Average Septic Tanks Costs and How They Work in Ireland

The following is a brief guide outlining how septic tanks work and what they generally cost.


 

About Septic Tanks in Ireland

Not to be confused with a ‘sewage treatment plant’ – a overall septic tank system is made up of three components; 1. The septic tank itself, 2. The percolation area and finally, the sub soil under the percolation which the effluent ultimately discharges into.

The tank itself can be made of precast concrete and generally has 2 chambers. Concrete septic tanks are generally more popular due to their structural integrity below ground and these are generally constructed in rectangular shapes.

Septic tanks are by far the most common domestic sewage system type to be found in Irish dwellings built pre-2005. They are also most likely to fail. The high failure rate is generally due to the poor standards, regulations and design in force pre-Celtic Tiger era. The high failure issue has being rectified in more recent years with the adoption of more rigorous code of practices for the installation of sewage systems.


 

Average Septic Tank Costs

The cost of a septic tank will ultimately be dependent on the type and size of the tank being installed. In Ireland a typical septic tank cost is approximately €1,500 to €2,000. The percolation area and groundworks associated with installing a standard septic tank are additional and typically cost in the region of €4,500 to €8,000 in addition to the septic tank.

Average Sewage Treatment System Costs

It is important not to confuse a septic tank with a wastewater or sewage treatment plant, which generally has a cost ranging from €3,500 to €4,500 depending on the individual site requirements. The polishing filter area and groundworks associated with installing a overall sewage treatment system are additional, and typically cost in the region of €5,000 to €7,000 for a site with good soakage. For a difficult site the polishing filter area and groundworks is likely to cost between €8,000 to €12,000 in addition to the sewage treatment plant.

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^ all estimates quoted are ballpark and are correct at time of publication (2024) and exclude vat.


 

Septic Tank Certification

All septic tanks in Ireland must have EN12566-1 certification. The tank must also conform to the Irish Standard – S.R.66:2015.  This septic tank certification contains the design population of the tank and images of the tank to allow the homeowner or builder confirm the tank is correct for a particular site.

Download the Sepcon Septic Tank Cert Here

Sewage Treatment System Certification

All sewage treatment systems sold in Ireland must have EN12566-3 certification. The tank must also conform to the Irish Standard – S.R.66:2015.  This  certification contains the design population of the tank and images of the tank to allow the homeowner or builder confirm the tank is correct for a particular site.

Download the Sepcon BAF Sewage Treatment System Cert Here


How a Septic Tanks Works

Stage 1 – The Septic Tank

Waste water enters the septic tank through the pipelines leading from the dwelling. While sitting in the tank, the solids and the liquids that make up the waste water begin to separate by natural breakdown. The solids sink to the bottom forming the sludge layer and the lighter particles of waster rising to the top, forming a layer known as scum. The sludge is left behind and eventually begins to build up which is why a septic tank must be emptied every few years.

Stage 2 – The Percolation Area

The waste water is now up to 90% free of solid waste and known as effluent, flows into the second chamber in the tank. Here, due to pressure in the tank caused by the incoming waste water in the first chamber, the effluent flows out into the percolation area through a series of perforated pipes. Once the effluent flows out through the pipes, it then flows through a layer of gravel before it finally reaches the soil.

Stage 3 – The Sub Soil

This is the last stage of the septic tank process where the biological organisms in the soil treat the waste ensuring that it permeates down and eventually out of the soil, joining up with the water on the surface. This stage is probably the most important as it ensures that the waste is no longer a health or environmental hazard which is why extensive soil testing is carried out prior to a septic tank installation to ensure that the soil is suitable.