Frequently Asked Questions

MS4 Program Basics

Stormwater runoff is a major source of flooding, erosion and the pollution of Connecticut’s waterways, and is certain to become even more of a problem as climate change progresses. Accordingly, the Connecticut Department of Energy and Environmental Protection (CT DEEP) has recently revised and expanded the principal permit used to regulate stormwater in the state: the “General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems,” or MS4.
121 of Connecticut's 169 towns are included in the MS4 General Stormwater Permit. Click here for a map of the towns. Each of these towns have or are part of an "urbanized area," which is a designation of the U.S. Census that takes into account population, population density, impervious cover, proximity to urban areas, and other factors.

State and federal institutions that operate their own stormwater system are now also included in the MS4 permit. This includes university campuses, like UConn, state prisons, military bases, hospitals, public housing authorities, office complexes, etc. that have more than one building and an average daily population of 1,000 or more people.
There is no specific/dedicated funding available to help with costs of complying with the new MS4 permit. It is a good idea to check with your regional Council of Government (COG) to see if they are coordinating any efforts to pool resources. In other states communities have formed collaboratives to share the responsibilities and costs of equipment, monitoring, public education, etc. One example is the Central Massachusetts Stormwater Coalition.
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They will be. DEEP is negotiating a special permit that is based on the MS4 permit and will cover the Department of Transportation.
While the requirements of the MS4 permit generally apply townwide, many of the sections focus on what are deemed "priority areas." There are three categories of priority areas:
  1. urbanized areas
  2. areas with directly connected impervious Area (DCIA) greater than 11%
  3. areas that drain directly to impaired waters
While all of these are considered priority areas, towns and institutions should give the highest priority to those areas of overlap between these three categories.
“Surface Water” means the waters of Long Island Sound, its harbors, embayments, tidal wetlands and creeks; rivers and streams, brooks, waterways, lakes, ponds, marshes, swamps, bogs, federal jurisdictional wetlands, and other natural or artificial, public or private, vernal or intermittent bodies of water. Surface water does not include ground water.

Stormwater Management Plan

Each MS4 Town/Institution must post its Stormwater Management Plan for public comment by April 1, 2017 (No joke!) and share a link or electronic copy along with a registration form to DEEP by April 3, 2017. The public must be allowed to comment for 60 days.
Yes! NEMO modified a template developed by the Western Connecticut Council of Governments (WESTCOG) for statewide use. It can be found here. NOTE: CT DEEP has not officially sanctioned this template, but it is based on the permit language and DEEP's MCM checklist.
There are many consultants in the area with experience in developing and implementing SWM Plans. NEMO does not have a recommended list. However some of the Councils of Government (COGs) have developed lists.
Public comments on your Stormwater Management Plan or your Annual Report should be sent to the DEEP Commisisoner.
By Email:

US Mail:
Water Permitting and Enforcement Division
79 Elm Street
Hartford CT 06106
Attn: Karen Allen


DCIA means directly connected impervious area. It is a stormwater geek's term for hard surfaces that contribute stormwater runoff to the storm sewer system. It is also sometimes referred to as effective impervious cover. Towns must calculate the DCIA for each of their outfalls. Any areas with a DCIA > 11% are considered "priority areas" for purposes of the permit and therefore an area that should be a communty's focus for activities.
UConn CLEAR worked with DEEP to identify a few methods to determine DCIA. The Mapping section has the details.
An impervious area is considered disconnected when the minimum amount of the "Water Quality Volume" has been retained in the area. This means for sites with DCIA < 40% - retain the volume of runoff generated by the first 1 inch of rainfall. For sites with > 40% DCIA – retain the volume of runoff generated by the first ½ inch of rainfall. You can retain stormwater on site in many ways as long as it infiltrates the ground or is reused without a surface or storm sewer discharge. In most cases, disconnection will be achieved through the installations, retrofits or redevelopment projects that incorporate Low Impact Development (LID) practices like rain gardens, bioretention, pervious pavements, green roofs, etc. It can also be accomplished by simply directing runoff to a vegetated area such as a lawn rather than into the stormwater system.

Water Quality Monitoring

Every 2 years CT DEEP submits its Integrated Water Quality Report to the U.S. EPA containing all of the known impairments to water bodies in the state. If you know your "waterbody segment ID" Click Here to review the list and locate your water body. (Note: DEEP has just released the draft of the 2016 report, but that is not expected to be finalized until Spring 2017.) Alternatively, NEMO has added the impairments listed in the most recent report (2014) to our CT MS4 Towns & Data Map. Now you can click on any impaired water body to identify the impairment. Only those impairments related to stormwater are covered under the permit.

NOTE: NEMO is working with DEEP to identify which listed impairments are considered related to stormwater.

Additional resources:
This handy-dandy decision tree should help you figure out which outfalls have to be screened and for what. For more information, visit the monitoring section of the website.
DNA testing is available to determine sources of fecal bacteria here. The case studies are older but the technology is widely used today.