I've got a tree growing over my septic field — what should I do?

A strip of lawn over the drain field that is greener and taller than everything around it and stays green through drought while the rest browns off. Soggy ground or standing water over the laterals, odor, slow drains or backups indoors, and lines of lush growth tracing exactly where the pipes run. On the tree side: roots surfacing near the field, and a tree noticeably more vigorous than its neighbors on the same lot. A drain field is a warm, wet, nutrient-rich zone a foot or two underground, which is the best habitat available to a root system. Roots do not break into sound pipe out of aggression — they follow moisture vapor to a joint or a hairline crack, push a fine root through, then thicken it. Once inside, the mass grows in the flow and blocks it. The failure being described is therefore a plumbing failure caused by a tree, which means it gets judged on the septic system's terms rather than on the tree's.