All CT municipalities within an “urbanized area” are required to comply with the MS4 General Permit. The following sections will serve as a guide, largely developed after CT NEMO’s program, for municipalities to understand the multiple aspects of the MS4 permit, and why it’s important.
Municipal MS4 General Permit
Requirements for all MS4 Permit holding municipalities:
- Submit a Stormwater Management Plan identifying 6 minimum control measures (MCM) that a municipality will undertake to prevent and/or treat polluted runoff;
- Submit Annual Reports to DEEP indicating the progress with implementing that plan; and
- Monitor the quality of water bodies through mapping and testing.
The current MS4 General Permit can be found at MS4 Stormwater General Permit (ct.gov).
Click below for more information on MS4 guidance.
Each MS4 municipality must develop a Stormwater Management Plan to guide its activities in compliance with the MS4 general Permit. Six Minimum Control Measures highlighted in the MS4 permit will form the basis of what communities must do to manage stormwater and its impacts.
View a sample Stormwater Management Plan made by the UConn NEMO program. Please note, this template is only a guide - towns should thoroughly examine their plan to ensure it represents their town and meets all MS4 requirements. Once completed, the plan also needs to be certified by a licensed Professional Engineer.
There are 6 minimum control measures (MCM) that are required by the CT MS4 General Permit to form the basis of what communities must do to manage stormwater and its impacts.
Included in each section is a link to CT NEMO resources that municipalities can use to comply with these MCMs.
1. Public Education and Outreach
2. Public Involvement and Participation
3. Illicit Discharge Detection and Elimination
4. Construction Site Stormwater Runoff Control
Each year municipal staff must be trained on various stormwater topics. This requirement is part of MCM 6 “Pollution Prevention and Good Housekeeping." To find more information on each training topic, view training materials.
NVCOG can organize trainings on behalf of municipalities or suggest a training resource. For more information or to request a training, contact tdougherty@nvcogct.gov.
The MS4 mapping requirements, which are highly technical and may be best accomplished by engaging a consultant, involve mapping stormwater infrastructure and estimating, tracking, and disconnecting Directly Connected Impervious Area (DCIA).
Note: Municipalities must disconnect their priority areas by 1% per year. This can be found under the Pollution Prevention/Good Housekeeping portion of the general permit (page 31). Visit the LID/GSI web page for additional information to accomplish this goal.
View CT NEMO’s webpage on mapping that includes resources, a task schedule, and educational videos.
Each MS4 municipality must submit an Annual Report indicating progress on implementing their stormwater management plan, as well as post their report on their municipal website for public comment and review.
The submission timeline each year is as follows:
- January 31st - Notify the public when the Annual Report and stormwater management plan will be made available for review.
- February 15th - Post the Annual Report and current stormwater management plan for public comment.
- April 1st - Submit the Annual Report to DEEP. Mail the review fee, which is $187.50 for municipalities, and the Annual Report transmittal form (download here) to CT DEEP Central Permit Processing Unit and email an electronic copy of the Annual Report to Stormwaterstaff@ct.gov.
View templates, timeline, and more information regarding creating an annual report for your municipality.
The MS4 general permit requires that municipalities establish several 'legal authorities' which could be ordinances, bylaws, regulations, standard conditions of approval, or other mechanisms. These required legal authorities aim to prohibit illicit discharges, require that Low Impact Development (LID) alternatives are considered for development and redevelopment, and to require the inspection of stormwater runoff control practices at construction and post-construction sites. It is recommended that municipalities implement this action as soon as possible, to enforce their stormwater management plan. To learn more, please visit the LID/GSI webpage.
The three topics legal authorities must cover are:
- Illicit Discharge Detection and Elimination Legal Authority
- Construction Site Legal Authority
- Pos-Construction Legal Authority
The example legal authorities linked here do not constitute legal advice. Please be sure to consult your town attorney.
The MS4 permit requires wet weather monitoring of all outfalls (which should be mapped by town staff or consultant) that discharge directly to any impaired waters.
The other monitoring requirement is part of tracking down illicit discharges via the IDDE program. This includes dry weather monitoring or sampling an outfall when no more than 0.1 inches of rainfall has occurred in the previous 24 hours.
Visit CT NEMO’s Water Quality Monitoring webpage which includes resources, task schedule, and educational videos.
NVCOG Support Services
Mapping
NVCOG can provide mapping tools and training assistance to municipalities for MS4 permit compliance, including:
- Finding the impaired waters in your area.
- Determining how much impervious cover is in your town and your watersheds.
- Providing a quick sense of where your priority areas are (any area that is in a census designated urbanized area, drains to an impaired waterway, or has greater than 11% impervious cover).
Please contact gprentiss@nvcogct.gov if you require any assistance.
Public Outreach and Education
NVCOG has contracted with the Pomperaug River Watershed Coalition to provide public outreach materials through the RiverSmart program.
MS4 and LID Local Regulation Assessment
NVCOG staff assist municipalities in meeting MS4 permit requirements by providing regulation assessments, regulatory recommendations, and ongoing technical support. Assistance is available upon request, please contact tdougherty@nvcogct.gov.
Additional Resources
UConn CLEAR Interactive Map
UConn CLEAR has developed a comprehensive interactive online map (2020) to assist with permit compliance.
MS4 Compliance Informational Events
In 2022, NVCOG held a hybrid Environmental Sustainability Forum on MS4 compliance for interested stakeholders in the region. View the live recording and event materials.
In 2024, NVCOG & UConn held an informational tour about how municipalities can reduce flooding and improve water quality in their communities through Low Impact Development. View the informational slides.
Stormwater Quality Manual
The Connecticut Stormwater Quality Manual provides guidance on the measures necessary to protect the waters of the State of Connecticut from the adverse impacts of post-construction stormwater runoff. The MS4 Permit refers to The CT Stormwater Quality Manual in several places.
Here is the most up to date version of the CT Stormwater Quality Manual. If any language in your current municipal regulations directly references the past manual specifically from 2004, it will need to be updated with the current regulation.
The New Stormwater Quality Manual: What You Need to Know, is available here CLEAR Webinar page.
The following are links to a webinar hosted by UConn CLEAR.