The 50 largest wastewater treatment plants in Massachusetts
Ranked by average flow · 437 MGD combined · 100% of the state's reported flow
Deer Island Wastewater Treatment Facility in Winthrop is the largest publicly owned wastewater treatment plant in Massachusetts by reported average flow, treating about 270.96 million gallons per day. The 50 plants below treat 437 MGD between them, 100% of the flow reported by all 65 plants in the state, and serve about 3,678,369 people. Every plant links to its profile with permit and compliance data. Treatment technology is shown with a free Klarifi account.
| # | Facility | City | Avg flow (MGD) | Population | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|---|
| 1 | Deer Island Wastewater Treatment Facility | Winthrop | 270.96 | 2,317,098 | MA0103284 | Jul 2005 | 3 |
| 2 | Upper Blackstone Wastewater Treatment Plant | Millbury | 30.02 | 257,969 | MAR053209 | Feb 2026 | 19 |
| 3 | New Bedford Wastewater Treatment Facility | New Bedford | 21.74 | 103,942 | MA0100781 | Nov 2013 | 14 |
| 4 | South Essex Wastewater Treatment Plant | Salem | 21.66 | 376,847 | MAL100501 | Dec 2030 | 33 |
| 5 | Brockton Advanced Water Reclamation Fac | Brockton | 14.52 | 120,494 | MAL101010 | Dec 2030 | 10 |
| 6 | Pittsfield Wastewater Treatment Facility | Pittsfield | 9.85 | 48,150 | MA0101681 | Oct 2026 | 85 |
| 7 | Taunton Wastewater Treatment Facility | Taunton | 7.32 | 39,644 | MA0100897 | Jul 2020 | 48 |
| 8 | Holyoke Water Pollution Control Facility | Holyoke | 6.07 | 34,070 | MAL101630 | Dec 2030 | 4 |
| 9 | Westborough Wastewater Treatment Plant | Westborough | 4.86 | 51,131 | MA0100412 | Apr 2027 | 2 |
| 10 | Northampton Wastewater Treatment Plant | Northampton | 4.21 | 26,565 | MA0101818 | Nov 2028 | 41 |
| 11 | Amherst Wastewater Treatment Plant | Hadley | 3.36 | 35,110 | MA0100218 | Jan 2029 | 44 |
| 12 | Billerica Wastewater Treatment Facility | Billerica | 3.3 | 35,443 | MA0101711 | Feb 2029 | 51 |
| 13 | Hoosic Wastwater Treament Plant | Williamstown | 3.26 | 22,403 | MA0100510 | Dec 2028 | 2 |
| 14 | Westfield Wastewater Treatment Plant | Westfield | 2.95 | 2,559 | MA0101800 | Nov 2028 | 0 |
| 15 | Gardner W W T F | East Templeton | 2.94 | — | MAG590013 | Oct 2027 | 78 |
| 16 | Marlborough DPW Water Division East Plt | Marlborough | 2.77 | — | MA0100498 | Mar 2027 | 16 |
| 17 | Rockland Wastewater Plant | Rockland | 2.21 | — | MAG590038 | Oct 2027 | 37 |
| 18 | Greenfield Water Pollution Control Facility | Greenfield | 2.2 | 13,193 | MAG590014 | Oct 2027 | 32 |
| 19 | Erving Wastewater Treatment Plant #2 | Erving | 1.77 | 956 | MA0101052 | Nov 2026 | 36 |
| 20 | Westerly Wastewater Treatment Facility | Marlborough | 1.58 | 40,085 | MA0100480 | Dec 2026 | 26 |
| 21 | Hull Wastewater Treatment Plant | Hull | 1.53 | 7,478 | MAL101231 | Dec 2030 | 3 |
| 22 | Newburyport Wastewater Treatment Facility | Newburyport | 1.52 | 17,891 | MAG590035 | Oct 2027 | 0 |
| 23 | Palmer Water Pollution Control Facility | Palmer (three Rivers) | 1.37 | 7,927 | MA0101168 | Nov 2028 | 5 |
