It was envisaged that the first 40km of this pipeline, made from ductile iron, would loop from Covenham to the Miningsby Reservoir; the second section, constructed from polyethylene and 21km long, would run from there to Boston itself. Altogether, this new system would be able to transport 27Ml/d of treated water to the town.
But our client had set challenging cost and carbon cutting targets: building the scheme in a regular manner would make it very difficult to achieve either.
What did we do?
As a framework partner to Anglian Water’s Special Projects delivery stream, and working as part of a joint project team including contractor JN Bentley, we undertook detailed network modelling and assessment of existing assets. Our findings identified the opportunity to transfer 40% of the required water supply to Boston through existing assets to the south of the town.
This discovery meant that the new system only needed to be able to supply 15.6Ml/day. The remaining 11.4Ml/day could be unlocked from the existing assets, with some enhancements to the infrastructure. This enabled the pipeline diameter to be reduced from 600mm to 500mm for the first 40km, and to 400mm for the last 21km. This approach also allowed us to downsize a new pumping station at Covenham. Careful consideration of the pipeline route avoided the need for an intermediate booster station which may otherwise have been required.
We then analysed possible pipeline materials and installation methods. We selected polyethylene, which offered the lowest cost and embodied carbon, and which allowed for varying thickness in the pipeline wall. By optimising this thickness along the whole length of the route, we minimised material usage and cost, and reduced installation times.
The pipe was delivered in long 18m sections, reducing the number of deliveries by 30%. The choice of material meant that the pipeline was flexible enough to follow the natural terrain far better than iron or steel, which helped avoid additional joints, bends and route diversions that a more rigid pipeline would have needed.
We converted a rock trenching machine to speed excavation and reduce the width of the trench itself, minimising the volumes of excavated and backfill materials handled and reducing the impact of construction on surrounding land. Further time, cost and carbon savings were made by using excavated material as backfill, reducing the need for imported material.
How did we add value?
A traditional solution would have cost £41.5M, with 20,700t of embodied carbon. This solution was delivered for £31.1M, with 8830t of embodied carbon. That’s a 57% carbon saving and 25% cost saving.
What’s next?
Our work with leaders of the emerging low carbon agenda such as Anglian Water was one factor that led the Infrastructure Working Group of the UK government’s Green Construction Board to commission us to research and author a landmark report, the Infrastructure Carbon Review.
Throughout the process we collaborated closely with Anglian Water’s board of directors. We found that if current low carbon best practice, such as demonstrated on this project, was adopted for all UK infrastructure, there would be a £1.5bn/year economic benefit.
We are now working to raise awareness of the practical steps that businesses can take to realise carbon and cost savings, provide advice and technical support, and measure and drive for carbon and cost reductions on every major project we work on.