The West Walton scheme, delivered by Barhale for Anglian Water @one Alliance, has now progressed into the commissioning stage and close to completion. All civil engineering work on site has been completed. This marks a significant milestone in the project and reflects the team’s dedication in overcoming a range of complex challenges to bring the site into regulatory compliance.

The scheme was essential to bring the site into compliance with its regulated Flow to Full Treatment (FFT) consent, a measure of how much wastewater a treatment works must be able to process at any time. Historically, West Walton could only treat 360–370 litres per second due to limitations in the existing equipment and infrastructure. This led to storm tanks filling earlier than permitted, resulting in non-compliant spills. The new requirement is to treat 464 litres per second a 29% increase on the original capacity — and the project was developed to ensure the site can now meet this standard.

To enable the increased FFT, three redundant Intermediate Settlement Tanks were structurally surveyed and fully refurbished. Two of these have been converted into Primary Settlement Tanks, while the third has been repurposed as a fourth Final Settlement Tank (FST), increasing the site’s treatment capacity alongside the three existing FSTs. Given the spatial constraints of the site, reusing existing assets was a practical and sustainable solution that minimised the need for new construction. This approach not only helped overcome space limitations but also supported wider sustainability goals by promoting the reuse of infrastructure and reducing carbon impact. Additional works included the installation of a new distribution chamber, connection pipework, a UMON 4 flowmeter with an eccentric plug control valve and bypass, and the diversion of returns liquor pumping flows into the new system. New de-sludging pumps were installed to transfer sludge to a newly constructed 180m³ buffer mixing tank, supported by upgrades to the intermediate pumping station, which now includes three pumps capable of delivering the required 464l/s.

The project also delivered a new 1000m³ sludge centrifuge tank with a pumped mixing system, new strain press sludge screens and feed pumps, refurbished Return Activated Sludge (RAS) pipework and concrete pads, and a new MCC kiosk installed on a steel platform. A hot tap was completed on the existing oxidation ditch to tie into the new FST feed, and new scum, Surplus Activated Sludge (SAS), and sludge pipework systems were installed to integrate with the improved treatment process.

The project faced major challenges, one being that Barhale was required to take over as Principal Contractor on 9th October 2023. The scheme was already behind schedule and operating without a fully developed design. The site was split into four design zones utilising Building Information Modelling (BIM) and work could not proceed in each zone until designs were signed off, resulting in further delays. As a result of the project encountering in excess of 300 services, the majority of which were unchartered, ongoing design revisions and disruption to Tier 2 contractor activities occurred.

Throughout the project lifecycle, Barhale managed a range of challenging operations, including deep excavations, extensive crane lifts, specialist tank refurbishments, plastic welding, and complex live flow diversions. A full site power switch-over was also completed over five days using a temporary generator.

The successful delivery of the West Walton scheme reflects the project team’s ability to overcome significant challenges while maintaining a clear focus on compliance, quality, and collaboration. Despite delays and complexities, the team’s commitment ensured that the site is now equipped to meet its regulatory obligations and support the long-term resilience of Anglian Water’s network. This project is another example of the value delivered through the @one Alliance and the strength of its delivery partners.