Barhale has secured a major infrastructure contract from Thames Water to undertake essential refurbishment works at Ashford Common Water Treatment Works in Surrey, helping to safeguard one of the capital’s most important drinking water supplies for years to come.
The project will see Barhale reline a key abstraction tunnel that forms part of the West London Abstraction system, which supplies raw water from a network of reservoirs feeding the Ashford Common treatment works before distribution across London.
The contract follows detailed inspections carried out by Barhale’s specialist Tunnels & Aqueducts team as part of the mandatory five-year inspection programme. Engineers identified inconsistencies within the Southern Inlet tunnel’s existing glass reinforced plastic (GRP) liner, which, if left unaddressed, could compromise the underlying wedgeblock tunnel structure.
Following a successful Early Contractor Involvement (ECI) phase, Barhale worked closely with Thames Water to refine the engineering design and develop practical construction solutions capable of overcoming the significant access constraints created by the site’s complex network of underground tunnels and utilities.
Construction will begin with the excavation of a three-metre-deep access point to expose the tunnel’s chimney and riser. Sections of the existing riser will then be carefully demolished to provide safe access to the tunnel invert, located almost 20 metres below ground level.
Once access has been established, specialist scaffolding systems will be installed throughout the tunnel, enabling engineers to safely remove the existing GRP liner. The team will then excavate the surrounding grout and concrete before constructing a new reinforced concrete lining designed to restore the tunnel’s long-term structural integrity and resilience.
The refurbishment forms part of Thames Water’s ongoing investment in maintaining critical water infrastructure and ensuring the long-term reliability of assets that support millions of customers across the capital.
Barhale is already familiar with the site, having previously completed a localised repair within the Northern tunnel following issues identified during earlier proactive inspections. A more comprehensive relining programme for that tunnel is also planned as part of future investment works.
The latest contract highlights the growing importance of asset renewal across the UK’s ageing water infrastructure, where proactive inspection, engineering expertise and targeted refurbishment are helping utility providers extend the lifespan of critical assets while maintaining resilient water supplies.
By combining detailed structural assessment with specialist tunnelling capabilities, the project will ensure Ashford Common Water Treatment Works continues to play a vital role in delivering safe, reliable drinking water to London while supporting the long-term resilience of one of the UK’s most important water networks.
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