"I have seen survey teams in and around the area but don't really know what that means. I have zero problems with my septic tank in the 7 years we have lived here. Never had an overflow nor ever had it pumped. So I suspect it is a hit and miss thing."
Couldn't agree more, this property has never had a problem nor has anyone else I have met around here. To be honest, it's actually hard to have a problem except for blatant incompetence in installation. Seems in CO some 40 years ago, the rule was dig a hole, pour in a gallon of water and if it percolates in 1 minute or maybe more (sorry?) it's good. Here? - my gosh, about once a month during the dry season, out at my back gate, it moves and jams as the ground dries, so I have a certain place I put the hose to run overnight and hundreds of gallons leave a "wet spot" no larger than a dinner plate and the gate moves back. Yes, I know, don't start, my point is that the ground here is so porous it's hard to imagine having a septic problem - other than total incompetence.
I rent, but I'd bet the owners will be facing a bill for much $$$$ thousands of dollars of assessment for something they don't need.