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Alexandria Membrane

Client: Scottish Water
Project: Alexandria CWT No.2
Location: Alexandria, West Dunbartonshire
Timeframe: 9 Weeks (3 Weeks for Membrane install, rest for proprietary works)
Team experience at Mackenzie: 42 years

Key project features:
Tank corrosion – concrete tank refurbishment
Automated asset integrity
Sensor technology
Reducing carbon emissions
Provide water quality confidence

The background
With the water industry striving to digitise its operations across the board, Mackenzie Construction, approached Scottish Water with a new and exciting innovation; a geomembrane leak detection system to improve and support smooth management and monitoring of their clean water tanks in West Dunbartonshire.

The challenge
With the type of longstanding, reinforced concrete tanks operating at this location, often damage can occur because of weather exposure, corrosion, age or trespassing, and any ingress within the tank risks contaminants entering clean, treated water. Tank integrity is most often validated using flood testing; where a controlled amount of water is temporarily retained over a surface to determine the effectiveness of the waterproofing system. This is feasible when tanks are offline and empty, however, waiting for an outage to inspect tanks for damage can greatly increase risk to the asset and the whole network. This also requires the need for people, and travelling between sites, increasing the carbon footprint of asset integrity operations.

The solution
Working with its supply chain, the team developed a strategy and sought out the most appropriate technology, installing the protective membrane to a Scottish Water clean water tank as part of an ongoing structural repairs project. To enable this, the deck drain (a geocomposite drainage sheet with HDPE cuspated core and non-woven polypropylene geotextile) was installed on top of the intelligent system and covered with 20/40mm washed rounded drainage stone overburden.

The first of its kind on Scottish Water tanks, the intelligent membrane is positioned over the tank to protect the treated water inside. Made up of layers of metallic fleece and impervious, plasticised PVC and encompassing a network of sensors wired to an automated fault-finding system, the membrane’s monitoring system is programmed to send an email alert as soon as any damage is detected, as well as sounding an audible buzzer at the control panel on-site.

Future defects will be identified by the systems leak detection system. This allows the membrane to be repaired as defects happen, without the costly removal and replacement of overburden which also poses significant risk of further damage to the membrane. If failures in water quality arise at the asset, fault finding is much easier as only access hatches are not covered by the roof membrane. Therefore, if ingress occurs and the leak detection system cannot locate the leak, then it is likely that the route of ingress, is through upstand interface or cover. Flood testing is also no longer required on the membrane, as electronic flood testing can be carried out instead, minimising risk of ingress caused by the contractor. In most cases, defects in the membrane are easily sealed with extruded butyl rubber or patches, with the expected service life within a 30-year warranty for buried materials.

Added value
With the solution provided by Mackenzie Construction and its subcontractors, the intelligent membrane provides constant feedback on the membrane’s integrity, even when tanks are live, to create a proactive, rather than reactive, approach to asset integrity. This type of reactive monitoring allows for localised repairs to be carried out rather than far more significant scopes of works which often involve the large-scale removal of overburden to identify and repair the issues. With a drive on reducing the carbon footprint of projects and helping clients achieve net zero targets, the vast reduction in size and scope of integrity works has significant advantages.

“Mackenzie Construction did a great job in successfully delivering a technically challenging program of works at Scottish Water’s Overton Alexandria water treatment works. Firstly, an internal 3D architectural scan provided a fully comprehensive internal condition assessment. Secondly, the installation of a pilot intelligent geomembrane as used in the oil industry offered a ‘smart’ waterproofing solution which could potentially transform the way in which Scottish Water manages its treated water storage portfolio of assets for years to come. I appreciated their attention to detail, innovative thinking and creative approach to problem solving to successfully reduce the risk to water quality at the site.”

Thomas Ferguson, Project Manager, Scottish Water