Municipal Stormwater

Stormwater Program for MS4


Stormwater runoff from an urbanized area is commonly transported through Municipal Separate Storm Sewer Systems (MS4s). Urbanized areas are associated with different activities that contribute pollutants to stormwater runoff. Additionally, urbanized areas are characterized by large amounts of impervious surfaces such as streets, sidewalks, driveways, parking lots, and roof tops. Stormwater runoff from impervious surfaces travels faster which results in damage to the waterbodies and causes flood­ing and hydrologic changes to the receiving waters. Elevated pollutant levels can impair waterbodies, degrade biological habitats, and pol­lute drinking water sources.

Discharges from MS4s are regulated under the Clean Water Act and OPDES Act as point source discharges. MS4 regulations were developed and implemented in two phases. Implementation of MS4 Phase I began in the early 1990s and required medium and large cities or certain counties with populations of 100,000 or more to obtain NPDES permit coverage for their stormwater discharges. The MS4 Phase II regulations became effective on March 23, 2003 and required regulated small MS4s in urbanized areas, as well as small MS4s outside the urbanized areas that are designated by DEQ, to obtain permit coverage for their stormwater discharges.

Phase I MS4s are covered by individual permits and Phase II MS4s are covered by a general permit OKR04. 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 to the MS4.

What is an MS4?

Per 40 CFR § 122.26(b)(8), an MS4 is a conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains) 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; and not part of a Publicly Owned Treatment Works (sewage treatment plant).

MS4 Phase I Program

Currently, there are two cities, City of Oklahoma City and City of Tulsa, which are regulated under the Phase I program.

The City of Oklahoma City MS4 Permit

The City of Oklahoma City MS4 Permit became effective on March 15, 2013 and expires at midnight on March 14, 2018.

Permit, Fact Sheet & Response to Comments

The City of Tulsa MS4 permit

The City of Tulsa MS4 permit became effective on October 16, 2011 and expired at midnight on October 15, 2016.
Permit, Fact Sheet & Response to Comments

MS4 Phase II Program

There are 51 small cities/counties which are regulated under the MS4 Phase II Program. A Regulated Phase II MS4 is an MS4 that is located wholly or partially within an Urbanized Area (UA) boundary as defined by the latest decennial U.S. Census and not a large or medium municipality. Regulated Phase II MS4s include systems that are operated by traditional communities such as municipalities, (such as counties, cities or towns) as well
as non-traditional communities such as military installations, universities and community development districts. Phase II MS4s located outside of UAs may also become regulated by designation by DEQ according to designation criteria set forth in the rules.

An urbanized area (UA) is a central place (or places) and the adjacent densely surrounding territory that together has a minimum residential population of 10,000 and a minimum average density of 1,000 people/square mile. All UA calculations and mapping are done by the U.S. Bureau of the Census. The determination of which MS4s are automatically designated as regulated Phase II MS4s is based solely on the boundaries of U.S. Bureau of the Census urbanized areas –not political boundaries. You may view a list of regulated MS4 Phase II cities and counties which have been determined based on 2010 Census by U.S. Bureau of the Census.

How to Apply for a Permit?

Before filling out an NOI, understand the requirements of OPDES General Permit OKR04 for small MS4, identify if there will be any co-permittee, assign responsible person for implementation and coordination for SWMP, identify the latitude and longitude of the centroid of the municipality/city, identify the all receiving water bodies, check whether there is an approved TMDL for an impaired waterbody, check whether municipality discharges into an Aquatic Resources of Concern (ARC) area, and prepare a Stormwater Management Program (SWMP) in accordance with the requirements of OKR04 Permit. Once the NOI and the SWMP have been completed, submit the following to DEQ:

  • Completed NOI
  • An application fee $100 and annual permit fee $748.11 (for FY15, annual fee is prorated for the new applicant based on the date of submission of an NOI to DEQ)

A summary of the SWMP (see Part IV of OKR04) and a map of showing your municipal boundaries.

Where to Submit an NOI?

Mail the completed NOI to Stormwater Permitting, Water Quality Division, Oklahoma DEQ, 707 N Robinson Ave, P. O. Box 1677, Oklahoma City, OK, 73101-1677.
A copy of the application packet can be emailed to

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