RMCF,
At the risk of sounding inquisitive why did this query float into your awareness when contemplating your septic tank?
Are you concerned its not installed properly, or are you worried about [broken link removed]?
If either of the above concerns are the source, I'm afraid that the answers will not be found in a layperson's review of planning drawings.
In terms of legal action, the statute of limitation expires for most offences after six years, apart from fraud, and the latter could be hard to prove.
ONQ.
[broken link removed]
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.