Wastewater Treatment Plants in New Hampshire
46 facilities · 39 MGD combined flow
Klarifi tracks 46 publicly owned wastewater treatment plants in New Hampshire with a combined average flow of 39 MGD, serving about 497,915 residents. 13 plants treat more than 1 MGD and 0 more than 10 MGD; 15 use lagoon systems and 15 have digesters or biogas infrastructure. The largest is Nashua WWTP in Nashua at 9.2 MGD. 28 NPDES permits expire this year and 4 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.
46 plant locations in New Hampshire; dot size follows average flow.
NPDES permits and renewals in New Hampshire
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 New Hampshire
| Facility | City | Avg flow (MGD) | Design (MGD) | NPDES permit | Expires | Technology | Violations (3y) |
|---|---|---|---|---|---|---|---|
| Nashua WWTP | Nashua | 9.2 | 16 | NH0100170 | May 2020 | Clarifiers, Biogas silos, Biogas balloons | 87 |
| Wrbp Franklin Wastewater Treatment Plant | Franklin | 3.53 | 11.5 | NH0100960 | Jun 2029 | Clarifiers, Biogas silos, Biogas balloons | 22 |
| Concord Wastewater Treatment Facility | Concord | 3.2 | 10.1 | NH0100901 | Aug 2027 | Clarifiers, Aerated lagoons | 9 |
| Pierce Island Wastewater Treatment Plant | Portsmouth | 2.38 | 4.8 | NH0100234 | Nov 2028 | Clarifiers, Biogas balloons | 47 |
| Rochester Wastewater Treatment Facility | Rochester | 2.35 | 5 | NH0100668 | Jun 2028 | Clarifiers, Aerated lagoons, Uncovered lagoons | 3 |
| Leavitt E. Magrath Wastewater Treatment Facility | Hampton | 2.08 | 4.7 | NH0100625 | Feb 2026 | Clarifiers | 27 |
| Huckleberry Hill Wastewater Treatment Facility | Dover | 1.91 | 4.7 | NHG58A003 | Jan 2026 | Clarifiers | 30 |
| Merrimack WWTF | Merrimack | 1.37 | — | NHR053094 | Feb 2026 | Clarifiers, Biogas silos | 9 |
| Keene Wastewater Treatment Facility | Keene | 1.26 | 6 | NH0100790 | Nov 2026 | Clarifiers | 8 |
| Claremont Wastewater Treatment Facility | Claremont | 1.2 | 3.9 | NH0101257 | Sep 2021 | Clarifiers, Biogas silos | 0 |
| Derry, Town Of, Wastewater Treatment Plant | Derry | 1.17 | 4 | NH0100056 | Feb 2016 | Aerated lagoons, Uncovered lagoons | 17 |
| Berlin Pollution Control Facility | Berlin | 1.12 | — | NH0100013 | Jun 2029 | Biogas balloons | 5 |
| Exeter Wastewater Treatment Facility | Exeter | 1.1 | — | NHG58A004 | Jan 2026 | Clarifiers, Aerated lagoons | 18 |
| Hanover Wastewater Treatment Facility | Hanover | 0.99 | 2.3 | NH0100099 | Jan 2021 | Clarifiers, Biogas silos, Biogas balloons | 45 |
| Lebanon Wastewater Treatment Facility | Lebanon | 0.89 | — | NHR053176 | Feb 2026 | Clarifiers, Biogas balloons | 2 |
| Durham Wastewater Treatment Facility | Durham | 0.83 | 2.5 | NHG58A005 | Jan 2026 | — | 8 |
| Milford Wastewater Treatment Facility | Milford | 0.78 | 2.15 | NH0100471 | Oct 2025 | Clarifiers, Biogas balloons | 191 |
| Hooksett Wastewater Treatment Facility | Hooksett | 0.68 | 2.2 | NH0100129 | Sep 2018 | Clarifiers, Uncovered lagoons | 1 |
| Suncook Wastewater Treatment Facility | Allenstown | 0.45 | 1.5 | NH0101390 | Jan 2027 | Clarifiers | 9 |
| Newmarket, Town Of - WPCF | Newmarket | 0.35 | — | NHG580013 | Nov 2026 | Clarifiers, Biogas silos, Biogas balloons | 17 |
| Colebrook Wastewater Treatment Plant | Colebrook | 0.3 | — | NHG580315 | Nov 2026 | — | 33 |
| Littleton Wastewater Treatment Plant | Littleton | 0.27 | 1.5 | NH0100153 | Oct 2025 | Carrousels / oxidation ditches, Biogas silos | 17 |
| Lancaster Wastewater Treatment Facility | Lancaster | 0.23 | 1.2 | NH0100145 | Sep 2025 | Aerated lagoons, Uncovered lagoons | 37 |
| Sunapee, Town Of-WWTP | Sunapee | 0.22 | — | NHG580017 | Nov 2026 | Carrousels / oxidation ditches, Biogas balloons | 27 |
| Town Of Bristol WWTF | Bristol | 0.21 | — | NHG580021 | Nov 2026 | Carrousels / oxidation ditches | 0 |
New Hampshire plants by treatment technology
All 46 plants in New Hampshire
Wastewater treatment in New Hampshire: 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.