Municipal Separate Storm Sewer Systems (MS-4)

What Is an MS4?

An 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 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)


  • Polluted stormwater runoff is commonly transported through Municipal Separate Storm Sewer Systems (MS4s), from which it is often discharged untreated into local water-bodies. To prevent harmful pollutants from being washed or dumped into an MS4, operators must obtain a National Pollutant Discharge Elimination System, (NPDES permit), and develop a stormwater management program.
  • Phase I, issued in 1990, requires medium and large cities or certain counties with populations of 100,000 or more to obtain NPDES permit coverage for their stormwater discharges.
  • Phase II, issued in 1999, requires regulated small MS4s in urbanized areas, as well as small MS4s outside the urbanized areas that are designated by the permitting authority, to obtain NPDES permit coverage for their stormwater discharges.
  • Generally, Phase I MS4s are covered by individual permits and Phase II MS4s are covered by a general permit. Each regulated MS4 is required to develop and implement a stormwater management program (SWMP) to reduce the contamination of stormwater runoff and prohibit illicit discharges.
  • These regulations were developed to ensure compliance with the federal Clean Water Act and work to increase the number of water bodies that can safely be used for swimming and fishing.

Minimum Control Measures

The MS4 Program contains elements called minimum control measures that when implemented should result in a significant reduction in pollutants discharged into receiving waters. The minimum measures are outlined below: 

Public Education & Outreach

The City of Ozark supports the James River Basin Partnership, (JRBP). JRBP mission is informing the public about water resources and the protection of those resources. The City of Ozark has provided employees to lead educational festivals and to participate in classroom teachings regarding water quality. Watershed festivals are conducted to teach all of Ozark’s public school 5th grade students about water quality, including stormwater issues. The 2010 Ozark festivals were held in February with 880 students attending. The City of Ozark has also provided technical support and field assistance to the JRBP. The City of Ozark sponsors and participates in regional erosion and sediment control educational workshops.

Public Involvement & Participation

The City of Ozark conducts public hearings for all preliminary plat requests. Pre-construction meetings are required prior to any construction project. Erosion control, water quality and maintaining Best Management Practices, (BMP’s), are addressed at these meetings. The City of Ozark organizes annual city-wide clean-ups and support volunteer groups that cleanup local streams. The City of Ozark has supported the River Clean-up each year since 2006. The 2011 annual river clean-up and benefit concert was held on June 11 on the James River from Delaware Town to Shelvin Rock. The clean-up float drew 198 floaters, removed 100 tires, 3/4 ton of metal and 5.4 tons of trash. Approximately 400 people from Ozark and the surrounding communities attended an evening concert held next to the Finley River in Ozark. Handout materials were available as well as education stations such as a ‘Stream Table’, macroinvertabrate display, and rain barrel demo. Visit the James River Basin Partnership online resource for more information.

Ozark's Annual MS4 Report to Missouri Dept of Natural Resources