Municipal Separate Storm Sewer Systems (MS4)

Urbanized areas are a densely settled core of census tracts or census blocks that meet minimum population density requirements. These urbanized areas are determined by the U.S. Census Bureau as having a population of 50,000 or more people.

Census Information

• 2010 Census Urban Area FAQs
• Missouri Populations Quick Facts - U.S. Census Bureau
• Redefining Urban Areas following the 2020 Census - U.S. Census Bureau

Missouri's Nine Urbanized Area Reference Maps 2010 - U.S. Census Bureau

• Cape Girardeau MO-IL Urbanized Area
• Columbia MO Urbanized Area
• Jefferson City MO Urbanized Area
• Joplin MO Urbanized Area
• Lee's Summit MO Urbanized Area
• Kansas City MO-KS Urbanized Area
• Springfield MO Urbanized Area
• St. Joseph MO-KS Urbanized Area
• St. Louis MO-IL Urbanized Area

Minimum Control Measures (MCMs) are required focus areas in MS4 permits. These are individual areas, however they can overlap or work together to make a successful Stormwater Management Program (SWMP).

Six MCMs Required for Phase II Regulated Communities

• EPA Stormwater Phase II Final Rule, Small MS4 Stormwater Program Overview
  • Public Education and Outreach
  • Public Participation and Involvement
  • Illicit Discharge Detection and Elimination
  • Construction Site Runoff Control
  • Post Construction Runoff Control
  • Pollution Prevention and Good Housekeeping
• Missouri’s MS4 General Permit Conditions

Resources for Developing MCMs

• National Menu of Best Management Practices (BMPs) for Stormwater
• Missouri Guide to Green Infrastructure - PUB2446
• Measurable Goals Guidance for Phase II MS4s - Designed to help MS4 operators comply with the measurable goals permitting requirements

• NPS Outreach Featured Products - EPA stormwater outreach materials toolbox
• Missouri 319 Grant Guidance for MS4s - PUB2890
• Municipal Separate Storm Sewer System (MS4) Stormwater Management Program Report MOR04 and Site Specific MO 780-1846
• Municipal Separate Storm Sewer System (MS4) Annual Stormwater Management Program Report for Comprehensive Permit (MOR04C) MO 780-3009
• Qualifying Local Program Application Procedure
• Stormwater Discharges from Municipal Sources-Developing an MS4 Program - EPA
• Stormwater Smart Outreach Tools - EPA

In response to the 1987 Amendments to the Clean Water Act, the Environmental Protection Agency (EPA) developed Phase 1 - Overview of the Storm Program of the National Pollutant Discharge Elimination System (NPDES). Phase I Stormwater regulations address runoff in medium and large communities determined by population size in 1990, identified 11 industrial categories required to obtain permits (with some exemptions), and addressed statewide land disturbance on five acres or greater. Missouri MS4s regulated under Phase I are Kansas City, Independence and Springfield.

EPA published the national Stormwater Phase II Final Rule Fact Sheet Series in the Federal Register Dec. 8, 1999. Phase II regulations expanded the program to include communities as determined by population size in 1999 (and subsequent decennial census counts) and land disturbance on one acre or greater. 

• Certain Communities were exempt under the Phase I Stormwater regulations in 1990, and became subject to Phase II regulations. Regulated MS4s were required to obtain a NPDES permit by March 10, 2003, and have their stormwater management program (SWMP) in place within five years from date of initial permit issuance. Approximately 160 MS4s are designated and currently regulated under the Master General Permit for Phase II MS4s.
• Industrial Classifications Modified There are still 11 categories of industrial classifications covering 30 sectors of industrial activity that are required to obtain stormwater discharge permits. However, the North American Industry Classification System classifies establishments by their main type of activity. There is also now an option for industrial no exposure certifications in lieu of an operating permit. Municipally operated industries exempted by the Intermodal Surface Transportation Efficiency Act of 1991, are no longer exempt under Phase II. Visit Stormwater Permits for more information.
• Land Disturbance Permits are now required for disturbing one or more acres. Permits must be in place before land disturbance begins at the construction site. This requirement applies statewide. Visit Construction Land Disturbance Permits for more information.