I ripped off that portion of the carpet to confirm it's a concrete slab underneath and no foundation cracks around there.

Wouldn't that rot the wood underneath? 

Depending on what area of SC, our soil is very loamy (sandy) because we're on the coast.

Some of it depends on the area you live in, how deep the lines are, the types of lines (cast iron, clay, pvc, etc), and the soil types and such.For a job like that, you should get three quotes and have them try and break the quotes down by labor, parts, permits, and such.

I'm not sure when this issue initially occurred but it comes back every year in the same areas.The way it looks make it seem like it is coming from underneath.

They attract bugs at night and then mice underneath.

You'd have to double check with a professional if your interpretation is acceptable, but I wouldn't think so.Don't forget, you still have to own the land underneath.

They more likely mean you need to know where you can and can't build, how deep your setbacks have to be, how much permits are going to be, does the city have funky ordinances that won't allow you to do what you want, what soil work do you have to do etc. 

You have a safety net underneath you.

The septic company said to allocate 30-35k saying the permitting process in the area and the soil make it difficult.