Wetter months in the chalk stream villages - problem of Groundwater Infiltration

Written by Charlotte Hitchmough.

 In villages along England’s chalk streams the rumble of road tankers has become synonymous with winter, as lorries pump foul water from sewers and drive the effluent to the nearest Sewage Treatment Works with spare capacity.

When  groundwater levels rise in wetter months, water makes its way into sewer pipes and fills them to a point that the sewerage system can’t cope. It’s known as ‘groundwater infiltration’, which sounds innocuous, but as residents of towns and villages like East Kennet, Marlborough and Aldbourne know, the impacts can be very messy, with dilute raw sewage flowing across streets and into rivers and streams. At its worst sewage backs up into houses and gardens.

The residents of East Kennet have been battling this problem for several years, with little sign of progress from Thames Water. They are frustrated that as far as Thames Water is concerned the situation is under control because the sewage is being pumped out and driven away. What is worrying is that this year is not particularly wet. The groundwater levels measured at Rockley show levels just above average but well within a normal range.

Groundwater levels measured at Rockley, showing groundwater above average, but well within the normal range. (dotted line: average, solid line: recorded)Groundwater levels measured at Rockley, showing groundwater above average, but well within the normal range. (dotted line: average, solid line: recorded)David Snape, the Parish Clerk said ‘if people had any idea of the cost of running these tankers 24/7 for months on end I don’t think they would put up with it. We want Thames Water to invest money in fixing the sewer instead of paying for lorries.’

As far as ARK is concerned we are frustrated that each year we have to wait for the river to be polluted before tankers arrive to deal with the problem. We’d much rather see a robust sewer system which is able to cope with fluctuations in groundwater levels. We certainly feel that before any more housing is proposed for this area, the sewer network needs to be fit for purpose.

There is a happier story at Aldbourne, which although not flooded at the moment, regularly suffers extensive groundwater and sewage flooding. Residents formed the effective  ‘Aldbourne  Drainage Improvement Group’ which, by bringing all the parties together and keeping up concerted pressure, has  driven actions to reduce sewer flooding and its impact. One outcome has been Thames Water’s  ‘Ramsbury and Aldbourne Drainage Strategy’ . If it is as good as its promises, it will replace and repair parts of the sewer network to keep groundwater out. To protect the river, Thames Water now has a Mobile Treatment Plant that can be brought in to service during high groundwater events so that raw sewage will no longer be pumped into the Bourne.

Thames Water has written a Drainage Strategy  for Marlborough that  is open for consultation now.  If you would like to have a copy to comment on please email This email address is being protected from spambots. You need JavaScript enabled to view it.

ARK will be working with the East Kennet Parish to press Thames Water for a solution like that which has been promised at Aldbourne.


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