity. Installation of a 6mm, 2D static screen to prevent solid material from entering water courses, thereby protecting the local environment. Scope of works & technical overview

The construction work was extensive and complex, involving multiple technical disciplines and precision engineering. The centerpiece of the scheme was a 10m deep by 8m wide caisson segmental shaft, providing the necessary volume for the storage tank. The shaft, constructed by Matt Durbin Associates, incorporated a steel cutting shoe to assist with ground penetration and maintain structural stability during installation.

Precast concrete units supplied by FP McCann were used to form the shaft walls. These back-bolted segments ensured watertight integrity and efficient assembly. The annulus between shaft segments and the surrounding ground was sealed using a polymer-modified cementitious grout from Reader Cement Products, which provided additional protection against groundwater ingress. The cover slab was manufactured off-site, transported in sections, and installed using a 90T crane, supported by pre-installed PCC beams.

[caption id="attachment_23677" align="alignnone" width="1200"] Placing the cover slab - Courtesy of Bartlett Contractors Ltd[/caption] Ground conditions & construction challenges

Geotechnical investigations had indicated the presence of sandstone rock formations at a depth of around 7m. To safely and efficiently remove this material while reducing health risks from Hand-Arm Vibration Syndrome (HAVS) and minimising noise pollution, a remote-controlled Brokk demolition robot was employed. This approach not only enhanced worker safety but also sped up excavation in the challenging geological strata.

The internal pipework comprised a combination of DN300/200 and DN100 ductile iron pipelines, chosen for their durability and resistance to corrosion. A hydro-ejector nozzle was installed to assist with mixing and settlement prevention within the tank. To facilitate this, 11kw Flygt submersible return pumps (NP 3153.185 SH 53-276) were mounted on guide rails, allowing for easy maintenance.

Mechanical & electrical installations

The overflow screening system featured a 2D peak screen with 6mm apertures, ensuring compliance with current discharge regulations. Supplied and installed by Eliquo Hydrok Ltd, the screen was engineered for low maintenance and reliable performance.

LCP4 level security covers from Steelway Brickhouse were installed atop reinforced concrete upstands; which also included fall arrest grills for improved safety. Additional health and safety provisions included the installation of davit sockets and lanyard points, enabling secure lifting and maintenance operations.

A new 110mm DNO electrical cable was laid over a 100m route to power the pumping station. Power distribution and telemetry monitoring were managed through a newly installed glass reinforced plastic kiosk, housing the motor control centre and telemetry outstation supplied by BW Controls. Both radar and float-based level detection systems were implemented in the tank to provide accurate, real-time flow data.

Pipeline & highway works

Gravity pipelines and 13 new manholes were installed throughout the network. Two manholes were specifically designed as overflow chambers to divert high flows into the storage tank. Pipework was laid using UPVC Funke Gruppe HS pipes ranging from 250mm to 315mm in diameter.

A 160m section of rising main and associated ducting was laid through London Road; a heavily trafficked route. To minimise disruption to the public and local businesses, this portion of the work was completed during the school holidays. Temporary parking arrangements were made by renting space at a nearby car wash and implementing a controlled permit system for residents.

The section of the works along Blackcross proved particularly complex due to poor ground conditions and the sub-standard condition of the existing highway. This required the excavation and reinstatement of multiple infrastructure elements, including PCC chambers, a 250mm gravity main, a 160mm OD SDR11 rising main, and two 110mm ducts. A tanker pull-in bay was also constructed using HB2 kerbing and Cellpave HD, with a grass infill to maintain the visual aesthetic of the surrounding parkland.

[caption id="attachment_23678" align="alignnone" width="1200"] (left) London Road rising main installation and (right) Blackcross pipe installation - Courtesy of Bartlett Contractors Ltd[/caption] CSO modifications & system integration

To rationalise the local sewer system, significant changes were made to two existing CSOs. One non-permitted CSO was decommissioned, and the remaining permitted CSO was upgraded to handle screened storm flows via the new storage tank and overflow infrastructure. Two existing overflow chambers were retrofitted to channel excess flows into the tank; creating a more controlled and environmentally compliant outfall process.

The discharge manhole on the existing 225mm diameter sewer was also modified, enabling seamless integration of the new storage and pump infrastructure into the legacy system.

Environmental & community considerations

Throughout the project, efforts were made to minimise disruption and reduce the environmental footprint. Measures included dust suppression, noise control, and timely communication with residents through letter drops and community events. Access to properties was maintained throughout, despite significant logistical challenges posed by road closures and restricted space.

