Septic Tank Soakaway

Soakaway is a term that can refer to a variety of systems – many of which were constructed in the past without precise specification. Factors that can influence their construction include ground type, location and size, not to mention the competence or otherwise of the installation. An older soakaway may be little more than a length of solid pipe linking the waste water treatment plant e.g. septic tank to a large pit filled with broken bricks, tiles and masonry, in other words not exactly made to any technical specification.

In contrast, modern soakaway systems consist of solid perforated or slotted pipe-work, arrayed in a loop formation and surrounded by a granular e.g. shingle fill. Constructing an efficient system which prevents polluting nearby watercourses and subsoil requires the use of proper materials so that waste water does not leave the pipe work prematurely but is filtered through the entire length of the fully perforated pipe-work – there’s little point in the wastewater leaving the pipe-work in the first few metres.

Why do Soakaway systems fail?

Failure of a soakaway can be the result of several factors. Soakaway sub-soil can get sealed by a build up of fat, grease or even clothing fibres that all pass through the septic tank system. Nearby tree roots can cause pipe damage and if traditional butted land drains have been used in the construction of the soakaway they can become silted up and block.

Significant and sudden changes to occupancy of a dwelling can easily overload the soak-away, e.g. if a young family move into a property previously occupied by an elderly couple, this will dramatically increase the volume of water being used and hence the amount of waste water generated

Prolonged or heavy rainfall can cause ground saturation and there have been occasions where a shift of the ground water table has resulted in a soakaway overload.

What are the early warning signs of failure?

The appearance of a sewage lake at the bottom of your garden is an obvious give-away but the signs may be less obvious – for example are you emptying the septic tank more often? Does waste water enter the tank from the outlet when the tank is being emptied? If so then your soakaway may need some attention.

How to investigate warning signs?

Pressure water jetting the outlet will eliminate a simple blockage but if this makes no difference then reach for your shovel! Sonar tracing equipment can be used to pinpoint where a blockage has occurred so you know where to dig. You will soon find out how your soakaway is constructed and also get an idea of the ground conditions around the soakaway. Weighing all these factors will help you decide whether to extend the existing soakaway or maybe re-route it somewhere else.

How to repair a defective soakaway?

If the ground type is suitable and you have enough area to work in it may be possible to extend the existing soakaway pipe-work. It may be necessary to utilise some kind of pumping chamber at the outlet of the septic tank which will raise the waste water to a more suitable area.

However when the ground conditions are unsuitable for a traditional soakaway to function adequately or nearby watercourse or river etc is being polluted by untreated waste, then your septic tank will need to be either converted into or replaced by a sewage treatment plant.