Supply Chain - Stormwater Storage - Storage Shafts

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 Southampton Shellfish Scheme comprises the upgrade to four wastewater treatment works and one combined storm overflow (CSO) discharging effluents to the Solent. The Water Industry National Environment Programme (WINEP) No Deterioration Shellfish Drivers (ND_SW) have dual targets: (i) to reduce the number of intermittent storm discharges to 10 significant spills or less per year (as a 10-year average) for the agglomeration of assets impacting Southampton Shellfish Water, and (ii) for the final effluent discharges, achieve a 6.6 log reduction in E. coli between crude sewage and the boundary of Southampton Shellfish Water. Additionally, WINEP U_IMP5 drivers resulting in an increase in flow to full treatment (FFT) were applicable at some of the sites, therefore design and construction for all drivers were combined under the same project.

Site	Pre-U_IMP5 initial calculated volumes (m3)	Post Post U_IMP5 impact to agglomeration (June 2021) (m3)	Final Volumes (m3)
Millbrook WwTW	Yes	Yes	Yes
Slowhill Copse WwTW	Yes	Yes	Yes
Woolston WwTW	Yes	No	No *
Ashlett Creek WwTW	Yes	No	Yes
Ensign Park CSO	Yes	No	No
Table 1: Southampton Shellfish Scheme drivers		* N/A, but FFT is being increased as a mitigation for ND_SW driver

Southampton Shellfish Scheme sites

The technical solutions considered during design included increasing the storm tank capacity and the hydraulic capacity of the wastewater treatment works (WwTW) to reduce the intermittent storm discharges, with UV irradiation or membranes being considered to achieve the disinfection requirements.

[caption id="attachment_14597" align="alignnone" width="1200"] UV irradiation system at Slowhill Copse WwTW (December 2023) - Courtesy of Southern Water[/caption]

Details of the five sites are as follows:

1. Millbrook WwTW treats for a population equivalent (PE) of 147,000 with biological treatment provided using a 4-stage Bardenpho Activated Sludge Process (ASP).
2. Slowhill Copse WwTW treats for a PE of 77,000 PE and provides biological treatment via a Modified Ludzack-Ettinger (MLE) configured ASP.
3. Woolston WwTW treats for a PE of 70,000 and has an MLE configured membrane bio-reactor (MBR).
4. Ashlett Creek WwTW treats for a PE of 15,000 and provides biological treatment via a sequential batch reactor (SBR).
5. Ensign Park is a combined sewer overflow (CSO).

Modelling & optimisation of storm volumes

The project drivers required a reduction of spill frequency at storm overflows for all the catchments that discharge into Southampton Shellfish Water. This impacted five separate wastewater treatment works catchments.

Early in the design, the Southern Water (SW) project team identified an efficiency opportunity of combining the FFT U_IMP5 (increase in flow to full treatment) Driver with the Shellfish Driver, which had a significant impact on reducing the volume of the storm storage tanks. SW held regular meetings and agreed the approach with the Environment Agency (EA) including alignment of Regulatory output dates to the end of the AMP period.

The assessment of storm storage is based on the agglomeration approach outlined in the EA PR19 shellfish guidance and methodology. The definition of a significant spill was agreed with the EA at the conceptual stage of the scheme. This assessment treated all the discharges as a single agglomeration.

[caption id="attachment_14601" align="alignnone" width="1200"] UV irradiation system at Millbrook (May 2023) - Courtesy of Southern Water[/caption]

In summary, the integrated combined driver approach provided the following benefits:

• Avoided abortive investment:
  • Storm tanks for ND_SW being oversized (increased FFT from U_IMP5 reducing storm flows).
  • UV irradiation system and associated feed pumping for ND_SW being undersized (increased FFT from U_IMP5).
• Reduced carbon impact:
  • By avoiding assets no longer required.
  • By avoiding an inefficient 2-stage construction approach.
• Avoided potential abortive third party land acquisition and development.
• Reduced construction, traffic movements and the impact to the local community, particularly within the urban areas.
• Avoided unnecessary impact to the environment and ecology.
• Avoided potential abortive works for 3rd party infrastructure (for example, power upgrades).

To develop the solutions required at each wastewater treatment works, the sewer network performance for the five catchments was designed using a 10-year rainfall dataset. The observed spill frequencies across the catchment had to be agglomerated to ensure that 10 significant spills or less per year was achieved over a long-term (10 year) average.

This meant the modelling was more complex and took a lot longer than a usual model build and verification exercise because of the need to assess all five catchments together.

Following subject matter guidance from across the industry, the project team used an innovative approach of using an extended rainfall series duration and a single rain gauge. In addition, the team targeted the storage volumes at sites where there was available capacity to arrive at the most efficient storage volumes that were significantly lower than the original estimates, all while complying with good industry practice. In summary, this included:

1. Extending the rainfall series for a longer period than 10 years to be more representative of long-term weather patterns, addressing extremely ‘wet’ periods within the original 10-year series.
2. Using a single rainfall profile as this coastal rain gauge is more representative of the rainfall falling on the main urbanised sections of the catchments.
3. An extended rainfall series to help address the annual frequency, extremeness and year-on-year variability of rainfall patterns and particularly wet or dry periods.

[caption id="attachment_14602" align="alignnone" width="1200"] Storm Shaft in Ashlett Creek (June 2024) - Courtesy of Southern Water[/caption]

Optimising storm storage volumes

The project team considered the best location for increasing the capacity of storm storage considering the cost/benefit for reducing significant storm spills. For example, at Millbrook WwTW redundant storm tanks were utilised that provided a volume of 3,140m³. The increase in volume at Millbrook enabled the storage volumes to be optimised across the agglomeration of sites with volumes being offset against other more constrained sites.

