I recently requested an "As built" drawing from my county health department
for the septic system. What they faxed back to me was not exactly what I
was expecting to see. It was dated 1960 and listed the owners, builders,
and inspector.

I happen to have a degree in engineering and I was expecting to see an
engineering drawing or something official (maybe even on vellum) - what I
got was best described as "back of the napkin with a coffee ring as a bonus
decoration". First, is that realistic, I don't want to harp on it if in
fact that's what they're all like, and second how truthfully can I take the
measurements and layout of the "drawing"?

I'm looking at the drawing and it looks like they deliberately routed the
drain field so that it goes off in weird angles, makes several beelines for
the massive Douglas Fir in my backyard and otherwise doesn't efficiently
utilize the space provided for it. I was expecting a nice layed out route
involving 90 deg bends and long branches. What I see is the first line
making a large oblique angle into the middle of the yard then sending
branches back toward the tree, finally connecting back to itself after
circling the tree.

Was it common to design the field to incorporate trees as a means of
absorbing water?