Municipal Stormwater

The General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems ("MS4 General Permit") regulates stormwater discharges from storm sewer systems owned by certain municipalities, public universities, and state and federal facilities.  Under this permit, each permittee is required to take steps to keep the stormwater entering its storm sewer systems clean by implementing control measures.  Control Measures can range from educating the public on stormwater issues to conducting site investigations and installing stormwater management structures. 

Permittees under this general permit are required to create a Stormwater Management Plan that describes how they intend to comply with the permit and submit annual reports to DEEP on their progress.  These documents should be publicly available on the permittee's website.

NOTES FOR THE 2025 PUBLIC NOTICES OF THE REISSUANCE OF THE SMALL MUNICIPAL SEPARATE STORM SEWER SYSTEMS (MS4) STORMWATER GENERAL PERMIT: 03/25/2025 – Notice of Tentative Determination: The Notice of Tentative Determination expresses the intent to reissue the general permit with the changes seen in the Draft Permit, and explains how public comments can be submitted. 03/25/2025 – Fact Sheet: The Fact Sheet explains the permit history and why certain changes are being proposed. DOCUMENTS FROM THE MARCH 2025 PUBLIC NOTICE **Draft MS4 General Permit** (84 pages, uploaded 03/26/2025) Fact Sheet for the Draft MS4 General Permit (23 pages, uploaded 03/26/2025) Notice of Tentative Determination - Intent to Reissue the General Permit for the Discharge of Stormwater associated with Small Municipal Separate Storm Sewer Systems (MS4) (3 pages, uploaded 03/26/2025)

The Annual Report template is available below. Please note that there are two versions: one for 2004 MS4 permittees and one for 2017 MS4 permittees (8 new towns and all institutions). DEEP strongly recommends the use of these templates but alternate formats will be accepted as long as all the required information is provided. As a reminder, the Annual Report should be completed and posted for public review/comment by February 15th and submitted to DEEP by April 1st.

Department of Transportation (DOT) Separate Storm Sewer System General Permit

The Department of Transportation submitted Application No. 201904533 on March 25, 2019 for the Discharge of Stormwater from Department of Transportation Separate Storm Sewer Systems (DOT MS4). A copy of the registration can be requested by emailing DEEP at DEEP.StormwaterStaff@ct.gov.

• DOT MS4 Stormwater Management Plan 
• DOT MS4 General Permit--Issued May 24, 2018 with an Effective Date of July 1, 2019
• Fact Sheet for DOT MS4 General Permit
• May 29, 2018 Notice of Issuance of DOT MS4 General Permit
• Summary of Changes Between Public Noticed and Final Versions of DOT MS4 GP
• Markup Between Public Noticed and Final Versions of DOT MS4 GP

Town by Town Water Quality Factsheets

The factsheets below provide a variety of water quality data in various formats for every city, town, or borough in Connecticut.

• Impervious cover across a town or city is presented in pie chart format as a percentage of the total town area.
• Links to specific Total Maximum Daily Load (TMDL) plans are available, as is information about annual stormwater quality monitoring for specific pollutants such as bacteria, total suspended solids, total nitrogen, total phosphorus, and turbidity.

• Town maps exhibit areas of highest or lowest impervious cover within the town and whether water bodies meet water quality standards for aquatic life and recreational use. Coastal towns also have maps that indicate whether their coastal waters meet water quality standards for shellfishing.

• Current Tier 1 Municipality Factsheets (alphabetical order)
  • Ansonia to Bridgeport
  • Bristol to Darien
  • Deep River to Ellington
  • Enfield to Groton
  • Guilford to Meriden
  • Middlebury to New Fairfield
  • New Haven to Old Lyme
  • Old Saybrook to Ridgefield
  • Rocky Hill to Stratford
  • Suffield to Watertown
  • West Hartford to Woodbury
• New Tier 1 Municipality Factsheets (Brooklyn, Haddam, Killingly, Mansfield, New Hartford, Plainfield, Sprague, Willington)
• Factsheets for Non-regulated Municipalities (alphabetical order)
  • Andover to Eastford
  • Franklin to Preston
  • Roxbury to Woodstock

Related Information

• Connecticut MS4 Guide from the UCONN Center for Land Use, Education, and Research (UCONN CLEAR)
• UCONN Center for Land Use, Education, and Research (UCONN CLEAR)
• EPA MS4 Main Page (contains MS4 program description, Minimum Control Measure explanation and tools for Public Outreach, IDDE, Construction and Post-Construction Runoff Control and Pollution Prevention/Good Housekeeping)
• Guidelines for Street Sweepings & Catch Basin Cleanings
• December 18, 2014 NRDC & EDC Petition for Writ of Mandamus to Require EPA to Comply with 2003 Order Strengthening MS4 General Permit Regulations

Stormwater Management

Content Last Updated October 9, 2023