Content area
Full Text
Thirlmere Reservoir in the Lake District supplies 150 Megalitres of water per day into the Manchester Ring Main. A new water treatment works at Lostock near Bolton, Lancashire is the largest clean water project in United Utilities' Asset Management Plan (AMP3) programme, agreed by Government after discussions with the Environment Agency, water companies and Ofwat. The objective of the design is to prevent Cryptosporidium from entering the water supply.
Design
A design-and-build approach has been adopted, based on an illustrative design and specification by the MWH Programme Management. The treatment process is direct filtration with raw water fed through a pumping station to an inlet works/flocculation chamber, followed by eight rapid gravity filters (RGF) (see Figures 1-4). It then passes through a chlorine contact tank before pumping to the treated water reservoir (TWR). Water is then transferred by gravity into the Manchester Ring Main.
It was necessary for a major part of the plant to be below ground level, thereby satisfying local concerns regarding visual impact. The ground consists of variable glacial deposits, sands and silts with artesian and sub-artesian conditions. With foundations up to 10m deep below an initial site strip of 3m, extensive sheet-piled cofferdams were required. Altogether, 1187 driven precast concrete piles were used to support major structures. A single cantilevered...