In the most advanced scheme of its type in the UK, Thames Water is using an innovative water storage technique from the Middle East and America to help  the water-stressed south-east England.

Thames  Water is currently running a £3.2 million operational scale trial at Horton Kirby in Kent using a borehole a quarter of a kilometre deep is helping groundwater scientists understand the potential for drinking water to be stored in a ‘bubble’ 250 metres below the ground.

 Desert regions across the world, including Las Vegas, already use this technique, called ‘Aquifer Storage and Recovery’ (ASR), and Thames Water groundwater experts began investigating it over 10 years ago.

Aquifers  - the layers of rock deep underground which groundwater can be extracted from  - already provide 30% of London’s tap water, with the Chalk aquifer at Horton Kirby being used to supply parts of Kent.

The new technology will see the aquifers put to use as underground storage reservoirs with drinking water stored below ground and brought up to the surface when needed e.g. in drought conditions.

 The new £3.2 million trial, shortlisted as a finalist in the 2015 Water Industry Achievement Awards for Water Resource Management Initiative of the Year is the most advanced ASR scheme in the UK.

In September 2014 the team began drilling a new borehole at Horton Kirby, and when work finished this January the drill had reached a depth of 250 metres and entered the Lower Greensand aquifer. Testing work carried out since 2005 had already identified the Lower Greensand as a suitable candidate for ASR.

 Groundwater resources manager at Thames Water, and UK Groundwater Forum member Dr Mike Jones said:

“This is an exciting time for water resource development in the UK. Aquifers are a vast reserve of water storage space. In the Thames Water area there is 10 times more storage space in shallow aquifers than in the raw water storage reservoirs we’ve built at the surface; there is even more storage in the deeper aquifers like this one, so we need to make use of it.”

He added:

“Aquifer storage isn’t the magical answer to the south-east’s water stress, as not all aquifers are suitable for this type of project - but it’s a great start and I’m confident this work will help us understand how we can best use our natural aquifer resources in the future, especially to help combat the effects of climate change.”

The groundwater in the deep Lower Greensand aquifer at Horton Kirby (estimated by carbon dating techniques to be 6,000 years old) cannot currently be used because it is low quality and there is insufficient quantity.

However, by repeatedly putting water into the aquifer, allowing it to rest then recovering it by pumping it back out, the aquifer is “cleaned”. This process, combined with the suitable make-up of the Lower Greensand aquifer, enables a bubble of good quality water to be stored as only the edge of the bubble mixes with existing water in the ground. The next challenge for the Thames Water team is to be able to store a greater volume of water without it seeping away.

 When in use, the ASR scheme will take ready-to-drink water from a mains water pipe and then store it in the aquifer. When the water is needed it will be taken back out and disinfected before going back into the public water supply. The water will not have to go through a complex treatment process as the water within the bubble is stored securely and does not mix with the natural, poorer quality groundwater in the Lower Greensand aquifer.

 Ed Uden, Groundwater Team Leader at the Environment Agency, said:

“This scheme is also good news for the River Darent, a chalk stream flowing through Horton Kirby and other villages in Kent. Instead of water being taken from the environment in the summer, which can cause the river flow to be reduced, the ASR scheme will allow up to 5 million litres per day to be taken from the water stored underground and put into drinking water supply, protecting the river.”

 “Thames Water, the Environment Agency and the Darent River Preservation Society (DRiPS) are all keen for this to happen, to ensure that water resources can be developed sustainably to meet demand and protect the environment.”

 Thames Water’s region is officially classed by the Environment Agency (EA) as being an area under serious water stress. There is 10 times more storage available underground in aquifers in the region than there is above ground at Thames Water’s raw water storage reservoirs

During 2015 and 2016 the Thames Water team will be testing how the Lower Greensand aquifer stores water by putting drinking water in and taking it back out again and testing the quality of the water recovered.

Specialists will also be checking the aquifer at points along the path of groundwater flow northwards through Kent to make sure the water stored stays in the aquifer and has no impact elsewhere.

Once the trial ends, the scheme will be developed into an operational water supply scheme between 2016-2020, which may require drilling of more deep boreholes. The innovative project that could make a significant contribution to help ease water storage issues in south-east England.