Millennium Main, Greenwich Peninsula, London

Client: Thames Water

Partners: Mgroup Water, DWG Infraco & Aecom

Project Duration: June 2023 – Ongoing

Project Overview

The Millennium Main is a critical 1000 mm trunk main transporting potable water from Nunhead Reservoir to Deptford, supporting population growth and long-term supply to the Greenwich Peninsula. Sections of the pipeline run through tunnels, where historic failures and deterioration of glass-reinforced plastic (GRP) pipes had been recorded. Extensive blistering raised concerns over structural integrity and long-term serviceability.

Working alongside M Group Water, DWG, AECOM & Thames Water initiated a major rehabilitation programme to identify a cost-effective, low-risk solution capable of extending asset life while maintaining hydraulic performance. The resulting project forms part of a £21 million investment to rehabilitate the trunk main using an innovative hybrid lining system - VIP-WECO PROLINE.

The Challenge

Early investigations identified uncertainty around the condition of the pipe annulus grout, a key factor influencing the remaining strength and longevity of the GRP pipes. Traditional methods for accessing and repairing annular voids carried significant risks, including additional stress on the pipe wall, increased drilling, and extended confined-space working.

The challenge was to develop a solution that could identify, access, and reinstate annular voids without compromising the pipe, while meeting potable-water compliance requirements and delivering whole-life value.

The VIP-WECO Solution

Advanced Pipe Penetrating Radar (PPR) and geophysical techniques were deployed to accurately assess the condition of the annulus and pinpoint void locations. Material testing confirmed that, with full annulus reinstatement, the GRP pipes could achieve more than 30 years of additional asset life.

Following a review of available rehabilitation options, a hybrid liner approach was selected, balancing cost, constructability, hydraulic performance, and programme risk. As part of this system, VIP-WECO seals were identified as a critical component in delivering a secure, compliant, and durable solution.

Working in collaboration with AECOM and project partners, VIP Polymers modified the VIP-WECO PROLINE Hybrid sealing system to meet the specific demands of a potable-water trunk main. This included achieving Regulation 31 approval, marking a first for this application in England and Wales.

The solution enabled the use of Bacel® Hardform to reinstate annular voids while maintaining structural integrity, significantly reducing the number of grout holes required. The adapted VIP-WECO Proline sealing system played a key role in enabling this approach, delivering estimated savings of £15–20 million compared with traditional methods.

To de-risk delivery, a full above-ground mock-up of the hybrid liner system was constructed, allowing installation methods, sequencing, and safety considerations to be validated before live works commenced.

Delivery and Results

Installation of the hybrid liner system began in June 2023, with works carried out by qualified operatives trained in high-risk confined-space environments. A total of 973 VIP-WECO PROLINE hybrid liner units were installed, with each unit air-pressure tested to confirm leak tightness.

Key benefits and outcomes included:

Significant reduction in confined-space working
Introduction of an innovative sealing solution with a design life exceeding 150 years
Successful asset approval through close collaboration between client and partners
Reduced drilling and intervention, minimising further risk to the GRP pipe
Delivery of a sustainable, future-proof rehabilitation strategy

The Millennium Main is currently programmed to return to service in August 2025.

“By working collaboratively with our client and partners to tackle a major challenge, we challenged our own processes and asset standards to deliver a cost-effective, sustainable, and safe solution.”
Nigel Butler, Contracts Director – M Group Water