Southampton Shellfish Scheme: Supply chain - key participants

• Client: Southern Water
• Delivery partners & outline/detailed design: GTB
  • Galliford Try
  • Binnies
• UV design & coastal & network modelling: Stantec UK
• Coastal & network modelling: Southern Water
• Civils & pipework: Knights Brown
• Civils & pipework: Impact Formwork
• Storm shafts & tunnelling: HB Tunnelling
• Piling works (Woolston WwTW): Rock & Alluvium
• Piling works (Woolston WwTW): Keller Foundations
• Storm tank remedials: Concrete Repairs Ltd
• Mechanical installation: Bridges Electrical Engineers Ltd
• Mechanical installation: Steelway
• Electrical installation: Field Systems Design
• Electrical installation: Loxton Electrical
• ICA: Total Automation & Power (TAP)
• MCCs: MCS Control Systems
• GRP kiosks: Industrial GRP Ltd
• Penstocks: Ham Baker
• UV: Trojan Technologies
• Membranes: Koch (KMS)

[caption id="attachment_14599" align="alignnone" width="1200"] Refurbishment of redundant storm tanks at Millbrook to provide 3,400m3 capacity - Courtesy of Southern Water[/caption]

Infiltration - optioneering

1. To optimise the significant storage volumes at the works, sustainable catchment opportunities were considered for the large, urbanised Millbrook and Woolston catchments by the removal of specific areas of groundwater infiltration and surface water from foul sewers.
2. The optioneering was undertaken using an optimisation software package to target impermeable areas (roads and roofs) connected to the network and working through simulations (up to 20,000) to assess parts of the catchment where connected roads and roofs could be removed from the foul sewer.
3. The benefit was not as expected when considering the agglomerations due to spills from the other assets. In addition, the timescale to achieve long-term reduction from impermeable area removed or groundwater infiltration would require a multiple AMP period.
4. Future opportunities using the optimisation techniques will be considered for similar CSO and storm spill frequency schemes to achieve sustainable catchment opportunities, by the removal of specific areas of groundwater infiltration and surface water from foul sewers.

Woolston WwTW - increasing FFT

The initial significant storm volumes at Woolston were extremely challenging given the location of the site within an urban environment and lack of available space. The project team identified an opportunity of increasing the FFT at Woolston, which provided a significant reduction in storage. The scope involved utilising hydraulic headroom within the works, and through the installation of additional MBR capacity and associated pump upgrades, enabled a 20% increase in FFT at Woolston WwTW (427 l/s to 534 l/s).

[caption id="attachment_14603" align="alignnone" width="1200"] Construction of the shaft at Woolston - Courtesy of Southern Water[/caption]

The programme to deliver the increase in FFT at Woolston was short and provided an early reduction in E. coli concentration discharging to the Solent. This early delivery reduced 20% of the total E. coli concentration across the agglomeration of sites and was fundamental in agreeing new regulatory dates for the SW_ND (storm storage) drivers. The combination of the integrated driver approach to reducing spills, the innovative modelling and optimisation of assets reduced storage volumes by circa 46,000m³.

The final volumes are as shown in Table 2:

Site	Initial calculated volumes (m3) (pre-U_IMP5)	Post Post U_IMP5 impact to agglomeration (June 2021) (m3)	Final Volumes (m3)
Millbrook WwTW	3,684	200	3,400
Slowhill Copse WwTW	13,678	2,000	2,000
Ashlett Creek WwTW	4,176	1,650	1,650
Woolston WwTW	27,422	13,120	5,000
Ensign Park CSO	3,806	280	280
Blechynden Terrace CSO	5,000	0 *	0 *
Newtown CSO	562	0 *	0 *
Table 2: Southampton Shellfish Scheme storm storage volumes		* Reduction driven by reduced spills in the agglomeration

New final effluent disinfection at Slowhill & Millbrook WwTWs (AMP7 & AMP8):

In response to a number of drivers, the EA has recently revised its approach to design and permitting of UV irradiation systems for the disinfection of final effluent. The aim is to move away from the use of generic assumptions, to follow international best practise with an approach which employs the use of a site-specific data in conjunction with performance validated UV irradiation equipment. This revised approach enables development of a significantly better understanding of performance and limitations on a site-specific basis.

Understanding the variation and impact of key wastewater characteristics on parameters such as UV transmittance and the UV dose-response relationship enables selection of a representative design envelope and minimum target UV dose. This enables the capital solution to be optimised, minimises power usage, operational costs and carbon impact while securing environmental performance.

[caption id="attachment_14609" align="alignnone" width="1200"] UV irradiation system at Millbrook (June 2024) post commissioning/FST under construction and (inset) UV irradiation system at Slowhill Copse WwTW - Courtesy of Southern Water[/caption]

The steps undertaken for the development of the design parameters and permit conditions for the UV irradiation systems at Slowhill and Millbrook WwTWs can be summarised as follows:

1. Coastal/estuary modelling was used to determine the dilution/dispersion factor available from the effluent discharge location to the Shellfish Water boundary. The boundary is due to extend closer to the discharge points in AMP8 (i.e. reducing the available dilution of the final effluent discharges), therefore disinfection targets were evaluated for both AMP7 and AMP8 during design. This enabled the overall system (channels, MCC and power requirements) to be designed with the ability to install the equipment required in AMP7 and accommodate further banks to meet the lower E. coli targets required to avoid abortive and/or extensive additional construction in AMP8.
2. A programme of sampling and analysis was carried out (from April 2020 to May 2021) to collect data on the variation of microbial and sanitary characteristics of the final effluent. The results were compared to the parameters available from historical site data in order to ensure that the sampling was representative of the expected range. Variation in UV transmittance was recorded using online instruments for assessment with flow data to understand their relationship. The UV dose-response relationship for E. coli for the final effluent was developed using collimated beam testwork to determine the target UV dose required to achieve the disinfection targets for permitting for both AMP7 and AMP8.
3. The data was used to develop a range of design parameters that were then used in conjunction with UV suppliers’ performance validation information to determine a range of UV irradiation system configurations. The options were evaluated considering the different levels of resilience, redundancy and risk of non-compliance with the EA’s proposed new permit conditions.

The new UV irradiation systems have been in operation at both sites since Autumn 2023 and are consistently achieving concentrations of E. coli in the final effluent discharges that will maintain the concentration at the Shellfish Water Boundary below the post PR19 target value of 5 cfu/100ml as a geomean.

[caption id="attachment_14600" align="alignnone" width="1200"] (left) Millbrook UV pumping station and (right) MBR cassette capacity being increased in Woolston WwTW - Courtesy of Southern Water[/caption]

Woolston WwTW - working with care

Due to the limited availability of operational land in Woolston, the new storm shaft is being constructed beneath a car park and green area own by Southampton City Council (SCC), the area also had a Multi-Use Games Area (MUGA). The project team and the representatives of the Council engaged in extensive discussions prior to submission of the planning application which ensured a positive outcome for both parties.

