Short answer: The county's sewer map shows no active district inside Mastic; on-site systems are the norm apart from any village-run or private plant the layer doesn't include. 32% sits in a proposed sewer district, which can rule out the septic grants.
Mastic in numbers
| Town | Town of Brookhaven |
|---|---|
| Area | 3.85 sq mi |
| In active sewer district | 0% |
| In proposed district | 32% · Proposed SCCRI Forge River Sewage Treatment Plant Expansion, Forge River Watershed Sewer District Phases III & IV |
| Groundwater zone | Zone VI 100% |
| FEMA flood zone | 2% |
| One-family lots / median | 4,252 / 0.23 ac |
| One-family lots outside active sewer districts | about 4,252 |
Computed 2026-11-07 from Suffolk County GIS (hamlet boundaries, sewer districts, groundwater management zones, FEMA flood zones, protection areas, tax parcels). Shares are of land area; a district boundary is not a hookup, and some village-run systems are missing from the county layer. Method and full table.
Sewer coverage
The county's sewer map shows no active district inside Mastic; on-site systems are the norm apart from any village-run or private plant the layer doesn't include. About 32% of Mastic is inside proposed districts (“Proposed SCCRI Forge River Sewage Treatment Plant Expansion”, “Forge River Watershed Sewer District Phases III & IV”). Suffolk's septic grants exclude homes in a proposed sewer district, so check the address on the county map before budgeting for an I/A upgrade. By parcel count, roughly 4,252 of Mastic's 4,252 one-family lots sit outside an active district; that is the local cesspool and septic population, before counting unconnected lots inside districts. Neighbouring areas: Moriches (0% sewered, median lot 0.51 ac); Poospatuck Indian Reservation (0% sewered, median lot 0.27 ac); Shirley (0% sewered, median lot 0.26 ac). By active-sewer share Mastic ranks 93 of the 165 Suffolk hamlets and villages we measured.
Groundwater, lots and flood exposure
Groundwater management Zone VI: Article 6's minimum lot for a new home on an on-site system here is 40,000 sq ft, unless the density is met another way or an exemption applies. County parcel records show 4,252 one-family lots touching Mastic, with a median of 0.23 acres (about 10,100 sq ft), below that minimum and the 134th-largest median lot in our Suffolk table. Also mapped: 2% of the land is in FEMA's 1%-annual-chance flood zone; 7% is Pine Barrens Core.
Before planning an I/A upgrade in Mastic, confirm whether your street is in the proposed district; if it is, the county and state grants may not apply.
Who handles what in Mastic
- Building and electrical permits: Town of Brookhaven
- System approvals and grants: SCDHS, 631-852-5700 (permits) / 631-852-5811 (grants)
Frequently asked questions
Is Mastic on public sewer?
Generally not: no active county sewer district covers Mastic on the county's map.
Can Mastic homeowners get septic grants?
Yes, if the home isn't sewered and isn't in a proposed sewer district (about 32% of Mastic is): up to $20,000 from Suffolk and up to $25,000 from the state.
County rules, licensing and grant steps: Town of Brookhaven overview, septic grants, replacement rules. More in Brookhaven: Shirley, Center Moriches, Mastic Beach, Yaphank.
Sources
Each source was re-read on November 7, 2026. Program amounts and rules change; the agency page is the authority.
- Suffolk County GIS Viewer map service (hamlets, villages, sewer districts, groundwater zones, flood zones, tax parcels)
- Suffolk County Sanitary Code, Article 6 (amended 12/1/2020)
- Suffolk County: Septic Improvement Program information
- Suffolk County: SIP property eligibility lookup
Need cesspool or septic work in Mastic?
Submit a request with your address. We match it to an independent, licensed Suffolk County operator who serves that address; the operator confirms the time and price with you.
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