The Basics of Municipal SWMP Plans

Cities, towns, and villages across the country play an important role in protecting water quality through their Municipal Separate Storm Sewer Systems (MS4s). A key part of this effort is developing and implementing a Stormwater Management Program (SWMP) Plan; a comprehensive strategy for reducing pollution in stormwater runoff.

Whether your municipality is developing its first SWMP or refining an existing one, here’s what you need to know.

What Is a Municipal SWMP Plan?

A Stormwater Management Program (SWMP) Plan is a written document that outlines how a municipality will comply with its MS4 permit requirements under the federal Clean Water Act.

It identifies local stormwater challenges and lays out specific actions (called Best Management Practices, or BMPs) to reduce the impact of stormwater on nearby streams, rivers, and lakes.

Why Do Municipalities Need SWMP Plans?

Municipalities with MS4 permits are required by state and federal law to manage stormwater discharges to protect water quality.

Without proper management, rainwater flowing over roads, parking lots, and other surfaces can pick up:

• Oil and grease

• Road salt

• Sediment

• Trash and debris

• Nutrients (nitrogen, phosphorus)

• Heavy metals
  - all of which can pollute downstream waters.

An SWMP Plan helps ensure that the municipality:

• Meets regulatory obligations

• Protects public health and natural resources

• Demonstrates environmental stewardship to the community

Core Components of a Municipal SWMP Plan

Under MS4 Phase II regulations, a municipal SWMP Plan must address six key areas known as Minimum Control Measures (MCMs):

1. Public Education and Outreach

• Inform the public about stormwater impacts

• Promote behaviors that reduce pollution (e.g., proper lawn care, pet waste disposal)

2. Public Participation and Involvement

• Engage residents and stakeholders in local stormwater efforts

• Organize clean-up events or volunteer monitoring programs

3. Illicit Discharge Detection and Elimination (IDDE)

• Detect and eliminate unauthorized discharges (like sewage or wash water) into the storm system

• Maintain an up-to-date storm sewer system map

4. Construction Site Runoff Control

• Require sediment and erosion controls at construction sites

• Inspect active construction sites for compliance

5. Post-Construction Stormwater Management

• Implement long-term controls (BMPs) for new development and redevelopment

• Maintain stormwater infrastructure like detention basins or green roofs

6. Pollution Prevention/Good Housekeeping for Municipal Operations

• Train municipal staff on pollution prevention

• Improve maintenance practices for roads, parks, and public facilities

• Manage salt and sand storage responsibly

Additional Plan Elements

A municipal SWMP Plan typically also includes:

• A description of the municipal stormwater system

• Measurable goals and target dates

• Tracking and reporting procedures

• Annual reporting requirements

Keeping Your SWMP Plan Current

An SWMP Plan is a living document - it should be regularly reviewed and updated:

• As new BMPs are implemented

• As monitoring results are evaluated

• As state and federal requirements change

• As the community grows and land use evolves

A thoughtful, well-maintained SWMP Plan is at the heart of a municipality’s efforts to manage stormwater responsibly. It helps protect local water quality, supports regulatory compliance, and builds public trust.

Municipal leaders, highway departments, and public works staff all play a role in making the plan a success, and in keeping local waterways healthy for future generations.