Sorry if this is going to the wrong place, but I wasn't able to find a
decent group other than this one.

I have this douglas fir in my backyard, probably 50+ years old, the people
who built the septic system deliberately routed the drain field around this
tree.

The septic system has been in operation for 50 years with no problems so I
suspect the douglas fir is probably older than 50 years and roots already
established, but I can't really tell.

My question is, given the fact that the roots of this tree are probably
always in damp soil, plus provided with lots and lots of organic matter from
the drain field would this tree be a candidate for rotting or would the tree
be one of the strongest and healthiest around the neighborhood? The city is
also threatening to buy our development out and that means sewer hookup -
that douglas fir will no longer be benefitting from my septic tank.

The only reason why I'm asking is because I'm having a 50+ year old birch
removed that is deader than a doornail and I wondered if I might take care
of this tree before it falls and does some damage. I live in an area where
60 to 70 mph gusts are not uncommon 2 to 3 times a year. Frankly that the
birch tree is still standing boggles my mind.

I happen to like the douglas fir where it is, it provides a home for the
birdies and squirrels and provides me with some shade in the summer.