Supply Chain - Stormwater Storage

Offwell is a small village on the outskirts of Honiton just off the A35. The existing sewage treatment works was constructed in the 1980s and serves a population of around 350. It was typical of the era, with an old style Dortmund tank with percolating filter and humus tank off the back end. Final effluent from here gravitates out from the site to Offwell Brook. The driver for the scheme was to reduce the number of unconsented spills to the environment by providing a capacity of 30m³ storm storage (exceeding the EA’s required storage volume of 25m³).

Project scope

At the scoping stage, Galliford Try worked closely with South West Water to establish the most cost-efficient solution when considering both operational expenditure (OPEX) and capital expenditure (CAPEX) to ensure South West Water achieved the best whole life costs. From this exercise it was established that the scope outlined below was to be included for construction on site:

• One new part buried concrete rectangular stormwater storage tank with capacity of 30m³.
• New LCP for the control of duty/standby pump for return of effluent within the storm tank.
• Relocate the existing MCERTS final effluent flow meter and re-test.
• New pipelines between existing equipment and new storm tank.

[caption id="attachment_12889" align="alignnone" width="1200"] Storm tank construction: (left) steelwork framework and (right) shuttering - Courtesy of Galliford Try[/caption]

Stormwater storage tank

Being a part-buried tank, a significant excavation was undertaken with appropriate temporary works associated to the angle of repose. Once completed, a blinding layer was installed at an appropriate level for the steelwork to be built up from.

The steel for the base was installed, shuttered, and poured in two due to a sump for the install of return pumps. Wall steelwork was then installed up to 2.5m above ground and shutter pans used for the concrete pour. The overflow from this then spills to an existing chamber on site and then to Offwell Brook.

MEICA

To enable on-site efficiencies, the majority of the LCP and kiosk were fitted out off-site in Galliford Try’s local depot, with the LCP being constructed in Plymouth and the kiosk being fitted out with the LCP and services within the same workshop.

Once completed and tested, this was transported directly to site where Galliford Try’s electrical team connected the LCP into the site network for both power and communications. Once on site, all that remained was to install the already put together framework and brackets for the isolators and ultrasonic junction box and install the pre-wired flow meters back to the already mounted heads within the kiosk.

This in turn lead to betterment of the programme and benefited by undertaking the off-site build in a controlled environment.

Site access

Access to site was challenging. The site was only accessible for construction vehicles through one road, which was a narrow, single lane track with a steep drop off on one side and tall hedge banks on the other, and there were infrequent passing places for larger construction type vehicles. It was difficult for the site team to manage construction activities and getting plant and materials to site.

After the first week of mobilising to site, Galliford Try found that the road with the verge was starting to degrade and potentially become unsafe. This was reported back to the Highways Commission. While waiting for further consultation, several other routes were identified and the project team looked at each of these routes to identify which was best suited.  After the Highways Commission responded, it was finally decided that to ease further degradation of the road that a handling/staging area was to be found in a local farmer’s yard and smaller vehicles were to be used to transport plant and materials to site.  This had an effect on programme and cost but was more manageable and safer to undertake, but left Galliford Try with one inevitable issue; concrete deliveries for the storm tank.

Galliford Try’s Client Liaison Officer notified residents on the few occasions that the concrete had to be transported through the village. Deliveries were restricted in size and were escorted through the village to prevent damage to any of the dwellings. This was undertaken for the base pour and the wall pours; with multiple wagons on each of the days.

Confined site

The footprint of the working area was confined to the site boundaries, only providing 950m² of space, of which only 180m² was usable for construction activities. Alongside this, there were some enabling works that required undertaking first to enable access into the construction zone, this consisted of:

• New final effluent flow meter chamber.
• Relocation of turbidity sensor.
• New sample chamber with weir plate.

Offwell Stormwater Storage: Supply chain - key participants

• Client: South West Water
• Project delivery, civils & MEICA: Galliford Try
• Civil design: Eastwood & Partners
• Tank construction: D Wall Construction Services
• Pumps: Xylem Water Solutions
• Metalwork: GT Fabrications
• Flow meter: Siemens
• Pipework: Saint Gobain PAM UK
• Kiosk: GR PRO Precision Manufacturing
• Instrumentation: Pulsar Measurement
• Aggregates: Steve Wills Haulage

[caption id="attachment_12892" align="alignnone" width="1200"] Regraded operational land - Courtesy of Galliford Try[/caption]

Carbon savings & in-house capability

Local resources and materials were used where possible including subcontractors, which as a result provided the local economy with a financial boost during the construction phase.

Where local suppliers were not available, Galliford Try strived to use off-site build solutions where possible to minimise commuting. Contractors from Exeter were used for the construction of the storm tank, all concrete for the project also came from Exeter, and local suppliers were used for aggregates from local quarries.

In-house resources that were utilised included project management, electrical design, LCP design/build, process control, and commissioning. The in-house workforce undertook  the site establishment, civil engineering, landscaping, MEICA works, and finally the demobilising the site.

Stakeholder management

At pre-construction phase, all third-party stakeholders were identified and entered onto a management plan. Galliford Try’s Customer Liaison Officer contacted all stakeholders prior to commencement to provide them with the appropriate project contacts should they have questions, queries, or complaints and to establish their requirements and desires throughout the construction phase of the works. As part of the management plan all communications where complaints or agreements are made are formally recorded, resolved, and closed out.

Conclusion

Initial progress on site was good with setting up site and setting the project up for an efficient delivery until the road issues occurred.

Once this was managed and materials and plant were getting to site the remainder of the project ran through a smooth transition and was delivered by the regulation date of 31 March 2024.

The Thames Tideway Tunnel project is a 25 km (16 mile) combined sewer under construction under the tidal section (estuary) of the River Thames as it runs through London. It will significantly increase the capacity of London’s sewerage system, large sections of which were built in the 19th century, and be able to capture, store and convey almost all of the raw sewage and rainwater that currently overflows into the Thames Estuary. The Tideway tunnel will connect 34 of the capital’s most polluting combined sewer overflows (CSOs), transferring the foul water to the Lee Tunnel for onward delivery to Beckton Sewage Treatment Works. The completion of the Thames Tideway Tunnel scheme, currently anticipated for 2025, will significantly improve water quality, capturing more than 95% of the spills that currently enter the river to the benefit of London’s almost 9 million residents.

Location

As part of works on the Central section of the Thames Tideway Tunnel scheme, Barhale was contracted by the Ferrovial and Laing O’Rourke joint venture (FLO JV), the lead contractor for the central section of the project, to deliver the heavy civils and civils structures that would intercept the sewage overflows and transfer these to the main Tideway tunnel beneath the river Thames.

The Victoria Embankment site was located in the City of Westminster, on the north side of the river Thames adjacent to, and south-west of, the Hungerford Bridge and Golden Jubilee footbridges. The site was bounded to the south-east by the River Thames and the north-west by the A3211, beyond which are the Victoria Embankment Gardens.

[caption id="attachment_10008" align="alignnone" width="1200"] (left) Works within the cofferdam in the Thames and (right) works ongoing within the cofferdam - Courtesy of Barhale[/caption]

Scope of work

The works were delivered in stages to provide protection to existing assets and engineering control over the structure’s movement. One of the first elements of work undertaken at Victoria Embankment was the construction of a 50m long secant piled wall that would retain and minimise ground movement on the dual carriage way and the Circle and District tube lines.

The next stage of the works comprised the diversion of the existing gas mains and the completion of the cofferdam. Once these were completed, piling operations could start. In total, 117 piles were installed: 47 (No.) 600mm bearing piles for the CSO structure and 70 (No.) 1200mm piles for the new river wall. These were required to provide adequate bearing capacity for the future structures.

The groundwater levels along the Tideway Central route, including Victoria Embankment, did not allow safe excavation of the shafts and tunnels and required the project team’s attention. A temporary works assessment was carried out along the route and verified by using pump tests, which modelled the required pumping capacity to dewater the existing aquifers.

At Victoria Embankment, Barhale installed four 106m deep Chalk Wells, six 65m deep Thanet Sand Wells, and six 50m deep Lambeth Group Wells. This system was also accompanied by in-shaft and tunnel wells that have targeted local pockets of water.

The 15m diameter shaft was built using three techniques. For the first 14m, the shaft was sunk using the caisson method and precast segments. This method was chosen for this section due to the granular material that was reported in the existing boreholes.

[caption id="attachment_10006" align="alignnone" width="1200"] Secondary lining works - Courtesy of Barhale[/caption]

Once past this layer, London Clay was encountered, and the excavation method was changed to underpinning. This method was used for excavating down to 32m below ground level. Due to the limitations of precast segments, the lining technology was changed to sprayed steel fibre reinforced concrete with a thickness of 600mm. This method allowed for better control of shaft profiles and portals for future works.

At formation level, a 2m deep reinforced concrete base slab was cast. The construction of this base slab required approximately 80 tonnes of steel and over 450m³ of high GGBS (ground granulated blast-furnace slag) concrete.

From this level a series of temporary works were implemented to allow the short connection tunnel to be excavated and supported using SCL (sprayed concrete lining). The connection tunnel is 18m long and varied in shape. During the first 14m, the tunnel internal diameter (ID) is 3.6m and in the last 4.5m the tunnel transitions to an ID of 4.9m.

The completion of the SCL works allowed for the site to transition to the full civils stage and start the works on the shaft and tunnel secondary lining and internal structures. Above ground level works that were released by the achievement of this milestone comprised the construction of new chambers that will deal with the intercepted flow and the new river wall that encompasses these structures and protects them from possible ship impact.

For these works at Victoria Embankment, Barhale used approximately 1400T of rebar and over 7000m³ of low carbon emission concrete, making this one of the bigger schemes that has been delivered during the Thames Tideway Tunnel project.

Tideway Central: Victoria Embankment: Supply Chain - key participants

• Main designer & contractor: FLO JV
  • Ferrovial
  • Laing O’Rourke
• Delivery contractor: Barhale
• RC piling: Expanded Piling
• Dewatering: WJ Groundwater
• Civils works: Flatley Construction
• Sawcutting/drilling: EDD (Euro Diamond Drilling) Ltd
• Waterproofing: Renesco
• Temporary electrical set-up: Select Site Solutions
• Concrete supplier: CEMEX UK
• Concrete supplier: Hanson UK
• Additives for SCL works: Normet
• Waterproofing: Sika
• Steel supplier: Express Reinforcements Ltd
• Steel supplier: HY-TEN Ltd
• Plant supplier: Select Cranes
• Plant supplier: Flannery Plant Hire

Challenging tunnel construction

The short connection tunnel at Victoria Embankment was design to be excavated and supported using the sprayed concrete lining method. This allowed for the short connection tunnel to wrap around and support the main tunnel during the break-out and final connection operation.