Upon completion, the site will be fully reinstated to parkland, ensuring the area is visually and functionally restored. The inclusion of green-friendly materials such as grass-filled Cellpave demonstrates a commitment to sustainable construction practices.

[caption id="attachment_23676" align="alignnone" width="1200"] (left) Blackcross reinstatement and (right) Asphalt reinstatement - Courtesy of Bartlett Contractors Ltd[/caption] Conclusion

The Long Close Flood Protection Scheme in Chippenham represents a significant achievement in sewer network enhancement. By combining innovative engineering with sensitive environmental and community planning, Wessex Water has delivered a future-proofed solution to a long-standing problem.

The project commenced in July 2024 and was completed by March 2025, meaning all four seasons were endured throughout the programme. The works have not only resolved immediate flooding risks but have also improved environmental compliance, enhanced hydraulic performance, and laid the groundwork for sustainable urban development in the region.

SDS Ltd has completed the installation of its latest smart rainwater management systems at homes in Forton, Lancashire, and Deal, Kent, as part of Water Companies’ ongoing efforts to reduce sewage spills into rivers and the sea. The company’s Intellistorm®-equipped rainwater harvesting tanks use smart technology to retain and release their contents automatically, thereby increasing, by several times over a standard water butt, their capacity to protect the sewers from being overwhelmed by excess surface water from heavy rainfall. More than sixty systems have already been installed by agreement with homeowners by SDS in January and February 2023 for United Utilities and Southern Water. The two Water Companies have committed to deploying several hundred tanks over the next few weeks, including at properties served by United Utilities at Wrea Green in Lancashire, and by Southern Water at homes in its “Pathfinder” locations in Kent and the Isle of Wight. Intellistorm® works by releasing water from the tank prior to rainfall. By analysing weather forecast data the system calculates how much water to release based on the roof size and the size and location of the tank. This ensures that there is always water available for homeowners to use, for example in their gardens, but also sufficient spare capacity in the tank to accommodate the next rainstorm. A typical water butt fills once in the winter and then remains full and overflows until water is taken out by the homeowner, often only when summer has arrived. Consequently, a standard butt contributes little to holding back water from sewer networks during the wettest months of the year. SDS has carried out an assessment of the performance data supplied by the initial 25 tanks at Forton after their first month of operation. Extrapolated across 12 months, and using average rainfall statistics, it has been established that the tanks could hold back up to 75 times their nominal volume, equivalent to each tank holding back 30,000 litres of water a year from the combined sewer at times of peak flows, which is when sewers typically overflow. In Forton alone this equates to a surface water attenuation volume of up to three quarters of a million litres of water per year*. That water is then released once the rain event has passed and the sewers can cope. [*based on average rainfall accumulations – these figures will vary if the weather is drier or wetter than the average]. Johnny Phillips, Surface Water Strategy Development Manager for United Utilities, said:

“We’re delighted to be launching this initiative in Forton. Having looked at a number of areas, we think the smart water tanks will make a real difference in the village and help to increase capacity in our sewer network and deliver local environmental improvements, and the early findings are backing this up.”

Dr Neil Sewell, Director of New Technology Services at SDS, said:

“We’ve made exciting enhancements to the Intellistorm® technology since our early projects with South West Water, Anglian Water and Severn Trent Water and we’re pleased to show how the latest version of the tanks begins to deliver some really strong performance in Forton and Deal.”

These projects show that Intellistorm®-equipped smart tanks have the potential to be a really valuable tool for Water Companies in the battle against sewer overflows and flooding, particularly when they are coupled with other sustainable drainage systems and sewer network improvements. They have the added advantage of providing a supply of non-potable water for homeowners, thus reducing the demand for mains-supplied, drinking-quality water for purposes for which its high level of treatment is not required, whether that’s for watering the garden and washing the car or even flushing the toilet and supplying the household washing machine. It is also a great way for local people to get involved with helping to solve flooding and pollution, thereby improving water quality in our rivers and bathing waters, as well as protecting the country’s declining natural water resources from over-abstraction, in order to feed a growing and increasingly water-dependent population. Thanks to their multiple benefits SDS is seeing significant interest from Water Companies in its Intellistorm® systems.     For more information: SDS Ltd | +44 (0)1934 751303 | www.sdslimited.com