From those conversations the project team learnt that the Council had worked to create a low nutrient coastal grass environment in the zone affected by the project. The topsoil had been amended and sown with the current species in previous seasons. Therefore, the agreed approach was to retain the topsoil stored on site and reinstate it at the end of the project, enabling the green area to grow and cover the old disused carpark.

The first activity after site mobilisation was relocating the reptiles that naturally inhabit coastal grass biomes. All areas with long grass that were part of the construction compound had the grass cut in two passes to encourage reptiles to move to nearby unaffected zones. Additionally, the top 100mm of soil was hand excavated with an ecologist carefully moving those reptiles still on site.

SW, working closely with the local Council, has ensured that the pre-existing facilities not only are kept despite the new structures being built, but that they are also improved. The number of parking bays and EV charging points will be maintained with improved access arrangements to avoid unwanted camping vans. The MUGA will be improved so the excessive slope that the old court had is removed and the pedestrian access to an adjacent park is protected with bollards, as previously vans used to park using part of the footpath.

[caption id="attachment_14596" align="alignnone" width="1200"] Landscaping over Woolston storm shaft - Courtesy of Southern Water[/caption]

Progress to date, successes and future phases

The storm tank at Millbrook WwTW and the increase in flow to treatment at Woolston WwTW were both commissioned in July 2022 while the projects to install UV irradiation at Slowhill and Millbrook WwTWs were commissioned in Autumn 2023. In combination, these improvements represent a reduction of 72,500 cfu/s of E. coli being discharged to the Southampton Shellfish Waters, which is more than 60% of the total E. coli concentration reduction when all the projects are completed.

Results from sampling carried out after commissioning have demonstrated that both UV irradiation systems at Slowhill and Millbrook have reliably achieved the target efficacy, with concentrations of E. coli in the effluent post disinfection regularly below 200 cfu/100ml. Additionally, concentrations of E. coli in the final effluent discharge from Woolston have been consistently below 35 cfu/100ml since July 2019, following commissioning of the MBR.

The next key milestones are 31 December 2024, when the new storm tank at Ashlett Creek WwTW will be commissioned, and 31 March 2025, when all the remaining storage and increase in flow to treatment drivers will be completed.

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.

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 Stroud Sewerage Strategy is a major investment by Severn Trent which is required to overhaul of the existing sewer network by installing almost 3.5km of enlarged sewer pipe, separating surface water from the sewage network, creating additional storage with smart controls to hold stormwater back during large storm events before returning it to the treatment works when the rainfall has subsided, and making improvements to Stanley Downton Sewage Treatment Works. This paper follows on from the case study published in Water Projects 2022, which focussed on the design and optioneering elements of the programme of works.

Scope of works

The Stroud Sewerage Strategy is made up of five key elements:

• Trunk sewer improvements.
• Combined sewer overflow & storage.
• Surface water separation.
• Infiltration reduction.
• Stanley Downton WwTW.

Construction started in March 2022 and details of the progress to date (July 2023) is covered in this case study.

New trunk sewer

In order to reduce the risk of sewer flooding and convey flows from the existing Wallbridge CSO, design and build contractor Galliford Try was required to design and build a second trunk sewer system, transferring flows 3.65km to the new CSO site on the outskirts of Stroud. The new sewer network will operate entirely under gravity, with no siphons and falls at a minimum gradient of 1:500. [caption id="" align="alignnone" width="1200"] (left) The launch of TBM Marvellous Mining Molly and (right) shaft with pipe jacks installed about to be benched - Courtesy of Galliford Try[/caption] Due to varying local topography and numerous obstacles along the route the team opted for a combination of open cut and pipe jack tunnelling techniques for the trunk sewer - details below.

Pipe diameter : Length	Details
750mm = 900m	Open cut works: 2-5m deep, includes 1 x River Frome crossing
1500mm = 769m	Open cut works: 3-6m deep, includes 1 x River Frome crossing
900mm = 35m	TBM Marvellous Mining Molly: 1 x tunnel drive crossing under A419
1200mm = 550m	TBM Lilian: 4 x tunnel drives under Dudbrige Road (dual carriageway), car parks and private land
1200mm = 650m	TBM Suzanne: 6 x tunnel drives under Stroudwater Navigation Canal & major gas mains
1500mm = 591m	TBM Florence: 3 x tunnel drives under A419, Stroudwater Navigation Canal & Painswick Stream

BSP Consulting Ltd carried out the structural design of all 12 tunnelling shafts (varying from 3.66m, 5m and 6m in diameter), with the ring segments and cover slabs supplied by Macrete (Ireland) Ltd. BSP also undertook the design calculations and documentation required for the five tunnelled highway crossings consents (CD622) and the buried service damage assessment reports for eight key service crossings along the route (the pipeline analysis was undertaken using Oasys software). Active Tunnelling Ltd developed a bespoke tunnel boring machine setup for the 900mm micro-tunnel which involved installing an initial 600mm laser guided auger followed by a forward reaming TBM head into the auger screw. This setup avoided the need to install a 1200mm pipe which would have caused additional risk to an existing underpass in close proximity. [caption id="" align="alignnone" width="1200"] TBM Marvellous Mining Molly in position to start mining - Courtesy of Galliford Try[/caption]

Stroud Sewerage Strategy: Supply chain - key participants

• Client: Severn Trent
• Design & build contractor: Galliford Try
• Hydraulic model: Richard Allitt Associates
• Principal ecologists: RammSanderson Ecology Ltd
• River & spillway reinstatement: Salix River and Wetland Services
• Silt mitigation: Frog Environmental
• Water vole licensing: Wildwood Ecology
• Land & planning Agents: Dalcour Maclaren
• Topographical Surveys: Geomap Ltd
• Ground investigation: Grange Geo Consulting
• Hydraulic model: Innovyze (Infoworks ICM)
• Physical model: Framatome BHR Group
• Shafts & pipejacking: Active Tunnelling
• Tunnel design: BSP Consulting
• Traffic management: Amberon Ltd
• Remediation & asbestos management: Churngold Construction
• Water main diversions: Heartland Pipelines
• Sewer lining: Colus Ltd
• Temporary PortaDams: OnSite Central
• Steel fabrication & penstocks: GT Fabrications
• Valves: AVK UK Ltd
• Open cut pipework: LCS Groundworks Ltd
• Open cut pipes: Marshalls CPM
• Electrical installation & MCC: Cema Ltd
• DI pipework: Electrosteel Castings (UK) Ltd
• Shaft rings & cover slabs: Macrete (Ireland) Ltd
• Jacking pipes: FP McCann Ltd
• Washwater pumps: KGN Pillinger
• Lifting equipment: T Allen Engineering Services
• Submersible pumps: Xylem Water Solutions
• CSO screens: Longwood Engineering Co Ltd
• Prefabricated chambers & backdrops: Polypipe Civils & Green Urbanisation
• Access covers: Steelway Brickhouse
• Manhole covers: Saint Gobain PAM UK
• Fencing & tree clearance: Landscape Maintenance Services

