What is the largest wastewater treatment plant in Montana?

City Of Billings Wastewater Treatment Plant in Billings, treating an average of 20.32 MGD under NPDES permit MTR000459. Town Of Lavina WWTF in Lavina is second at 18.51 MGD.

How much wastewater do Montana’s largest plants treat?

The 50 largest plants treat 100 MGD combined, 98% of the flow reported by all 109 publicly owned plants in Montana.

How is plant size measured?

By reported average daily flow in million gallons per day (MGD) from EPA discharge monitoring reports, the standard measure of a plant’s size. Design capacity, the flow a plant is permitted to treat, is usually higher and is shown on each profile.

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The 50 largest wastewater treatment plants in Montana

Name: Largest wastewater treatment plants in Montana
Creator: Klarifi
License: https://klarifi.io/terms-of-service

Ranked by average flow · 100 MGD combined · 98% of the state's reported flow

City Of Billings Wastewater Treatment Plant in Billings is the largest publicly owned wastewater treatment plant in Montana by reported average flow, treating about 20.32 million gallons per day. The 50 plants below treat 100 MGD between them, 98% of the flow reported by all 109 plants in the state, and serve about 383,624 people. Every plant links to its profile with permit and compliance data. Treatment technology is shown with a free Klarifi account.

All plants in Montana →The 50 largest US plants →Montana NPDES permits →

The 50 largest publicly owned wastewater treatment plants in Montana by average flow (MGD), with population served, NPDES permit, expiry and three-year violation count.
#	Facility	City	Avg flow (MGD)	Population	NPDES permit	Expires	Violations (3y)
1	City Of Billings Wastewater Treatment Plant	Billings	20.32	117,116	MTR000459	Jan 2028	7
2	Town Of Lavina WWTF	Lavina	18.51	—	MTG580013	Dec 2027	1
3	Two Medicine Water Co.	Browning	17.08	—	MTDW0003I	Jun 2024	0
4	City Of Missoula WWTF No Exposure	Missoula	9.3	47,463	MT0022594	Apr 2020	8
5	City Of Bozeman WWTP	Bozeman	6.55	38,264	MT0022608	May 2017	0
6	City Of Kalispell WWTP	Kalispell	3.96	30,040	MT0021938	Jul 2020	11
7	City Of Helena WWTP	Helena	3.01	32,091	MT0022641	Sep 2017	33
8	Lewistown WWTP	Lewistown	1.82	7,675	MT0020044	Aug 2017	32
9	Havre WWTF	Havre	1.68	9,762	MT0022535	Aug 2026	0
10	Deer Lodge WWTP	Deer Lodge	1.13	2,900	MT0022616	Feb 2018	3
11	Miles City WWTP	Miles City	1.11	9,074	MT0020001	Sep 2023	3
12	Wolf Point, City Of	Wolf Point	1.08	2,743	MT0030571	Jun 2023	13
13	City Of Polson WWTP	Polson	0.86	5,148	MT0020559	Aug 2024	0
14	City Of Glendive Water Resource & Recovery Facility	Glendive	0.85	5,185	MT0021628	May 2027	3
15	Town Of Belt - WWTP	Belt	0.82	655	MT0021571	Jun 2022	92
16	Water Reclamation Facility	Livingston	0.69	8,061	MT0020435	Oct 2021	0
17	City Of Hamilton Wastewater Treatment Plant	Hamilton	0.67	4,784	MT0020028	Dec 2026	0
18	City Of Glasgow Parks Maintenance Bldg	Glasgow	0.61	3,826	MT0021211	Nov 2026	21
19	City Of Shelby Wastewater Lagoons	Shelby	0.57	3,728	MT0031488	Feb 2025	20
20	Town Of Poplar WTP	Poplar	0.54	3,289	MT0030597	Jun 2025	174
21	Northern Cheyenne Utility Commission Wastewater Treatment Plant	Lame Deer	0.48	2,522	MT0029360	Jun 2029	737
22	Stevensville Waste Water Treatment Plant	Stevensville	0.47	1,983	MT0022713	May 2024	5
23	Choteau Sewage Treatment Ponds	Choteau	0.47	1,952	MT0020052	Aug 2026	3
24	Anaconda-Deer Lodge County Wastewater Holding Ponds And Ip Beds Facility	Anaconda	0.44	—	MTX000231	May 2024	0
25	Ennis WWTP	Ennis	0.44	1,371	MT0030732	Apr 2019	8
26	Three Forks WWTF	Three Forks	0.44	2,049	MT0020401	Apr 2027	5
27	Hot Springs, Town Of	Hot Springs	0.43	557	MT0020591	Jun 2023	32
28	Columbia Falls WWTP	Columbia Falls	0.41	3,643	MT0020036	May 2030	0
29	Bigfork County Water And Sewer	Bigfork	0.37	4,683	MT0020397	Apr 2023	1
30	City Of Belgrade- Belgrade Wastewater Treatment Plant	Belgrade	0.36	10,460	MTX000116	Sep 2023	30
31	Libby WWTP	Libby	0.33	2,879	MTR000752	Jan 2028	34
32	Great Falls WTP	Great Falls	0.33	—	MT0000442	May 2029	0
33	City Of Bozeman - Lyman Creek Reservoir	Bozeman	0.3	—	MT0031631	Nov 2029	0
34	City Of Laurel, Water Treatment Plant	Laurel	0.29	—	MT0030261	Oct 2027	0
35	Manhattan WWTF	Manhattan	0.29	3,366	MT0021857	Aug 2015	20
36	Town Of Terry WWTF	Terry	0.26	—	MTG580017	Dec 2027	520
37	City Of Townsend Wastewater Treatment Plant	Townsend	0.23	—	MTG581020	Dec 2022	0
38	Forsyth WWTP	Forsyth	0.23	1,948	MT0021288	Jan 2026	0
39	City Of Plentywood	Plentywood	0.22	2,032	MTG580008	Dec 2027	0
40	East Helena WWTF	East Helena	0.18	1,944	MT0022560	Nov 2024	72
41	City Of Conrad WWTF	Conrad	0.17	2,318	MT0020079	Nov 2023	12
42	Big Timber	Big Timber	0.16	1,809	MT0020753	Apr 2017	45
43	Town Of Fairfield WWTP	Fairfield	0.16	776	MTG580003	Dec 2027	13
44	River Rock Subdivision	Belgrade	0.16	3,399	MTX000147	Sep 2022	0
45	Town Of Columbus - Waste Water Treatment Facility	Columbus	0.15	1,857	MT0031801	Oct 2028	25
46	City Of Troy Wastewater Treatment Facility	Troy	0.15	—	MTG581038	Dec 2022	30
47	Town Of Drummond WWTP	Drummond	0.13	272	MTG580002	Dec 2027	46
48	Montana State Hospital Sewage Treatment Lagoons	Warm Springs	0.13	—	MTG581004	Dec 2022	4
49	Town Of Broadus WWTF	Broadus	0.11	—	MTG580015	Dec 2027	24
50	Town Of Eureka WWTP	Eureka	0.11	—	MTG581032	Dec 2022	0

Treatment technology for each plant is shown with a free Klarifi account. Create one →

Largest plants in Montana: 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 · Centrate · Ozonation · 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. “The 50 largest wastewater treatment plants in Montana (2026).” Updated October 26, 2026. https://klarifi.io/facilities/montana/largest

Need a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.

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