Municipal Separate Storm Sewer System (MS4)

The federal Clean Water Act (CWA) requires storm water discharges from certain types of urbanized areas to be permitted under the National Pollutant Discharge Elimination System (NPDES) program.  In 1990, Phase I of these requirements became effective, and municipalities with a population served by a municipal separate storm sewer system (MS4) of 100,000, or more, were regulated. In 1999, Phase II became effective, and any entity responsible for an MS4 conveyance, regardless of population size, could potentially be regulated.

In Indiana, storm water discharge permits are issued by the Indiana Department of Environmental Management (IDEM). Under Phase I requirements, only the City of Indianapolis met the designation criteria, and was issued an individual NPDES storm water permit. To comply with Phase II requirements, a new general NPDES permit rule was written. The new general permit rule, referred to as Rule 13, provided permit coverage for most Phase II MS4 entities.

A general permit is a single permit that is written to cover multiple permittees with similar characteristics. No written draft permit is issued to the permittee under a general permit. Instead, the requirements and conditions of this type of permit are found in Indiana Administrative Code, under the appropriate general permit rule. Notice of Intent (NOI) letters for this type of permit can be by either a single MS4 entity, or multiple MS4 entities.  The City of Terre Haute, Vigo County, Seelyville, West Terre Haute, Indiana State University, Ivy Tech Community College, and Rose Hulman Institute of Technology are co-permittees of a  general permit with the City of Terre Haute taking the lead position within the group for reporting and communications with IDEM.

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