Interception chamber

Galliford Try was required to design a new interception chamber to convey all the flows of the existing Nailsworth Sewer into the new network. Working on a live network and dealing with large flow rates naturally led the team to design a prefabricated chamber to minimise the installation time. Designers from Galliford Try and Polypipe Civils & Green Urbanisation developed a solution that incorporated a permanent backdrop, temporary flume pipe and four connections (750mm, 750mm, 1200mm and 1500mm in diameter). It was built off-site in three sections and assembled on site in one day. [caption id="" align="alignnone" width="1200"] (left) Installation of prefabricated chamber within live sewer line and (right) inside the prefabricated chamber - Courtesy of Galliford Try[/caption]

River Frome crossings

Due to the need to retain a constant gradient, both sewer crossings under the River Frome were very shallow with very little cover to the erodible bed level. Without creating syphons, open cutting through the river was the only feasible solution. A temporary bypass channel was constructed and lined using Salix River and Wetland Services coca matting and Frog Environmental rock rolls to prevent mobilising sediment during the works. Temporary PortaDams from OnSite Central Ltd were installed to isolate a section of river. RammSanderson Ecology Ltd provided ecological support, including moving 1554 fish between dams (129 brown trout, 493 brook lamprey, 715 bullheads, 209 sticklebacks, five eels and three roach). This element of work required a huge amount of planning and permits from Galliford Try’s Environmental Team, the Environment Agency and Natural England. [caption id="" align="alignnone" width="1200"] Construction of bypass channel and (inset) installation of the temporay PortaDam from OnSite Central Ltd  - Courtesy of Galliford Try[/caption]

New CSO shaft

Construction of the new 25m diameter, 28m deep combined sewer overlflow shaft started in summer 2023. A detailed update will be published on WaterProjectsOnline.com later in the year.

Surface water separation

The 3.88 hectares of impermeable surface area being separated from the existing catchment is situated in Stroud town centre and involved designing a new 555m long, 300mm diameter, intricate surface water sewer network within the constraints of a densely built-up area to intercept flows which otherwise would have ended up in the combined network and added to the spill events in the downstream catchment. Galliford Try undertook GPR surveys and numerous trial holes to create a map of existing buried assets and plan a route for the new sewer network. To reduce service diversions to a minimum, a number of bespoke manholes were designed, and the Galliford Try team proposed relining the existing foul sewer rather than replacing it which considerably reduced disruption and construction timescales on site. Flows from the newly separated network are transferred to Stroudwater Canal via a 232m long connection across a supermarket and council car park and under an existing retaining wall. Due to the interface with the general public and potential upheaval of working in car parks, Galliford Try chose to install the 600mm diameter pipes by using a laser guided auger. In conjunction with specialist Active Tunnelling Ltd, drive and reception pits were carefully positioned within car parking bays and the route designed to minimise disruption as far as practicable. On completion of the works, all affected stakeholders were positive and complimentary over the tidiness of the work sites. [caption id="" align="alignnone" width="1200"] (left) Excavation of shaft and (right) preparations for open cut rising main installation - Courtesy of Galliford Try[/caption]

Infiltration reduction

To free up capacity for foul flows in the existing network, Galliford Try eliminated 3 l/s of infiltration with specialist Colus Ltd by installing 475m of liners and injecting two-part polyurethane sealant at key locations. The constant groundwater flow was caused through a combination of old cracked sewers, old brick manholes with blown mortar and badly made connections onto the existing network.

Conclusion

At the time of writing (July 2023), the last remaining parts of the project include modifications to the storm return pipework at Stanely Downton WwTW, and the demolition of the existing Wallbridge CSO site. These works will be undertaken upon completion and commissioning of the new assets. The whole team from engineers, design, procurement, commercial and project management working on this difficult project have pulled together to overcome numerous unforeseen physical, environmental, financial and stakeholder challenges in Stroud. The author wishes to credit everyone involved; sub-contractors, supply chain and the client for achieving what has been delivered to date.

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.

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.

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.

In February 2020, Storm Dennis brought flooding to the area of Glenboi during which 24 houses were flooded as the culverted watercourse system became inundated and exceedance flows made their way into the existing Glenboi Surface Water Pumping Station. The existing pumping station could not handle the exceedance flows and therefore Rhondda Cynon Taff Council sought Welsh Government funding to procure a new and improved capacity pumping station via a design and build competitive tender process. The contract was awarded on an NEC4 Option A Design and Build, and following submission of a competitive design and build tender process, envolve infrastructure was successfully appointed as the delivery partner for the >£1m project.

Project scope

The works comprised:

• Proposed underground wet well attenuation tank and pumping chamber.
• Fenced compound with impermeable hard standing to access the pumping station wet well with permeable hard standing beyond, accessed via pedestrian gate.
• Valve chamber.
• Connection onto existing rising main.
• New headwall to the newly provided existing rising main.
• Connection from existing highway drainage system.
• Kerbed bituminous pavement lay-by.
• Substation maintenance compound and electrical cabinet and plinth, and emergency generator plinth.
• Installation of electrical connection.
• M&E works associated with the pumps and a telemetry warning system.

