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The effects of flooding on sewage treatment systems and septic tanks

Living in Great Britain means we are generally accustomed to lots of rain! However, sustained periods of heavy rain can be more problematic than a few puddles, and flooding is becoming an issue in several areas of the UK. If you have a septic tank or sewage treatment system with a soakaway (drainage field) installed, you need to be especially alert for any problems.



If there is an excessive amount of rainfall, the soil can lose its ability to effectively absorb water which leads to saturated ground. When this reaches its peak, any further rainfall will result in surface flooding. If stream and river levels reach full capacity and burst their banks, this problem will be exacerbated further.



Flooding can occur with a septic tank or sewage treatment system in three main ways:

  • Through the lid/cover of the tank
  • Through underground pipe joints, riser pieces and manhole covers between the tank and the property it is serving
  • Through the outlet pipe which discharges the effluent to the soakaway (drainage field) or surface water



If your system floods, there is a real risk of human sewage contaminating the ground and watercourse. Human sewage contains high levels of bacteria and viruses which are harmful to humans, animals and the environment. If you or the surrounding environment is exposed to flood water containing human sewage, you risk serious problems including:

  • Polluting nearby watercourses and having an impact on aquatic life
  • Contaminating water supplies
  • Contaminating arable land used for food production
  • Contracting infections and disease from contact with sewage
  • Contamination of land with grazing livestock


It’s not only these issues that you need to consider, however. If you have a sewage treatment plant, it is likely to be powered by either a motor/gearbox or air blower. If these flood then these will need to be replaced, as they cannot recover from water submersion.


If you are concerned that your system has been flooded, or is at risk of flooding, it’s best to get these issues diagnosed sooner rather than later to avoid causing harm to the environment. Give our team a call on 01388 537050 and we can arrange an engineer to provide a full inspection of your system.


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