City doesn't know that my property has a septic tank

[Ashraf Spahi]

I recently purchased a property built in 1970 through an auction that I am looking to rehab and flip. One of the items I want to rehab is the driveway which needs asphalt resurfacing. 

I was at the building permit office today and inquired what I would need to show in order to get the permit approved. They asked whether the property was septic or municipal sewer because nothing showed up in their system in case the septic system is under the driveway so I went next door to talk to the septic tank department and they told me they have no record of my property having a septic tank and to check with the water department. 

I visited the water department and they weren't sure either. (it's an unincorporated area which receives utilities from various neighboring divisions) They only told me that I was only connected for water and not sewer. Meaning I have a septic tank. 

My question is: When I let the city know that I do in fact have a septic system after I get a team out to figure out where it exists; What would happen? Would they just make note of it? Would they ask me to do a bunch of tests and inspections that could end up costing lots of money?