Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | APRIL 2015 | 19 Project focus T hames Water is progressing well with its operational trial of aquifer storage and recovery (ASR) in Kent, a project which could help ease future water shortages in South East England. Water resource management Thames Water trials aquifer storage in Kent Project focus ● Aquifer used to store 'bubble' of treated water underground ● £3.2M operational trial is most advanced of its type in UK ● Reserve could help supply London in severe drought conditions ● Thames Water's region is classed by the EA as an area under serious water stress, and additional water storage is required to prepare for future droughts ● Aquifer storage and recovery (ASR) could help provide the answer as there is much more space underground in aquifers than there is on the surface in reservoirs ● The drinking water stored needs to be kept separate from the existing groundwater in the aquifer, which is poor quality and contains iron, ammonia and arsenic • Drivers Unlike other forms of aquifer recharge, the water is kept in a 'bubble' underground, maintaining its integrity and ensuring it needs minimal treatment when it is brought up again for use in the water supply. The £3.2M operational trial, the most advanced scheme of its type in the UK, is being carried out via a series of 250m deep boreholes into the Lower Greensand aquifer near Horton Kirby in north Kent. It builds on a pilot scheme carried out by the utility during AMP4 (2005-10) and is intended to create a substantial reserve of water which can be pumped out at a rate of 5 megalitres per day during drought conditions. While Thames Water already recharges the Chalk Aquifer through its North London Artificial Recharge Scheme (NLARS), the Lower Greensand is more suitable than the Chalk for ASR, explains Thames Water's Groundwater Resources Manager Dr Mike Jones. "The British Geological Survey did some work a few years ago where they ranked the Lower Greensand as the top target in the UK for ASR," Jones tells WWT. "That's simply because it's a much more homogenous aquifer, in the sense that it's layered, and not as fractured as the Chalk Aquifer is. If you try to store a bubble in a fractured chalk aquifer, it would shoot away from the borehole along the fractures and you would have no bubble integrity at all." Thames Water's new ASR borehole is situated in a field near Horton Kirby, north Kent More commonly used in desert regions in the USA and Middle East, ASR involves drinking water being pumped into an aquifer where it can be stored and brought up again in times of need such as drought. JAmES BRockETT EDITOR, WATER & WASTEWATER TREATMENT

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