What is MS4

Phase II NPDS Storm Water Regulations

 Municipal Separate Storm Sewer Systems (MS4s)

Under the 1987 Clean Water Act Amendments, the U.S. EPA developed new stormwater regulations to address storm water that might impact water quality.  These new regulations were set up in two Phases depending upon population and are enforced by the U.S. EPA through the Indiana Department of Environmental Management (IDEM).  Phase I dealt with areas serving an urban population greater than 100,000 people and in Indiana affected only Indianapolis .  Phase II has also been implemented and affects nearly 200 MS4 entities within the state.  In Indiana , MS4 designation includes cities, towns, universities, colleges, correctional facilities, hospitals, conservancy districts, homeowner’s associations and military bases located within mapped urbanized areas, as delineated by the U.S. Census Bureau, or, for those MS4 areas outside of urbanized areas, serving an urban population greater than 7,000 people.  In addition to these generalized criteria, designation of MS4 entities is potentially determined by other factors, including population growth and documentation which indicates water quality impairments.

To meet the new requirements each designated MS4 entity was required to submit a permit application to IDEM, due by November 4, 2003 for most designated entities.  The permit period runs for five (5) years.  The permit application requires development of a Storm Water Quality Management Plan (SWQMP) which is basically an action plan for the MS4 entity to institute six requirements called minimum control measures (MCM):

1. Public Education and Outreach
2. Public Involvement and Participation
3. Illicit Discharge Detection and Elimination
4. Construction Site Storm Water Runoff Control
5. Post-Construction Storm Water Management in New Development and Redevelopment
6. Pollution Prevention/Good Housekeeping for Municipal Operations Maintenance.

Although the MS4 entity will have five years to implement the SWQMP, some of the protocols were required to be complete earlier than others, including development of local ordinances to enable oversight, management and enforcement of local storm water dischargers.

There are a number of MS4 Materials that are found on our website under Useful Links and Documents that you may use to increase your knowledge of storm water issues. Please feel free to use the link to IDEM’s Stormwater Management Program website also for more information.