Short answer: An I/A (Innovative and Alternative) system is a septic system that removes nitrogen. In Suffolk County it is required for new houses, qualifying additions and major reconstructions filed on or after July 1, 2021, and it is the system the county and state grants pay for. Replacing a failed cesspool on its own needs at least a septic tank and leaching ring, unless your town requires more.
Last updated: November 2026. Every rule and number below links to the county, state or town document it came from. This is homeowner guidance, not legal advice; the Suffolk County Department of Health Services (SCDHS) or your town makes the call on a specific property.
What an I/A system is, and why Long Island counties want them
A cesspool or a conventional septic system was never built to remove nitrogen. Suffolk and Nassau both put the discharge of an average home system at about 40 pounds of nitrogen a year, and Suffolk's FAQ ties that nitrogen to algal blooms, fish kills and the loss of shellfish beds.
An I/A system adds a treatment stage. Wastewater passes through an aerobic compartment where bacteria convert nitrogen to nitrate, then an oxygen-depleted stage where other bacteria strip the oxygen off the nitrate and release nitrogen gas. Every general-use and provisional-use technology approved in Suffolk relies on that biological process. The treated water still goes to a leaching structure in the ground, so an I/A system replaces the tank side of your system, not the need for a place for water to drain.
The yard looks different afterwards. Suffolk's homeowner sheet lists what stays visible: tank covers at grade (they must remain accessible), a control panel with alarms, and air intake and vent piping.
When Suffolk County requires one
- New or expanded houses and major reconstruction. Construction applications filed with the Office of Wastewater Management on or after July 1, 2021 must include an I/A system when the project is a new or expanded single-family residence or a major reconstruction and is allowed an on-site system (Article 6, §760-614). "Expanded" includes an addition that needs the sanitary system changed and adding bedrooms beyond what OWM previously approved. "Major reconstruction" means work costing more than 50% of the existing structure's market value.
- Exemptions. An existing house is exempt when the work is not a major reconstruction and adds no bedrooms beyond the approved count, or when it is not a major reconstruction, the footprint and square footage don't change and the house stays at five bedrooms or fewer. Where bedrooms are added, a conforming conventional septic system is the minimum. Parcels inside a proposed sewer district approved by the Health Commissioner are excluded from the I/A requirement.
- Cesspool replacement. Since July 1, 2019, replacing or retrofitting any cesspool or septic system needs SCDHS approval, and the new system must meet current standards: at minimum a septic tank ahead of a leaching structure. A cesspool can no longer be swapped for a cesspool. The county rule does not force an I/A system in that case.
- Town codes can go further. East Hampton requires a low-nitrogen system for any voluntary replacement of an existing sanitary system, new buildings and substantial expansions (Town Code §210-3-2). Southampton requires an I/A system in its high-priority area for new residential construction, any substantial upgrade SCDHS requires, and floor-area increases of 25% or more (§123-52).
Walk through your own situation in Is an I/A system required for my property?
Nassau County
We found no Nassau County rule that requires an I/A system for an existing home. Nassau's S.E.P.T.I.C. program is a voluntary grant for owners who choose to upgrade. Residential approvals generally run through the town, city or village building department, and the installer must hold a Nassau County Home Improvement License. See Nassau County cesspool and septic regulations.
Approved I/A technologies
Suffolk approves technologies in stages: experimental, piloting, provisional and general use. Provisional systems have no installation cap, but the first 20 year-round systems are sampled every other month for 24 months; a provisional technology may receive general use approval if those 20 systems average 19 mg/L total nitrogen or less.
| Technology (Suffolk residential) | Approval stage | Approval date |
|---|---|---|
| Fuji Clean CEN | General use | 2/16/2022 |
| Hydro-Action AN | General use | 10/19/2021 |
| Orenco AX Series | General use | 7/9/2024 |
| SeptiTech STAAR | General use | 11/9/2023 |
| Nitrogen Reducing Biofilter (Box) | Provisional use | 6/28/2024 |
| Nitrogen Reducing Biofilter (Lined) | Provisional use | 4/25/2023 |
| Norweco Hydro-Kinetic | Provisional use | 4/21/2017 |
The same list shows technologies in piloting (8 to 12 systems each, for example Amphidrome, AquaPoint BioClere, Hoot-ANR, the unlined Nitrogen Reducing Biofilter and two ECOPOD models added May 30, 2025) and experimental use (2 to 5 systems). Those can't be chosen as an ordinary replacement. The county notes that general-use approvals are for residential systems; commercial systems remain provisional.
