How many wastewater treatment plants are there in Maryland?

Klarifi tracks 118 publicly owned wastewater treatment plants in Maryland with a combined average flow of 282 million gallons per day, serving about 1,822,419 residents. 20 of them treat more than 1 MGD and 5 more than 10 MGD.

What is the largest wastewater treatment plant in Maryland?

Back River Wastewater Treatment Plant in Baltimore is the largest plant in Maryland by average flow, treating about 114.1 MGD.

What treatment technologies are common in Maryland?

41 of Maryland's plants use lagoon systems and 14 have biogas or anaerobic digestion infrastructure, based on Klarifi's aerial imagery review.

How many NPDES permits in Maryland are up for renewal?

12 permits held by Maryland plants expire in 2026 and 7 in 2027. Renewals typically bring new limits and trigger upgrade projects.

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Wastewater Treatment Plants in Maryland

Name: Wastewater treatment plants in Maryland
Creator: Klarifi
License: https://klarifi.io/terms-of-service

118 facilities · 282 MGD combined flow

Klarifi tracks 118 publicly owned wastewater treatment plants in Maryland with a combined average flow of 282 MGD, serving about 1,822,419 residents. 20 plants treat more than 1 MGD and 5 more than 10 MGD; 41 use lagoon systems and 14 have digesters or biogas infrastructure. The largest is Back River Wastewater Treatment Plant in Baltimore at 114.1 MGD. 12 NPDES permits expire this year and 7 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.

118 plant locations in Maryland; dot size follows average flow.

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.

All NPDES permits in Maryland →12 permits expiring in 2026 →7 permits expiring in 2027 →11 permits expiring in 2028 →Find plants near you on the map →

Largest wastewater treatment plants in Maryland

The 25 largest publicly owned wastewater treatment plants in Maryland by average flow, with NPDES permit, expiry, treatment technology and three-year violation count. Source: EPA ICIS-NPDES via Klarifi.
Facility	City	Avg flow (MGD)	Design (MGD)	NPDES permit	Expires	Technology	Violations (3y)
Back River Wastewater Treatment Plant	Baltimore	114.1	—	MDL021555	Dec 2030	Clarifiers, Uncovered lagoons, Biogas silos, Biogas balloons	32
Patapsco Wastewater Treatment Plant	Baltimore	49.01	—	MDL021601	Dec 2030	Clarifiers, Biogas silos, Biogas balloons	22
Piscataway Swge Plnt	Accokeek	19.79	—	MDL021539	Dec 2030	Clarifiers, Biogas silos, Biogas balloons	25
Little Patuxent Water Reclamation Plant	Savage	16.68	25	MD0055174	May 2031	Clarifiers, Biogas balloons	8
Sod Run Wastewater Treatment Plant	Perryman	10.81	—	MDL056545	Dec 2030	Clarifiers, Uncovered lagoons, Biogas silos, Biogas balloons	0
Annapolis WRF	Annapolis	8.48	13	MD0021814	Jan 2030	Clarifiers, Uncovered lagoons, Biogas silos	6
Ballenger-Mckinney WWTP	Frederick	6.92	7	MD0021822	Dec 2030	Clarifiers, Biogas balloons	1
Parkway Wastewater Treatment Plant	Laurel	6.35	—	MDL021725	Dec 2030	Clarifiers, Biogas silos	2
Ocean City Wastewater Treatment Plant	Ocean City	5.88	—	MDL020044	Dec 2030	Clarifiers, Biogas silos, Biogas balloons	2
City Of Frederick Wastewater Treatment Plant-2012	Frederick	5.4	8	MD0021610	May 2031	Clarifiers, Aerated lagoons, Carrousels / oxidation ditches, Biogas silos	23
City Of Salisbury Wastewater Treatment Plant	Salisbury	5.05	—	MDL021571	Dec 2030	Clarifiers, Biogas silos	83
Broadneck Water Reclamation Facility	Annapolis	3.68	—	MDL021644	Dec 2030	Clarifiers, Carrousels / oxidation ditches	106
Westminster WWTP	Westminster	3.41	5	MD0021831	Jul 2031	Clarifiers	9
Easton WWTP	Easton	2.02	—	MDL020273	Dec 2030	Clarifiers, Uncovered lagoons, Carrousels / oxidation ditches	2
Freedom District WWTP	Sykesville	1.97	3.5	MD0021512	Oct 2029	Clarifiers, Carrousels / oxidation ditches	32
Conococheague WWTP	Williamsport	1.84	4.1	MD0063509	May 2031	Clarifiers, Carrousels / oxidation ditches	0
Maryland City Water Reclamation Facility	Laurel	1.53	—	MDL062596	Dec 2030	Clarifiers	27
The City Of Bowie (ssos)	Bowie	1.4	—	MDL021628	Dec 2030	Clarifiers, Carrousels / oxidation ditches	8
Northeast River Advanced WWTP	Charlestown	1.25	—	MDL052027	Dec 2030	Clarifiers, Uncovered lagoons, Carrousels / oxidation ditches	38
Town Of La Plata	La Plata	1.04	—	MDL020524	Dec 2030	Clarifiers, Uncovered lagoons	111
Celanese WWTP	Cumberland	0.8	—	MDL063878	Dec 2030	Clarifiers	0
George'S Creek WWTP	Westernport	0.77	0.7	MD0060071	May 2026	Clarifiers, Aerated lagoons, Uncovered lagoons, Carrousels / oxidation ditches	0
Crisfield WWTP	Crisfield	0.74	—	MDL020001	Dec 2030	Clarifiers	45
Wssc Damascus WRRF	Gaithersburg	0.72	1.5	MD0020982	Dec 2028	Clarifiers	3
Mount Airy WWTP	Mount Airy	0.69	1.2	MD0022527	Dec 2025	Clarifiers	142