To put this in stages, the Victoria Embankment team was required to construct the tunnel using SCL and line the asset using cast in situ reinforced concrete and reduce its diameter to a constant 3m ID. The main tunnel team would be required to build the main tunnel using a segmental lining and cast in situ a reinforced liner, missing only the break-out area towards the Barhale connection tunnel. Once the segments were broken out, the two independent concrete structures would be joined together using cast in situ reinforced concrete.

The ground condition investigations for the connection tunnel identified a band of sand in the middle of the tunnel excavation, with a thickness of 1m and the presence of water.

On the assumption of the layer thickness and presence of water, a temporary design was progressed to support the excavation while spraying concrete. The designer prescribed the use of a pipe arch canopy support system for the narrower, 3.6m ID section of tunnel, with piles providing support for the remaining 4.9m ID section. The dewatering specialist prescribed the use of shaft wells and in-tunnel wells to allow efficient dewatering of the layer.

[caption id="attachment_10007" align="alignnone" width="1200"] (left) Commencement of shaft works, and (right) diversion works within Victoria Embankment -Courtesy of Barhale[/caption]

During the initial 3 to 4m of tunnel excavation, the face log showed an increase of the sand layer band and larger volumes of water than expected.

The sand layer covered approximately half of the excavation face at this point. As works progressed through the next 4m, additional wells continued to be drilled into the tunnel to target the water presence and the band of sand kept extending. Nine meters in, and the sand layer presence ranged from midway up to, and 3m above, the tunnel crown.

The encountered sand layer was also very fine which made spraying concrete challenging. As the concrete was sprayed, the sand bond was so small that the sprayed concrete was pilling off in small increments, making the excavation bigger. To prevent this occurrence, fast setting grout was sprayed as an initial layer and only then sprayed concrete.

This amendment to the plan did not solve the issue of the water presence and problems wet sand causes to excavations, especially tunnels.

An additional amendment to the plan had to be made. The team set out to space proof and conducted a feasibility study to understand if banker bars could be deployed. The temporary works design was then independently checked by a second design consulting company and approved by client FLO JV.

Barhale safely implemented the temporary works support, which meant installing eight advances of banker bars and spraying the primary concrete lining against them.

Works completion

The complex civils works on Victoria Embankment CSO Project to intercept the combined sewer overflows and to divert them into the Thames Tideway Tunnel presented challenging and unexpected ground conditions. Demonstrating agility and innovation, the Barhale team was able to deliver an excellent solution which both met the project timeline and provided best value for money.

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.

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:

1. 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’.
2. By 2045, water companies will have improved all remaining storm overflows discharging into or near ‘high priority sites’.
3. 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.

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.

Hawkchurch is a small village on the Devon/Dorset border, 3 miles north-east of Axminster and 4 miles north of the fishing town of Lyme Regis. The existing sewage treatment works was constructed in the 1980s and serves a population of around 500. It was typical of the era, with an old style Dortmund tank with percolating filter and humus tank off the back end. Final effluent is pumped from the site to an outfall into the Blackwater River. The project driver was to reduce the number of unconsented spills to the environment by providing a capacity of 45m³ storm storage and inlet works screening to remove solids and enhance the operation of the works.

Project scope

At the scoping stage, Galliford Try worked closely with South West Water to establish the most cost-efficient solution when considering both operational expenditure (OPEX) and capital expenditure (CAPEX) to ensure South West Water achieved the best whole life costs. From this exercise it was established that the scope outlined below was to be included for construction on site:

• A new above-ground concrete storm tank with capacity of 45m³ (exceeding the EA’s required storage volume of 40m³).
• New access platform to span the storm tank for washing down of the storm tank.
• New LCP for the control of duty/standby pump for return of effluent within the storm tank.
• One Jacopa wave screen to be installed on the overflow from the storm tank.
• One new HAIGH 590 series, 6mm 2D mechanically cleaned screen and 10mm 1D hand raked bypass screen from Haigh Engineering to be installed within existing inlet channel.

The site

Access to site was challenging, as the site was only accessible via one narrow road with infrequent passing places for the larger vehicles required to get construction equipment and materials to site. Additionally, the footprint of the site was only 880m² of which only 180m² was usable for the construction activities.

[caption id="attachment_12435" align="alignnone" width="1200"] (left) Piling rig set up, (middle) piling reinforcement, and (right) piles cropped - Courtesy of Galliford Try[/caption]

The stormwater storage tank

Prior to construction it was identified that there was contaminated water within the ground. After the initial sampling, Galliford Try requested further sampling to take place to identify if this was a one-off fuel spill or not. After the second survey, it was identified that contaminated water was still present and was an issue that required managing.

Galliford Try’s environmental team looked into the best practice options to manage this, and then engaged AGS Ground Solutions Ltd to undertake a Tier 2 survey of the site, as it was considered possible that a new fissure could be created during the piling stage which could expose the contaminated water to the environment.

Through further studies and multiple discussions around this topic, to mitigate the risk, Galliford Try utililised contaminated water handling plant and pumps from Siltbuster Ltd to manage flows. Along with this, Reconomy was engaged for the removal of any contaminated arisings.

The new storm tank was built upon twelve piles due to the strata within this area a mixture of Charmouth mudstone formed some 190 million years ago and poorly stratified angular rock with clayey hillwash. To undertake the piling, a piling mat and temporary works were required, which allowed Aarsleff Ground Engineeing to mobilise to site and install the twelve CFA piles at 450mm nominal diameter.

Throughout the piling exercise, contaminated water was managed through the Siltbuster Ltd plant, and the piling activity was successfully completed with zero impact to the local water courses.

With the piling compete, steel for the base was installed and tied into the piling reinforcement, shuttered and poured in two sections due to the need for a sump to install the return pumps. Wall steelwork was then installed up to 3m above ground and shutter pans used for the concrete pour.

Overflows from the new tank will spill into an existing chamber on the site and to screen these flows further, Jacopa Ltd fitted a new 2D wave screen to screen all flows to 6mm within the storm tank.

[caption id="attachment_12436" align="alignnone" width="1200"] (left) Base shuttered and wall starters, and (right) steelwork for base slab - Courtesy of Galliford Try[/caption]

Inlet works screening

One of South West Water’s aims is for everyone to feel confident about the water at their favourite beach, river, or lake. Galliford Try have installed a number of inlet works enhancement screens on multiple sites throughout Devon as part of SWW’s WaterFit Programme, and through this have gained useful experience in installing screens whilst managing flows through to the works.

Following discussions on how to manage flows at Hawkchurch STW, a new 590 Series screen from Haigh Engineering Ltd was installed into the inlet channel. Flows are screened to 6mm, with bypass flows screened to 10mm.

Hawkchurch Storm Tank: Supply chain - key participants

• Project delivery, civils & MEICA: Galliford Try
• Ground surveys: AGS Ground Solutions Ltd
• Civil design: Eastwood & Partners
• Contaminated water handling: Siltbuster Ltd
• Removal of contaminated arisings: Reconomy
• Piling: Aarsleff Ground Engineering
• Tank construction: D Wall Construction Services
• Steelwork: GT Fabrications
• Wave screen: Jacopa
• Inlet screens: Haigh Engineering Ltd
• Pumps: Xylem Water Solutions
• Pipework: Saint Gobain PAM UK
• Flow meter: Siemens
• Instrumentation: Pulsar Measurement
• Kiosk: GR PRO Precision Manufacturing

[caption id="attachment_12431" align="alignnone" width="1200"] (left) Jacopa wave screen in the storm tank, (top right) Inlet screen installation in the channel, and (bottom right) inlet screen in action - Courtesy of Galliford Try[/caption]

Carbon savings & in-house capability

Local resources and materials were used where possible including subcontractors, which as a result provided the local economy with a financial boost during the construction phase. Where local suppliers were not available, Galliford Try strived to use off-site build solutions where possible to minimise commuting.

In-house resources that were utilised included project management, electrical design, LCP design/build, process control, and commissioning. The in-house workforce undertook  the site establishment, civil engineering, landscaping, MEICA works, and finally the demobilising the site.

Stakeholder management

At pre-construction phase, all third-party stakeholders were identified and entered onto a management plan. Galliford Try’s Customer Liaison Officer contacted all stakeholders prior to commencement to provide them with the appropriate project contacts should they have questions, queries, or complaints and to establish their requirements and desires throughout the construction phase of the works. As part of the management plan all communications where complaints or agreements are made are formally recorded, resolved, and closed out.

Conclusion

Initial progress on site was good with setting up site and setting the project up for an efficient delivery until delays were encompassed by switching the piling rig out due to the environmental considerations. Once this was managed and piling underway, the remainder of the project ran through a smooth transition and was delivered by the regulation date of 31 March 2024.

Marhamchurch is a small village around 2.4km south of Bude and has a population of just over 800. Sewage from this village is pumped to a nearby large sewage treatment works which processes the waste from Bude and the surrounding area. The existing Marhamchurch Sewage Pumping Station (SPS) was built around 50 years ago and was not designed to hold the volume of stormwater nor pass forward the volume of water which is now required to achieve the bathing water quality driver. Marhamchurch SPS does have an emergency overflow which connects to the River Neet and it is this river which discharges into the Bude bathing water area. South West Water had a driver to ensure a design standard of no more than an average of two significant (>50m³) spills per bathing season (as per the Environment Agency definition).

