Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | december 2014 | 17 the new pump booster station within Thames Water's secluded Bradfield Windmill WTW. The remaining 11.9km pumped section would then be laid direct to Cold Ash. Further advantages were won by also siting the transfer main's motor control centre (MCC) at Bradfield. The vast majority of the high density polyethylene (HDPE) pipeline was laid in a conventional open trench, some 2m deep. The alignment was unusually flat and, with three excavators plus a specialised trencher on site, the excavation was opened up in maximum 200m lengths. The team's best rate was 250m of completed pipeline a day, an achievement helped by a further value-engineered innovation. Conventional pipe bedding, surround protection and 100mm cover material, would have been imported shingle with the trench then backfilled with the excavated soil. But Optimise decided to reuse some of the as-dug gravel, chalk and sandy clay instead, converting it on site into a shingle substitute. A riddler bucket, equipped with geared spinning wheels, was fitted to a standard excavator arm to cut and grind the mixed ground into shingle- sized rock and the replacement bedding material was used for over 70 per cent of the route. JMH Directional Drilling routed the pipeline beneath the M4 near junction 12, and under the Rivers Pang and Bourne. A total 1km of the mains was directionally drilled, with the motorway crossing demanding 12m cover. The booster station at Bradfield WTW, housing two 50kw high li• pumps, was a small 20m long glass reinforced plastic hut. Alongside it, the MCC - installed by Nomenca in an adjacent treatment works building - will remotely record flow rates, pump output and reservoir levels at both ends of the pipeline. This is monitored and controlled remotely by Thames Water. Now fully commissioned, the pipeline is supplying a maximum 5ML/day to Cold Ash Reservoir, and the original feed mains from Speen WTW will be shut down. An actuated plug valve, installed in the mains can, when needed, reverse the flow allowing the reservoir itself to boost Speen's water supplies, and this too will further safeguard the new EA reduced raw water abstraction licence - and the Desmoulin's Whorl snail. Top: most of the alignment runs beneath privately owned land Inset: map of Speen pipeline bottom: replace- ment bedding material was used for 70 per cent of the route • Perspectives Stakeholder engagement manager, Optimise, rachel Groves: "The programme will help the environmental condi- tion of the River Kennet and improve the sustain- ability of the water use. The new pipeline will also help to safeguard New- bury's water supply in the future by providing an additional water supply route into the area." Optimise site engineer, Thady Gavin: "The pipe laying part of the programme went well, and while the project was not technically complex, its main challenge was its sheer scale and size. The scheme was one year in design and planning before construction started and that year of hard work really paid off." • Innovations ● Pipe insertion was deployed using the old cast iron pipe as an outer sleeve for the first 1km long run of the new pipeline. The net cost saving over conven- tional trench construction was put at approximately £200,000. ● Collaborative thinking by the design team looked at different ways to plan the route to ease planning consent and reduce the scope of pumping required, despite adding slightly to the route length. ● A specialised trencher was used to speed the pipe laying process by up to 250m a day. ● Utilisation of site-won material, some 9400m 3 , led to faster construction, no imported shingle and hun- dreds of eliminated lorry journeys, totalling a cost saving of around £700,000.

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