The 50 largest plants in Maryland →Maryland capital improvement plans →

Maryland plants by treatment technology

Activated sludge and clarifiers (41)Lagoon systems (41)Oxidation ditches (16)Anaerobic digesters and biogas (14)

All 118 plants in Maryland

Facility	City	Flow (MGD)
Back River Wastewater Treatment Plant	Baltimore	114.1
Patapsco Wastewater Treatment Plant	Baltimore	49.01
Piscataway Swge Plnt	Accokeek	19.79
Little Patuxent Water Reclamation Plant	Savage	16.68
Sod Run Wastewater Treatment Plant	Perryman	10.81
Annapolis WRF	Annapolis	8.48
Ballenger-Mckinney WWTP	Frederick	6.92
Parkway Wastewater Treatment Plant	Laurel	6.35
Ocean City Wastewater Treatment Plant	Ocean City	5.88
City Of Frederick Wastewater Treatment Plant-2012	Frederick	5.4
City Of Salisbury Wastewater Treatment Plant	Salisbury	5.05
Broadneck Water Reclamation Facility	Annapolis	3.68
Westminster WWTP	Westminster	3.41
Easton WWTP	Easton	2.02
Freedom District WWTP	Sykesville	1.97
Conococheague WWTP	Williamsport	1.84
Maryland City Water Reclamation Facility	Laurel	1.53
The City Of Bowie (ssos)	Bowie	1.4
Northeast River Advanced WWTP	Charlestown	1.25
Town Of La Plata	La Plata	1.04
Celanese WWTP	Cumberland	0.8
George'S Creek WWTP	Westernport	0.77
Crisfield WWTP	Crisfield	0.74
Wssc Damascus WRRF	Gaithersburg	0.72
Mount Airy WWTP	Mount Airy	0.69
Perryville Wastewater Treatment Plant	Perryville	0.64
Chestertown WWTP	Chestertown	0.63
Delmar WWTP	Delmar	0.54
Piney Orchard WWTP	Odenton	0.52
Pocomoke City Wastewater Treatment Facility	Pocomoke City	0.52
Taneytown Wastewater Treatment Plant	Taneytown	0.51
Oakland WWTP	Oakland	0.5
Hampstead WWTP	Hampstead	0.48
Manchester WWTP	Manchester	0.43
Worton-Butlertown WWTP	Worton	0.42
Fruitland WWTP	Fruitland	0.41
Denton WWTP	Denton	0.4
Poolesville WWTP	Poolesville	0.34
Indian Head WWTP	Indian Head	0.3
St. Michael'S WWTP	Saint Michaels	0.29
Town Of Emmitsburg	Emmitsburg	0.27
Snow Hill WWTP	Snow Hill	0.26
Boonsboro WWTP	Boonsboro	0.26
Rock Hall WWTP	Rock Hall	0.22
Federalsburg WWTP	Federalsburg	0.21
Rising Sun Town Of WWTP	Rising Sun	0.2
Smithsburg WWTP	Smithsburg	0.19
Middletown - East WWTP	Middletown	0.19
Grantsville WWTP	Grantsville	0.16
Middletown WWTP	Middletown	0.15
Myersville WWTP	Myersville	0.14
Twin Cities WWTP	Secretary	0.13
Hancock WWTP	Hancock	0.13
Jefferson WWTP	Jefferson	0.13
Union Bridge WWTP	Union Bridge	0.12
