Wastewater treatment plants in Maryland
117 facilities · 281 MGD combined flow
Klarifi tracks 117 publicly owned wastewater treatment plants in Maryland with a combined average flow of 281 MGD, serving about 1,822,510 residents. 22 plants treat more than 1 MGD and 4 more than 10 MGD; 32 use lagoon systems and 14 have digesters or biogas infrastructure. The largest is Back River Wastewater Treatment Plant in Baltimore at 107.68 MGD. 12 NPDES permits expire this year and 7 next year.
Every plant below links to a profile with average and design flow, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city. Treatment technology and verified contacts are shown with a free Klarifi account.
117 plant locations in Maryland; dot size follows average flow. Boundaries: U.S. Census Bureau.
NPDES permits and renewals in Maryland
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 Maryland
| Facility | City | Avg flow (MGD) | Design (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| Back River Wastewater Treatment Plant | Baltimore | 107.68 | — | MDL021555 | Dec 2030 | 32 |
| Patapsco Wastewater Treatment Plant | Baltimore | 51.59 | — | MDL021601 | Dec 2030 | 22 |
| Piscataway Swge Plnt | Accokeek | 19.8 | — | MDL021539 | Dec 2030 | 25 |
| Little Patuxent Water Reclamation Plant | Savage | 16.76 | 25 | MD0055174 | May 2031 | 8 |
| Sod Run Wastewater Treatment Plant | Perryman | 9.48 | — | MDL056545 | Dec 2030 | 0 |
| Annapolis WRF | Annapolis | 7.94 | 13 | MD0021814 | Jan 2030 | 6 |
| Ballenger-Mckinney WWTP | Frederick | 7.11 | 7 | MD0021822 | Dec 2030 | 1 |
| Parkway Wastewater Treatment Plant | Laurel | 6.09 | — | MDL021725 | Dec 2030 | 2 |
| City Of Frederick Wastewater Treatment Plant-2012 | Frederick | 5.68 | 8 | MD0021610 | May 2031 | 23 |
| The City Of Bowie (ssos) | Bowie | 5.09 | — | MDL021628 | Dec 2030 | 7 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
Maryland plants by treatment technology
All 117 plants in Maryland
Wastewater treatment 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 October 26, 2026.
Wastewater terms: WWTP · POTW · MGD · NPDES permit · Oxidation ditch · Anaerobic digester · 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. “Wastewater treatment plants in Maryland.” Updated October 26, 2026. https://klarifi.io/facilities/marylandNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.