Stormwater is runoff from rain or snowmelt on impervious surfaces such as rooftops, paved streets, highways and parking lots. As it flows, it picks up contaminants from vehicles, landscaping products, farms, and construction sites. This polluted runoff is often transported through municipal storm sewer systems, eventually flowing into local water bodies, significantly affecting water quality. Polluted runoff can cause problems such as bacterial contamination (E.coli.) that make water unsafe for human recreation or consumption. It can also contain excess nutrients (such as phosphorus and nitrogen) that can lead to fish die-offs or other impacts to wildlife.

Storms and Infrastructure Challenges

In addition to water quality, the increasing quantity of stormwater is another concern. Communities across Connecticut are witnessing increased frequency and severity of heavy rainfall events. The majority of traditional stormwater infrastructure, however, has been built to out-of-date standards and cannot handle the flows from these storms. This results in flooding that causes economic, environmental, and public health strain in our communities.

Daily events per year with precipitation totals equal to or exceeding 2, 3, 4, and 5 inches from 1958–2022 (blue lines). The trends shown suggest an increase in the frequency of extreme precipitation, with larger increases for the more extreme precipitation events. Figure adapted from original in the Fifth National Climate Assessment (Theim, 2024).

NVCOG's Commitment

NVCOG is committed to promoting sustainable solutions for the communities in our region to both limit stormwater quantity and improve stormwater quality. Sustainable stormwater management involves building resilience against flooding as well as preserving water quality through smarter, more holistic infrastructure and site design. This webpage provides information about best stormwater management practices and how to implement General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems (MS4) requirements and Low Impact Development to improve stormwater management.

Regulations

Stormwater is regulated through the General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems (Municipal MS4 General Permit, MS4 General Permit, or MS4 Permit). The Permit requires communities to reduce barriers to Low Impact Development (LID) practices which minimize impervious surfaces in favor of preserving natural site hydrology or mimicking natural process that allow for evaporation or infiltration which promotes ecosystem health.

To see more information, click the drop down menu below.

Stormwater Regulations (MS4)

The most relevant permit for municipalities, the General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems ("MS4 General Permit") is mandated by the EPA and administrated by the CT DEEP.

This permit requires each qualifying municipality to take steps to preserve the water quality within storm sewer systems before releasing the water back into the environment. It also encourages the use of LID installations to minimize the amount of stormwater entering the sewers.

The elements of this permit include public education, staff training, mapping, reporting, and more. For more information on municipal MS4 compliance, visit the MS4 Compliance webpage.

Low Impact Development and Green Infrastructure

Low Impact Development (LID) is a practice that aims to use or mimic the natural landscape to mitigate the effects of flooding and water pollution from stormwater runoff.

Green Stormwater Infrastructure (GSI) is an LID concept and refers to specific installations designed to infiltrate water into the ground rather than let it run off impervious surfaces.

It is important to recognize the difference between LID and GSI. LID is the conceptual and planning framework that aims to mimic the natural landscape, while GSI is the actual infrastructure that accomplishes LID goals when developing.

To learn more, please visit the LID/GSI webpage.

NVCOG Stormwater Management Initiatives

NVCOG has undertaken the following initiatives to educate municipalities on LID and the MS4 General Permit.

  • Advocate with regulators to ensure the MS4 General Permit is implementable for municipalities.
  • Encourage LID implementation in NVCOG involved projects.
  • Assist municipalities with MS4 compliance requirements.
  • Provide education, outreach, and technical support on stormwater management.