Client: Severn Trent Water
Date: September 2023 - December 2024
Seven Trent Water (STW) was facing a tight deadline to make essential regulatory upgrades at its Spernal WWTP, a medium-sized sewage treatment plant in Warwickshire.
To deliver the works Costain used Production Thinking – our approach to combining modern methods of construction with new technologies – to ensure that the programme of works could be achieved more efficiently, on time and within budget.
The challenge
To meet the water industry national environment programme (WINEP) regulations for AMP7, STW needed to install a tertiary treatment system at its Spernal WWTP to reduce phosphorus and ammonia levels in the final effluent and clean up local rivers.
This required the construction of a number of critical infrastructure assets, including:
- A Motor Control Centre (MCC)
- 2.5km of ducting with 23 concrete draw pits
- Chemical dosing plant
- Moving bed biological reactor (MBBR) plant
- Comag Tertiary Solids Removal (TSR) Plant
- Two pump stations
What is production thinking?
At Costain, we use Production Thinking to achieve predictable, best-in-class delivery of infrastructure projects. It combines modern methods of construction with new technologies and materials, digital tools and smart decision-making to boost productivity and efficiency across all of our infrastructure projects.
The approach, developed in line with guidance created by the Construction Productivity Taskforce, covers all stages of a project lifecycle:
- Pre-manufacturing – boosting offsite and modular construction and embedding principles of established methodologies such as the design for manufacturing and assembly (DfMA)
- Operational efficiencies - utilising new technologies and materials and application of lean tools.
- Automation – the adoption of AI and robotics.
In order to deliver the necessary infrastructure upgrades on time and within budget at Spernal, Costain implemented a number of innovations designed to improve efficiency of the delivery, without compromising on safety.
Modularisation to reduce onsite assembly time and increase safety
To construct the new Motor Control Centre at Spernal, Costain recommended a DfMA approach. This engineering method was effective in significantly reducing the onsite assembly time, improving the quality of the end-asset and construction safety.
The ‘plug-and-play’ MCC was rapidly assembled on-site, with the high-quality steelwork completed in just three days with the kiosk assembled in just one day. In addition, the structure required only minimal excavation, with a 30m3 flat concrete slab used in favour of a traditional buried concrete bund. Not only did this enable the foundation base to be blinded, fixed, shuttered, and poured within just 48 hours, but it also meant that the MCC was installed without affecting the existing wastewater services that were in operation and situated in close proximity to the site.
The efficiencies gained through taking a DfMA approach resulted in a 65% reduction in time to complete the MCC, falling from 16 days to just six days.
Standardising concrete draw pits to improve quality and reduce cost
Costain also used Production Thinking techniques to deliver 2.5km of ducting with 23 draw pits in just eight weeks. Instead of building traditional draw pits in situ, the team recommended using standard ‘off-the-shelf’ precast concrete draw pits. By standardising all 23 draw pits, the scope of works was reduced significantly, meaning that two draw pits could be fully installed every day, including excavation, foundation, backfill and cover slabs. This meant that, despite the material cost of the precast draw pits being higher, the overall cost of delivery was 40% cheaper than using traditional methods when combining the total labour, plant and material costs.
In-house lifting for greater control and efficiency savings
Given the complicated location of the site and tight footprint, which was adjacent to a number of live services, it was important to maintain close control of all of the project’s lifting procedures. All lifting plans were brought inhouse, improving efficiency by avoiding duplication of effort and paying a premium for ‘contract lifts’. It also meant that Costain could improve safety standards by having greater control of important lifting safety procedures - Hands off, Step Away, Safe Space (HOSSAS) – developed by Costain and now adopted across the industry.
Using connected and automated plant equipment
Costain used remote-controlled Tracked Carriers to transport material across the site safely and efficiently. The emissions-free machines, travelling at a maximum speed of 3mph, could transport up to four tonnes of materials and equipment to hard-to-reach areas.
Predictable, best in class delivery
- Only 16 months to deliver all project scope requirements ahead of the regulatory compliance deadline
- 65% reduction in time to complete the MCC, falling from 16 days to just six days
- 30,000 tonnes of excavated material
- 2.5km of ducting and 23 draw pits installed at 40% cheaper rate than traditional methods
- 350,000+ hours worked with no workplace incidences.
- 30+ subcontractors worked with across the supply chain, with the majority based locally
Creating a sustainable future
675
Litres of water per second is treated to reduce ammonia and phosphorus, resulting in cleaner local rivers
>15%
Biodiversity net gain
130
Tonnes of CO2 mitigated through on-site delivery
“Costain brought excellent energy and innovation to this project. We were particularly impressed by the speed and quality of the work delivered, and how the team was able to adapt quickly when challenges arose. The results speak for themselves, and the team has set a high bar to deliver high quality infrastructure upgrades quickly and safely.”
Shahzad Mehmood Project manager at Severn Trent Water
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