Those trees must be growing really well. lol.
When the drain field has problem, the spetic tank can not drain fast enough and it may overflow and clog the sewage line (dirty water flooding inside house).
Depending on size, I think it could easily cost a few thousand to fix, or close to $10k to replace it. I did caustic treatment of one drain field (close to $2k) but it still caused clog (no flood) in the winter. ($500 same day pumping).
If you are considering to connect to city sewage, please look up the connection fee for that lot. In my area it is $12k. Digging/piping cost is on top of that.
https://buildingadvisor.com/buying-land/septic-systems/how-a-septic-system-works/
