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Vyrnwy Aqueduct Modernisation Programme

Project Location:

Various

Client Name:

United Utilities

Project Description:

The Vyrnwy Aqueduct programme is a major refurbishment of one of United Utilities’ oldest and most strategic clean water assets. Constructed between 1881 and 1938, the three 42” diameter mains have supplied water to millions for over a century.


Phase one, completed in September 2024, focused on high-pressure jetting, cleaning, and seal repairs on the 42” steel main (Line 3), alongside the installation of new sluice valves, bulk supply points, and crossovers. Phase two is now underway and involves the slip-lining of the remaining 42” cast iron mains (Lines 1 and 2) using 900mm PE (SDR17/21/13.6) pipe.


This essential work follows a prohibition notice issued by Ofwat and is scheduled for completion by December 2028.

Key Stats:

  • The three pipelines were originally constructed between 1881 and 1938.

  • Each line isolated individually – only one pipeline worked on at any given time.

  • Works include jetting, sealing, valve replacement and 900mm slip-lining.

5 Years

Duration

Challenge

  • Gaining access to legacy pipelines for jetting and repair works.

  • Failure of ageing valves and associated apparatus.

  • Acceleration of slip-lining required to meet regulatory ODI targets.

  • Minimising customer impact throughout delivery.

  • Ensuring safety during handling and refurbishment of large, ageing pipes.

Solution

  • Developed and installed a welded manway to enable safe access, re-sealing, and future inspections and maintenance.

  • Replaced seized air valves to ensure reliable recommissioning of each line.

  • Invested in the UK’s largest pipe pusher to enable 2km slip-lining operations.

  • Procured a suite of specialist 42” equipment, including rapid window cutters, rotary cutters, and 900mm pipe handlers with a power pack.

Outcome

  • Strong collaboration with United Utilities to deliver end-customer-focused outcomes.

  • Avoided a major road closure and a 1-hour detour through innovative use of a pipe pusher.

  • Set a UK record for longest pipe push on a 900mm PE line.

  • Enabled United Utilities to exceed its Ofwat ODI performance commitments.

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