Lagoon systems: wastewater treatment plants in New Hampshire
12 plants · 26% of the state · 8 MGD combined
Klarifi identifies 12 publicly owned wastewater treatment plants with lagoon systems in New Hampshire, 26% of the 47 plants in the state (8 MGD combined). The largest is Rochester Wastewater Treatment Facility in Rochester at 2.88 MGD.
Lagoon systems treat wastewater in large earthen ponds over weeks of retention time, with or without mechanical aeration. They serve thousands of small towns because they are cheap to run, but they struggle with ammonia and nutrient limits, fill with sludge over decades and are the plants most often converted or upgraded when a permit is renewed.
The largest lagoons in New Hampshire
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Rochester Wastewater Treatment Facility | Rochester | 2.88 | NH0100668 | Jun 2028 | 3 |
| 2 | Derry, Town Of, Wastewater Treatment Plant | Derry | 1.46 | NH0100056 | Feb 2016 | 16 |
| 3 | Exeter Wastewater Treatment Facility | Exeter | 1.45 | NHG58A004 | Jan 2026 | 18 |
| 4 | Lancaster Wastewater Treatment Facility | Lancaster | 0.68 | NH0100145 | Sep 2025 | 69 |
| 5 | Ashland Wastewater Treatment Facility | Ashland | 0.35 | NH0100005 | Jan 2027 | 5 |
| 6 | Penacook Wastewater Treatment Plant | Concord | 0.3 | NH0100331 | Jul 2025 | 5 |
| 7 | Waterville Valley Wastewater Treatment Plant | Waterville Valley | 0.2 | NH0100781 | Mar 2027 | 6 |
| 8 | Lisbon Wastewater Treatment Facility | Lisbon | 0.18 | NHG580421 | Nov 2026 | 26 |
| 9 | Charlestown Wastewater Treatment Plant | Charlestown | 0.17 | NH0100765 | Sep 2025 | 20 |
| 10 | Whitefield Wastewater Treatment Facility | Whitefield | 0.13 | NHG580002 | Nov 2026 | 22 |
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 New Hampshire
Lagoon systems in other states
Lagoon systems 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 October 26, 2026.
Wastewater terms: WWTP · POTW · Biosolids · Activated sludge · Oxidation ditch · all terms