We are on a shared septic tank system that’s pretty ancient. It’s at least 30 years old, not in our control, and is not even working or registered. We would like to install our own system. What is involved? What are the relevant planning rules? Are there grants available?
For the benefit of our readers, in Ireland domestic septic tanks must be registered. This requirement was introduced in 2012. New septic tanks and percolation systems also require planning permission to ensure important environmental and public health standards are met.
The local authority needs to ensure the proposed system will not contaminate groundwater aquifers or nearby wells, group schemes and watercourses, that it is positioned safely away from buildings and boundaries, that it is rightly sized for the number of occupants, and that it complies with Environmental Protection Agency design standards. As every house relies on its system working correctly, proper oversight is essential.
So, what’s the procedure? If I were preparing a planning application for a new house, I would first prepare a site layout showing the proposed location of the septic tank and percolation area, making assumptions about the pipe runs and ensuring the required separation distances from buildings, boundaries and watercourses are met. This information is then provided to a site suitability assessor (SSA), who carries out ground investigations and designs the most appropriate system.
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In your case, as the site already exists, I would suggest contacting an SSA first. They can visit the property and assess whether there is sufficient space for a compliant septic tank and percolation area. If the site is suitable, they will advise you on the next steps. If space is limited, they may instead recommend a wastewater treatment system. These systems provide additional treatment before the effluent enters the ground and often require a smaller polishing filter or percolation area, making them better suited to confined sites.
The SSA will ask you to arrange for a digger to excavate trial holes to specific dimensions. They will also require a water supply to carry out percolation testing. In simple terms, the soil must allow water to drain at the right rate. That is, not too fast and not too slow.
The SSA will ask you to arrange for a digger to excavate trial holes to specific dimensions. They will also require a water supply to carry out percolation testing. In simple terms, the soil must allow water to drain at the right rate. That is, not too fast and not too slow.
Wastewater treatment systems are also recommended where the soil conditions mean a standard septic tank may not provide sufficient treatment before the effluent reaches groundwater.
The design is based on the number of bedrooms rather than the number of bathrooms, because occupancy is the key. The SSA will also complete a desktop assessment using mapping of groundwater, flood risk, geology and nearby water sources.
Once the assessment and system design are complete, these documents, together with the required drawings, maps, newspaper notice and site notice, are submitted to the local authority as part of the planning application. Once permission is granted, the existing drainage will need to be redirected to the new system and the old connections properly decommissioned.
At present, there are no grants available for installing a new domestic septic tank or wastewater treatment system.
Brigid Browne is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland
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