Solution

Galliford Try was appointed by South West Water to find a solution to meet the bathing water driver. A two-fold approach was undertaken; namely to increase the pumping station’s pass forward flows from the current 8 l/s to 18 l/s, and to provide a new pumping station which would contain 100m³ of on-site stormwater storage and thus reduce the likelihood of having to utilise the pumping station’s emergency overflow. The increased pass forward flow rate and on-site storage capacity was based on a 2050 design horizon. The existing Marhamchurch SPS sent flows to Helebridge STW via a now mothballed sewage treatment works at Helscott, which had been turned into another sewage pumping station. Not only was this a very convoluted route for the flows to take as they were pumped in the opposite direction to the Helebridge STW, but the existing pipe diameter and condition did not lend itself to accommodate the increase in flows. The solution was to therefore lay a new rising main from the Marhamchurch SPS and connect into the existing Helscott Rising Main heading to Helebridge, thereby removing the ‘dog leg’ section of existing pipework. [caption id="" align="alignnone" width="1200"] (top left) Existing site prior to improvement works, (top right) site clearance, (bottom left) construction of temporary footpath and haul road to shaft and (bottom right) shaft cutting edge construction - Courtesy of Galliford Try[/caption]

The new pumping station

The existing Marhamchurch SPS site is on a very small parcel of land which could only be accessed down a narrow un-metalled lane, with low hanging trees. It would not have been possible to send construction plant down this lane, however the adjoining landowner (farmer) was more than happy to allow access to his fields to undertake the improvement works to the pumping station. With easy access now available from the A39 (main road) a shaft solution was adopted for the pumping station storage solution. A 6.4m diameter shaft would just fit on the existing South West Water plot of land adjacent to the existing control building which, at just under 9m working depth, would provide the additional storage volume required for this project. The shaft would house new pumps and with a vehicle rated cover slab installed, parking would still be available for the South West Water maintenance teams. The shaft was located on the opposite side of the site to the incoming flows and existing wet well. The existing pump dry well was positioned below ground between this existing wet well and the new shaft, so the solution was to core holes through the dry well and pipe the incoming flows through and into the new shaft. This meant that the limited wet well capacity could also be used for stormwater storage and by raising the existing emergency overflow screen within this existing wet well chamber, the overall shaft depth could be reduced to just under 9m depth as previously mentioned and thus saving money and reducing construction related CO₂ emissions, compared to a solution which did not utilise the existing asset storage capacity.

Marhamchurch SPS: Supply chain - key participants

• Client: South West Water
• Project design & delivery: Galliford Try
• Shaft construction: Active Tunnelling Ltd
• Horizontal directional drilling (HDD): Gmac Utilities Ltd
• HDD equipment: Ditch Witch UK
• Temporary works/shoring: MGF Ltd
• Pumping: Pump Supplies Ltd
• Control panel: Galliford Try
• Screens with lifting system: Eliquo Hydrok Ltd
• PE pipe: Jewson Civils Frazer
• Pumps: Xylem Water Solutions
• Precast concrete: FP McCann
• Slurry recycling plant: Gmac Utilities Ltd
• Shaft steelwork: Galliford Try Fabrications
• Bulk materials: Steve Wills Haulage

Shaft construction

Active Tunnelling Ltd was engaged at the pre-construction phase for the shaft construction works which included full design and installation of the shaft and the corresponding cover slab. To ensure ease of construction, a haul road was cut through the adjoining field from the existing gate access to the works area. The field was steeply sloped and therefore the haul road had to be cut into the slope to follow the natural ground contour to provide safe access for road going vehicles such as concrete lorries, articulated delivery lorries and cranes. [caption id="" align="alignnone" width="1200"] (top left) Shaft collar constructed ready for sinking, (top right) shaft excavation with 27t excavator, (bottom left) first ring constructed ready for casting concrete jacking collar and (bottom right) shaft sinking in relation to public footpath - Courtesy of Galliford Try[/caption] Ground conditions as identified in the borehole logs indicated a few meters of made ground and sub soil overlaying the Bude Metasandstone formation. The Bude formation had a reputation of being very hard and competent in places so Active Tunnelling Ltd opted to sink the shaft as a caisson with the option of underpinning if it could no longer be pushed down. Thankfully at this location the Bude formation did not prove too much for the excavators used to sink the shaft and it was successfully sunk as initially planned. The arisings were removed from the shaft using an excavator mounted grab, before being loaded onto a tractor and trailer and tipped for drying further down in the field located adjacent to the pumping station. One of the most challenging activities associated with the shaft was construction of a crane pad for the roof slab installation. A 180t mobile crane was needed to offload and install the various precast concrete panels which made up the shaft roof, however as the field was sloping steeply near the working area, a significant cutting around 3.5m deep had to be made in order to create an area level enough for the crane to set up on. Groundwater also became an issue at the cut edge into the hill and a drainage system had to be installed to divert the groundwater away from the crane pad to comply with the temporary works requirements on the design.

The new rising main

From the new shaft pumping station the rising main route was quite obvious. It would pass through two fields on the east side of the A39 before passing below the A39 and the River Neet, then connect into the existing rising main from Helscott to Helebridge, located on the western bank of the River Neet. The River Neet is classed as a major river and the connection point was on a designated flood plain so confirmation was obtained at pre-construction phase with the Environment Agency that they had no objection to the proposed solution, construction method and that South West Water’s statutory undertaker rights were applicable. Similar permissions were obtained from Cornwall Council for installation of the rising main below the A39. [caption id="" align="alignnone" width="1200"] Directional drilling with slurry recycling operation - Courtesy of Galliford Try[/caption] The river and A39 were not to only obstacles to overcome in this local area, there were sensitive fibre optic cables and also a medium pressure gas main. The chosen solution to overcome these obstacles was to directionally drill into the Bude Metasandstone and pass below everything at varying depths agreed with each stakeholder. Due to the location of the directional drill and also working on a flood plain next to a tourist ‘hotspot’, it was decided to minimise the construction site footprint west of the A39 as much as possible. To achieve this a slurry recycling plant was used to process drilling arisings with the processed arisings loaded straight into site dumpers and taken off to the tip. The rising main itself was 180PE pipe which was butt fusion welded in advance of the drilling operation. The initial plan was to directionally drill the entire 486m of rising main however the Bude Metasandstone is a very strong rock and in places was less than 600mm below the field surface. The Gmac Utilities Ltd directional drilling team successfully drilled the road and river crossing at depth however the remaining section of rising main which was located at the interface between the sub-soil and the Metasandstone was almost impossible to control the drill line and level. It was therefore decided that traditional open cut excavation methods would be used to complete this section of the rising main.

Environment

This project was ultimately driven by the need to improve the environment through the improvement of the local bathing water quality. Prior to works commencing a thorough environmental, ecological and habitat survey was undertaken to ensure the project would have minimal impact on the surrounding area. [caption id="" align="alignnone" width="1200"] (left) Shaft drop pipe and pump sump with baffle plate and (right) shaft fit-out - Courtesy of Galliford Try[/caption] At pre-construction stage it initially made sense to locate the new pumping station on the western side of the existing building next to the existing wet well however this would have meant the felling of a very large and mature Ash tree (showing no signs of Ash die-back) and would have also resulted in around 2m of the new structure being visible above ground, due to its location on the downward side of the boat lift incline. Both the felling of a mature tree and the visual impact of a structure at this location was deem too significant to ignore and by moving the new pumping station location to the east of the existing building, constructability improve and therefore cost reduced. An existing hedge bank and a few immature trees had to be felled in order to allow access to the site to undertake construction works. A replacement Cornish hedge bank was constructed to replace what was lost at the end of the project and replanted with native hedge and tree species with the aim of improving what was removed once the young plants had established.

Stakeholders

From pre-construction phase through to completion, keeping key stakeholders informed of the works was identified as critical for the successful delivery of the project. A dedicated Galliford Try Client Liaison Officer was allocated to the project and the local village was informed of works through information signs, letter drops and information posted in the local village shop. The existing pumping station was located on a popular locals and tourist footpath which followed the old Bude canal system, with its location positioned half way up an old canal boat lift. A public information board was positioned at this location and was aimed at providing some basic information to tourists who were walking past the site. The local landowners were personally kept informed of progress by the site team and a great working relationship was established which resulted in successful reinstatement and handing back of the farmland following project completion. [caption id="" align="alignnone" width="1200"] Shaft crane pad construction - Courtesy of Galliford Try[/caption] Through this close relationship, one of the landowners asked that a manhole cover be removed following abandonment of the soon to be redundant rising main and the site team suggested that they could fill in and re-profile a small depression left following the removal of an overhead power cable pylon. A few little gestures such as these went a long way with the landowner and were not underestimated by the site team.

Budleigh Salterton is a seaside town on the coast in east Devon, at the start of the World Heritage Jurassic Coast, with a population of just over 5,000 people. It has been described as a picturesque town with a two-mile pebble beach for the hardy swimmers braving the seas for a dip in the beautiful clear water. South West Water’s objective was to ensure that the bathing water quality at Budleigh Salterton does not deteriorate to below ‘excellent’ within the next 20 years. This was to be achieved by providing in-line tank storage in combination with the removal of 0.31ha of surface water from the combined system, in order to ensure that no greater than two significant (>50m³) spills per bathing water season was achieved by 31 March 2022.

Project background

The project comprised the installation of an in-line 190m³ stormwater tank constructed from two 83m lengths of 1200mm diameter precast concrete pipes laid adjacent to the existing sewer. The inlet to the storage tank is controlled by the level within the existing sewer. So when the flow increases within the sewer, the level rises and starts filling the tanks. The outlet flow has a weir fitted with a flow control Hydro-Brake® allowing 25 l/s to pass forward. The project was constructed within a grassed field which was within a flood risk area.

Temporary works piling

The excavation support system (the temporary works) consisted of a 90m long x 4m wide cofferdam within the flood risk area. Galliford Try constructed an engineered haul road which doubled as the piling platform from which specialist sub-contractor, Elite Sheet Piling Ltd, installed 310 (No.) GU13, 6m long sheet piles using a 35t excavator mounted, side griping MOVAX pile driver. Once the sheet piles were installed, the ground between the sheet piles was removed and taken off site. The sheet piles were designed to cut off any groundwater entering their excavation from the adjacent river. One of the major risks to the scheme was that as soon as Galliford Try excavated the large 90m long 4m wide trench it would be inundated with groundwater, making it impossible to safely install the precast concrete pipe sections. The cofferdam worked perfectly; cutting off all incoming groundwater. Once the ground trapped within the cofferdam was removed, the excavation remained dry during the pipe installation.

Drainage blanket

Following the excavation of the cofferdam, a drainage blanket was installed in the bottom of the trench. This comprised a 200mm thick layer of 50mm singled sized stone which was then covered over with a 1000 guage geotextile membrane from Terram; helping to prevent the intermixing of solid particles between the layers of soil and acting as a filter layer stopping any fine material getting into the drainage blanket layer. [caption id="" align="alignnone" width="1200"] (left) Piling installation by Elite Sheet Piling Ltd, and (right) drainage blanket installation - Courtesy of Galliford Try[/caption]

Pipe installation

With the drainage blanket complete, Galliford Try started the installation of the 62 (No.) 1200mm diameter precast concrete pipe sections, which were laid on 20mm pipe bedding materials and aligned using a pipe laser. The pipe laser was installed by the site engineer at the correct location with the exact fall from end to end of the 90m cofferdam. A 20t excavator was used to lift the pipe sections along the haul road and down into the cofferdam where the pipe laying gang would place them in accordance with the pipe laser. Once all the pipe sections were installed, the team backfilled the pipe sections with pipe bedding then, as dug soil back up to ground level.

