Soakaway & Drainage Problems – Septic Tank flooding

Soakaway & drainage problems - Septic Tank flooding

Septic Tank Drainage Soakaways

There are many reasons why you may be experiencing Soakaway & drainage problems – Septic Tank flooding, including failure of the septic tank itself, however by far the most common cause for septic tank flooding is due to the receiving soakaway and not the septic tank.

A septic tank uses natural anaerobic bacterial action, combined with gravity, to seperate solid waste from the effluent. Septic tanks are designed to slow down the flow of the sewage to allow this to happen. Modern tanks are resin-moulded and very efficiently use internal baffles to slow the flow and allow the solid waste to drop out.

Soakaway & drainage problems – Septic Tank flooding

A pipe removes the liquid effluent – which will still contain a small proportion of solid material – from the septic tank into a soakaway system. A septic tank soakaway is not the same as a rain water soakaway. Septic tank soakaways disperse effluent slowly over a 24 hour period. Rain water soakaways disperse high flows of clean water over short periods. During periods of heavy rain a blocked soakaway will prevents the effluent from percolating through the ground and this will result in the soakaway, septic tank and the foul drainage pipe work flooding. Septic tank soakaways can fail for a number of reasons and these include:


The Ground Conditions and soil type

If the soakaway has been constructed in  non-permeable soils such as sandy clay, silt clay and clay then the effluent from the septic tank  cannot filter away through the soakaway then flooding of the septic tank will occur causing it to overflow, causing a health hazard. When building a soakaway it is important that the percolation characteristics of the ground in both the summer and winter months is taken into account.


Natural Water Table

Septic tank soakaway systems often fail during winter months.  This is because the ground water table rises during the winter and may result in the soakaway being below the natural water table.  Tthe septic tank, soakaway and foul drainage pipework may all be at the same level as the surrounding water table, resulting in the flooding throughout the system which can be moderate or severe.

Problems with septic tank systems operating in high water table areas can be overcome by installing a septic tank conversion system or Water Treatment Plant which meets current foul water drainange standards.


Root Ingress

Ifhe soakaway lies in close proximity to trees and shrubs then roots can enter the soakaway pipe work and block the pipes.  Root ingress into soakaways is the cause of many soakaways blocking, causing flooding of the whole septic tank system.  As a minimum, removal of the trees and shrubs is required, and clearing the soakaway pipes of the roots.  In some cases it wold be necessary to construct a new soakaway system in an area free of plant roots.


Physical damage to the soakaway pipe work.

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.  It is common for these clay wear pipes to become dislodged, resulting in soil entering the pipe work and blocking the soakaway.


Additional wastewater entering the septic tank.

A septic tank and the receiving soakaway are designed based on the size of property and number of occupants it serves, 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 soakaway system.


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.


Age of the Soakaway

Older 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 wastewater and emptying frequency.

Contact Us at Sussex Water Treatments to find out how we can assist with your particulr septic tank darainage and soakaway problems.