Why some lots need them
A standard septic system relies on enough good soil to finish treating the wastewater. When there isn't enough — or the lot is small, or groundwater or rock is shallow — the state may require an advanced system that cleans the water more before it reaches the soil.
What's involved
Treatment unit
Adds air and bacteria or uses filter media to break down more waste.
Disposal field
Often smaller than a standard field because the water is cleaner.
Power and alarm
Pumps or blowers run on electricity; an alarm warns of problems.
Maintenance
Regular servicing is part of owning one.
Budget for it
Advanced systems cost more up front and have ongoing service costs. If you're buying land, find out early whether one will be needed. See conventional vs advanced.
Septic questions
How do I know if I need one?
The site evaluation and permit review decide.
Do they smell?
A properly working, maintained system shouldn't.
What happens if the power goes out?
Short outages are usually fine; use less water until power returns.