There is a large chunk of dark red nearish to me on this map that could be described as one of the least inhabited parts of the state (state forest + wildlife refuge).
Though the groundwater level is probably rather high there so that might mean less chance for it to be filtered out through the soil.
Add a -f to your umount and you can clear up those blocked processes. Sometimes you need to do it multiple times (seems like it maybe only unblocks one stuck process at a time).
When you mount your NFS share you can add the "soft" option which will let those stuck calls timeout on their own.