Stronsay: Innovative solutions on a small island
ESD Joint Venture
Delivering Scottish Water's non-infrastructure capital programme safely, efficiently, sustainably and collaboratively.
The mission from Scottish Water, which ESD Joint Venture chose to accept, was to help them improve the water supply to people living on the Isle of Stronsay in Orkney (resident population – approximately 349 people). Anyone who is unfamiliar with life in isles like Stronsay will find this story an education in the unique challenges that people in island communities around the world face – and overcome.
The ‘Island Factor’, as it is often known, varies widely from island to island; on Stronsay, it involves a mix of high transportation costs, a fragile ecosystem, a traditional reliance upon imported diesel for energy, and a specialised?economy based upon farming, fishing and a small (but growing) tourism industry.
Orkney and its islands have a strong track record in showing how island communities can innovate new solutions for better living standards and tackling issues like equitable access to energy, water and other utilities. For example, the European Marine Energy Centre (EMEC) is located on the mainland of Orkney, just to the south of Stronsay, with a grid-connected tidal test site piloting some of the most cutting-edge renewable technologies.
Back in 2013, Scottish Water pioneered the use of small wind turbines for powering the island’s water treatment works, which lie close to its central village of Whitehall. Most recently, the ESD team, made up of experts from Galliford Try, MWH Treatment and Binnies, have also found the location one that richly fosters innovative thinking.
Their plan for improving the island’s water supply was to install two new tanks to provide storage, with associated pipework, a new kiosk and draw pits for electrical and data cabling. They also needed to add a dechlorination chamber, which would allow Scottish Water to remove treated water before releasing it, thus protecting the surrounding environment.
Four months and countless litres of water saved
The first challenge for Gregor Matheson, ESD’s Site Manager in Orkney, was to ensure that the project could source its workforce as much as possible from Orkney and the Highlands:
“Logistically, it is quite a struggle to get contractors with the right expertise out on site. I was doing a three-and-a-half hour commute myself to get to site every day by ferry, just to give you an idea of the challenges! There is limited accommodation on the island and the local hotel was seasonal. We used three local companies - Heddle Construction, RS Merrimans & Orkney Builders – backed up by contractors from the Scottish mainland when needed. Our experience of sourcing local has been extremely positive: we found some very good tradespeople here who have got on board with our way of doing things very fast.”
“The maritime climate was much more challenging: it’s quite common for materials to rot down very fast here as the sea salt spray can reach as far as three or four miles inland. People can come out in the morning after stormy weather and it’s almost like a snow shower, leaving white spray across car windscreens. You have to factor that into the planning: what will be the lifetime of a component subjected to this level of corrosion? Having to dismantle and send parts away for refurbishment and respray is often the reality after a few years.”
“High winds can play havoc with planning too – 50 miles per hour is not unusual, even in the summer months. A previous ESD project on nearby Sanday was delayed for a year due to winds stirring up turbidity in the loch and making it impossible to continue work.”
Gregor and his site team’s first job was to install a main concrete slab to hold the two huge 17m long tanks. Water tanks are normally made of concrete, but with no concrete batching facilities on Stronsay, concrete for the base pour was brought to the island by four mixer lorries on the public ferry.
The quantities required for the construction of the concrete tank would have involved bringing out a batching plant to the island. Logistically and environmentally, ESD felt this was a poor option, and began investigating stainless steel as an alternative material.
Working with Shetland’s Ocean Kinetics, ESD planned a smooth, faster and less disruptive solution. Ocean Kinetics fabricated the tanks at their own site in Lerwick. Work was completed in a controlled clean environment, avoiding the harsh elements on site.
Gregor approached Scottish Water's Public Health team and discussed the possibility of changing the planned testing. The new plan was to conduct the bulk flushing, hydrostatic testing and water sampling at the Shetland site too, where they had a bigger water network to source from. This was to minimise the amount of water used on the island of Stronsay and reduce the demand on the WTWs.
After factory testing was complete, a?full suite of contamination tests was carried out on each tank. This is a vital process which ensures that there are no toxic hydrocarbon residues left in the tanks that would be hazardous and hard to remove later on. The tanks were then sealed prior to transportation to Orkney by barge.
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But how to complete testing on Stronsay in an efficient way?
Gregor explains: “We decided to conduct the flushing and sampling at the fabrication site in Shetland. That meant that we only had to fill the tanks once when they arrived here, and gently refresh them to maintain the required chlorine residual level. It also avoided the need of having to produce another 900m3?of water to the tanks on Stronsay. By choosing stainless steel, we not only avoided environmental disruption during the build, but also have a more easily recyclable solution for the tanks’ end of life.”
All in all, the Whitehall DSR project allowed WiS (Water into Supply) in just 84 days too, reducing time and cost as well as environmental impact.
Project Manager Joe Oldroyd added:
“We estimate that by using pre-fabricated tanks, we saved around four months of construction time on site, which is also great for the local community, as it minimises disruption to them too.
“This was a remarkably smooth project given the challenging conditions, and I put this down to the great communication that Gregor established with the people on the island, local council and harbours, who were very helpful. Gregor kept the chain of sub-contractors and Shetland site working to a well-thought-out plan and maintained close communication between everyone throughout.”
The result of the team’s 84 days is to secure a future supply of cleaner water for local people and increase the water pressure significantly for many properties (a result of locating the tanks 2.5 metres higher than the existing tank, utilising gravity).
Thanks to:
Kirsty McCall Carlo Bertoncini and the ESD Design Team
Joe Oldroyd