The difference is that there is a minimum distance between the drain
field of an on-site septic system and the well on the same property and
from the property lines so as to allow a minimum distance to neighbors'
wells. Although I agree with you, that the sodium, chlorides etc. don't
settle out in the septic tank, the law in the vast majority of areas
says no to putting it on or in the ground; dry well or not.

Gary
Quality Water Associates
www.qualitywaterassociates.com