Illicit Discharge Detection and Elimination


Illicit discharges inlcude nearly anything that isn't stormwater such as illegal dumping in storm drains, animal wastes, fertilizers, industrial and commercial waste, sewage, leaves, etc. Towns and instituions need to identify and remove non-stormwater discharges to their MS4.

Relevant terms

  • Priority areas: means areas in the Urbanized Area and in catchments with >11% DCIA or catchments that discharge to an impaired waterbody. If any one of these conditions exists, it's part of the priority area.

  • Illicit discharge: means any unpermitted discharge to waters of the state that does not consist entirely of stormwater or uncontaminated groundwater except those discharges identified in Section 3(a)(2) of the MS4 general permit when such non-stormwater discharges are not significant contributors of pollution to a dischage from an identified MS4.

  • Sanitary Sewer Overflow (SSO): means a discharge of untreated sanitary wastewater from a municipal sanitary sewer.


Task list

Where the deadline for new MS4 permittees differs from the deadline for exisiting permittees, the second deadline in parenthesis applies to new permittees.



Permit page

Maintain inventory of known SSOs (5 year look back)

Oct 30 2017

App B p2

Citizen reporting program in place

Jul 1 2017


Record illicit discharge abatement activities

Jul 1 2017


Develop written IDDE program

Jul 1 2018
(Jul 1 2019)

22 & AppB p4

Establish IDDE legal authority

Jul 1 2019

23 & AppB p5

Map all MS4 outfalls

Jul 1 2019
(Jul 1 2020)

23 & AppB p2

Complete dry weather outfall sampling (for high & low priorty outfalls)

Jul 1 2020
(Jul 1 2022)

AppB p8

Detailed MS4 mapping

Jul 1 2020
(Jul 1 2022)

AppB p3


IDDE Workshop Materials

The NEMO program and Fuss and O'Neill presented a workshop on IDDE on 9/27/17 at Newington Town Hall. Most of the presentations were recorded. The presentation slides and recordings (where available) can be found below.

IDDE Overview, presented by David Dickson, UConn CLEAR

IDDE Written Program, presented by Erik Mas, Fuss and O'Neill

IDDE Mapping Requirements, presented by David Dickson, UConn CLEAR

Catchment Assessment and Ranking, presented by Bill Guenther, Fuss & O'Neill

IDDE Dry Weather Screening, presented by Bill Guenther, Fuss & O'Neill

IDDE Catchment Investigation, presented by Bill Guenther, Fuss & O'Neill

Impaired Waters Monitoring, presented by Erik Mas, Fuss & O'Neill

Case Study: UConn Screening and Monitoring Program, presented by Mike Dietz, UConn CLEAR