Lagoon systems: wastewater treatment plants in Maryland
41 plants · 35% of the state · 151 MGD reported by 39 plants
Klarifi identifies 41 publicly owned wastewater treatment plants with lagoon systems in Maryland, 35% of the 118 plants in the state (151 MGD reported by 39 plants). The largest is Back River Wastewater Treatment Plant in Baltimore at 114.1 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 Maryland
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Back River Wastewater Treatment Plant | Baltimore | 114.1 | MDL021555 | Dec 2030 | 32 |
| 2 | Sod Run Wastewater Treatment Plant | Perryman | 10.81 | MDL056545 | Dec 2030 | 0 |
| 3 | Annapolis WRF | Annapolis | 8.48 | MD0021814 | Jan 2030 | 6 |
| 4 | City Of Frederick Wastewater Treatment Plant-2012 | Frederick | 5.4 | MD0021610 | May 2031 | 23 |
| 5 | Easton WWTP | Easton | 2.02 | MDL020273 | Dec 2030 | 2 |
| 6 | Northeast River Advanced WWTP | Charlestown | 1.25 | MDL052027 | Dec 2030 | 38 |
| 7 | Town Of La Plata | La Plata | 1.04 | MDL020524 | Dec 2030 | 111 |
| 8 | George'S Creek WWTP | Westernport | 0.77 | MD0060071 | May 2026 | 0 |
| 9 | Perryville Wastewater Treatment Plant | Perryville | 0.64 | MDL020613 | Dec 2030 | 57 |
| 10 | Chestertown WWTP | Chestertown | 0.63 | MD0020010 | Sep 2026 | 5 |
| 11 | Delmar WWTP | Delmar | 0.54 | MD0020532 | Jul 2031 | 6 |
| 12 | Pocomoke City Wastewater Treatment Facility | Pocomoke City | 0.52 | MD0022551 | May 2028 | 0 |
| 13 | Oakland WWTP | Oakland | 0.5 | MD0020648 | Mar 2024 | 1 |
| 14 | Hampstead WWTP | Hampstead | 0.48 | MD0022446 | Aug 2030 | 25 |
| 15 | Fruitland WWTP | Fruitland | 0.41 | MD0052990 | Feb 2029 | 36 |
| 16 | Denton WWTP | Denton | 0.4 | MD0020494 | Jul 2025 | 0 |
| 17 | Poolesville WWTP | Poolesville | 0.34 | MD0023001 | Nov 2027 | 6 |
| 18 | St. Michael'S WWTP | Saint Michaels | 0.29 | MD0023604 | Nov 2030 | 0 |
| 19 | Town Of Emmitsburg | Emmitsburg | 0.27 | MD0020257 | Feb 2030 | 10 |
| 20 | Boonsboro WWTP | Boonsboro | 0.26 | MD0020231 | Dec 2030 | 1 |
| 21 | Rock Hall WWTP | Rock Hall | 0.22 | MD0020303 | Jul 2029 | 7 |
| 22 | Rising Sun Town Of WWTP | Rising Sun | 0.2 | MD0020265 | Apr 2028 | 22 |
| 23 | Smithsburg WWTP | Smithsburg | 0.19 | MD0024317 | Mar 2031 | 14 |
| 24 | Middletown WWTP | Middletown | 0.15 | MD0024406 | Jul 2026 | 0 |
| 25 | Twin Cities WWTP | Secretary | 0.13 | MD0055352 | Sep 2028 | 58 |
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 Maryland
Lagoon systems in other states
Lagoon systems in Maryland: 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.