Early contractor involvement (ECI) and design

Envolve’s ‘one-team’ integration model with Hydrock and Rhondda Cynon Taf in conjunction with the expertise of envolve’s in house design manager and construction team, formed an integral part of the collaborative delivery model. Envolve infrastructure’s sector leading ‘one-team’ approach guaranteed a collaborative partnership from the outset, facilitating an efficient and coordinated design process with Rhondda Cynon Taf. Envolve’s responsibility during the design process reviewed suitability and efficiency of the outline design, planned construction methodology & proposed constructability options to collaboratively develop the final design. Temporary works designs for the entire project were procured and managed by envolve’s in house design manager. [caption id="" align="alignnone" width="1200"] (left) Pipework within the shaft and (right) precast concrete segmental shaft rings - Courtesy of envolve infrastructure[/caption] ECI was integral to the final design solution from the outset, close collaboration with Rhondda Cynon Taf developed a more efficient and reduced cost engineering solution to meet the project objectives, providing a cost-effective and value driven solution. ECI began with a partnership with Hydrock developing the detailed design. Envolve’s ECI strategy was to further investigate and interrogate the outline design, whilst minimising risk and embodied carbon through streamlining constructability and increasing operational efficiency. The design and delivery team undertook a review of the design philosophy in tandem with Rhondda Cynon Taf’s conceptual design. A proposal was drawn up, identifying the benefits of a deeper wet well shaft in lieu of a smaller shaft with accompanying storage tank. This approach mitigated the requirement for a reinforced concrete retaining wall adjacent to the existing highway. Further investigation into the most efficient shaft construction identified the benefits of constructing a ‘wet’ cassion, in lieu of a conventional ‘dry’ construction. This construction method mitigated potential subsidence risk to 7 local residential properties and the main B4275 carriage way as there would no longer be a requirement to lower the existing high water table by our selected engineering solution. In enlarging the proposed shaft, envolve was also able to house the proposed pumping equipment within the shaft itself, significantly reducing the overall footprint of the facility. The final visual impact of the project was prioritised to provide adjacent residents with the least impactful and sustainable reinstatement on completion of the project. In lieu of a large tarmac area, a sustainable permeable hard standing was specified. On site ECI works undertook ground investigation to determine the classification of waste material for excavation arisings including sampling and laboratory testing. Envolve’s design solution successfully met Rhondda Cynon Taf’s requirement for a 250m³ storage tank with an outflow of 200 litres per second, achieved via a 6m diameter and 11m deep shaft with incorporated pumping station, all within the minimal footprint of the land available. This significant design improvement ensured the final engineering solution worked within the site boundaries, also providing Rhondda Cynon Taf with an £800k cost saving for the overall project. In summary, the outputs of our ECI expertise resulted in the following improvements to the final project design:

• One deeper wet well in lieu of smaller shaft.
• Removal of storage tank.
• Removal of reinforced concrete retaining wall.
• Mitigation of groundwater risk through ‘wet’ caisson construction.
• Housing of the pumping equipment within the enlarged shaft.
• Sustainable permeable hard standing in lieu of a tarmac.

Once work commenced on site, envolve was appointed as principal contractor and principal designer. [caption id="" align="alignnone" width="1200"] (left) Birdseye view of the wet caisson shaft under construction and (right) precast concrete segmental shaft rings at the base of the shaft - Courtesy of envolve infrastructure[/caption]

Glenboi FAS: Supply chain - key participants

• Principal designer & contractor: envolve infrastructure
• Detailed design: Hydrock
• Shaft construction: HB Tunnelling UK
• Confined space emergency/rescue provisions: Pulse Safety Solutions
• Crane Hire: Davies Crane Hire
• Precast concrete shaft rings: Marshalls Civils & Drainage
• Precast cover slab: Tracey Concrete

Construction

During the pre-construction phase, an access/egress plan was agreed with all stakeholders via early engagement, identifying all affected residents and stakeholders and agreeing the most efficient access/egress routes and locations for the site compound and working area. A traffic management plan was drafted and agreed with the residents, always ensuring appropriate access and egress whilst minimising the interface of construction activities with the local community. A central main compound location housed the shared project office facility, material storage and waste processing facilities. Envolve’s yard team operated a quarantine zone for deficient/damaged materials to reinforce an uncompromised approach to quality management. Envolve’s customer liaison officer (CLO) held an open day with the local community informing them of the planned works, this was an opportunity to get to know the local community and address any concerns or specific requirements they would need. Ahead of mobilisation, the CLO delivered compliment letters to all affected stakeholders, providing direct contact details for all matters relating to the project. The main construction activities were as follows:

• Site set up including stakeholder notice boards and branding.
• Service diversions, including installation of new 300mm diameter gravity surface water inlet.
• Excavate and cast the shaft collar, excavate and sink shaft.
• Cast base & mechanical installation of rising main, pumps and inlet mains.
• Construction of new valve chamber arrangement.
• Placement of cover slab with 110t mobile crane.
• Construction of permeable hard-standing, including tanker lay-by.
• External soft landscaping.

[caption id="" align="alignnone" width="1200"] Birdseye view of the construction site - Courtesy of envolve infrastructure[/caption]

Directly employed resource

A delivery resource strategy was created from envolve’s highly experienced directly employed staff and workforce. Their in-house training team facilitated training requirements ahead of commencement. With self-delivery teams supplemented with specialist local subcontractors with whom envolve had longstanding relationships. During the project, envolve recruited local specialist resource to enhance the existing teams. Construction operations were managed by envolve’s specialist site management team supported by their in-house SHEQ department.

Sustainability and carbon management

In adherence to envolve’s carbon reduction strategy and net zero commitment, a permanent power supply connection was made for the main compound with a ‘green’ electricity supplier, removing the need for temporary diesel power generation for the duration of the project. Embodied carbon was an integral part of the initial design process, envolve’s design solution to construct one large ‘wet’ well shaft, mitigated the need for an additional storage tank and reinforced concrete wall, all of which combined to a significant reduction in excavation, disposal, material procurement and associated vehicular movements for the site. Further selection of the precast concrete sections from a UK-based supplier provided support for the local supply chain and reduced unnecessary transportation emissions. The benefits of specifying a permeable pavement solution for the site will help reestablish a more natural hydrologic balance and reduce runoff volume by trapping and slowly releasing precipitation into the ground instead of allowing it to flow into storm drains and out to receiving waters as effluent. [caption id="" align="alignnone" width="1200"] Completed shaft and cover slab - Courtesy of envolve infrastructure[/caption]

Construction design management

CDM15 regulations were discharged through the development of a detailed construction phase plan and through collaborative working. The design was approved through a detailed design process review, regular meetings and early engagement, retaining a collaborative relationship with the team. Stakeholders remained at the heart of the delivery, through conducting weekly progress meetings for the duration of the scheme covering design, construction progress, environmental and third party interfaces.

