You are finally adding the second floor to the ranch in Rocky Point. Two more bedrooms, a bigger footprint, and then the architect mentions that the plans now need a new septic system, and not the kind your parents had. In Suffolk, that is the rule for a house going past five bedrooms with more floor area.
What goes in the ground now
The old Long Island cesspool was a precast ring with open sides. Wastewater went in, solids stayed, and liquid soaked into the sand. Suffolk banned new cesspools and, from July 2019, closed the loophole that let people swap a failed one for another. The Peconic Estuary Partnership says a replacement must have, at a minimum, a septic tank ahead of a leaching structure.
There are two kinds of systems going in today.
Conventional. A septic tank, where solids settle and grease floats, followed by one or more leaching pools or a drain field. No power, no moving parts.
Nitrogen-reducing, or I/A. I/A stands for innovative and alternative. These units add a treatment stage that removes nitrogen before the water reaches the ground. Suffolk’s Article 19, adopted in 2016, sets how they are tested and approved, and the Peconic Estuary Partnership says full approval requires 20 systems averaging under 19 mg/L of nitrogen over three years.
When each county asks for what
| Date | Rule | Where |
|---|---|---|
| July 1, 2018 | Companies must report pumpings and replacements to the county health department | Suffolk |
| July 1, 2019 | Replacing or retrofitting a cesspool or septic system needs county health department approval; at least a septic tank ahead of the leaching structure | Suffolk |
| July 2021 | I/A systems required for new construction in unsewered areas, and for renovations taking a house past five bedrooms with more footprint or floor area | Suffolk |
Sources: LongIsland.com (Dec 2017), Peconic Estuary Partnership, RiverheadLOCAL (Oct 2020).
In Nassau, the paperwork runs through your city, town or village building department. Nassau’s grant roadmap asks for stamped architectural or engineering drawings submitted to the local building department, its approved permit, and a certificate of occupancy or equivalent. Nassau’s Septic FAQ adds that state law does not let the same firm both design and install these systems, so expect a separate designer.
What a new system costs
| Who | What | Range | Date |
|---|---|---|---|
| EZ Cesspool, Greenlawn | Most residential installations in Nassau | $10,000 to $25,000 | Apr 2026 |
| EZ Cesspool, Greenlawn | Aerobic treatment system | $10,000 to $20,000 | Apr 2026 |
| Quality Cesspool, Greenlawn | Traditional full replacement | $10,000 to $25,000 | Oct 2026 |
| Quality Cesspool, Greenlawn | Nitrogen-reducing system | $20,000 to $40,000 | Oct 2026 |
| Suffolk Times, citing county speakers | I/A system | Upwards of $30,000, with one estimate over $50,000 | May 2024 |
| Nassau Soil and Water Conservation District | Average design and installation under Nassau’s grant | $24,115 | Sep 2022 data |
EZ Cesspool says installation labor is typically 50% to 70% of the total. Restoration, permits and engineering are on top, and none of the companies above puts a firm number on them, so ask for each as its own line.
The tank itself
EZ Cesspool’s guide gives these prices for the tank alone, before labor:
| Material | Price per tank |
|---|---|
| Concrete | $700 to $2,000, lasting 40 years or more with maintenance |
| Plastic or polyethylene | $500 to $2,000 |
| Fiberglass | From about $1,500 for 1,000 gallons |
The same guide sizes tanks at 750 to 900 gallons for two or three bedrooms, 1,000 gallons for four, and 1,250 to 2,000 gallons or more for bigger homes.
Running costs after it is in
A conventional tank and leaching pool has no power bill. A nitrogen-reducing unit does. EZ Cesspool puts the aerator’s electricity at $5 to $15 a month. The Peconic Estuary Partnership’s cost model puts average yearly operation and maintenance, power included, at about $620 to $903. Both counties expect a professional to service these systems at least once a year.
Grants that cut the cost
Suffolk. The county’s Septic Improvement Program offers up to $20,000, and the state’s Septic System Replacement Program up to 75% of eligible costs, capped at $25,000. Together that is the “up to $45,000” the county announced in August 2026. Only installers on the county’s approved list can install grant-funded systems, and the county grant is paid directly to the installer.
Nassau. The SEPTIC program offers up to $20,000 to eligible single and two-family homes, small businesses and nonprofits that are not connected to a sewer.
Both have eligibility rules, so check before you sign a contract. The Suffolk grant guide and Nassau grant guide go through them.
Who is allowed to install
Suffolk’s code requires a conventional septic system installation endorsement for any conventional installation, replacement or major repair. It takes a Long Island Liquid Waste Association training class and certification test, or a county-approved equivalent. Installing a nitrogen-reducing system takes the separate installer endorsement, which requires manufacturer certificates on top of the conventional one. In Nassau, the county’s grant materials require a Nassau County home improvement license.
What to ask the installer
- Are you on Suffolk’s approved installer list, or do you hold a Nassau home improvement license?
- Which system are you proposing, and is it on the county’s accepted list?
- Who is the designer, and who files with the health department or building department?
- What does the price include: tank, leaching pools, digging, restoration, permits, electrical work?
- Who services it after it is in, and what does that cost a year?
- Have you already checked whether I qualify for the grant?