Meadow Lane Stormwater Tank: Supply chain - key participants

• Delivery contractor: Galliford Try
• Modelling: Arcadis
• Piling contractor: Elite Sheet Piling Ltd
• Hydro-Brake®: Hydro International
• Geotextile membrane: Terram
• Cofferdam shoring: MGF Ltd
• Precast concrete pipe sections: FP McCann
• Pump hire: SLD Pumps & Power

Other elements

At each end of the storm tank, Galliford Try installed tee sections of pipe creating a manifold, which connected the twin pipe together to form one large tank. Galliford Try then constructed six inspection chambers to provide access and to house the Hydro-Brake® flow control. This only allows a pass forward flow of 25 l/s at maximum design head; above these flow rates it weirs over a bypass to prevent the sewer backing up. Once the storm event is over, the stormwater within the tank is slowly released back into the existing sewer during periods of dry weather flow. [caption id="" align="alignnone" width="1200"] (top left) 1200mm precast concrete pipe sections, (bottom left) backfilling the stormwater tank, and (right) Hydro-Brake® from Hydro International in flow control chamber - Courtesy of Galliford Try[/caption]

Summary

By providing 190m³ of offline, gravity return storm storage in the field adjacent to Halse Hill, Budleigh Salterton, the spill performance at Meadow Road CSO has been improved in line with South West Water and Environment Agency targets. As the storage is to be provided offline, normal dry weather flow is to be maintained through existing sewer. The agreed storage tank volume, flow control device and overflow weir level were derived from the Arcadis modelling report and taken as the scheme output for the storage element. The final tank volume selection/spill performance of the promoted option was operationally reviewed by the SWW operations team, commissioning engineer and asset management.

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.”

Marchmont is a residential area of Scotland’s capital city, Edinburgh. The area is characterised by four and five storey sandstone tenements blocks built in the Scots Baronial style. Most of the area was developed in the 1870s and 1880s and there has been little change to its structure since then. It is a mile from Edinburgh’s Old Town and is located right by the popular Meadows and Bruntsfield Links. The area remains popular with older residents, young professionals and students due to the short distance to the University, the city centre and the abundance of parks on their doorstep. For several years, persistent flooding has been impacting businesses and residents in the area of Edinburgh due to a lack of capacity in the existing sewer network and an increase in frequency and intensity of heavy rainfall events.

Introduction

Scottish Water is investing £8.9m to increase the sewer network capacity and storage within the Marchmont catchment which will reduce the risk of flooding to businesses and residents who have been affected by flooding.

Starting on site in August 2022, Marchmont Road Flood Alleviation Project is being delivered by Scottish Water’s alliance partner Caledonia Water Alliance, with completion scheduled for December 2024.

[caption id="attachment_14698" align="alignnone" width="1200"] Google Maps image showing location of the site[/caption]

The solution involves the installation of 700m of new and upsized sewer along Marchmont Crescent off Marchmont Road, which connects back to the existing network at Meadow Place. Storm flows will then spill via a new bifurcation chamber on Marchmont Road into a new 20m diameter, 3,000m³ volume offline storm storage tank located within Bruntsfield Links.

Sewer levels will be monitored in the downstream network and following a heavy rainfall event, storm flows will be pumped back into the network.

Project scope

1. Construct a 20m internal diameter, 17m deep attenuation tank using underpinning methods to provide 3000m³ of storage and housing a internal tank cleaning system Vacflush™ column from CSO Group Ltd.
2. Install two pumps (duty/standby) with two DN250 DI rising mains with pumped return to the existing combined sewer network.
3. Install approximately 700m of new, upsized sewer ranging from DN250-DN900, with a range of materials: ductile iron, concrete, polyethylene and GRP.
4. Install 24 PCC manhole to a depth of 4.5m.
5. Retain the existing mature trees around Bruntsfield Links and Marchmont Crescent, by using two trenchless construction methods:
6. Guided auger bore on Marchmont Crescent with a steel sleeve 762mm OD with a GRP slip lines within 672mm internal diameter. The works had to be undertaken below mature tree roots.
7. Timber Heading in two directions within Marchmont Road into Meadows Park and out into Meadows Place to avoid RPAs and to maintain traffic flow on a major bus and emergency services route.
8. Install a bespoke PCC bifurcation chamber/break discharge chamber.
9. Install two kiosks: (i) MCC kiosk for pump operation, and (ii Vacflush™ kiosk for tank cleaning system.

[caption id="attachment_14702" align="alignnone" width="1200"] Storm tank under construction - Courtesy of Paul Milligan & CWA[/caption]

Marchmont Road FAS: Supply chain - key participants

• Project delivery: Caledonia Water Alliance (CWA)
• Designers: AECOM/CWA
• Shaft & timber heading trenchless work: Fineturret Ltd
• MEICA installation & commissioning: Ferrier Pumps Ltd
• Pipe drive/pipe jack: Pipeline Drillers Ltd
• VacFlush™: CSO Group Ltd
• Composite steel reinforced pipe: Aquaspira Ltd
• Storm tank pumps: Xylem Water Solutions
• Access covers: EJ Group
• Precast supplier: Macrete (Ireland) Ltd
• Temporary ground support: Groundforce
• Over pumping: Selwood

Construction issues and carbon, cost & programme savings

Excavation within rock: Bedrock was encountered throughout the site approximately 1m below ground level. This resulted in slow digging periods for pipelaying within Marchmont Road and lengthy road closures.

Deep excavations in public space: The installation of the below-ground attenuation tank required excavations down to 17m within public green space. This has required extensive excavation support.

Trenchless construction: At both areas of trenchless construction, CWA deployed methods which preserved the mature trees in the area as required by City of Edinburgh Council ensuring compliance with the approved planning conditions and avoiding reputational damage to CWA and Scottish Water.

[caption id="attachment_14700" align="alignnone" width="1200"] Marchmont FAS project site - Courtesy of Paul Milligan & CWA[/caption]

Changes to the pipe specification within the augerbore: For the trenchless construction elements, for both safety of personnel and carbon reductions, the design was changed for DN900 ductile iron pipework to DN900 Aquaspira; a composite steel reinforced pipe. The Aquaspira pipework installed was over 7.5 times lighter per metre than the equivalent ductiile iron pipework. This allowed for the pipework to be pulled by hand along the track.

GPR pipeline installation within augerbore: There were significant carbon savings with the installation of GPR pipe, which is 10% of the weight of the equivalent diameter concrete pipework.

Removal of valve chamber: As agreed with Scottish Water during the detailed design stage, CWA designed a 5.5m wide x 5m long x 5.1m deep PCC valve chamber. The reason for this removal was that the relevant fittings and valves could be accommodated within the attenuation tank and downstream flow meter chamber. This was met with the acceptance and praise from Scottish Water as it reduced the excavation within Meadows Park, meaning a greater chance of planning approval, and a result, in carbon savings. The removal of the valve chamber for flood alleviation schemes with large diameter storage tank installation, is being promoted as a new standard for future designs.

Storm tank construction

The new storm tank will hold up to 3.5 million tonnes of stormwater, which will be directed to the tank via the new pipework. The tank fills up during a storm, and the water is pumped back into the sewer network once the storm subsides. This allows further capacity for future storm events.

The new storm tank was constructed under the Bruntsfield Links to reduce the risk of internal and external sewer flooding in the Marchmont area. CWA hit a huge milestone in March 2024, when the roof of the storm tank was lowered into place. The roof is made up from reinforced concrete beams and slabs, and weighs over 400 tonnes, covering the 15 metre wide by 20 metre deep tank.

[caption id="attachment_14701" align="alignnone" width="1200"] Storm tank roof installation - Courtesy of Paul Milligan & Caledonia Water Alliance[/caption]

Interface with the public & other utilities

Due to the location of works being adjacent to property and business owners, Caledonia Water Alliance was required to maintain access to these properties at all times. This dictated the construction programme and traffic management set-up. As a result, it has also driven the construction methods of sections of the works; such as the timber heading trenchless construction.

The urban environment of the works resulted in the excavation works being in close vicinity/below other public utility providers’ assets. This has required close liaison with providers, watching briefs, vibration monitoring and change to construction methods.

Local residents have been kept informed throughout all phases of the project as well as regular one on ones with local businesses. A public information event was held in Meadows Park before the work commenced, allowing customers to discuss the upcoming project with professionals from both CWA and Scottish Water.

The dense rock breaking in close proximity to residential tenements proved challenging and expected noise levels were published on the customer notice board on a weekly basis. Extensive pre/post condition surveys were offered to all residents. Site hoarding was specially designed to include information about the project and the local history of Marchmont.  Scottish Water campaigns such as ‘Bin the wipes’ were also promoted.

Together with Scottish Water, CWA helped launch a new water ‘top-up-tap’ in Meadows Park to leave a legacy for the park users and reduce the amount of single use plastic bottles. On completion of the project, the area around the tank will be seeded with a wild meadow mix chosen by the Marchmont community.

[caption id="attachment_14697" align="alignnone" width="1200"] Customer information event - Courtesy of Scottish Water[/caption]

Conclusion/summary

The next phase (five) of the project commenced on 7 July 2024 to upsize the sewers work on Marchmont Crescent. Phase 5 involves excavating within the road to install larger sewer pipes, and to install new manholes.

Due to the extensive works being carried out, traffic management will be in place to ensure the safety of customers and residents. Throughout the road closures, CWA have ensured that local business will remain open. To further minimise the impact to residents and business, all work is being conducted in short phases.

At the end of the project, CWA will fully reinstate Meadows Park and are planning to team up with the local community to plant wild meadow seeds in the area.

The project is due to be completed by December 2024.

The WINEP Durham Transfers Project was designed to improve the quality of the Blackdene Burn, a watercourse located in the north Durham area. During AMP7, sewage treatment works (STW) sites within Northumbrian Water Group (NWG) ownership were identified for improvements in phosphorus concentrations within final effluent discharge to the environment. The scope of this project is to address the improvements at both Plawsworth STW and Pity Me STW, which currently discharge to the Blackdene Burn.

Background

Esh-Stantec was appointed by NWG to progress the proposed solution; a phased approach whereby, during AMP7, final effluent from both STWs will be transferred to a discharge point on the River Wear via transfer pumping stations. The transfer of flows will be facilitated via new rising mains and gravity sewerage which will connect immediately upstream of the existing outfall from Brasside STW. In line with the phased approach, planned upgrades to Brasside STW in AMP8 will increase its treatment capacity and allow for the eventual abandonment of Plawsworth and Pity Me STWs along with chemical dosing to meet planned phosphorus limits discharging to the River Wear.

