| System | Typical installed cost | Ongoing |
|---|---|---|
| Aerobic treatment unit (ATU) | $10,000–$20,000 | maintenance contract + air pump every 5–10 yrs |
| Mound / raised fill | $12,000–$25,000 | same as conventional |
| Drip irrigation dispersal | $12,000–$25,000 | filter and pump service |
| Low-pressure dosing | $10,000–$18,000 | pump service |
| Performance-based (engineered) | $15,000–$30,000+ | per design |
Suffolk County specifics. The county's own figure for an average nitrogen-removing I/A system is about $25,000, plus engineering and design, which you contract separately and pay for yourself. Against that: the County Septic Improvement Program pays up to $20,000 direct to an approved installer, and the New York State Septic System Replacement Program pays up to 75% of eligible costs capped at $25,000, either to the installer or back to you. Together, up to $45,000. On a $25,000 quote the state share is the larger of the two, because 75% binds long before the $25,000 cap does. Running costs are $300–$600 a year for the maintenance contract, plus $75–$250 a year in electricity (county figures). The math in full
When you're required to go advanced: the county site evaluation says so. It is not a contractor upsell — the sanitarian's finding controls what can be permitted. If a contractor proposes an advanced system before the county has evaluated the site, ask why.