St Saviour’s Treatment Works

ST SAVIOUR’S WATER TREATMENT WORKS

Guernsey’s water supply is a lifeline for the island. But ensuring the population has clean and safe water on tap takes a lot of work behind the scenes. Guernsey Water is currently undertaking a major project at one of its main treatment works in Guernsey – a £2.5million refurbishment at St Saviour’s.

Guernsey Water’s St Saviour’s site encompasses a key water treatment works along with the island’s only impounding dam and the landmark large reservoir. It’s also home to a popular walking trail for islanders. But those enjoying a peaceful walk may notice even more activity than usual down at the plant – there is a major refurbishment ongoing at the site.

Mark de la Mare is a project engineer at Guernsey Water, who is heavily involved with the project. He explained why they are working on the treatment plant.

“The St Saviour’s water treatment works has used membrane technology since 2004. Those membranes were renewed during 2012-2013 and had a life expectancy of around ten years. The membranes are nearing the end of their asset lives and it has been taking a lot of man hours to keep the treatment works operating correctly. “St Saviour’s is one of our three main treatment works in Guernsey, along with King’s Mills and Juas, which was brought back on-line when Longue Hougue was taken out of commission. Both Juas and King’s Mill use rapid gravity filter technology so that was clearly something we looked at when it came to refurbishing St Saviour’s.”

Prior to the installation of the membrane technology, a rapid gravity filter system had been in place at St Saviour’s as well. So, working in conjunction with UK consultants, Guernsey Water assessed their options. Due to the set-up of the treatment works and the civil structures that currently exist there, they decided to explore two viable options – either replacing the existing membranes or converting the plant back to the conventional process of rapid gravity filtration. When those options were compared against resilience, water quality, sustainability, operability and

whole life cost, it was decided that a rapid gravity filter system was the correct solution for the site. That ‘new’ process would involve reverting to the site’s former setup – but with some modern improvements, as Mark explained.

“The use of rapid gravity filters is a well-established process that has been used for a very long time, but there are ways to make it even more effective. The St Saviour’s site will revert to its original process but will now also incorporate UV disinfection, which didn’t exist when it was converted to membrane technology. It means that we can use a proven, effective process but also have the reassurance of UV treatment. It’s the approach we have taken with both King’s Mills and Juas, and it made the most sense here.

“When the membranes were installed, the system was one of the only options that provided a reliable barrier to cryptosporidium (the cause of a diarrheal disease). Now, with the advances in modern technology, UV disinfection also provides an equally effective level of protection, while also allowing the use of the more costeffective conventional process.”

For Guernsey Water, using the same technology at all its treatment works clearly has benefits and Mark said the utility is looking to take advantage of its staff’s existing expertise when it comes to this project.

“We would often go out to tender for major projects like this, but for the St Saviour’s works we are doing the majority of work in-house. Our mechanical fitters who are usually responsible for our operational maintenance will also be undertaking this work. They completed similar projects at Juas and King’s Mills so they certainly have the expertise and the experience, but this job will be even more challenging.” Those challenges arise because the treatment works has to stay on-line during the course of the project. When Juas, for example, was being brought back online, the Longue Hougue works it was replacing was still in production. At St Saviour’s a phased approach will mean that parts of the site are worked on while others are still online. It will be a tricky balance between maintaining output but also allowing the project to progress efficiently.

The phased nature isn’t the only obstacle – Covid has also caused issues with the £2.5million project. A 3D walkthrough of the works needed to be completed for the UK consultants to use as they couldn’t visit the island in person. Specialist contractors will also need to be brought in for areas such as installing the filter floors – while procurement is also an issue. But Mark said they have managed the risks as much as possible.

“We approached this project in a different way to how we would usually manage it and ordered the majority of items, such as the pumps etc., upfront to ensure that they will be here when we need them. As well as the problems caused by Covid, Brexit has caused issues with getting the equipment we need to the island. But we are progressing well at this stage.”

While Guernsey Water is still finalising the detailed design and some aspects of the project, construction started on site in June. The original timeline aimed to have the conversion completed by summer 2023, but that may change as the project progresses. What won’t change is the end product for consumers – while the project is a major one for Guernsey Water, they believe it will go unnoticed by islanders as the taste and quality of the water supplied by St Saviour’s is not expected to be affected.

Before AT ST SAVIOUR’S A PHASED APPROACH WILL MEAN THAT PARTS OF THE SITE ARE WORKED ON WHILE OTHERS ARE STILL ONLINE. IT WILL BE A TRICKY BALANCE BETWEEN MAINTAINING OUTPUT BUT ALSO ALLOWING THE PROJECT TO PROGRESS EFFICIENTLY.