MS4s in the Bay Watershed Graphic credit: CBPO
MS4s in the Bay Watershed
Graphic credit: CBPO

In 1987 the Clean Water Act was amended to include stormwater discharges in the NPDES program. In 1990 Phase I of the program was implemented, requiring permits for stormwater discharges from all Municipal Separate Storm Sewer Systems (MS4s) in communities of 100,000 people or greater as well as construction sites disturbing 5 acres of land or more. In 1999, Phase II of the program went into effect requiring permits for MS4s of 50,000 people or greater or with a density of 1000 people per square mile, and construction sites disturbing 1 or more acres of land. For more information about what local governments are required to do under these permits, click here. Today, there are more than 500 communities within the Bay watershed that are now regulated under these permits. The graphic to the right shows the geographic distribution of them across the watershed as of April 30, 2015.

CSN has put together a number of resources to help guide MS4 permittees on meeting their MS4 permit requirements and those of the Bay TMDL. Head on over to our MS4 Portal to get started!

MS4 Portal

Welcome to the newly created Ms4 Portal! A location for all of your MS4 needs.

This portal was created to share resources with MS4 permittees that will help you meet your MS4 permit and Bay TMDL requirements. Learn more…