Stormwater Management

Municipal Separate Storm Sewer System (MS4) Program


Discharges from MS4s are regulated under the Virginia Stormwater Management Act (VSMP) and the Clean Water Act (CWA) as point source discharges.

A MS4 is a conveyance or system of conveyances that is:

  • Owned by a state, city, town, village, or other public entity that discharges to waters of the U.S.

  • Designed for or used to collect or convey stormwater (including storm drains, pipes, ditches, etc.)

  • Not a combined sewer

  • Not part of a Publicly Owned Treatment Works (sewage treatment plant).


MS4 regulations were developed and implemented in two phases. Implementation of the first phase began in the early 1990s and required that operators of MS4s serving populations of greater than 100,000 people (per the 1990 census) apply for and obtain a permit to discharge stormwater from their outfalls.


The second phase of MS4 regulations became effective March 23, 2003, and requires that operators of small MS4s in "urbanized areas" (as defined by the U.S. Census Bureau's latest decennial census) obtain permit coverage for stormwater discharges.


Small MS4s include storm sewer systems operated by cities, counties, towns, federal facilities such as military bases, Veteran’s Affairs hospitals and research facilities, Department of Defense facilities and parkways, and state facilities such as VDOT, community colleges and public universities. 

Discharges from small MS4s are regulated under the General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems which is administered by the Department of Conservation and Recreation (DCR).


Under that permit, small MS4s must develop, implement and enforce a program that includes the following “six minimum control measures":

  • Public education and outreach on stormwater impacts

  • Public involvement and participation

  • Illicit discharge detection and elimination

  • Construction site stormwater runoff control

  • Post-construction stormwater management in new development and redevelopment

  • Pollution prevention/good housekeeping for municipal operations


Similar to the Phase I programs, small MS4 programs must be designed and implemented to control the discharge of pollutants from their storm sewer systems to the maximum extent practicable in a manner that protects the water quality in nearby streams, rivers, wetlands and bays.


VDOT falls under Phase II and is covered under DCR’s MS4 General Permit with an effective date of July 1, 2008. The permit allows VDOT to operate its own MS4 Program. Implementation of a comprehensive Stormwater Management (SWM) Program to reduce the contamination of stormwater runoff and prohibit illicit discharges is required to comply with the MS4 Permit conditions.


For more information regarding minimal control measures, visit the U.S. Environmental Protection Agency at http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm.

Page last modified: Oct. 14, 2012