The designed solution allows for projected growth across the Plawsworth and Pity Me catchments (including the completion of the significant Sniperley development) with an AMP8 solution transferring all raw flows from Plawsworth and Pity Me to the upgraded Brasside STW for treatment, with final effluent from Brasside STW ultimately discharging to the River Wear.

The objective of this appointment is to provide the assets required to enable to the transfer of flows from Pity Me and Plawsworth STWs in the AMP7 and AMP8 scenarios. It is anticipated that the project will be completed in December 2024.

[caption id="attachment_18551" align="alignnone" width="1200"] Piling operations by Francis & Lewis International Ltd, for the construction of the pipe bridge substructure - Courtesy of Esh-Stantec[/caption]

WINEP Durham Transfer: Supply chain - key participants

• Client: Northumbrian Water
• Principal designer & contractor: Esh-Stantec
  • Esh Group
  • Stantec UK
• Structural consultant: James Christopher Consulting Ltd
• M&E, including supply & installation of generators, MCCs & pumps to wet wells: Retroflo Ltd
• Directional drilling of 3km of rising main & installation of all AV chambers: Ken Rodney Construction Ltd
• Auger boring under the East Coast Mainline, coordinating with Network Rail, & supply/installation of track monitoring: Terra Solutions Ltd
• Design, manufacture, & installation of pipe bridge: Francis & Lewis International Ltd
• Design & sinking of segmental shafts: Active Tunnelling Ltd
• Temporary works/shoring: MGF Ltd

New transfer stations

The first stage of the scheme involves the transfer of fully treated, final effluent to the River Wear, meaning that Plawsworth and Pity Me STWs remain fully operational throughout the construction of all assets which will become live prior to the upgrade of Brasside STW.

Plawsworth Transfer Station: The new transfer assets at Plawsworth STW were carefully designed and sequenced around the limited working room in the site and the requirement to maintain treatment operations during construction. The Plawsworth Transfer Pumping Station comprises:

• A 4m diameter, 6m deep wet well shaft (sunk as a caisson).
• MCC and associated kiosk.
• Generator and associated kiosk.
• Above-ground valve arrangement.
• Flow meter chamber and all associated interconnecting pipework and ducting.

In AMP7, final effluent flows are intercepted and directed into the new wet well before being pumped to the River Wear. Due to the transfer of final effluent, a reduced emergency storage volume has been provided within the new wet well.

In AMP8, following upgrades to Brasside STW, raw flows will be intercepted upstream of the inlet works and diverted to the new SPS for transfer to Brasside via a new 250mm rising main. As part of the conversion from a treatment works to a terminal pumping station, the existing humus tank will be re-purposed to provide additional emergency storage in line with EA guidelines for the transfer of raw sewage flows and minimise emergency overflow spills to the environment.

In addition to emergency storage, a permanent standby generator has been incorporated into the design which will automatically cut in if there is a loss of power to the site.

The pumping station was designed as a three pump station (duty/assist/standby) to transfer ultimate AMP8 flows up to 32 l/s, however, in the AMP7 scenario,  the pumping station will operate as a duty/standby/standby station, with the individual pumps sized to transfer 24 l/s of final effluent to maintain a minimum velocity in the rising main.

Pity Me Transfer Station: The main works at Pity Me STW comprises the following:

• A 6m diameter, 9m deep wet well shaft (sunk as a caisson) with built-in emergency storage volume sized for ultimate raw flows.
• MCC and associated kiosk.
• Generator and associated kiosk.
• Valve chamber.
• Flow meter chamber and all associated interconnecting pipework and ducting.

Similar to Plawsworth, the pumping station was designed as a three pump station to transfer 34 l/s in AMP7, with a duty/standby/standby arrangement, and up to 61 l/s in AMP8, after conversion to a duty/assist/standby arrangement. In both the final effluent and raw flow scenarios, pumped flows will exit the works via a new 280mm rising main.

[caption id="attachment_18550" align="alignnone" width="1200"] Active Tunnelling constructing the new wet well shaft at Pity Me STW
Courtesy of Esh-Stantec[/caption]

Transfer rising mains

Approximately 2.1km of 250mm PE rising main and associated air valve/washout chambers has been installed from Plawsworth STW. The rising main pipework was installed predominantly via a trenchless technique, namely horizontal directional drilling (HDD), primarily due to lack of available access from the adjacent A167 highway to facilitate traditional open cut construction, as well as unfavourable ground conditions.

A new 280mm  rising main was installed over an 850m length from Pity Me STW. Due to a tight working corridor situated between a garden centre and the Blackdene Burn, as well as the requirement to cross beneath the A167, a highly trafficked highway, the rising mains was also installed via HDD. This use of a trenchless installation technique minimised disruption to local business and removed the requirement for traffic management on a busy commuter route.

eDNA samples taken from ponds adjacent to Pity Me in the feasibility stage confirmed the presents of great crested newts. In lieu of protracted traditional population surveys and subsequent licenced activities to mitigation including fencing and capture to clear the working area, a District Level License (DLL) was secured from Natural England and works were completed under an approved method statement with supervision from a consultant ecologist.

The 280mm and 250mm rising mains from Pity Me and Plawsworth connect to a common chamber located at the high point of the new network, where they will discharge flows to a new DN400 gravity sewer.

[caption id="attachment_18547" align="alignnone" width="1200"] Construction of new valve chamber and associated pipework at Pity Me STW - Courtesy of Esh-Stantec[/caption]

New gravity sewerage

2.4km of new DN400 gravity sewerage, with associated manhole chambers, was constructed to receive the pumped flows from both Pity Me and Plawsworth STWs. Careful consideration was given to the design of the new sewerage to ensure capacity (including future growth) and self-cleansing requirements are met in all flow scenarios, including when Pity Me and Plawsworth transfer pumps operate either in isolation or in parallel.

The construction of the new gravity sewer poses some complex crossings and challenging ground conditions. The crossing of Chester Low Road, another busy road for both commuters and customers of a popular local retail park, The Arnison Centre, was originally planned for open cut excavation. However, subsequent on-site observations with regard to topography, a number of high-risk services including high voltage electric cables and a uPVC water main, and running sands within nearby open cut trenches led to the conclusion that it would not be possible to safely support the excavation during construction. Therefore, the road crossing was completed via guided auger bore. Not only did this mitigate the disruption and health and safety risks associated with damaging services, but it also minimised disruption to local businesses and residents as the road remained operational throughout the process.

East Coast Main Line crossing

Further downstream, the new gravity line is also set to cross beneath Network Rail’s East Coast Main Line. The proposal is to install a 610mm sacrificial steel sleeve via a guided auger bore beneath the embankment, once complete the 400mm NB gravity pipe will be sleeved and the anulus grouted. Extensive liaison is ongoing with Network Rail in the lead up to the under track crossing (UTX) to gain the necessary approvals and fully understand the constraints which must be met during construction. These constraints include but are not limited to 24/7 working for the duration of the tunnelling works, installation of track monitoring and an approved contractor on standby in case there is a requirement for emergency track repair.

[caption id="attachment_18549" align="alignnone" width="1200"] Aerial view of working area at Brasside STW - Courtesy of Esh-Stantec[/caption]

Brasside pipe bridge

Approximately 800m upstream of the Brasside STW outfall connection, the sewer crosses a watercourse located within a steep ravine and dense woodland at the existing Brasside Sewage Pumping Station (SPS).

At the optioneering stage of the project, it was proposed that this crossing would take place via an inverted siphon arrangement. However, subsequent hydraulic modelling deemed that, due to topography constraints, it would not be feasible to achieve sufficient capacity while maintaining self-cleansing velocities in both the AMP7 and AMP8 flow scenarios without connecting to the existing outfall further downstream. This would have required construction works within ancient woodland, imposing the requirement for Environmental Impact Assessment (EIA) and potentially preventing the obtention of a Lawful Development Certificate.

Therefore, to mitigate the risk of repeat maintenance issues and potential asset failure, a pipe bridge was progressed as the preferred option having discounted a further interstage pumping station at the low point due to a lack of space within the existing Brasside SPS site and the associated operational carbon and expenditure.

The route of the pipe bridge was designed to mitigate environmental impact, by including bends within the bridge structure and above ground pipework to take advantage of existing operational land and avoid clearance of significant trees within a conservation area. The interface between the bridge structure and the above ground ductile iron pipework has been carefully modelled and iteratively designed to assess the impact of bridge movement and deflection on the pipe joints and select joints which provide appropriate tolerances for these movements.

[caption id="attachment_18552" align="alignnone" width="1200"] Construction of pipe bridge structure by Francis & Lewis International Ltd - Courtesy of Esh-Stantec[/caption]

Conclusion

The design of the WINEP Durham Transfers Scheme serves to meet regulatory deadlines by achieving a sustainable multi-stage solution which meets the needs of the current and future catchment population.

At the time of writing (July 2024), construction is progressing well, and all rising main pipework and transfer station substructures have been installed. The gravity sewer is predominantly complete with the two key crossings remaining, pending final Network Rail approval to complete the rail crossing and final structural design of the pipe bridge to install the above-ground pipework adjacent to Brasside SPS.

The current construction programme shows that flows will be turned in December 2024, transferring final effluent to the River Wear in the interim and, in AMP8, transferring raw flows to Brasside STW for treatment. This will achieve the removal of treated effluent from the Blackdene Burn, in turn significantly improving water quality while meeting WINEP obligations. Furthermore, the completion of the scheme in AMP8 will serve to rationalise the NWG sewage network in the area and improve the resilience of the network by serving catchment growth and improving treatment capacity.

The Burnley integrated catchment scheme is one of United Utilities' (UU) largest AMP7 projects with a value of £77m. The project is being delivered by UU’s construction delivery partner (CDP) framework by Advance-plus, a joint venture between MWH Treatment, J Murphy & Sons (JMS) and Stantec UK. The project commenced in 2020 and through two previous articles, UU and Advance-plus have shared the project background, the story of developing the solution and design, and commencing the build. In this year’s article, the project delivery team is pleased to provide an update on the construction progress and a look at the journey ahead as the project remains on course to achieve the December 2024 regulatory completion date.

A summary of the project requirements and 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 3 (WINEP3) 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 enhanced, treated effluent permit standards, and management of storm discharges in the defined reaches, to achieve a compliance with the WFD 99%ile wet weather intermittent standards. The project also includes the U_MON3 spill monitoring and U_MON4 flow monitoring drivers. 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 interdependent in delivering a total of ten regulatory outputs. [caption id="" align="alignnone" width="1200"] ASP under construction - Courtesy of United Utilities[/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 primary settlement tank (PST).
• New 1300 l/s inter-stage 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 existing final settlement tanks.
• New surplus activated sludge (SAS) thickening process.
• New ferric and caustic dosing plants.
• Associated motor control centres (MCCs), SCADA upgrade, and power upgrade.