Social value

Through collaboration with Glenboi Primary School, envolve invited its pupils for a site visit and talk with the delivery teams to explain what the project was and how it would improve their community. 30 pupils from the school attended the safe viewing area, outside of the site boundary and within a safety zone which was especially set up for the visit by the construction team. The team spent the afternoon discussing the effects of climate change and the problems this was causing to the local environment, the purpose of the project and the benefits they will see for years to come with lots of interesting and thought provoking questions from the pupils! There was even time for the pupils to dress up in PPE and have their photo taken in one of the especially prepared small excavators! [caption id="" align="alignnone" width="1200"] School visit to site from Glenboi Primary School and the footpaths and outdoor learning facilities - Courtesy of envolve infrastructure[/caption] Following this, further support was provided to the school with the offer to complete their woodland walk and outdoor learning facility with accessible footpaths connecting the outdoor classrooms. A prestigious opening ceremony was hosted by the school for the grand opening with fantastic poems and songs performed by the pupils – there was even a special cake baked in appreciation of the relationship envolve developed with the school over the lifetime of the project. The woodland learning facility will hopefully provide years of outdoor learning opportunities for the school and its pupils. Envolve operate a successful apprenticeship programme which sees a handful of placements throughout the business each year, these roles span from Commercial through to Engineering. This project presented a unique opportunity for an Engineering placement and a person from the programme was allocated to the project for its duration as part of their development plan.

Summary

Through inspirational stakeholder engagement and community integration, the project not only delivered on its engineering outputs but also engaged a cohort of young people from the local primary school, highlighting the sustainability and climate objectives of the project and hopefully inspiring future careers in the engineering sector. The collaborative approach nurtured a transparent and trustworthy relationship between envolve and Rhondda Cynon Taf, demonstrating how this close working relationship directly influenced the development of an efficient and value led engineering solution which will benefit the community of Glenboi for years to come. Envolve’s anticipated programme duration of 14 weeks significantly improved on the client’s required programme completion date of May 2023.

The 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 Thames Tideway Tunnel Project is a 25 km (16 mi) combined sewer under construction under the tidal section 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 the raw sewage and rainwater that currently overflows into the Thames Estuary. The Thames 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 STW. 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.

Project summary and location

As part of works on the west section of the Thames Tideway Tunnel scheme, Barhale was contracted by the BAM Nuttall Morgan Sindall Balfour Beatty (BMB) joint venture, to construct a series of complex underground structures that would intercept the sewage overflows from the West Putney Storm Relief Sewer for transfer to the main Tideway tunnel beneath the River Thames. The site was located in Richmond, on the south side of the River Thames between Hammersmith Bridge and Putney Bridge, and adjacent to Barn Elms Sports Centre.

Scope of work

The scope of works included the construction of a 35m deep x 6m internal diameter drop shaft and a 215m long x 3m outside diameter connection tunnel. Surface level works include 6m deep reinforced concrete (RC) interception chambers, an RC culvert and an RC MEICA building, comprising an electrical intake room, telemetry room and control room for system alarms and automated actuated valves installed by the lead contractor. Barhale also built an 800m long, 4m wide access road, and installed additional sections to address Environment Agency and local authority requirements relating to existing flood defences and protected trees in the proximity of the works. The drop shaft’s construction required initial and primary spray concrete lining (SCL), with a secondary cast-in-place concrete lining to encase a new 26m long x 90mm diameter stainless steel vortex drop tube pipe. The shaft was constructed using steel fibre reinforced concrete, applied by an Oruga robotic spray machine as the excavation progressed in 1.2m increments. [caption id="" align="alignnone" width="1200"] (left) Excavation at the shaft base and (right) 2.5m ID tunnel excavator machine (TEM) being lowered into drive shaft - Courtesy of Barhale[/caption]

Detailed mapping and innovative control

Unlike most other Tideway sites, Barn Elms is comparatively small and the connection tunnel drive through the London Clay Formation had to be delivered from a relatively narrow 6m diameter shaft. More than two months were spent preparing a plan and mapping out the tunnel drive route to ensure the team did not encounter any unexpected problems during the drive. The requirement was that the tunnel excavator machine (TEM), which needed to be compatible with 3m diameter jacking pipes, would not have been recoverable from a standard reception shaft as the connection to the main tunnel was right under the River Thames. To address this challenge, Barhale collaborated closely with Tunnel Engineering Services (UK) Ltd to design and construct a TEM whose internal parts could be dismantled, removed and re-used after the project’s completion. The new TEM was brought to site without any engineering guiding systems so the team also needed to address the question of control. Drawing on Barhale’s extensive mining experience, traditional and digital equipment was installed on the machine to control the steer, roll and the pitching degree. Digital pressure gauges were also fitted to ensure that the limit on the jacking pressure was not exceeded. The TEM was steered by four pairs of hydraulic cylinders located between the hood and the machine body. Using information available on the geometry of the TEM and the jacking pipes, plus knowledge of the maximum allowable joint deflection of the jacking pipes, it was calculated that the steering cylinder should not be opened more than 20mm when all other cylinders are fully retracted. [caption id="" align="alignnone" width="1200"] (left) Barn Elms shaft under construction and (right) the 2.5m ID tunnel excavator machine (TEM) being lowered into drive shaft - Courtesy of Barhale[/caption] The TEM roll represents the machine’s rotation about its central axis and there was a continuous tendency to clockwise or anti-clockwise spin. To overcome the issue, inclinometers and laser targets were installed within the machine and used for base readings for roll calculation. Installing the bespoke guidance equipment, and in-detail mapping of every stage of the drive, ensured that the TEM was able to operate effectively and carry out the pipe jack successfully. A further challenge was the safe handling and maintenance of the 14 tonne, 3m diameter precast concrete jacking pipes. To address the issue, Barhale purchased a 20 tonne SWL welding roller to be used as a base stand so that the pipes could be rotated 360°. This solution enabled the team to inspect each pipe thoroughly without the need for access equipment and working at height. It also brought a huge benefit in the preparation of the inter-jack stations. Using this system, the inter-jack hydraulic cylinders could be installed around the circumference of the jacking pipes by the fitters from standing position. Overall, the use of the welding rollers saved the Barhale team time, eliminated the risk of working at heights, and reduced the number of lifting operations. This idea was nominated for a Tideway RightWay award.

