Nutty Nut, I have to agree with MOB, in terms of the cost of rectification...sorry pkelly! For my sins I have quite a bit of expertise in the whole area of site assessments and wastewater treatment, having worked in this field for several years, so I may be able to give you some background info!
pkelly,
firstly, the builder was wrong to state that the County Council was responsible. The Local Authority can specify a testing format for site assessments. Presently, most Local Authorities require tests to be done in accordance with Appendix A of Wastewater Treatment Manuals Treatment Systems for Single Houses, published by EPA, 2000. Web address: [broken link removed]
Considering the test was done in 2001, there's a good chance that the tests were carried out using S.R.6: 1991, published by NSAI, 1991. Some Local Authorities in fact still use this document, because it's refered to in the Building Regulations. In any case, both of these documents are very flawed, but they do contain a section where the site assessor makes recommendations. If you can go into the County Council offices and access the planning application for your site it could shed some light onto the situation. I was involved in an arbitration before where a builder and his mate the engineer falsified reports to get planning and build a house...one look at the site assessment report and then at the site and I instantly knew it was a fake!
The next point, and probably more important than the issue of falsification is whether or not the site assessor had sufficient insurance cover (if any) for the work he was doing? To carry out a site assessment, it is vital that you have Professional Negligence Indemnity Insurance. This is insurance to cover you in the event of you being negligent in carrying out your work. A copy of the insurance cert should be submitted with every report, but this very rarely happens! Find out who the site assessor was and make a phone-call to him (presuming he's still in business!), singing-dumb and claiming you need to get an assessment carried out...ask if he has Professional Indemnity insurance. If he's out of business his PI insurance could still be open for a claim from you!
As for nutty nut's statement that he could claim that outside factors over the last 5 years have reulted in the water table becoming higher thus leading to the present problem, I don't really buy it! I have never come accross such a thing happening. That's not to say it couldn't happen, but for it to happen to the extent where it leads to the problems you encountered are hard to imagine. Be careful here, because the builder might have played some part in your present situation! The site assessment could have been perfect, but the builder may not have constructed the percolation area as per the design, e.g. he might not have located it in the correct area, or he could have used poor materials in the construction (i.e. heavy subsoils, such as clay, rather than looser topsoil). It's also not unheard of for guys installing septic tanks to put them in backwards!
You need to get onto your solicitor, as MOB said. But remember, your solicitor, at best, knows the law! He is most definately not experienced in dealing with drainage issues on sites! For that reason you will need to contact an experienced engineer who can carry out a full post-mortem on the site assessment, the installation of the septic tank/perc. area, and the present problems. If the engineer is experienced in dispute resolution, he may also be able to apportion the blame, to assist the solicitor. The solicitor will also need to check the contract documents for the construction of the house (if there are any!)...there may be an arbitration clause, meaning dispute resolution will be by that method!
Clear as mud, eh?!