Wastewater treatment plants in Massachusetts
65 facilities · 437 MGD combined flow
Klarifi tracks 65 publicly owned wastewater treatment plants in Massachusetts with a combined average flow of 437 MGD, serving about 3,693,933 residents. 26 plants treat more than 1 MGD and 5 more than 10 MGD; 8 use lagoon systems and 13 have digesters or biogas infrastructure. The largest is Deer Island Wastewater Treatment Facility in Winthrop at 270.96 MGD. 31 NPDES permits expire this year and 18 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.
65 plant locations in Massachusetts; dot size follows average flow. Boundaries: U.S. Census Bureau.
NPDES permits and renewals in Massachusetts
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 Massachusetts
| Facility | City | Avg flow (MGD) | Design (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| Deer Island Wastewater Treatment Facility | Winthrop | 270.96 | 480 | MA0103284 | Jul 2005 | 3 |
| Upper Blackstone Wastewater Treatment Plant | Millbury | 30.02 | — | MAR053209 | Feb 2026 | 19 |
| New Bedford Wastewater Treatment Facility | New Bedford | 21.74 | 30 | MA0100781 | Nov 2013 | 14 |
| South Essex Wastewater Treatment Plant | Salem | 21.66 | — | MAL100501 | Dec 2030 | 33 |
| Brockton Advanced Water Reclamation Fac | Brockton | 14.52 | — | MAL101010 | Dec 2030 | 10 |
| Pittsfield Wastewater Treatment Facility | Pittsfield | 9.85 | 17 | MA0101681 | Oct 2026 | 85 |
| Taunton Wastewater Treatment Facility | Taunton | 7.32 | 8.4 | MA0100897 | Jul 2020 | 48 |
| Holyoke Water Pollution Control Facility | Holyoke | 6.07 | — | MAL101630 | Dec 2030 | 4 |
| Westborough Wastewater Treatment Plant | Westborough | 4.86 | 7.7 | MA0100412 | Apr 2027 | 2 |
| Northampton Wastewater Treatment Plant | Northampton | 4.21 | 8.65 | MA0101818 | Nov 2028 | 41 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
Massachusetts plants by treatment technology
All 65 plants in Massachusetts
Wastewater treatment in Massachusetts: 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 · Equalization tank · Centrate · 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 Massachusetts.” Updated October 26, 2026. https://klarifi.io/facilities/massachusettsNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.