What is the largest wastewater treatment plant in South Dakota?

Rapid City Water Reclamation Facility in Rapid City, treating an average of 10.62 MGD under NPDES permit SD0023574. Watertown, City Of in Watertown is second at 5.27 MGD.

How much wastewater do South Dakota’s largest plants treat?

The 25 largest plants treat 26 MGD combined, 100% of the flow reported by all 120 publicly owned plants in South Dakota.

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.

Try for free Log in

The 25 largest wastewater treatment plants in South Dakota

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

Ranked by average flow · 26 MGD combined · 100% of the state's reported flow

Rapid City Water Reclamation Facility in Rapid City is the largest publicly owned wastewater treatment plant in South Dakota by reported average flow, treating about 10.62 million gallons per day. The 25 plants below treat 26 MGD between them, 100% of the flow reported by all 120 plants in the state, and serve about 152,574 people. Every plant links to its profile with permit, technology and compliance data.

All plants in South Dakota →The 100 largest US plants →South Dakota NPDES permits →

The 25 largest publicly owned wastewater treatment plants in South Dakota by average flow (MGD), with population served, NPDES permit, expiry, treatment technology and three-year violation count.
#	Facility	City	Avg flow (MGD)	Population	NPDES permit	Expires	Technology	Violations (3y)
1	Rapid City Water Reclamation Facility	Rapid City	10.62	96,450	SD0023574	Jun 2022	Clarifiers, Uncovered lagoons, Biogas silos, Biogas balloons	4
2	Watertown, City Of	Watertown	5.27	25,026	SD0028614	Jun 2018	—	1
3	Lead - Deadwood Sanitary District	Deadwood	1.9	3,290	SD0020796	Jun 2020	—	2
4	Pierre, City Of	Pierre	1.61	—	SD0020176	Jun 2027	—	3
5	Vermillion, City Of	Vermillion	1.42	—	SD0020061	Sep 2017	Aerated lagoons, Uncovered lagoons, Biogas silos, Biogas balloons	2
6	Spearfish, City Of (wtp)	Spearfish	1.21	12,193	SDG860058	Oct 2027	—	4
7	Harrisburg - City Of	Harrisburg, City Of	0.47	—	SD0023728	Jun 2031	Uncovered lagoons	0
8	Hot Springs, City Of	Hot Springs	0.43	—	SD0022918	Dec 2017	Clarifiers, Biogas silos	1
9	Oacoma, Town Of	Oacoma	0.37	—	SD0020737	Dec 2027	Aerated lagoons	5
10	Mobridge, City Of	Mobridge	0.35	—	SD0020028	Jun 2024	Biogas silos, Biogas balloons	0
11	Volga, City Of	Volga, City Of	0.34	—	SD0021920	Dec 2028	Uncovered lagoons	34
12	Whitewood Water	Whitewood	0.3	—	SD0021466	Feb 2023	Aerated lagoons, Uncovered lagoons	4
13	Hartford, City Of	Hartford	0.29	4,128	SD0021750	Dec 2024	Aerated lagoons, Uncovered lagoons	117
14	Ft Pierre - City Of	Fort Pierre	0.22	—	SD0023582	Jun 2027	—	40
15	Summerset, City Of	Summerset	0.22	2,477	SD0027758	Apr 2031	Uncovered lagoons	0
16	Hill City, City Of	Hill City	0.2	—	SD0020885	Feb 2027	—	1
17	Dell Rapids, City Of	Dell Rapids	0.2	3,949	SD0022101	Sep 2019	Uncovered lagoons	1
18	Beresford, City Of	Beresford	0.19	—	SD0020079	May 2031	Uncovered lagoons	5
19	Lennox, City Of	Lennox	0.18	—	SD0021768	Dec 2027	Uncovered lagoons	3
20	Iroquois, City Of	Iroquois	0.14	—	SDG922438	Aug 2026	Uncovered lagoons	33
21	Keystone, Town Of	Keystone	0.14	—	SD0024007	Jun 2025	—	21
22	North Sioux City, City Of (wtp)	North Sioux City	0.1	5,061	SD0020567	Dec 2030	—	7
23	Springfield, City Of	Springfield	0.1	—	SD0028647	Sep 2029	Uncovered lagoons	120
24	Roslyn, Town Of	Roslyn	0.07	—	SD0022802	Dec 2028	Uncovered lagoons	3
25	Elkton, City Of	Elkton, City Of	0.01	—	SD0020788	Jun 2024	—	17

Largest plants in South Dakota: 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.

Try Klarifi for free

Create your own trial account and explore how Klarifi can help you.

Try for free