Last Updated: Tuesday, 06-Jan-2009 16:49:12 EST

MS4 Program

	What is a Municipal Separate Storm Sewer System (MS4)? A conveyance or system of conveyances (including roads, catch basins, curbs, gutters, ditches, man-made channels, or storm drains): Owned or operated by a public body Designed and used for collecting storm water Is not a combined sewer Is not part of a Publically Owned Treatment Works (POTW)

The U.S. EPA's storm water program addressed storm water runoff in two phases. Phase I addressed storm water runoff from large and medium MS4s. Large municipalities with a separate storm sewer system serving a population greater than 250,000 and medium municipalities with a service population between 100,000 and 250,000 had to obtain NPDES permits. Initial application deadlines for large and medium municipalities were November 16, 1992 and May 17, 1993, respectively. As part of their individual NPDES permit applications, the large and medium MS4s had to develop a storm water management program (SWMP).

The Phase II regulations address storm water runoff of MS4s serving populations less than 100,000, called small MS4s. More particularly, small MS4s located partially or fully within urbanized areas (UAs), as determined by the U.S. Bureau of the Census, and also on a case-by-case basis for those small MS4s located outside of UAs that Ohio EPA designates into the program. Automatically designated Small MS4s, those in UAs, were required to apply for permit coverage and develop and submit a SWMP by March 10, 2003.

Small MS4 (Phase II) Program Overview

Urbanized Areas

U.S. EPA developed a Fact Sheet (PDF 239K) explaining how urbanized areas affect water quality through increased runoff and pollutant loads and what homeowners can do to prevent storm water pollution.

Ohio EPA developed two general permits which are issued to Phase II Small MS4 communities. The Baseline General Permit allows a full 5 years for SWMP development/implementation; whereas, the Alternative General Permit for MS4s Located within Rapidly Developing Watersheds requires development/implementation of the Construction and Post-Construction minimum control measures within 3 years. The alternative general permit was issued to a select group of MS4s that Ohio EPA considers being located within rapidly developing watersheds.

Regulated Small MS4s

• Appendix 6 (Automatically designated MS4s) (PDF 18K)
• Appendix 7 (Potentially designated MS4s) (PDF 100K)

Small MS4 Informational Materials

• Ohio EPA MS4 Workshops
• USEPA Storm Water Phase II Fact Sheets 
• USEPA National Menu of Best Management Practices
• USEPA Measurable Goals Guidance for Phase II Small MS4s
• USEPA Storm Water Phase II Compliance Assistance Guide (PDF 1,466K)
• OEPA Guidance Brochure for Phase II Small Municipal Separate Storm Sewer System (MS4) Operators (PDF 95K)
• USEPA Storm Water Case Studies

Permit Compliance Materials

Potential Funding Sources

For Additional Information:

see the Storm Water Program Contacts page.

Back to Storm Water Program page.