Can I suggest that you contact the DOE and get up to speed on all the new guidelines in relation to septic tanks.
Approved persons have to inspect and assess the site and percolation area, and there are moves to undertake tests on the tank/ system itself.
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In that sense, going for a cut-price system that doesn't deliver what you need based on your particular site topography, location, boundaries and layout would be ineffective, costly and premature.
AFAIK you now need to get your site professionally assessed and you may find references on here on AAM and on Boards.ie as well and the Dept. of the Environment website.
FWIW.
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.