This is a nuisance and over the years there's been an awful lot of confrontation over the issue. I'm from Mayo and as you can imagine the soil is mostly wet in a lot of areas. People over the years used different (political) strokes to get over the septic tank saga, then went on to build, but I can tell you in almost all cases they had big problems. If you're on bad ground don't build, that's my advise to you. I know there's all sorts of septic tanks out there, etc, etc, etc, but with detergents, bleaches, nappy wipes, perfumed wipes and all that yuk the drainage becomes impossible and all these things stop the bacteria from doing its work, you end up getting tanks overflowing, tring to get tankers in around the house to empty tanks, their cost and frequency will be a nightmare, believe me. Don't build on bad land unless there's mains sewerage, that's my advice to you.