Wastewater Treatment Plants in Massachusetts
66 facilities · 393 MGD combined flow
Klarifi tracks 66 publicly owned wastewater treatment plants in Massachusetts with a combined average flow of 393 MGD, serving about 4,158,803 residents. 27 plants treat more than 1 MGD and 5 more than 10 MGD; 9 use lagoon systems and 14 have digesters or biogas infrastructure. The largest is Deer Island Wastewater Treatment Facility in Winthrop at 233.7 MGD. 31 NPDES permits expire this year and 17 next year.
Every plant below links to a profile with average and design flow, treatment technology, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city.
66 plant locations in Massachusetts; dot size follows average flow.
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 | Technology | Violations (3y) |
|---|---|---|---|---|---|---|---|
| Deer Island Wastewater Treatment Facility | Winthrop | 233.7 | 480 | MA0103284 | Jul 2005 | Biogas silos, Biogas balloons | 3 |
| Upper Blackstone Wastewater Treatment Plant | Millbury | 24.1 | — | MAR053209 | Feb 2026 | Clarifiers | 15 |
| Greater Lawrence Wastewater Treatment Facility | North Andover | 21.7 | — | MAL100447 | Dec 2030 | Clarifiers, Biogas silos | 10 |
| South Essex Wastewater Treatment Plant | Salem | 17.57 | — | MAL100501 | Dec 2030 | — | 33 |
| New Bedford Wastewater Treatment Facility | New Bedford | 16.7 | 30 | MA0100781 | Nov 2013 | — | 14 |
| Brockton Advanced Water Reclamation Fac | Brockton | 9.9 | — | MAL101010 | Dec 2030 | Clarifiers, Biogas silos, Biogas balloons | 10 |
| Pittsfield Wastewater Treatment Facility | Pittsfield | 7 | 17 | MA0101681 | Oct 2026 | Clarifiers, Carrousels / oxidation ditches, Biogas silos, Biogas balloons | 84 |
| Haverhill Wastewater Treatment Facility | Haverhill | 6.58 | — | MAL101621 | Dec 2030 | — | 4 |
| Taunton Wastewater Treatment Facility | Taunton | 5.36 | 8.4 | MA0100897 | Jul 2020 | Clarifiers, Biogas balloons | 52 |
| Holyoke Water Pollution Control Facility | Holyoke | 5.02 | — | MAL101630 | Dec 2030 | Clarifiers | 4 |
| Westborough Wastewater Treatment Plant | Westborough | 4.17 | 7.7 | MA0100412 | Apr 2027 | Clarifiers, Carrousels / oxidation ditches, Biogas balloons | 2 |
| Northampton Wastewater Treatment Plant | Northampton | 3.84 | 8.65 | MA0101818 | Nov 2028 | Clarifiers, Biogas balloons | 40 |
| Amherst Wastewater Treatment Plant | Hadley | 3.33 | 7.1 | MA0100218 | Jan 2029 | Clarifiers | 42 |
| Billerica Wastewater Treatment Facility | Billerica | 2.88 | 5.5 | MA0101711 | Feb 2029 | Clarifiers | 52 |
| Westfield Wastewater Treatment Plant | Westfield | 2.4 | 6.1 | MA0101800 | Nov 2028 | Clarifiers | 0 |
| Gardner W W T F | East Templeton | 2.28 | — | MAG590013 | Oct 2027 | Clarifiers, Biogas silos | 75 |
| Hoosic Wastwater Treament Plant | Williamstown | 2.04 | 6.5 | MA0100510 | Dec 2028 | Clarifiers | 2 |
| Marlborough DPW Water Division East Plt | Marlborough | 2.04 | 5.5 | MA0100498 | Mar 2027 | Clarifiers | 13 |
| Rockland Wastewater Plant | Rockland | 2 | — | MAG590038 | Oct 2027 | Clarifiers, Biogas silos | 32 |
| Erving Wastewater Treatment Plant #2 | Erving | 1.72 | 2.7 | MA0101052 | Nov 2026 | Clarifiers, Aerated lagoons, Biogas balloons | 36 |
| Newburyport Wastewater Treatment Facility | Newburyport | 1.45 | — | MAG590035 | Oct 2027 | Clarifiers, Biogas silos, Biogas balloons | 0 |
| Greenfield Water Pollution Control Facility | Greenfield | 1.44 | — | MAG590014 | Oct 2027 | Clarifiers | 31 |
| Plymouth Wastewater Treatment Facility | Plymouth | 1.31 | — | MAG590040 | Oct 2027 | Uncovered lagoons, Biogas balloons | 5 |
| Palmer Water Pollution Control Facility | Palmer (three Rivers) | 1.2 | 5.6 | MA0101168 | Nov 2028 | Clarifiers | 4 |
| Westerly Wastewater Treatment Facility | Marlborough | 1.16 | 2.89 | MA0100480 | Dec 2026 | Clarifiers | 26 |
Massachusetts plants by treatment technology
All 66 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 September 11, 2026.