Katrine Water Treatment Project, Glasgow, United Kingdom

With commissioning of the new 240,000m³/day direct filtration plant underway and set to continue through August and September, Scottish Water's Katrine Water Project is well on-track for its scheduled completion in late December 2007.

MJ Gleeson – subsequently acquired in 2006 by Black and Veatch – was the main contractor for the project, which comprises several linked elements across the Strathblane, Milngavie and Balmore area. In addition to the construction of the new WTP itself, the project also called for the modification of the existing pumping station at the adjacent Balmore plant, together with the provision of an additional 160,000m³ treated water storage capacity. Associated building work included providing facilities for filter backwashing, washwater recycling and chemical dosing. Twelve kilometres of large-diameter mains and other related pipework also needed to be laid.

The £120m project is the largest single water treatment scheme in Scottish Water's £1.8bn current round of investment and will provide Greater Glasgow with a state-of-the-art supply..

LOCH KATRINE'S WATER SUPPLY HISTORY

The use of Loch Katrine to supply Glasgow has its origins in Victorian times. In the early part of the 19th Century, a mere 30 public wells – and a handful of private ones – provided the city’s only sources of water. In 1848, after a second outbreak of cholera again decimated the poorest inhabitants, moves began to bring the water supply under municipal control in an attempt to overcome the growing public health problem.

Five years later, John Fredrick Bateman – a civil engineer of considerable contemporary repute – concluded his study to find the best potential source for Glasgow, recommending the high quality water of Loch Katrine. The House of Commons passed the necessary bill in April 1855.

The resulting supply system took three and half years to complete and involved the construction of a dam on the loch, 26 miles of aqueduct, a similar length of trunk mains, 46 miles of distribution pipes and the Mugdock storage reservoir at Milngavie. Queen Victoria herself officially opened the scheme – seen as the engineering marvel of its day – on 14 October 1859.

Over 140 years later, changes to European and UK water quality standards, particularly in respect of disinfectant by-products and micro-organisms such as Cryptosporidia, formed the main driver behind the project.

In November 2001, a planning application was submitted to East Dunbartonshire Council for the construction of a treatment facility at Barrachan and an associated service reservoir at Bankell Farm. Amid concerns that the scale of the proposed development would reduce amenity of existing reservoirs, the application was refused in August 2002. In the same month the detection of cryptosporidium in the Mugdock reservoir led to some 140,000 Glaswegians being advised to boil tap water intended for drinking, food preparation, teeth cleaning and bathing infants.

Scottish Water appealed to the Scottish Executive in October 2002 and a revised planning application addressing the concerns that had been raised was submitted the following month. In February 2003, planning permission was granted and, on 22 March 2004 construction began on the main works at Milngavie.

WATER TREATMENT

The most suitable treatment process for the new plant was selected after a comprehensive appraisal of the available options, the treatment parameters required and the results of the earlier on-site trial. Running for a year, the £1m pilot plant drew water from the Craigmaddie Reservoir which was then split into three process streams – rapid gravity filtration, dissolved air flotation / rapid gravity filtration and immersed membrane filtration.

In addition, two plumbosolvency test rigs were used to investigate the best approach to control lead within the distribution system. After independent assessment of process suitability, coagulation and filtration was selected as the most appropriate for the Katrine Water Project.

The direct filtration process at the new plant has two distinct phases – conditioning and filtration.

The water is first dosed with lime to achieve a stable pH and provide optimum conditions for the aluminium sulphate coagulant, thus maximising flocculation; filter performance is enhanced by the subsequent addition of a polyelectrolyte. Coagulated water passes to mechanically mixed flocculation tanks before flowing under gravity to the plant's filtration columns.

Using anthracite/sand dual-media, the size, configuration and flow rate of the deep filters installed were designed using data arising from the pilot project, incorporating a higher loading than previous full-scale operations based on the latest understanding of the process. Periodic upflow backwashes maintain the filter columns' operational efficiency.

Sodium hypochlorite is then added to disinfect the filtrate, which is subsequently further conditioned by the addition of lime to adjust the pH, with a final dosing of orthophosphoric acid to stop any residual lead remaining in the old network dissolving and entering the supply.

ASSOCIATED WORKS

The Strathblane Cross Connection, which was completed in 2002 at an additional cost of £1.9m allows raw water from the Katrine Aqueduct to be transferred to the Lomond Aqueduct – a pre-existing cross-connection already permitting flow in the opposite direction. The new connection enables savings to be made on pumping costs, since gravity fed water from Loch Katrine can be used to supply the Balmore Water Treatment Works, rather than relying solely on pumped water from Loch Lomond.

Adding £5m to the overall budget, the A second element of the project – the Balmore to C5 main – now provides water to around 140,000 customers in the East of Glasgow, a new supply which was itself made possible as a result of the Strathblane Cross Connection.

The draw down of the Craigmaddie reservoir – reducing the level by around 10m – was also necessary to enable essential work to be carried out safely. The reservoir was out of service from 21st July 2006, during which time Glasgow received water from Mugdock reservoir – which had itself been drawn down during earlier work on the project in 2005 – and the Milngavie service reservoir at Bankell. Craigmaddie was refilled in April 2007 and then reintroduced into supply after a period of settling at the end of May.

New valves and pipe work have also been installed on the M5 Main, adjacent to the main works entrance, with work continuing to construct the new valve chamber and complete installation during September. Once this is finished, the Pilot Plant area will be reinstated and trees planted in the winter of 2007/8 and final landscaping will be completed in spring 2008.

KEY PLAYERS

Recently acquired by Black and Veatch, Gleeson was appointed main contractor by Scottish Water. A-Plant Acrow was the sole supplier of formwork/falsework systems and supplied a number of the brackets and forming systems used under agreement with MEVA. Thames Water provided the pilot plant equipment and the process assessment was done by the Water Research Centre.