Barn Elms CSO Connection Tunnel: Supply chain - key participants

• Main designer & contractor: BMB JV
• Delivery contractor: Barhale
• Reinforced concrete works/formwork: Flatley Construction
• Secondary lining shuttering: EFCO UK
• Spray concrete lining: Shotcrete Services Ltd
• Steel fibre reinforced concrete: CEMEX UK
• Tunnel boring machine: Tunnel Engineering Services (UK) Ltd
• Precast jacking pipe segments: Macrete (Ireland) Ltd
• Stainless steel vortex generator: BMB JV
• Stainless steel vortex drop tube pipe: BMB JV
• Precast concrete cover slabs/planks: Barhale
• Ventilation/odour control: Specialist Plant Associates
• Demolition robot: Brokk Global
• Robotic concrete spray machine: MEYCO Oruga

[caption id="" align="alignnone" width="1200"] Shaft cover slab under construction - Courtesy of Barhale[/caption]

Challenging tunnel construction

The tunnel was constructed using a pipe jacking technique in which the TEM was attached to a muck conveyor. The pipes were jacked continuously from the drive shaft as the excavation of the tunnel face progressed. This was a relatively large pipe and the team encountered a significant challenge about 30m into the pipe jack when small cracks were identified in nine of the eleven pipes that had been installed. The defective sections needed to be replaced. The two un-cracked pipe sections were at the rear of the pipe jack and had not entered the ground so were relatively easily removed, however, it remained necessary to remove the other nine sections. This would only be possible by breaking out the pipe sections. A recovery strategy was developed which was centred on the fabrication of a bespoke shield which could be jacked along the line of the existing cracked pipes. A special hood was devised which, as the shield moved forward, would pass above the damaged sections providing support to the tunnel roof. It would protect the workforce and equipment and allow work on the removal of the pipe sections to begin. A further consideration was that damage to the original concrete lead pipe meant it could no longer be used. It would have taken too long to recast a new concrete section so the steel shield was also designed so that it could be jacked in and used as a replacement. To start the recovery, each of the individual damaged concrete pipe sections was circumferentially and longitudinally cut into small sections. The breaking out was carried out by a Brokk demolition robot which moved down the existing pipework ahead of the shield. [caption id="" align="alignnone" width="1200"] (left) The probe drill in use, forward probing of the tunnel face before full excavation as part of the WPP and (right) temporary support from within the sacrificial outer skin of the TEM once the tunnel drive was completed - Courtesy of Barhale[/caption] Once each concrete section had been broken out, the Barhale team could move in and pull the concrete from the invert back to the pit bottom for removal. Positioning the Brokk in advance of the shield meant that the removal of the material was not impeded. Proceeding section by section, it took two and a half weeks to reach the TEM. Removal of the damaged lead pipe revealed that, under the pressure of sitting stationary in the ground for five months while the recovery strategy was devised and implemented, the tail skin of the machine had deformed more than anticipated. By restarting and moving the TEM followed by the recovery shield forward into virgin ground, the Barhale team was able to relieve the pressure on the tail skin. This permitted the removal of the hood and the docking of the steel lead pipe after which the drive could be restarted. Replacing the damaged reinforced concrete pipes created quite a challenge, but with the support of the project team, a pioneering solution to change the cracked pipes was developed. The recovery shield that Barhale developed not only enabled the damaged tunnel to be replaced but also enabled access to the TEM face where repairs and enhancements had to be conducted. Additionally, the purpose made tunnel shield was designed to allow complete dismantling upon completion of the tunnel drive, allowing the final connection to the main tunnel.

Secondary lining

The pipe jack was followed by a cast-in-place secondary liner to the pipe jack tunnel. Barhale worked with suppliers to design and procure an automated tunnel liner system that significantly improved the quality of the tunnel secondary liner. [caption id="" align="alignnone" width="1200"] Secondary lining shutter in place within the sacrificial TEM outer skin at the junction of the main Tideway central tunnel - Courtesy of Barhale[/caption] This consisted of a specialist automated tunnel formwork system that would ensure the tunnel secondary lining was constructed efficiently by pouring each section in one pass. This improved quality by reducing the number of construction joints compared to more traditional methods. As the equipment is fully automated, the hydraulic stop ends ensure a robust seal when pumping concrete. A mechanical travel system enabled quick set-up for each subsequent pour with minimal resources and it removed the need to manually strike and reconstruct formwork for each section of the lining.

Designed for life

The client required 120-year design life for the precast concrete jacking pipes. To achieve this, Barhale’s engineers worked closely with the client’s designer, materials engineers and precast experts to develop a detailed quality assurance system that included concrete mix trials and quality audits at our supplier’s facility. In addition, Barhale implemented a stringent quality control regime that covered the pre- and post-pouring of the pipes, curing, handling and transportation of the pipes. Carrying out the works required excellent stakeholder management throughout. Heavy plant deliveries were required to fall within stringent Tideway traffic management plans. Thorough planning and consultation with the supply chain, client representatives and third party stakeholders were also key for excellent HSE performance. Barhale supported BMB with meetings and workshops with asset protection teams, Thames Water, the Environmental Agency, the local authority and local council groups. [caption id="" align="alignnone" width="1200"] Shaft cover slab under construction - Courtesy of Barhale[/caption] Peter Leyton, Construction Director for the BAM Nuttall Morgan Sindall Balfour Beatty JV, praised the Barhale team for its hard work and effort in getting the TEM to the main tunnel connection:

“The resolution in the team, to come from where we were earlier and then to work through all the issues that were put in the way, is a huge testament. Also, the control of the movement in the main tunnel has been excellent and a great reflection on the efforts put in by all of the team.”

Located in south Devon, Galmpton STW treats foul water for the hamlet of Galmpton and the surrounding catchment, including the coastal village of Hope Cove (Inner Hope Cove and Outer Hove Cove) about 1km away. As is typical with several coastal hamlets and villages in the West Country, the catchment regularly deals with significant rain events that run the risk of potentially overwhelming the outlying pumping stations; resulting in spills that may have a detrimental effect on the bathing water quality. The Hope Cove area is no different and Galliford Try was selected to support a multi-disciplined multi-contractor strategy to ensure that the local bathing waters, which are extremely important to locals and tourists alike, were protected despite increased numbers of storm events now and into the future.

