Water and Effluent Treatment Magazine
Issue link: https://read.utilityweek.co.uk/i/867569
JUNE 2015 WET NEWS 7 Holding back the years • Service reservoirs play a key, if sometimes unsung, role in the supply of clean water. One such reservoir dating back more than a century has received a new lease of life – and despite its technical challenges. the Malpas Service Reservoir. Recent investigations discov- ered water ingress to the tank and the existing brickwork walls were found to be in a poor state. Stonbury, a specialist con- tractor to the water industry, was commissioned to undertake a comprehensive internal refur- bishment together with some external repairs. The project came with a number of challenges – not least carrying out work on the internal roof, where roof vents were allowing in rainwater. This required erecting scaffolding and an extensive area of safety netting. External access to the roof also posed safety risks as the roof had a low load bearing capacity. In addition, the contract came with a tight deadline of just 12 weeks because of the need to get the reservoir back into use to meet the higher cus- tomer demand of water in late spring. UU also specified a very high quality surface internal finish, ensuring that the reservoir will enjoy the maximum service length a„er completion. This raised the contract value to in excess of £500,000, but the higher specification has given the service reservoir an expected 30 years of additional life; against an estimated new build cost of £5M. Stonbury assigned a team of 15 full time personnel to the project, including specialist contractors for the steel fabrication and con- struction of new stainless steel stairs within the reservoir. Spider web effect The project commenced in November 2016 – it was com- pleted in early April this year – with overbanding to the floor joints, applying the longer lengths first while keeping the joints clean ready for the weld- ing. Ultimately, some 3,804m of overbanding were required to ONSITE REfURbiShmENt Applying a total of 3,804m of thoroflex overbanding created a spider web effect in the circular-shaped reservoir Carrying out works on the internal roof required an extensive area of safety netting. Photos: Stonbury A team of specialist engi- neers then undertook a detailed survey of the roof vents (which had been allowing in rain water) and the grating to the floor channel to determine the scope of work required, while the blasting grit was removed from the reservoir floor by another team. By week six of the project, the overbanding to the floor of the reservoir had been success- fully completed, and the inter- nal surface of the reservoir walls, comprising Staffordshire blue engineering bricks, had been sufficiently prepared for mesh to be fixed to the walls I n common with a large number of service reservoirs, Malpas Service Reservoir, owned and operated by United Utilities (UU), dates back many years. The 20.5Ml balancing res- ervoir was built in 1913 close to the village which gave it its name and lies close to the southern border of Cheshire, a few miles from the border with Wales. Then, as now, it formed an important 'staging post' for water flowing from Lake Vyrnwy in North Wales into north-west England. Lake Vyrnwy was con- structed in the 1880s with a capacity of 59.7Gl, originally to supply water to Liverpool via a 68-mile aqueduct constructed by Liverpool Corporation. Other pipelines were subsequently added, and the water from Lake Vyrnwy now forms part of a net- work of sources supplying a much wider area. Roof Today, the Malpas Reservoir helps serve a population across a wide area of Cheshire. And while originally it was built as an open tank for clean water storage, a„er regulations changed, the circular tank was enclosed with a steel-clad roof. Having served its purpose well for more than a hundred years, time had taken its toll on cover the 3,849m 2 of flooring creating a spider web effect in the circular-shaped reservoir. Priority was given to com- pleting the joints near the flume first, so it could be fixed back into position. At the same time, another team commenced grit blasting the walls to prepare them for resurfacing, as well as cleaning the other surfaces, including the steelwork within the reservoir. Work started first on the walls at the lower section, allowing regular checks on the profile to ascertain if the amount being removed was adequate and even. the roof vents had to be refurbished to prevent rainwater ingress