Refurbishment of the Vyrnwy Large Diameter Trunk Main

United Utilities have a massive project to refurbish the Vyrnwy Large Diameter Trunk Main (LDTM). This Victorian water main supplies up to 55 million gallons per day to over 900,000 customers in Cheshire and Merseyside in the North West of England. This equates to 12% of all water supplied by the water company. The existing LDTM consists of three mains each 50 miles long and between 39" and 42" in diameter. The construction of the gravity system started in the 1890's and the first two unlined cast iron mains were installed in under 15 years, a real credit to Victorian engineering. Refurbishment of the Vyrnwy LDTM is formalised within a legal undertaking with the UK Water Quality Regulator the Drinking Water Inspectorate (DWI). The project is being carried out to reduce the risk of supplying discoloured water to customers caused by re-suspension of solids resulting from historic deposition of iron and manganese. These deposits have accumulated as a result of historically high concentrations of iron and manganese in the water supplied from Oswestry WTW, prior to the completion of work to improve the treatment process. Investigations have identified that internal corrosion also contributes to the risk of supplying discoloured water. With a project value of 250m US Dollars a unique approach was required to ensure the correct engineering solution was developed. A full review of all the cleaning and lining techniques available now and within the next five years was carried out during the outline design phase. The review confirmed that there are only a few lining techniques applicable for use on such a large diameter unlined cast iron main. In addition, cleaning techniques could be utilised on Line 3, a bitumen lined steel main. The review also showed that there are new techniques available in the market place, but these are not yet suitable for use on larger diameter trunk mains or on unlined cast iron. To enhance United Utilities Water (UUW) engineering understand of the available lining techniques two field trials were carried out using thin walled Polyethylene (PE) liners. Folded liner in 2009 and swage liner in 2010, both were carried out on a parallel 1 mile section of the Vyrnwy LDTM. This trial was carried out to test a number of engineering assumption made in the development of the ten year construction schedule and to ensure lessons learnt could be incorporated into the main works. From the work carried out to date United Utilities have developed an enhanced understanding of what to consider when refurbishing large unlined cast iron pipelines. This includes, but is not limited to, the following: 1) Prediction and control of discolouration events in distribution networks; 2) Assessment and selection of PE interactive liners; 3) The use of structural and semi-structural liners and end termination fittings; 4) Onsite experience of inserting up to 850m of PE liner in one operation; 5) The manufacturing process of cast iron mains in the late 1800's; and 6) Development of a cast iron remaining life assessment tool in conjunction with MWH United Utilities have gained a large amount of knowledge and information from this project over the last fours years and it is important that this and the lesson learnt are shared with the wider industry.