Wastewater treatment plants in Delaware
8 facilities · 10 MGD combined flow
Klarifi tracks 8 publicly owned wastewater treatment plants in Delaware with a combined average flow of 10 MGD, serving about 49,789 residents. 4 plants treat more than 1 MGD and 0 more than 10 MGD; 3 use lagoon systems and 0 have digesters or biogas infrastructure. The largest is South Coastal STP in Frankford at 4.37 MGD. 1 NPDES permits expire this year and 0 next year.
Every plant below links to a profile with average and design flow, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city. Treatment technology and verified contacts are shown with a free Klarifi account.
8 plant locations in Delaware; dot size follows average flow. Boundaries: U.S. Census Bureau.
NPDES permits and renewals in Delaware
Every plant discharges under an NPDES permit that is renewed every five years, usually with tighter limits. The renewal year is the year a plant budgets for upgrades.
Largest wastewater treatment plants in Delaware
| Facility | City | Avg flow (MGD) | Design (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| South Coastal STP | Frankford | 4.37 | — | DEL050008 | Dec 2030 | 5 |
| Seaford Wastewater Treatment Plant | Seaford | 1.61 | — | DE0020265 | Oct 2020 | 0 |
| Howard Seymour Water Reclamation Plant | Lewes | 1.29 | — | DE0021512 | Oct 2023 | 1 |
| Selbyville Wastewater Treatment Facility | Selbyville | 1.24 | — | DE0020010 | Apr 2028 | 1 |
| Laurel Water Department | Laurel | 0.5 | — | DE0020125 | Oct 2028 | 62 |
| Delaware City Wastewater Treatment Plant | Delaware City | 0.42 | — | DEL021555 | Dec 2030 | 2 |
| Milton Wastewater Treatment Plant | Milton | 0.23 | — | DE0021491 | Apr 2016 | 11 |
| Port Penn Wastewater Treatment Plant | Port Penn | 0.04 | — | DE0021539 | Oct 2026 | 1 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
Delaware plants by treatment technology
All 8 plants in Delaware
| Facility | City | Flow (MGD) |
|---|---|---|
| South Coastal STP | Frankford | 4.37 |
| Seaford Wastewater Treatment Plant | Seaford | 1.61 |
| Howard Seymour Water Reclamation Plant | Lewes | 1.29 |
| Selbyville Wastewater Treatment Facility | Selbyville | 1.24 |
| Laurel Water Department | Laurel | 0.5 |
| Delaware City Wastewater Treatment Plant | Delaware City | 0.42 |
| Milton Wastewater Treatment Plant | Milton | 0.23 |
| Port Penn Wastewater Treatment Plant | Port Penn | 0.04 |
Wastewater treatment in Delaware: questions
Sources and methodology
Flow, permit and violation figures come from the EPA's ICIS-NPDES discharge monitoring records. Population served comes from the Clean Watersheds Needs Survey 2022. Treatment structures are identified by Klarifi's review of aerial imagery, and capital improvement projects are extracted from published municipal budget documents. Violations are counted over the last three years of monitoring reports.
Data refreshed October 26, 2026.
Wastewater terms: WWTP · POTW · MGD · NPDES permit · Activated sludge · Oxidation ditch · all terms
Cite this page
Journalists, researchers and educators are welcome to quote these figures. Please credit Klarifi as the source and link to this page.
Klarifi. “Wastewater treatment plants in Delaware.” Updated October 26, 2026. https://klarifi.io/facilities/delawareNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.