Pipework The last year has seen great strides being made across the site and various process areas, with major civils structures constructed and taking shape. The very constrained nature of the site, existing processes and services, and the need to lay many kilometres of small and large diameter underground pipework has proven to be a major constructability challenge. Most of the pipework installation has been self-delivered by J Murphy & Sons with Saint Gobain PAM UK being the main supplier of the pipework and fittings. Detention tank The new detention tank, has been constructed by A-Consult Ltd using 64 precast concrete panels, standing 10.4m high. The panels were precast in their factory before being transported to site for erection and subsequent post tensioning. Utilising this construction technique, with design for manufacture and assembly (DfMA) brings benefits in terms of quality, time and safety. The tank has successfully passed its water test and is currently being drained. The feed pumping station has been constructed and the mechanical installation of pumps, mixers and pipework is now in progress. [caption id="" align="alignnone" width="1200"] Detention tank on water test - Courtesy of United Utilities[/caption] Primary settlement tank The new primary settlement tank (PST) civils construction is also complete, again undertaken by A-Consult Ltd using the precast concrete panel method of construction. It has also successfully passed its water test. Mechanical installation by EPS Water is now in progress on the ‘H’ frame steel structure which will support the scraper bridge. The design of the PST incorporates a fixed bridge arrangement with rotating scrapers beneath. This arrangement is necessary as the PST will eventually be covered with a GRP roof for odour mitigation. The odour control fans, ductwork and vent stack are scheduled to be installed in December. [caption id="" align="alignnone" width="1200"] PST4 and ASP lane 1 on water test - Courtesy of United Utilities[/caption] Interstage pumping station Due to the topography and hydraulic levels across the site, a new interstage pumping station (IPS) is required to pump the effluent leaving the four PSTs up to the new activated sludge plant (ASP) distribution chamber. Civils FRC works are being undertaken by STAM Construction Ltd and contain 94 tonnes of rebar and 900m³ of in situ poured concrete. The pumping station structure is complete and has undergone successful water testing. The internal benching is complete and the next activities planned for the coming period will be the mechanical installation of the pumps and pipework. As the pumping station is vital to keep all flows passing through the treatment process, a standby generator will also be installed. The IPS is a two compartment design to facilitate future maintenance activities preventing the need to take it completely out of service. The new pumps have been supplied by Xylem Water Solutions who have supported the designers in providing efficient selections for the large submersible pumps and optimising the layouts of the pump chambers. Activated sludge plant The ASP distribution chamber is currently being constructed with all four concrete walls having now been poured. These are curing and the structure will undergo a water test in September 2023. [caption id="" align="alignnone" width="1200"] ASP constructed and water tested - Courtesy of United Utilities[/caption] 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. Civils construction of the ASP is complete and fully water-tested with the mechanical installation of the internal pipework, aeration grids, diffusers and access platforms and walkways taking place over the next few months. Suprafilt Ltd will be supplying and installing the internal pipework, aeration grids and diffusers. Mechanical installation of the pump stations and access steelwork etc will be undertaken by Fluid Sealing & Engineering (FSE). BioMag^® The Evoqua Water Technologies detail design for the new BioMag^® process has been finalised and the building layout confirmed. The main equipment including four Magdrums and two shear mills, process tanks, silo and pumps, which have been manufactured and are ready for delivery to site when required. The BioMag^® building is currently under construction by Gallaway Construction. The steel frame has been erected and the gantry crane and roof cladding have been installed. External wall cladding is in progress, after which attention will turn to the internal fit-out and installation of the BioMag^® equipment. [caption id="" align="alignnone" width="1200"] BioMag^® building being erected - Courtesy of United Utilities[/caption] Final settlement tanks (FST) There are four existing final settlement tanks which required refurbishing to ensure adequate performance and asset life are achieved. The scope includes 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 is being delivered by Jacopa and comprises refurbishment of the bridge, scraper assemblies, and other ancillary equipment. Three of the four FSTs have now been refurbished with the final one due to be undertaken towards the end of the year. Surplus activated sludge (SAS) thickening Civils works has been ongoing in the SAS thickening process area for the last couple of months with the storage tank, drum thickener, poly plant and kiosk bases all constructed. Underground services, ducts and pipework have also been installed and tested. The filtrate return pumping station construction is in progress with the mechanical installation due to follow on. Chemical dosing The new ferric and caustic dosing plants comprise storage tanks, dosing rigs and dosing pipelines, all of which have been designed and well progressed in manufacture. These are being supplied by NPS Engineering Group. A new chemical delivery facility will also be provided with civils construction in this area commencing towards the end of the year and installation of the new dosing plants taking place early 2024. [caption id="" align="alignnone" width="1200"] 3D model of chemical dosing area - Courtesy of United Utilities[/caption] HV 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. Motor control centres (MCCs) To control all the new assets a number of new MCCs housed within kiosks are required around the site, along with a new site-wide SCADA system. The MCCs are all in various stages of manufacture and factory testing. The electrical installation and system integration works, including dry testing, will be undertaken in phases over a period of months as the programme for each of the new process areas dictates. The MCCs are being built by Technical Control Systems Ltd, electrical installation will be by PICOW Engineering Group and system integration by Tata Consultancy Services. Looking forward to commissioning Commissioning of the new treatment process, and transitioning from the old process in a controlled staged approach, will be complex. The existing treatment stream and process compliance cannot be put at risk or compromised and months of hard work and planning for commissioning has already taken place. Wet commissioning is due to start in April 2024, gradually increasing flows into the new treatment process over several months while the new biological process builds up and matures to a point where the improved treatment standards are being met. The forecast project in use date is October 2024. [caption id="" align="alignnone" width="1200"] Aphex construction planning software map view - Courtesy of United Utilities[/caption]

Burnley WwTW Catchment Strategy: Supply chain - key participants

• Construction Delivery Partner: Advance-plus JV
  • MWH Treatment (Advance-plus jv)
  • J Murphy & Sons (Advance-plus jv)
  • Stantec UK (Advance-plus jv)
• CFD modelling: CER Technologies Ltd
• GPR & topo surveys: Atlantic Geomatics (UK) Ltd
• Flood risk assessment: Ambiental Environmental Assessment Ltd
• Physical modelling: Hydrotec Consultants Ltd
• Dewatering design: OGI Groundwater Specialists Ltd
• Concrete construction: STAM Construction Ltd
• Concrete supply: CEMEX UK
• 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
• Earthworks: D Morgan plc
• Blower building: Saredon Steel Buildings Ltd
• Access metalwork: Tushingham Steel Fabricators
• BioMag process: Evoqua Water Technologies
• BioMag building: Gallaway Construction Ltd
• BioMag mechanical installation: Alpha Plus Ltd
• Ventilation: Air Technology Systems Ltd
• Pumping station mechanical installation: Fluid Sealing & Engineering (FSE)
• HV cable installation: Smith Brothers Ltd
• Transformers: Winder Power
• Electrical installation: PICOW Engineering Group
• MCCs: Technical Control Systems Ltd
• Systems integration: Tata Consultancy Services
• Standby generators: DTGen
• SAS glass coated steel tank: Stortec Engineering Ltd
• PST fixed scraper bridge: EPS Water
• Epoxy coated carbon steel pipework & wall starters: Freeflow Pipesystems Ltd
• Dosing systems: NPS Engineering Group
• 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 Water & Wastewater
• Aeration system: Suprafilt Ltd
• SAS tank air mixing system: Utile Engineering
• Submersible pumps: Xylem Water Solutions
• Valves: AVK UK Ltd
• Kiosks: Industrial GRP

Lindred Road CSO (PEN0056)

Work at this existing combined sewer overflow (CSO) site comprises the construction of an online 1,950m³ detention tank which will hold stormwater during times of heavy rainfall, reducing discharges to the watercourse. New pumps within the tank will return the effluent to the sewer for onward treatment at Burnley WwTW. The 15m diameter x 20m deep detention tank, is of segmental shaft construction and is located within the very busy and congested Lomeshaye Industrial Estate in Nelson, and was 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 has been required. [caption id="" align="alignnone" width="1200"] Lindred Road detention tank during construction - Courtesy of United Utilities[/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. 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 2023. The inlet and outlet pipework for the tank has now been installed, 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. All buried pipework, chambers and ducts etc have been completed and reinstatement of the area is in progress. The civils and pipework has been undertaken by SGC Civil Engineering Ltd and the mechanical works by Fluid Sealing & Engineering (FSE). A new motor control centre and power supply is being installed for this facility. The new control kiosk was delivered and installed in July 2023 and the electrical installation is currently ongoing with the new power supply due to be energised in October. Testing and commissioning is scheduled to start in November, with the site achieving project in use in February 2024.

Lindred Road Detention Tank: Supply chain - key participants

• Civil design detention tank: COWI UK Ltd
• Detention tank shaft: Joseph Gallagher Ltd
• Civils & pipework: SGC Civil engineering Ltd
• Mechanical works: Fluid Sealing & Engineering (FSE)
• Precast roof sections: Macrete (Ireland) Ltd
• Precast shaft segments: FP McCann
• MCCs: Technical Control Systems Ltd
• Kiosks: Industrial GRP

[caption id="" align="alignnone" width="1200"] Lindred Road: Aerial view of detention tank - Courtesy of United Utilities[/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 is to construct a new chamber over the downstream sewer, and install a new real time controlled actuated penstock valve that will regulate and optimise flows passed forward to Hyndburn, whilst reducing spills from the existing CSO. A new control kiosk and power supply are also required. 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 has been procured and a new access track for future operation and maintenance, as well as the build, will be required and constructed. The detailed design is complete and some enabling works to set up site have been undertaken. For the main construction activity, a complex temporary works arrangement will be required, with large scale over-pumping, to carry out the works on the live sewer. Plans are currently being made to install temporary isolation rails and plates during a suitable dry weather period in preparation. This site is scheduled to be complete in spring 2024.

