Permit Basics

MS4 Permit History

DEEP issued its first General Permit requirements in 2004 covering 113 municipalities. In 2016, DEEP issued a new permit that will become effective July 1 2017. The new permit applies to the 113 existing MS4 towns as well as 8 new towns and all state and federal instiutions that operate a stormwater system. (See the Towns & Institutions section for a listing of who is included.)

Why an MS4 Permit? Video

What's the big deal about stormwater?

Stormwater picks up various pollutants as it travels over impervious surfaces, carrying them through storm systems and into local waterbodies. This pollution then impacts water quality, aquatic life and habitats, ecosystems and habitats, and other impairments. For more information, check out our Stormwater Basics page.

Stormwater Basics


2017 MS4 Permit

All CT municipalities within an "urbanized area" are required to comply with the MS4 General Permit to discharge stormwater into CT's water bodies. The basic requirements of the permit are to:

1) Submit a Stormwater Management Plan identifying 6 minimum control measures that a municipality will undertake to prevent and/or treat polluted runoff;

2) Submit Annual Reports to DEEP indicating the progress with implementing that plan; and

3) Monitor the quality of water bodies.

The full permit is provided below:

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2017 Permit Changes At A Glance

2004 MS4 Permit 2017 MS4 Permit
Who is Covered? A municipality that owns and operates a storm sewer system in an Urbanized Area; based on the 2000 census A municipality that owns and operates a storm sewer system in an Urbanized Area; based on the 2010 census (New: Brooklyn, Haddam, Killingly, Mansfield, New Hartford, Plainfield, Sprague, and Willington). Also includes state and federal institutions such as prisons, colleges, hospitals, and military facilities.
Public Outreach & Education Requires public education program to distribute educational materials or conduct outreach activities Additionally: Specifies what topics public education should target. Specifies how outreach materials can be distributed. Adds a timeline for implementation of this program.
Public Involvement Requires compliance with Freedom of Information Act. Requires development of a public participation plan for the Stormwater Management Plan. Additionally: Specifies where/when to post notice of the availability of the Stormwater Management Plan and Annual Report for public review
Illicit Discharge Detection & Elimination (IDDE) Requires implementation of a regulatory mechanism to prohibit illicit discharges Additionally: Specifies where to look for illicit discharges. Requires citizen reporting program. Requires a more specific legal authority. Adds a timeframe.
Construction Requires program to reduce construction runoff pollution Additionally: Provides more detail about the legal authority required. Requires consistency with Stormwater Quality Manual in addition to the 2002 Guidelines for Soil Erosion and Sedimentation Control. More detail is provided for construction review and inspection, notification of requirements of the DEEP construction general permit, public involvement and long-term maintenance of stormwater treatment ponds. Requires MS4 to plan how all related departments and boards will coordinate with each other.
Post-Construction Implement program to address stormwater runoff from new or redeveloped projects, and create a legal authority. Implement appropriate BMPs, and ensure long term maintenance. Additionally: Requires LID measures to be used, as well as other elements from the construction general permit. MS4 is required to map its Directly Connected impervious Area (DCIA).
Good Housekeeping/Pollution Prevention Employee training; park & open space maintenance, fleet & building maintenance, new constructions & land disturbances, stormwater system maintenance; streetsweeping; catch basin cleaning; repair/upgrade MS4 structures/outfalls when necessary Additionally: Timelines for all parts; more specific parks/open space procedures; pet waste management; waterfowl management; specific buildings and facilities procedures; specific vehicle and equipment procedures; leaf management; specific catch basin cleaning instructions; snow management practices; interconnected MS4 coordination; additional measures for impaired waters
Monitoring Monitor 6 stormwater outfalls once per year during a rain storm. Screen outfalls for discharges to impaired waters only; Representative outfall sampling in the last two years of the permit only; Screen outfalls during rain storm and test for nitrogen, phosphorous, bacteria, or turbidity, dependent on the identified cause of impairment; Outfalls exceeding certain threshholds will be targeted for a follow up investigation and will need to change the BMP

Compliance Funding

As of July 1st, 2021, Connecticut municipalities can now implement their own stormwater utilities. These utilities function the same as other utilities, such as water or sewage, charging a fee on impervious cover in order to generate sustainable funding for stormwater management. Just as residents pay a fee for how much water they use, which in return funds the drinking water services within their area, stormwater utilities charge residents and property owners on the amount of impervious cover on their property. The fee is not based on property tax, but on impervious cover, allowing all properties, even tax-exempt properties, to contribute to the stormwater fund.

For more information, check out our Stormwater Utilities page and out Stormwater Utility and MS4 Compliance Fact Sheet.