The persistent winter rainfall experienced across southern England is presenting particular problems for drainage even when no apparent flooding has taken place.
The flooding in the Somerset Levels and the Thames Valley has grabbed the attention of the headlines and politicians but there are less spectacular problems associated with drainage across a much wider area.
In our own local area a pub was closed for three weeks when the rising level of ground water prevented the pubs sewage system from functioning properly. The pub in question relies on mains drainage. Properties that are reliant on non-mains drainage are not only more susceptible to drainage problems but are entirely responsible for sorting out any problems.
The persistent rain has raised the natural water table levels, this can effective many septic tank soakaway systems. If the water table raises above the base of a soakaway then it cannot function correctly.
What then happens :-
1. The sewage entering the septic system still flows in and and also has added flows if drain pipes leak etc due to the excessive ground water, this puts extra pressure on the soakaway, which is not partly or totally ineffective because there is no sub-soil below it in which to allow soakage.
2. the septic system starts to fill above its normal operating levels, solids tend to now move from there holding position more into the outlet area and in turn into the soakaway. The solids can then contaminate the soakaway system, thus reducing its effectiveness even further.
3. The septic system fills to even high levels, the foul drain pipes back up, sewage can then emerge through manholes and gullies around the home leading to pollution.
4. The septic effluent can also raise through the soil and garden areas through the top of the soakaway and through the access covers of the septic tank itself.
5. Areas in flooded locations are now becoming polluted with septic effluent, with little sign of any improvement in current weather conditions heath issues are becoming more of a concern.
6. If pollution levels are high then home owners may be forced to leave their homes as a result of septic contamination.
7. Long term prevention – Install systems that are water tight, including all drainage pipework and have a pumped outlet to may be a raised soakaway location, a sewage treatment plant will also produce much cleaner treated effluent that can reduce contamination issues in wet weather flooded areas.