Nassau's S.E.P.T.I.C. program accepts Hydro-Action AN Series, Norweco Singulair TNT and HydroKinetic, Orenco Advantex AX20, Fuji Clean CEN Series and SeptiTech STAAR.
We list technologies, not companies. The county's own documents name the distributors and the installers approved for grant work.
The permit path in Suffolk, step by step
This is the order the county's 2026 grant process overview and septic-grant page lay out for a grant-funded replacement.
- Check eligibility and sewer status. Look up the property on the county's SIP eligibility map. A home already on sewer, or inside a proposed sewer district, is outside the grant program.
- Apply for the grants before any work. The county SIP application also files for the state SSRP grant. Grants must be issued before the system is installed.
- Hire a design professional. A licensed engineer or architect designs the system and files the permit application with the SCDHS Office of Wastewater Management (OWM). They also identify any town, village, wetlands or state permits.
- Get the OWM permit. OWM issues the Permit to Construct. For a straight swap of an existing cesspool or septic system, an approved installer can instead apply through the county's hauler portal; a replacement tied to an addition goes through a residential application.
- Pick an installer and lock the price. For grant-funded work the installer must be on the county's SIP-approved list. You sign Assignment of Payment forms so the county pays the installer directly, and the county issues a Grant Eligibility Memo based on the quote.
- Install, start-up and inspection. SCDHS witnesses the system start-up. The design professional files as-built plans; the installer files installation and abandonment certifications for the old system.
- Register and sign the maintenance contract. An Operation & Maintenance Agreement and the I/A registration form are submitted from the maintenance provider. Article 19 makes the owner responsible for keeping that contract active.
- Grant payment. After the inspector's certification letter, the county pays the SIP and SSRP grants to the installer named on the Assignment of Payment forms.
Permit application fees, engineering and design, and post-installation landscaping are the owner's costs and aren't covered by the county grant. OWM questions go to 631-852-5700; grant questions to 631-852-5811.
What Article 19 asks of an I/A owner
- Register the system with SCDHS before construction, and re-register every 36 months.
- Keep an active Operation and Maintenance Contract with a company holding a Suffolk Liquid Waste License and the I/A service-provider endorsement (Endorsement K). Tell SCDHS within 30 days if you change providers.
- At least one O&M visit a year. The provider reports every service visit to the county.
- The owner pays for repairs and must keep the components accessible.
- When the property is sold, the seller notifies SCDHS within 60 days and the buyer registers the system within 60 days.
Grant-funded systems can't be removed or switched off without written SCDHS approval. The county SIP grant pays for the first three years of maintenance.
What one costs
Installation: In a November 2024 presentation, SCDHS put the average cost to install an I/A system and leaching, including removing the old system, under the grant program was about $34,000 in the East End towns and $28,500 in the West End towns, with engineering and site restoration on top. The county's installer price sheet for a four-bedroom home (November 2025) runs from about $15,000 to $74,000 depending on whether the old leaching rings can be reused. The full breakdown is in our cesspool and I/A cost guide.
Running costs, from the county's May 2026 homeowner sheet (figures the county says come from vendors):
| Item | Approximate cost | How often |
|---|---|---|
| Operation & maintenance contract | $300 to $600 | Per year |
| Pumping | About $500 | About every 3 years |
| Electricity | $75 to $250 | Per year |
| Blower/aerator replacement | About $450 | Every 10 years |
| Recirculation pump replacement | About $700 | Every 10 years |
| Float replacement | About $100 | Every 5 to 10 years |
| Control panel | About $1,200 | 20+ years (rare) |
Grants
In Suffolk, the county SIP grant is up to $20,000 and the state SSRP grant up to 75% of eligible costs with a $25,000 cap, both through one county application. Nassau's S.E.P.T.I.C. grant is up to $35,000 per the program administrator (Nassau County Soil & Water Conservation District); the county page still lists $20,000; confirm at 516-364-5861. East Hampton, Southampton and Shelter Island add town rebates. Eligibility, stacking and how payment works are in our Long Island septic grants guide.
