“I still have to do my M-S4,” is a statement often heard at multiple stages of a project. However, this is not a one-and-done simple task.

A stormwater permit for a municipal separate storm sewer system (M-S4) is issued by a state agency on behalf of the Environmental Protection Agency (EPA). The M-S4 permit requires permittees to continue to work on meeting the intent of the Clean Water Act. So, the system is in place to protect the environment and protect the health and safety of the community.

Implementation of the M-S4 permit varies from state to state and permittee to permittee. The trigger for a M-S4 permit is tied to population, which influences what is referred to by the definition of an urban area by the Code of Federal Regulations (CFR). With the dense nature of the permit and many other competing priorities, many permittees find themselves stretched thin and unable to tackle all parts of the permit. This increases their risk of noncompliance and, therefore, of being fined.

The solution is to be proactive. Permittees need to understand the permit, the required tasks to be in compliance and the time it would take for them to complete the tasks. As required by the CFR, each M-S4 permit is similar in structure. It requires the permittee to continue to advance the following programs and processes related to stormwater management:

Public education and outreach on stormwater impacts. The permittee proactively educates the community on stormwater in various ways that could include printed and/or digital flyers and sponsoring the installation of residents’ rain barrels.

Public participation. The permittee must encourage and sponsor the public's participation in stormwater-related activities, such as stream cleanups.

Illicit discharge detection and elimination. The permittee must identify and fix cross connects with the storm sewer system. This task could include identifying and mitigating dumping into the storm sewer systems.

Construction site stormwater runoff control. Many designers and contractors don't realize that the requirements for erosion and sediment control were initiated and continue to be tracked by the M-S4 permit.

Post-construction stormwater management. This section of the M-S4 permit initiated design, construction and maintenance of permanent stormwater best management practices (BMPs) — also known as green infrastructure or stormwater control measures — for frequent rainfall events.

Pollution prevention and good housekeeping for municipal operations. A permittee understands and tracks stormwater management activities of everyday operations. This task could include reviewing stockpiles at a public works facility, studying how dumpsters are managed or analyzing how the quality of rainfall runoff may be impacted.


Compliance with M-S4 permit is not just one task for one project — it is much bigger than that. With multiple priorities at hand, working with a consultant who is well-versed in stormwater management and the nuances of the permit requirements is one way to stay in compliance and avoid fines.

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Brenda Macke is a project manager and stormwater engineer who specializes in MS4 permit task assistance and the planning, design and maintenance of resilient stormwater management systems. Her passion is planning and designing sustainable stormwater infrastructure; she has worked on both regional and national projects focused on helping communities and agencies meet NPDES Phase II regulations, FEMA requirements and EPA consent orders.