Location

The South Devon catchment comprises of a small inland hamlet, Galmpton, and two larger villages, Inner Hope and Outer Hope, which are joined together along the shore at Hope Cove. Hope Cove consists of two sandy bays, also named Inner and Outer Hope. As the name suggests, Inner Hope is more sheltered and is home to a small harbour tucked away behind the rocks at the northern end.

The northernmost beach is generally the more popular of the two, benefitting from a seasonal lifeguard service. Both beaches are sandy and backed by the red sandstone cliffs familiar to this part of Devon.

[caption id="attachment_10756" align="alignnone" width="1200"] Aerial shot showing Galmpton STW on the right and rising main scar through the fields on the left - Courtesy of Galliford Try[/caption]

Project strategy

The intention was simply to enhance the system, enabling more combined flows to be sent to the works, protecting storage in the network for longer, and preventing spills. The strategy was to be a combination of surface water separation, which removes rainwater (collected by impervious areas such as roads, driveways and roofs) from the sewer network and delivered by infrastructure partners Glanville Environmental, enhanced upgraded pumping stations, a new rising main and additional stormwater storage at the works, allowing for treatment through the unaltered works once the storm event had subsided.

Objective

To meet the Water Industry National Environment Programme (WINEP) for Bathing Waters in North Devon driver, which was for Galmpton STW to have an average of no more than two spills per bathing season greater than 50m³ in aggregation with Outer Hope Pumping Station, Galmpton Hope Cove STW SSO and Inner Hope Pumping Station CSO/EO.

Scope of works

The Galmpton STW Bathing Waters Project was awarded to Galliford Try who undertook the following:

1. Significant enhancements to Outer Hope Cove Pumping Station: Following a catchment model study, it was decided that the significant enhancements to the Outer Hope Cove Pumping Station, required for the overall scheme, would gain an early benefit as the pre-construction phase was being completed for the more complex elements of the strategy.
2. New rising main from Outer Hope Cove to Galmpton: Following the successful increase in flows to the works and away from the shoreline, Galliford Try installed a new 180mm diameter PE rising main. The 1km long pipeline from Outer Hope Cove SPS to Galmpton STW threaded through and under the historical fishing village and across farmland, outside of the tourist season.
3. New 700m³ of below-ground stormwater storage: Galmpton STW had stormwater storage tank with pumped return which needed to be replaced. Above-ground tanks were discounted in favour of a below-ground shaft given the natural beauty and sensitive nature of the location. In parallel with the rising mains works, Galliford Try installed a below-ground shaft storage tank at the sewage treatment works fitted with tank cleaning flushing bell and storm return pumps.
4. New mechanical screening: A new MecMex screen was installed on the inlet flow balancing tank to ensure all flow to the new tank and overflow were screened to 6mm.
5. Inner Hope Cove Pumping Station upgrade.

[caption id="attachment_10754" align="alignnone" width="1200"] Galmpton stormwater storage tank following the installation of the flushing bell and air valve release pipework - Courtesy of[/caption]

Programme

Work started in September 2022 with the set up compound located in field adjacent to Galmpton STW. In October 2022 Galliford Try started on the rising main up through the Rossiter Estate. By January 2023 Galliford Try started the rising main works through Outer Hope Cove village, which was completed by mid-March 2023.

Active Tunnelling started work on the 12m diameter, 11m deep shaft on 2 February 2023, and the shaft base and pump sump with temporary return pumps were completed on 31 March. The shaft roof was installed on 20 April, and permanent pumps and MEICA completed in May. By June 2023, Inner Hope PS had been upgraded and Galmpton STW was reinstated and handed back to South West Water.

Galmpton Catchment: Supply chain - key participants

• Principal designer & contractor: Galliford Try
• Civils design: Pell Frischmann
• PCC shaft design & construct: Active Tunnelling Ltd
• Surface water separation: Glanville Environmental
• Site investigation/ground surveys: AGS Ground Solutions
• Traffic management: Amberon Ltd
• Installation of rising main: AT Group (SW) Ltd
• Rising main pipe: Burdens
• Precast concrete shaft segments & roof beams: FP McCann
• MecMex screen, flushing bell & pipework: Eliquo Hydrok Ltd
• Pumps: Pump supplies Ltd
• Storm tank return pumps: Xylem Water Solutions
• Tarmac reinstatement works: Walton Civil Engineering & Surfacing Contractors

[caption id="attachment_10753" align="alignnone" width="1200"] Storm tank roof installation main beam lift - Courtesy of Galliford Try[/caption]

Social local economic value

The project design showed this scheme would reduce stormwater spills to under two per bathing water season. All stormwater spills would also now be settled and screened, meaning that the two beaches at Inner Hope and Outer Hope should experience less spills, and a much higher quality of water, both now and into the future given the weather modelling horizon of several decades.

In the summer months these beaches are very popular with tourists and used continually through the winter by local surfers and cold-water swimmers.

Risk management

The biggest risk was being able to get all the large plant and equipment required to construct such a large below ground tank onto the very remote site. There were many tiny lanes and poor access routes roads. Galliford Try often planned the large plant movements over night while marshalling the lanes. During the rising main installation, Galliford Try had to lay the new main up an existing road which was only wide enough for one car width. With agreement from the local traffic management officer, we had to run a give and take arrangement with an escort.

[caption id="attachment_10758" align="alignnone" width="1200"] Galmpton storm tank with the precast concrete roof installed - Courtesy of Galliford Try[/caption]

Stakeholder management

There were a number of local residents very interested in the project which Galliford Try’s Client Liaison Officer managed by a forum and weekly updates, our rising main works did impact a number of properties and restrict access. Galliford Try regularly informed and talked to the landowners and residents on a daily basis to ensure they were happy. The scheme did receive a number of emails from local residents concerned about the works and how they would be impacted, again Galliford Try’s project team dealt with all the issues through the forum and talking with the people involved.

Carbon savings

There were significant carbon savings on this project. With agreement from Rossiter Estate, all spoil from the shaft was used to re-profile part of the adjacent field removing undulations against the South West Water boundary. This removed all muck away (90-100 muck wagons) with the additional benefit of significantly reducing traffic through the village.

Conclusion

Galliford Try’s project team managed to get a temporary system up and running before 31 March 2023, ensuring another regulatory compliance date was achieved for the client and the main scheme was handed over to South West Water in June 2023 in line with contract programme.

The Harbour Master at Outer Hope said:

“I have noticed a huge improvement in water quality in the coves and on the beach, which was already of a high standard".