My undereducated guess is trees should not have septic fields within their drip lines. The previous owners had two white ash and a shingle oak well over the field. My neighbors seem to recall the original field lasted 25 years and this one is probably 35 ish and its doing ok but the input line was replace fifteen ago.

SO, sometimes you get lucky but who knows.

the tree will be moved in fall.. when it loses its leaves.. not now ...

birch are incredibly surface rooted ... i would go with 50 feet or so ... but that is just guessing..

you are asking tree peeps.. a septic question.. and i dont know if we have the info you need.. with any specificity ...

what is the native soil ... my mineral sand... would be very different from a clay soil ... not only in regard to how the tree spreads its roots.. but also how the field drains ...

ken

Thanks for the replies. I understand about asking tree people a septic question but i did't really know where to start. I have clay soil so i assume that this is worse??? :-) I thought 15 feet was pretty close as well.