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 has identified that by reducing the time it takes for the storm tanks to be returned into the treatment stream would ensure that the river water quality objectives could be achieved. The existing storm return pumping station is made up of fixed speed pumps operating at a duty of 100 l/s. A new variable speed storm return pumping station will be constructed which will be capable of returning flows across the range of 30 l/s to 330 l/s. This means that the contents of the storm tanks can be returned much quicker after a storm subsides. [caption id="" align="alignnone" width="1200"] Hyndburn WwTW - 3D model of storm return pumping station - Courtesy of United Utilities[/caption] A new below-ground wet well type pumping station will be constructed with three high-flow pumps and two low-flow pumps which provides a more flexible and efficient system with greater turn down capability. A new single rising main will return the storm flows back to the head of the treatment works. A new kiosk and motor control centre will also be installed. Planning permissions are in place and all pre-start surveys and investigations have been completed. Detailed design is nearing completion and the site has just been established. Construction is due to start in earnest in September on the new pumping station excavation. The winter months will see the civils works progress, with mechanical and electrical works due to start in spring. The project in use is forecast for July 2024.

The digital toolbox

4D digital rehearsals which link the 3D model to the programme have been used extensively by the site team to validate the constructability and sequencing of the works. Visualisation allows all parties to truly understand the construction sequence, interfaces and interdependencies which is relevant on such a congested work area with multiple subcontractors operating in close proximity. They have helped to identify high risk activities and plan mitigation measures. They also help provide programme and cost certainty and facilitate stakeholder engagement. Over the last year Aphex, a powerful construction planning software tool which enables the delivery teams to better plan and work together has been introduced. This has been used for short term, look-ahead planning, which is linked to, and aligned with the master schedule in P6. It has also enabled the construction teams to control the build, assign ownership, communicate and track plans on a daily basis. [caption id="" align="alignnone" width="1200"] Aphex construction planning software Gantt chart - Courtesy of United Utilities[/caption]

Challenges and collaboration

A large and complex project of this type, across several sites, brings enormous and numerous challenges. These include health and safety management of large scale, complex construction in constrained working areas, on live operational sites and in 3rd party and public areas, while also working in environmentally sensitive areas and requiring engagement and interfacing with customers. Successful delivery would not happen without true collaboration. From the outset of the project we delivered a team development programme and established a co-located office which has proven to be invaluable in creating a great culture and an open and collaborative working environment over the last three years. Challenges and emerging risks and issues are dealt with almost on a daily basis as a team. The project teams continually work together to ensure that delivery stays on track, the highest standards are maintained and everyone goes home safe and well.

In recent years, the village of Boherbue in north-west Cork has undergone considerable expansion, resulting in increased demand for housing. This growth has presented challenges, particularly for the existing wastewater treatment facility, which has struggled to cope with the surge in population. Additionally, the plant has fallen short of the Environmental Protection Agency’s treatment standards, underscoring the pressing need for an upgrade. Of particular concern is the discharge of treated wastewater into the River Brogeen, a protected conservation area that serves as the habitat for the freshwater pearl mussel. In collaboration with Uisce Éireann (Irish Water) and Cork County Council, a comprehensive project has been undertaken to modernise and enhance the capacity of the treatment plant. This initiative not only addresses the immediate needs of Boherbue’s growing community but also ensures compliance with environmental regulations.

Early Contractor Involvement

The project, delivered under the innovative Early Contractor Involvement (ECI) framework, aimed to address the overloaded and outdated infrastructure while ensuring compliance with regulatory standards and meeting the evolving needs of the community. The innovation in this project lies in its multifaceted approach to efficiently treat wastewater, reduce carbon emissions, and protect natural ecosystems.

Leveraging the ECI framework allowed for the integration of innovative solutions such as solar energy, natural sludge drying reed beds, and the preservation of existing constructed wetlands for stormwater overflow. This innovative approach not only sets a new standard for sustainable wastewater treatment but also ensures long-term environmental benefits for Boherbue and its natural surroundings.

[caption id="attachment_16527" align="alignnone" width="1200"] Google Earth image of Boherbue[/caption]

The scope of works for the upgraded facility included:

1. A new inlet works.
2. A stormwater storage tank.
3. Biological treatment processes.
4. Tertiary solids removal cloth filtration system.
5. Sludge drying reed beds.

A description of these key features follows.

New inlet works

An inlet works with fine screening to 6mm in 2D and a manual bypass screen to 19mm with a stone trap upstream of the screens were installed. The screens were designed to cater for the Phase 2 Formula A flows of 23.2 l/s screens are to be designed to cope with a minimum of 150% of the design capacity for works under 2,500 PE, i.e. a design capacity of 35 l/s based on the Design Formula A. The hydraulic design of the inlet works was also based on the fine screen(s) being blinded by a minimum factor of 70%. The screen selected by the ECI team was the Definitive Ecology SF/T3 in-tank screw screen, with SDACA (specially designed anti-clog auger) system to ensure compliance with the screening handling requirements.

[caption id="attachment_16526" align="alignnone" width="1200"] Inlet works preliminary treatment - Courtesy of Glanua[/caption]

Stormwater tank

Flows exceeding the plant’s peak design flow, overflow by gravity (weir discharging via overflow screen) to the stormwater holding tank, which has been designed to provide a retention time of two hours for the difference between the Design Formula A and FFT flows plus 40 l/PE for SWO compliance as only 1:7.1 dilutions will be available for the WwTP effluent in the Brogeen River (based on DWF and 95th percentile river flow).

The stormwater holding tank is provided with a Eliquo Hydrok CWF flushing bell in order to automatically clean the tank once the storm flows have abated and the tank has been emptied; which is an innovative approach to this, requiring no energy input.

The CWF Storm Flush system is a highly effective non-powered cleaning system for all stormwater retention tanks, utilising the sewage stormwater for the flushing process thus requiring no additional fresh water. Storm return pumps located in a sump within the storm tank, which will reduce retention of larger volumes of waste and reduce the risk of odour.

Biological treatment processes

The secondary treatment stage for Boherbue includes the following:

• Two anaerobic selector tanks with three separate selector cell volumes.
• Two 624m³ aeration tanks with 109m³ of anoxic volume each for denitrification.
• Settlement provided by two 5m diameter/3.5m side wall depth secondary settlement tanks.

[caption id="attachment_16524" align="alignnone" width="1200"] Secondary aeration treatment - Courtesy of Glanua[/caption]

Each aeration tank is 15.6m length x 5m width x 4m working depth. Aeration is provided to the tanks using a fine bubble diffused aeration system designed to achieve an overall peak standard oxygen transfer rate of 66.15 kgO₂/h (i.e. 33kg O₂/h per cell).

The aeration system comprised three screw blowers from Kaeser Kompressoren operating on a duty/duty/standby basis, with automatic changeover of the standby blower on a time-basis; ensuring equal use of the equipment. Air from the blowers is forwarded to each aeration cell by an air header, which feeds individual branches into the aerobic cells. The diffusers are disc membrane units from Xylem Water Solutions.

Tertiary solids removal systems

Following settlement, secondary treated effluent is passed onto a tertiary solids removal treatment stage for final effluent polishing prior to discharge to the Brogeen River. The TSR process was required in order to ensure compliance with the WwDL ELVs, and in particular with the phosphorus ELV of 0.25mg/l, through coagulation/flocculation and filtration treatment.

[caption id="attachment_16528" align="alignnone" width="1200"] Cloth filter tertiary treatment - Courtesy of Glanua[/caption]

During the design stage and evaluation of the ECI team, the supplier Eliquo Hydrok was found to have the most reliable, energy and cost-efficient equipment that includes both flocculation and filtering stage. The package unit includes a flocculation stage comprised of one stream with two chambers that split into the cloth filters.

Sludge drying reed beds

The implementation of sludge drying reed beds (SDRB), which significantly increases sludge concentration to up to 40% dry solids (DS) after 10 years of operation is a key innovation. This revolutionary approach reduces sludge export volumes by more than tenfold compared to conventional methods, thereby minimising transportation and dewatering costs while substantially reducing the carbon footprint of the Boherbue WwTP. SDRB sludge can also be directly land spread without the need for additional chemical conditioning, further enhancing its environmental benefits.

There are numerous benefits in the inclusion of the sludge drying reed beds vs traditional sludge management practices. These include but are not limited to the following:

• Reduction of carbon footprint of the plant by approximately 45 T over a 10-year period.
• Carbon capture via natural plant growth.
• Up to 25% organic matter removal due to mineralisation.
• Dewatering process completed with zero energy consumption.
• At full design loads, the SDRBs will remove over 49 (No.) 20,000 litre tankers from the road per annum.

[caption id="attachment_16533" align="alignnone" width="1200"] Sludge drying reed beds to process wastewater sludge naturally - Courtesy of Glanua[/caption]

The construction of the sludge drying reed beds (SDRBs) commenced in early February 2023, incorporating earth embankments and precast concrete wall sections for formation. Each cell was meticulously lined to ensure water-tightness, with feed and drainage pipework installed for optimal functionality. Reeds were planted in late April to establish and grow during the summer months, aided by the importation of sludge to promote growth. This comprehensive approach ensures the effectiveness and sustainability of the SDRBs in treating wastewater and reducing the carbon footprint of the Boherbue WwTP.

Solar technology

The use of solar technology underscores the project’s commitment to renewable energy sources, contributing to further reductions in carbon emissions. By leveraging these innovative technologies and practices, the initiative sets a new standard for sustainable wastewater treatment, offering a replicable model for other treatment plants to follow. This holistic approach not only improves operational efficiency but also promotes environmental stewardship, paving the way for a cleaner and more sustainable future in the wastewater sector.

50Kw solar panels from The Low Carbon Energy Company Ltd have been installed which will produce 42,500Kwh of electricity per year. This alone will introduce a carbon saving of 13.7T/CO₂ per year which shows significant savings versus a traditionally built wastewater treatment plant of this kind.

[caption id="attachment_16532" align="alignnone" width="1200"] Solar panels for clean, renewable energy - Courtesy of Glanua[/caption]

Reuse of constructed wetlands

The integration of the existing constructed wetlands into the wastewater treatment facility which was core to the design development brought a multitude of benefits, ranging from low operational costs, support for diverse ecosystems as well as sustainable water management. The wetlands improve water quality of streams and rivers in surrounding area creating conditions for aquatic life to thrive, and also create a scenic area in the village, promoting biodiversity and providing a habitat for small animals.

