Cost for a large septic system for 10 lots

Im looking at a property that has a crushed d box, now the tank is good, and the leach field has life and theres plenty of acreage to add another leach field but dep wants a whole new system put in and the owner has to keep pumping the tank two times a week. Ive called dep to figure out what size tank and what would be needed in terms of leach field length and laterals but i was wondering if any one here has even a ball park figure of what this would cost. If dep was accommodating id replace the d box, add 3 more laterals from the d box and then but airation in the tank to clean up the exisiting leach field. Also might drill a hole in to the existing tank and put a pipe to take away the scum layer into a separate tank so the leach field doesnt get clogged with baby wipes and oil. Would really appreciate any insight on this issue. Thank you.

Will need an engineer to spec it out if the state is already involved (most likely, at least where we operate). Conceptually discussed a 15 unit system last year (thankfully didn’t need to install it) that was close to $100k.

Thank you for the response, a 100k is very doable for the cap rate rate im looking at.