Under the 1987 Clean Water Act Amendments, the U.S. EPA developed new regulations to address storm water that might impact water quality. These new "Municipal Separate Storm Sewer System" (MS4) regulations were set up in two Phases dependent upon population and are enforced by the U.S. EPA, and more specifically in Indiana, through the Indiana Department of Environmental Management (IDEM).
Within Indiana, Phase I dealt with areas serving an urban population of 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.
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 obtain a permit from IDEM. The initial permit period runs for five (5) years. The permit application required the development of a Storm Water Quality Management Plan (SWQMP) which is basically an action plan for the MS4 entity to institute six requirements, or minimum control measures (MCM):