If you are thinking about this in Fl. check with the local agency, there is a fee and an inspection before the drain fields are covered, the unit must meet specs too in certain areas (flood plain) the septic has to be raised above ground and certified that it is at the proper elevation. They can order the tank removed if it does not meet specs.
I found out this info several years ago when I moved to Citra, fl and had to install a well (75 ft from septic) and septic to get my house built and we had to raise the septic tank above ground (found during the inspection).