Municipal Separate Storm Sewer Systems, or MS4s, are publicly owned systems, such as storm drains, pipes, ditches or swales that collect or move runoff to surface waters. MS4s must obtain permit coverage and develop a stormwater management program. Phase 1 MS4 permits are issued to communities with a population size greater than 100,000, while Phase II permits are issued to smaller communities. The designated MS4 may be a county, city, township, transportation agency, university, or a number of other “non-traditional” permittees.
Because every MS4 faces unique stormwater challenges each management program is unique. But every program includes the same six focus areas that the Environmental Protection Agency considers essential for success, called Minimum Control Measures or “MCMs”:
On this page, you can find resources for each of the MCMs, along with case studies from MS4s of all sizes that demonstrate successes and lessons learned.