I think that it is important to include mention of the fact that the distances you quoted, although laid out in law, are to be applied where space permits.
Where the lay out of the site makes it impossible to comply with all of these distances, then it is possible to obtain a derogation from the relevant authorities.
In cases where there is a problem in relation to the compliance with the legal distances, then it is imperative that a proper survey is carried out (by a company that neither supplies nor installs any of the equipment needed) so that the relevant derogation can be obtained.
A friend in our village has just had plans approved for a waste water installation that is only about 4 meters from a well simply because there is nowhere else on his land to put it. The well, although capable of functioning, has not been used for many years and he has had to sign a declaration that he will neither use well water for drinking or other domestic purposes, nor connect the well to the house in any way. (Future use for watering the garden will be fine.)
For those who have problems of space limitations, and especially complications in relation to old disused outside wells, the main point is not to worry too much because the answer is to have the professional survey done and a solution to the problem will be found by consultations between the surveyor and the relevant authorities.
As you say, SPANC will have to approve … whatever is actually done, by whoever. So it’s good to get them on board in the early stages - this can save time and money.
I have always found them helpful and willing to consider things from all angles.