Pinto/md Water Services WWTP	Pinto	0.12
Talbot County Region V WWTP	Tilghman	0.11
Clear Spring WWTP	Clear Spring	0.11
Antietam WWTP	Sharpsburg	0.11
Oxford WWTP	Oxford	0.11
Fountaindale WWTP	Middletown	0.09
Chesapeake City North WWTP	Chesapeake City	0.09
Cecilton WWTP	Cecilton	0.09
New Windsor WWTP	New Windsor	0.09
Sudlersville WWTP	Sudlersville	0.09
Church Hill Wwtp/ Mes	Church Hill	0.09
Ewell WWTP	Ewell	0.08
Cherry Hill WWTP	Elkton	0.08
Hebron WWTP	Hebron	0.08
Port Deposit WWTP	Port Deposit	0.08
Point Of Rocks WWTP	Point Of Rocks	0.07
Trappe WWTP	Trappe	0.06
Mill Bottom WWTP	Mount Airy	0.06
Pleasant Branch WWTP	Ijamsville	0.06
Accident WWTP	Accident	0.06
Tolchester WWTP	Chestertown	0.06
Richlyn Manor WWTP	Perry Hall	0.05
Vienna WWTP	Vienna	0.05
Sharptown WWTP	Sharptown	0.04
Millington WWTP	Millington	0.04
Pheasant Ridge Mhp,llc.	Mount Airy	0.03
Preston WWTP	Preston	0.03
Clifton On The Potomac WWTP	Newburg	0.02
Friendsville WWTP	Friendsville	0.02
Crellin WWTP	Oakland	0.02
Galena WWTP	Galena	0.02
Betterton WWTP	Betterton	0.02
Harbor View WWTP	Chesapeake City	0.02
Bloomington WWTP	Bloomington	0.01
I-70 WWTP	Myersville	0.01
Flintstone WWTP	Flintstone	0.01
Crestview Estates WWTP	Frederick	0.01
Kennedyville WWTP	Kennedyville	0.01
Point Lookout State Park WWTP	Scotland	0.01
White Rock WWTP	Frederick	0.01
Charles Co Comm Coll	La Plata	0.009
Kitzmiller WWTP	Kitzmiller	0.0084
Greenbrier State Park WWTP	Boonsboro	0.0066
Mount Carmel Woods WWTP	La Plata	0.0063
Spring Meadows WTP-Harford Cou	Jarrettsville	0.006
Northern Garrett High School	Accident	0.005
Hunter Hill WWTP	Hagerstown	0.005
Sha - Sideling Hill Rest Area WWTP	Hancock	0.0043
Barton Business Park WWTP	Cumberland	0.004
Sandy Hook Wastewater Treatment Facility	Knoxville	0.004
Victor Cullen Center WWTP	Sabillasville	0.004
Oldtown WWTP	Oldtown	0.003
Greenridge Forestry Camp	Flintstone	0.002
North Caroline High School	Ridgely	0.002
Runnymede WWTP	Westminster	0.002
New Germany State Park WWTP	Grantsville	0.001
Tracey'S Elementary School	Tracys Landing	0.00083
Ridgely WWTP	Ridgely	0.000000097
Brunswick WWTP	Brunswick	—
Funkstown WWTP	Funkstown	—
Glen Arm Wastewater Treatment Plant (formerly Grumman Wwtp)	Glen Arm	—
Rawlings WWTP	Rawlings	—
Trout Run WWTP	Mountain Lake Park	—

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 September 11, 2026.

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