Municipal stormwater (MS4)

Water from rainfall flowing along gutter to storm drainRain and snow melt run over the abundant impervious surfaces in urbanized areas — roads, sidewalks, driveways, parking lots, roof tops, etc — and pick up pesticides, fertilizers, oils, metals, pathogens, salt, sediment, trash, and other pollutants and carry them into storm drains. Storm drains discharge directly into lakes rivers, streams, and wetlands, so stormwater runoff is a leading source of water pollution. Road salt, oil and gas from vehicle fueling, spilled materials, pesticides and fertilizers applied to lawns, and leaves and lawn clippings are just a few of the many sources of pollutants in urban stormwater.

In addition, stormwater runoff from impervious surfaces travels faster and in larger quantities, which results in damage to rivers, streams, and wetlands; destruction of aquatic habitats; and elevated pollutant levels reaching surface waters. Impervious surfaces also prevent stormwater from soaking into the ground and recharging groundwater. Local public entities that own or operate municipal separate storm sewer systems (MS4) play a key role in preventing stormwater runoff from harming Minnesota’s valuable water resources.

What is an MS4?

A municipal separate storm sewer system (MS4) is a conveyance or system of conveyances (roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, storm drains, etc.) that is also:

  • Owned or operated by a public entity (which can include cities, townships, counties, military bases, hospitals, prison complexes, highway departments, universities, sewer districts, etc.)
  • Designed or used for collecting or conveying stormwater
  • Not a combined sewer
  • Not part of a publicly owned treatment works

MS4s in Minnesota must satisfy the requirements of the MS4 general permit if they are located in an urbanized area and used by a population of 1,000 or more or owned by a municipality with a population of 10,000 or more, or a population of at least 5,000 and the system discharges to specially classified bodies of water. Minnesota state rule (Minn. R. 7090) establishes criteria and a process for designating future MS4s; see the Stormwater rules page for more information. 

The MS4 general permit is designed to reduce the amount of sediment and other pollutants entering state waters from stormwater systems. Entities regulated by the MS4 general permit must develop a stormwater pollution prevention program and adopt best practices. Learn more on the Complying with the MS4 general permit page. A general permit covers multiple entities with similar operations and types of discharges. Issuing general permits allows for faster and more efficient permitting compared to issuing individual permits.

Reissuing the permit

The MS4 general permit is issued for five years, after which it must be reissued. As part of the reissuance, MPCA staff consult with permittees and stakeholders and solicit public comment to look for ways to improve and revise the permit.

The MPCA plans to issue the new MS4 General Permit (MNR040000) on Monday, November 16, 2020. The MPCA will make every effort to post the final permit in advance of the issuance date for early viewing. Interested parties can expect to see responses to public comments, permit application forms, and guidance material on November 16, 2020. Existing MS4 permittees will have 150 days (April 15, 2021) to complete and submit the permit application forms to the MPCA. A mid-November issuance provides existing MS4 permittees an opportunity to begin planning accordingly and use the winter months, when field work tends to slow down, to work on the permit application forms.

In the permit application forms, MS4 permittees will need to describe:

  • Current stormwater pollution prevention program (SWPPP)
  • Status of meeting permit requirements in the six minimum control measures (MCMs)
  • Best management practices (BMPs) to address total maximum daily load (TMDL) waste load allocations (WLAs)
  • Names or position titles responsible for implementing each required component of the SWPPP

Once an MS4 permittee completes the permit application, they must submit it to the MPCA for preliminary review. If the application is incomplete, MPCA staff will notify the MS4 permittee of the deficiencies in writing. If MPCA staff determine the application is complete, the application will go on public notice for 30 days. Once the MS4 permittee has addressed any applicable public comments or hearing requests, the MPCA will make a final determination and issue coverage under the new permit. The MS4 permittee has 12 months from the date coverage is extended to meet the new permit requirements.

Stormwater financial assistance

The MPCA has various opportunities for obtaining grants or loans for stormwater projects in Minnesota. Visit the following MPCA webpages for information on water-related financial assistance:


MS4 stormwater program staff


Duane Duncanson (651-757-2323)

Municipal stormwater policy Scott Fox (651-757-2368)

Permit writer

Cole Landgraf (651-757-2880)

Technical assistance and compliance enforcement

Samantha Connolly (651-757-2166)
Carlee Kjeldahl (651-757-2171)
Cole Landgraf (651-757-2880)
Nick Nistler (651-757-2564)

TMDL/MS4 Permit technical assistance

Anna Bosch (218-316-3929)

Application processing

Melanie Preczewski (651-757-2085)

See the MS4 staff page to find the staff assigned to your MS4. Call 800-657-3864 outside the metro area.