Boherbue WwTP: Supply chain - key participants

• Precast concrete: Glanua Group
• Designers: Jennings O’Donovan & Partners
• Designers: Construct Engineering
• Precast concrete: Shay Murtagh Precast
• Precast concrete: Carlow Tanks
• Precast concrete: FLI Precast Solutions
• Precast concrete: Tracey Concrete
• PLCs & automation: UMAC Systems
• Inlet screens: Definitive Ecology
• Tertiary solids removal cloth filters: Eliquo Hydrok Ltd
• Aeration blowers: Kaeser Kompressoren
• Aeration diffusers: Xylem Water Solutions
• Solar panels: The Low Carbon Energy Company Ltd
• CWF Storm Flush system: Eliquo Hydrok Ltd
• Steel modular buildings: Shanette

[caption id="attachment_16530" align="alignnone" width="1200"] (left) Precast concrete aeration tanks reduced construction time and safety risks and (right) view of final clarifiers and cloth filters - Courtesy of Glanua[/caption]

Innovative construction methods

Throughout the entire design process, Glanua Group and Uisce Éireann’s PMO team evaluated several project aspects such as energy efficiency (BEP), TOTEX costs, and environmental impact.

• Energy efficiency of all motors and equipment (BEP).
• Process and equipment selected on TOTEX costs (including CAPEX, OPEX and capital replacement at end of life).
• The impact to the local environment was carefully assessed for all design options considered during the planning phase.

Modular and off-site construction

Modular/off-site construction was used to reduce the carbon footprint and on-site safety risks, with precast panels and BCAR-compliant steel modular buildings used to promote efficient delivery and enhance safety.

Precast panels were instrumental in constructing the main aeration tank, reducing construction time and mitigating safety risks compared to traditional in situ methods. Precast wall sections were used to separate the sludge drying reed beds sections to reduce the footprint size and again to reduce construction time and safety risks. Throughout the project, precast process tanks were used extensively contributing to streamlined construction processes and improved safety measures.

A BCAR-compliant steel modular building from Shanette was used for the control room, laboratory, and caretaker’s office facilities. This has a significantly lower carbon footprint than that of a conventional block-built structure and in turn reduced health and safety risks significantly during construction due to fabrication being completed before assembly on site.

[caption id="attachment_16529" align="alignnone" width="1200"] Off-site fabrication of steel building, fully assembled as works have been completed (April 2024) - Courtesy of Glanua[/caption]

Sustainability

The construction of the Boherbue Wastewater Treatment Plant is an example of Uisce Éireann and Glanua Group’s commitment to sustainability across various dimensions, including environmental, social, and economic considerations.

The inclusion of sludge drying reed beds demonstrates dedication to environmental sustainability. These beds offer an innovative solution for sludge management, reducing the environmental impact of waste disposal while also providing opportunities for ecological conservation.

By using nature-based solutions to treat and manage sludge, the carbon footprint associated with traditional disposal methods is minimised; thereby mitigating environmental harm. The SDRBs also significantly reduces operational costs, providing a long-term cost-effective solution.

The integration of solar technology underscores the commitment to renewable energy and carbon reduction. By harnessing solar power to supplement the energy needs of the wastewater treatment plant, reliance on fossil fuels is reduced, contributing to the transition towards a more sustainable energy future. This not only reduces operational costs but also mitigates greenhouse gas emissions, thereby supporting climate action efforts and environmental preservation.

Socially, the decision to reuse the existing wetlands demonstrates dedication to maintaining and sustaining biodiversity in the Boherbue community. By incorporating natural elements into the design, not only is disruption to local ecosystems minimised, but also to the overall health and vitality of the local environment.

Darran O’Leary, Programme Manager at Uisce Éireann said:

“We are delighted to have delivered this important project for the community of Boherbue. The modernisation and improvement of the wastewater infrastructure will accommodate further growth in the area and ensure that cleaner and safer treated wastewater is being discharged into the Brogeen River.

“It also adds biodiversity value to the area and remains sensitive to the surrounding landscape. This, coupled with the use of solar energy, demonstrates our commitment to putting sustainability at the heart of everything we do”.

Boherbue WwTP upgrade works is a flagship project for sustainable and carbon saving treatment processes and will serve as a reference project for future similar projects within the industry.

By demonstrating the feasibility and benefits of integrating renewable energy, advanced treatment technologies, and ecological conservation practices, this project sets a precedent for industry-wide innovation and best practices.

It complies with stringent Environmental Protection Agency (EPA) discharge consent standards, while minimising impact on the existing landscape, demonstrates a commitment to environmental sustainability, operational efficiency, and community well-being, making it a catalyst for positive change within the wastewater treatment sector and beyond.

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
• 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.

The town of Giffnock is situated approximately 6 miles south-west of Glasgow and has a population of around 12,500. In June 2022, Scottish Water launched a £6.8m, year-long, investment project aimed at mitigating the risk of sewer flooding on Braidholm Road. This initiative is intended to significantly improve conditions for households that have previously experienced internal property flooding. A new offline underground storage tank with a capacity of 1.6 ML was installed beneath the grassed open space on the south side of Braidholm Road next to the junction with Whitton Drive and Graffham Avenue.

Project scope

The project involved constructing a storm overflow chamber, a storm overflow diversion pipe, and a 13m wide x 13m deep underground stormwater storage tank, as well as enhancing the current sewer infrastructure, to safeguard residences on Braidholm Road against sewer flooding during extreme weather circumstances.

Project challenges

The logistics of constructing the stormwater storage tank in the middle of a residential area were huge and residents faced significant disruption. The project team had to overcome several challenges, such as:

• Managing groundwater levels and ensuring adequate dewatering throughout the construction process.
• Protecting the existing sewer network and other underground services from damage or interference.
• Minimising noise and vibration during the excavation and piling works, which involved driving 120 piles to a depth of 14m.
• Securing access and traffic management for the delivery of heavy plant and equipment, including a 120-tonne crane and a 35-tonne excavator in a built-up residential area.
• Maintaining communication and engagement with the local community and stakeholders, providing regular updates and addressing any concerns or complaints.

[caption id="attachment_14764" align="alignnone" width="1200"] Site establishment - Courtesy of Whitehouse Studios[/caption]

Constructing the shaft

One of the key features of the project was the construction of a segment ring shaft, which is a novel and innovative method of creating a deep circular shaft using precast concrete segments from Macrete (Ireland) Ltd. Over a period of five months, eleven segments measuring 12.5m each were carefully lowered into an excavation and sequentially stacked to create a sealed shaft structure. In total, approximately 1800m³ of material were dug out and 400m³ of concrete were utilised in the construction.

This technique reduces the amount of concrete and steel required, as well as the carbon footprint and disruption associated with traditional shaft construction methods.

Braidholm Road Flood Alleviation: Supply chain - key participants

The project was managed by Investment Delivery, Scottish Water’s in-house delivery vehicle, and delivered by George Leslie Ltd, one of Scottish Water’s capital delivery partners.

• Principal contractor: George Leslie Ltd
• Design consultant: AECOM
• Civil engineering: JOS Civil Engineering
• Tunnelling: Pipeline Drillers Ltd
• Ground support systems: Groundforce
• Ground support systems: Mabey Hire Ltd
• Piling: Burnside Plant Hire Ltd
• Steelwork: MacGregor Technical Services Ltd
• MEICA: ID Systems
• Kiosk: Quinshield Ltd
• Shaft segments: Macrete (Ireland) Ltd
• Pumps: Xylem Water Solutions
• Landscaping: MW Groundworks Ltd

Project adopts low carbon approach

The Braidholm Road project is one of the first in Scotland to adopt a low carbon approach for the construction of sewer infrastructure.

Over 1,000 tonnes of low carbon concrete was used to construct a 13m deep stormwater tank and overspill chamber, whilst hydrotreated vegetable oil (HVO) was used as fuel, ‘huge’ electric batteries came in place of generators, and recycled aggregates were utilised.

Scottish Water are committed to delivering net zero emissions by 2040 and beyond and every project we undertake is a step towards achieving that aim. The carbon saving in Braidholm Road is the equivalent of 220 return flights from Paris to New York.

[caption id="attachment_14761" align="alignnone" width="1200"] Work on Braidholm Road - Courtesy of George Leslie Ltd[/caption]

Benefits

Scottish Water is a public sector body answerable to the Scottish Parliament through Scottish Ministers and our principal activities are the supply of water and wastewater services to around 5.4 million customers in homes and businesses across Scotland covering an area of 30,810 square miles.

Our vision is to be trusted to care for the water on which Scotland depends. Reflecting that, our customers expect us to provide excellent customer service by delivering high levels of water quality and environmental performance, all for an affordable price. Using Scotland’s natural resources and the skills of our people, Scottish Water is committed to improving our services for customers and communities while protecting and enhancing the environment of Scotland.

The new stormwater storage tank can hold the equivalent of more than half an Olympic size swimming pool of water (1.6 megalitres) during periods of extreme weather events, providing extra capacity, both within the tank and the local sewers alleviating pressure on the wastewater network.

This project is important to Scottish Water as it continue to build the trust and confidence of our customers and communities across Scotland through maintaining and investing in our assets.

Engagement

In the initial phase prior to construction, a plan for entry and exit was developed through early discussions with stakeholders, pinpointing all community members and stakeholders impacted and establishing the most effective routes and locations for the site compound and work area. A traffic management plan was drafted in consultation with the residents, ensuring ongoing access while reducing any disruptions from the construction activities within the community.

The key site compound was positioned at a central main location to include the project office and material storage; this was purposefully set some distance from the construction site to diminish any disturbance to the residents.

The Scottish Water and the George Leslie joint project communication team organised a community open day to share details about the upcoming works, allowed for engaging with the locals, and addressed any issues or needs they might have had. Prior to starting on-site work, they distributed informational letters to all stakeholders affected, which included direct contacts for any project-related inquiries.

[caption id="attachment_14760" align="alignnone" width="1200"] Site reinstatement - Courtesy of Whitehouse Studios[/caption]

During the construction, all interactions regarding information requests, complaints, or consents were formally documented, responded to, and resolved according to the management plan.

The commitment and cooperation of the community were crucial to the success of this significant and multifaceted engineering project, and Scottish Water is grateful for the community’s goodwill and understanding throughout the process.

Conclusion

The Braidholm Road project, delivered by Scottish Water partner George Leslie Ltd, has successfully implemented a multi-million-pound, year-long initiative to prevent sewer flooding in Giffnock for Scottish Water.

Despite the challenges of managing logistics, noise, vibration, groundwater levels, and maintaining community engagement, the project team overcame these obstacles to deliver a low carbon approach to sewer infrastructure.

This project not only alleviates pressure on the wastewater network by providing extra capacity but also demonstrates Scottish Water’s commitment to net zero emissions by 2040, building trust and confidence in customers and communities across Scotland.

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:

1. Preliminary treatment in the form of screening and grit removal.
2. Secondary treatment in the form of two oxidation ditches and two final settlement tanks.
3. 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
• 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:

1. The project took place on a live treatment plant, which had to remain fully operational during construction.
2. 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.
3. 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.