Mayflower Water Treatment Works

A major new treatment works to support sustainable growth in and around Plymouth has seen collaboration put front and centre of water engineering.

With a growing need for sustainable and climate resistant capacity in the region as the population and economy grow, Mayflower water treatment works became a flagship project for South West Water as it looked to support the population.

This new works costing £60million to serve Plymouth and the surrounding area. It replaces the 1950s Crownhill works and uses suspended ion exchange with resin regeneration system, and ceramic membrane microfiltration.

A project of this scale and innovation raised concerns, however, that delivering such a major project might reduce the available capacity and cohesion needed to deliver its broader baseline of work across the Framework.

As a result, a partnership approach was proposed, with Pell Frischmann and Arcadis working together as the H50 Alliance to share resources and specialisms across the project.


To make the Alliance work and to ensure it developed as an alliance of equals, Pell Frischmann and Arcadis co-located staff. Pell Frischmann provided a MEICA Design Manager while Arcadis provided a Project Manager and Civils Design Manager, and each discipline had a team of specialists drawn from across the two companies.

The partnership has proven a great success.

From feasibility to detailed design work, this major development has benefited from a very high level of engagement by the client. By combining software and other resources as partners in the alliance, we have been able to provide South West Water with the best possible people working on all parts of the project at all times.

This had big implications for the firms as they worked with supply chains, the client, and each other.  Rather than information being funnelled through a formal hierarchy of sub-contractors, contractors, and client, there was a multi-directional exchange with all partners able to discuss project developments and opportunities together.

As a result, the design process was undertaken smoothly, with extremely strong interaction at all levels with the client thanks to combined expertise being available at all times in one place. The use of highly advanced BIM modelling was particularly valuable in this regard, as a tool for not just design and implementation, but for communication and examination with the client and contractors.

The project also benefited from an unprecedented level of personal interaction between engineers across the two companies, and the development of a remarkable BIM model enabled South West Water to talk through every aspect with all of the right people around the table, rather than a tier one contractor serving as a channel between client and sub-contractors. 

Ground material challenge

Along with the scale of the project, the ground itself threw up a significant technical challenge  

Pell Frischmann undertook three-dimensional computer aided settlement modelling to determine the ground improvement required to return an acceptable settlement response to multiple and locally complex foundation arrangements.  

A particular concern was that ground rock was argillaceous - slate shale type material – which exposed to water degrades into a clay material unsuitable for foundations. This presented two challenges. First, contractors had to be educated about the long-term implications so that this rock was not used beneath foundations. This was done with a report into weathering on the material, and a series of site visits, education, and research programmes to ensure people recognised the material in question.

Having done that, an alternative rock base was needed. This was aided by our computer modelling with could identify weak zones of bedrock and thick zones of overburden by materials not suitable for foundation materials. That enabled us to plan what material would need to be brought onto site, and what would be dug out on site.

Expanding collaboration

The design work was such a success that South West Water has continued with the same approach on the procurement, construction, and commissioning phase of the Mayflower project, with Balfour Beatty and Interserve working in alliance with each other.

Beyond the water industry, Pell Frischmann has taken inspiration from this success and have built an alliance approach in transport, where the Midland Metro Alliance has brought together design partners, contractors, and the client under one roof (literally) for the delivery of an expanded tram network in the midlands.


  • icon-arrow250,000 - people around the Plymouth area
  • icon-arrow55 - Mili Litre of water per day, with a capacity of 90ML per day
  • icon-arrow£60 - million of investment by South West Water

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