I have an existing well and want to build farther back on my property can I be lets say 100 feet or more away from the original well this is a deep well.

Also I have a mound system can I do the same with that?

If you have good pressure, you should be fine, particularly if it is a submersible. Mine is 100+ ft away and runs great. I assume by mound system you are talking a septic drain field? You may need to do another perc test before moving or installing another system. Check with your local license agy.

If you are on multiple lots, be sure the 100ft doesn't put you in the other lot