Chlorine disinfection: wastewater treatment plants in Massachusetts
25 plants · 38% of the state · 356 MGD combined
Klarifi identifies 25 publicly owned wastewater treatment plants with chlorine disinfection in Massachusetts, 38% of the 66 plants in the state (356 MGD combined). The largest is Deer Island Wastewater Treatment Facility in Winthrop at 233.7 MGD.
Chlorine or chloramine disinfection, often followed by dechlorination before discharge, remains the most common effluent disinfection in the United States. Plants on gas chlorine are candidates for conversion to hypochlorite or UV, a recurring capital project driven by safety rules and permit limits on residual chlorine.
The largest plants with chlorine disinfection in Massachusetts
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Deer Island Wastewater Treatment Facility | Winthrop | 233.7 | MA0103284 | Jul 2005 | 3 |
| 2 | Upper Blackstone Wastewater Treatment Plant | Millbury | 24.1 | MAR053209 | Feb 2026 | 15 |
| 3 | Greater Lawrence Wastewater Treatment Facility | North Andover | 21.7 | MAL100447 | Dec 2030 | 10 |
| 4 | South Essex Wastewater Treatment Plant | Salem | 17.57 | MAL100501 | Dec 2030 | 33 |
| 5 | New Bedford Wastewater Treatment Facility | New Bedford | 16.7 | MA0100781 | Nov 2013 | 14 |
| 6 | Pittsfield Wastewater Treatment Facility | Pittsfield | 7 | MA0101681 | Oct 2026 | 84 |
| 7 | Haverhill Wastewater Treatment Facility | Haverhill | 6.58 | MAL101621 | Dec 2030 | 4 |
| 8 | Holyoke Water Pollution Control Facility | Holyoke | 5.02 | MAL101630 | Dec 2030 | 4 |
| 9 | Northampton Wastewater Treatment Plant | Northampton | 3.84 | MA0101818 | Nov 2028 | 40 |
| 10 | Amherst Wastewater Treatment Plant | Hadley | 3.33 | MA0100218 | Jan 2029 | 42 |
| 11 | Billerica Wastewater Treatment Facility | Billerica | 2.88 | MA0101711 | Feb 2029 | 52 |
| 12 | Westfield Wastewater Treatment Plant | Westfield | 2.4 | MA0101800 | Nov 2028 | 0 |
| 13 | Hoosic Wastwater Treament Plant | Williamstown | 2.04 | MA0100510 | Dec 2028 | 2 |
| 14 | Erving Wastewater Treatment Plant #2 | Erving | 1.72 | MA0101052 | Nov 2026 | 36 |
| 15 | Newburyport Wastewater Treatment Facility | Newburyport | 1.45 | MAG590035 | Oct 2027 | 0 |
| 16 | Greenfield Water Pollution Control Facility | Greenfield | 1.44 | MAG590014 | Oct 2027 | 31 |
| 17 | Plymouth Wastewater Treatment Facility | Plymouth | 1.31 | MAG590040 | Oct 2027 | 5 |
| 18 | Palmer Water Pollution Control Facility | Palmer (three Rivers) | 1.2 | MA0101168 | Nov 2028 | 4 |
| 19 | Orange Wastewater Treatment Plant | Orange | 0.61 | MAG590019 | Oct 2027 | 508 |
| 20 | Montague Wastewater Treatment Facility | Montague | 0.54 | MA0100137 | Dec 2028 | 237 |
| 21 | Hadley Wastewater Treatment Plant | Hadley | 0.34 | MAG580013 | Nov 2026 | 6 |
| 22 | Manchester Wastewater Treatment Facility | Manchester | 0.29 | MAG580043 | Nov 2026 | 33 |
| 23 | Leicester Water Supply WWTF | Leicester | 0.09 | MAG580027 | Nov 2026 | 5 |
| 24 | Huntington W W T P | Huntington | 0.03 | MAG580024 | Nov 2026 | 19 |
| 25 | Hardwick WWTP | Hardwick | 0.01 | MAG580017 | Nov 2026 | 14 |
Contacts and project signals for every plant on this list
Klarifi adds verified decision-maker contacts, permit limits, discharge monitoring data and the capital projects planned in each city, filterable by technology, size and compliance record.
Other technologies in Massachusetts
Chlorine disinfection in other states
Chlorine disinfection 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.