The most common cause for a septic tank flooding is due to the receiving drainage field / soakaway and not the septic tank. If a drainage field / soakaway fails and prevents the effluent from percolating through the sub-strata this will result in the septic tank and the foul drainage pipe work from the property surcharging. Septic tank drainage fields / soakaways can fail for a number of reasons and these include:
1 – Ground Conditions
The soakaway being constructed in ground conditions which are non-permeable such as sandy clay, silt clay and clay. This would result in the effluent that discharges to the soakaway filling the soakaway and subsequent flooding of the septic tank, or potentially effluent bursting out of the ground causing a health hazard.
It is important that the percolation characteristics of the ground are suitable in both summer and winter months. To identify whether the ground conditions are suitable for a drainage field / soakaway and to determine the size required it is necessary to conduct a Percolation Test. Without the results of a Percolation Test there is no way of knowing the size of drainage field / soakaway required or if this disposal method would indeed work.
2 – Natural Water Table
The drainage field / soakaway being under the natural water table. This can often be the cause for septic tank soakaway systems failing during winter months only. When a drainage field / soakaway is operating underneath the natural water table the septic tank, soakaway and foul drainage pipework will be at the same level as the surrounding water table and as a result the flooding within the system can be moderate or severe.
Problems with septic tank systems operating in high water table areas can be overcome by installing a Mantair septic tank conversion system.
3 – Root Ingress
The drainage field / soakaway being constructed in close proximity to trees and shrubs. Roots of trees and shrubs planted too close to a drainage field / soakaway can enter the drainage pipe work and block the pipes. Root ingress into drainage fields / soakaways is the cause of many systems blocking and as a result flooding of the septic tank system. Mantair offers a unique insurance claims management service to our customers for situations where root ingress has damaged a drainage system.
4 – Physical Damage
Physical damage to the drainage field / soakaway. In some cases a septic tank can flood due to the receiving soakaway pipe work becoming damaged and broken. This can often be due to heavy machinery moving over the soakaway and crushing the pipes. Older ‘but-jointing’ soakaway systems were constructed using clay wear pipes and it is common for these clay wear pipes to become dislodged due to ground movement, resulting in soil entering the pipe work and blocking the soakaway.
5 – Increase in Flow
Additional waste water entering the septic tank. A septic tank and the receiving drainage field / soakaway are designed to cater for a certain volume of flow per day. If the flow being discharged to a septic tank increases and the tank is not designed for this additional flow then problems can be experienced with both the septic tank and drainage field / soakaway system.
6 – Sodium Binding
Excessive use of detergent based products i.e. dishwasher tablets, washing powders etc. will lead to eventual failure of the soakaway. This is caused by a process called sodium binding where the sodium present in detergents cause any silt or clay particles in the sub soil to bind together to form am impervious layer. The same effect occurs if a water softener is present as the softened water will have relatively high sodium content.
7 – Age of the Soakaway
Older drainage fields / soakaways can fail due to a build-up of sludge solids. The level of sludge solids passing through the septic tank are due to a number of reasons, including size of the tank, nature of the waste water and emptying frequency.
8 – Prefabricated Septic Tanks
Within most prefabricated septic tanks are internal baffles or cones which are designed to prevent solids and floating material from passing through the tank. In some instances baffles and cones can collapse resulting in solids and floating material passing through the tank and into the drainage field / soakaway.