Where Suffolk's I/A systems are
SCDHS reported approximately 5,344 I/A systems installed countywide as of October 2024.
| Town | Approx. I/A installs (10/2024) |
|---|---|
| Southampton | 1,881 |
| East Hampton | 1,465 |
| Brookhaven | 730 |
| Southold | 308 |
| Shelter Island | 250 |
| Islip | 240 |
| Huntington | 197 |
| Smithtown | 126 |
| Riverhead | 90 |
| Babylon | 57 |
The two towns with their own rebate programs and code requirements account for well over half. Each town page has the sewer-district, groundwater-zone and rebate details for that town.
Frequently asked questions
What is an I/A septic system?
An Innovative and Alternative Onsite Wastewater Treatment System (I/A OWTS) is a septic system that treats wastewater biologically to remove nitrogen before it reaches the groundwater. Under Suffolk's approval list, a provisionally approved technology may receive general use approval if its first 20 tracked year-round systems average 19 mg/L of total nitrogen or less.
Is an I/A system required in Suffolk County?
For construction projects, yes: applications filed with the Office of Wastewater Management on or after July 1, 2021 for a new or expanded single-family residence or a major reconstruction must include an I/A system, with exemptions (Article 6, §760-614). Replacing a failed cesspool on its own requires at least a septic tank and leaching structure, not an I/A system, unless a town code says otherwise (East Hampton does).
Which I/A systems are approved in Suffolk County?
General use (no cap): Fuji Clean CEN, Hydro-Action AN, Orenco AX Series and SeptiTech STAAR. Provisional use: Nitrogen Reducing Biofilter (Box and Lined) and Norweco Hydro-Kinetic. Several more are in piloting or experimental phases. Source: the county's list revised May 30, 2025.
How much does it cost to run an I/A system?
Suffolk County's homeowner sheet (May 2026, based on vendor information) lists an operation and maintenance contract at about $300 to $600 a year, pumping about every 3 years at about $500, and electricity of $75 to $250 a year. Nassau County's FAQ says maintenance agreements typically cost about $300 a year.
Do I have to keep a maintenance contract on an I/A system?
Yes, in Suffolk. Article 19 requires every owner to keep an active operation and maintenance contract with a company holding a Liquid Waste License with the I/A service endorsement, and at least one O&M visit a year. Nassau's grant program requires a maintenance agreement for the life of the system.
What happens to an I/A system when I sell the house?
In Suffolk, the seller must notify the Department of Health Services in writing within 60 days of the transfer, and the buyer must register the system within 60 days. Registration is renewed every 36 months.
Sources
Each source was re-read on November 7, 2026. Program amounts and rules change; the agency page is the authority.
- Suffolk County Sanitary Code, Article 6 (amended 12/1/2020)
- Suffolk County Sanitary Code, Article 19 (I/A OWTS management)
- Suffolk County DHS: Changes to wastewater practices effective July 1, 2019
- Suffolk County DHS: List of approved I/A OWTS (revised 5/30/2025)
- Suffolk County: Septic Improvement Program FAQ (4/2026)
- Suffolk County: Septic Improvement Program grant process overview (2026)
- Suffolk County: Septic Improvement Program information
- Suffolk County DHS: What homeowners should know about I/A OWTS (5/5/2026)
- Suffolk County DHS presentation, 11/19/2024 (hosted by the Town of Shelter Island)
- Nassau County: S.E.P.T.I.C. program
- Nassau County: Septic FAQ
- Town of East Hampton Code §210-3-2 (low-nitrogen systems)
- Town of Southampton Code §123-52 (I/A OWTS required)
Have a cesspool or septic question on Long Island?
Submit a request and we match it to an independent, licensed Suffolk or Nassau County operator who serves your address. The operator contacts you to confirm the work and the price.
Request Service →