| 24 | Hudson W W T F | Hudson | 1.33 | 19,692 | MAG590029 | Oct 2027 | 78 |
| 25 | Middleborough WPCF | Middleborough | 1.21 | — | MAG590042 | Oct 2027 | 12 |
| 26 | Plymouth Wastewater Treatment Facility | Plymouth | 1.08 | 12,121 | MAG590040 | Oct 2027 | 5 |
| 27 | Orange Wastewater Treatment Plant | Orange | 0.9 | 3,747 | MAG590019 | Oct 2027 | 511 |
| 28 | Uxbridge Wastewater Treatment Facility | Uxbridge | 0.9 | 8,412 | MAG590003 | Oct 2027 | 24 |
| 29 | Concord Wastewater Treatment Facility | Concord | 0.83 | 5,492 | MAG590030 | Oct 2027 | 5 |
| 30 | Medfield Wastewater Treatment Facility | Medfield | 0.77 | 8,870 | MAG590008 | Oct 2027 | 664 |
| 31 | Salisbury Wastewater Treatment Facility | Salisbury | 0.73 | 6,401 | MA0102873 | Jan 2021 | 14 |
| 32 | Spencer Wastewater Treatment Plant | Spencer | 0.66 | 4,749 | MAG590010 | Oct 2027 | 20 |
| 33 | Ipswich Wastewater Treatment Plant | Ipswich | 0.66 | 6,824 | MAG590036 | Oct 2027 | 2 |
| 34 | Lee Wastewater Treatment Facility | Lee | 0.58 | 5,157 | MAG590023 | Oct 2027 | 1 |
| 35 | Montague Wastewater Treatment Facility | Montague | 0.53 | 5,764 | MA0100137 | Dec 2028 | 267 |
| 36 | Lenox Center Wastewater Treatment Facility | Lenox | 0.5 | 3,379 | MAG590024 | Oct 2027 | 12 |
| 37 | Manchester Wastewater Treatment Facility | Manchester | 0.44 | 3,418 | MAG580043 | Nov 2026 | 37 |
| 38 | Marion Wastewater Treatment Facility | Marion | 0.44 | 3,335 | MA0100030 | Nov 2022 | 15 |
| 39 | Charlton W W T P | Charlton | 0.41 | — | MAG580039 | Nov 2026 | 192 |
| 40 | North Brookfield Waste Water Treatment Plant | North Brookfield | 0.4 | 938 | MAG580037 | Nov 2026 | 27 |
| 41 | Merrimac Wastewater Treatment Plant | Merrimac | 0.36 | 3,993 | MAG580030 | Nov 2026 | 0 |
| 42 | Hadley Wastewater Treatment Plant | Hadley | 0.32 | 2,952 | MAG580013 | Nov 2026 | 10 |
| 43 | Oxford Rochdale Wastewater Treatment Plant | North Oxford | 0.26 | 3,183 | MAG580026 | Nov 2026 | 0 |
| 44 | Templeton W W T P | Templeton | 0.26 | — | MAG580038 | Nov 2026 | 19 |
| 45 | M C I Norfolk Walpole | Norfolk | 0.21 | — | MAG580036 | Nov 2026 | 5 |
| 46 | Cohasset Wastewater Treatment Facility | Cohasset | 0.18 | 4,646 | MAG580033 | Nov 2026 | 82 |
| 47 | Leo L. Dubois WPCF - Bridgewater Correction Complex | Bridgewater | 0.17 | — | MAG580040 | Nov 2026 | 42 |
| 48 | Stockbridge W W T P | Stockbridge | 0.16 | 1,398 | MAG580029 | Nov 2026 | 0 |
| 49 | Sunderland Wastewater Treatment Facility | Sunderland | 0.16 | 2,720 | MAG580005 | Nov 2026 | 0 |
| 50 | Douglas W W T P | East Douglas | 0.15 | 2,223 | MAG580006 | Nov 2026 | 132 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
Largest plants 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 · Anaerobic digester · Lift station · 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. “Largest wastewater treatment plants in Massachusetts (2026).” Updated October 26, 2026. https://klarifi.io/facilities/massachusetts/largestNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.