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 more than 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.


IDDE Ordinance

Outline of the IDDE legal authority requirements.

Example IDDE ordinance available on the Legal Authorities page.

Written IDDE Program Template

Example IDDE Program template [905 KB] (developed by Fuss and O'Neill).

IDDE Workshop Materials

9/27/17 IDDE workshop presentations (below Task list)

Example Manhole Inspection form [60 KB] (developed by Fuss and O'Neill)

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.

Activity Deadline 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 22
Record illicit discharge abatement activities Jul 1 2017 23
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 presentation

IDDE Overview

September 27th, 2017
Presented by: David Dickson, UConn CLEAR


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idde mapping requirements presentation

IDDE Mapping Requirements

September 27th, 2017
Presented by: David Dickson, UConn CLEAR

Presentation on the IDDE mapping requirements for the MS4 Permit.

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catchment investigation presentation

Catchment Assessment and Ranking

September 27th, 2017
Presented by: Bill Guenther, Fuss & O'Neill

Presentation on Catchment Assessment and Ranking Procedures of the MS4 Permit.

View Presentation                          View Slides

impaired waters monitoring presentation

Impaired Waters Monitoring

September 27th, 2017
Presented by: Erik Mas, Fuss & O'Neill

Presentation on Impaired Waters Monitoring under the 2017 CT MS4 Permit.

View Presentation                          View Slides

case study presentation

Case Study: UConn Screening and Monitoring Program

September 27th, 2017
Presented by: Mike Dietz, UConn CLEAR

Case Study presentation on UConn's IDDE screening and sampling procedure.

View Presentation                          View Slides

dry weather screening presentation

IDDE Dry Weather Screening

September 27th, 2017
Presented by: Bill Guenther, Fuss & O'Neill

Presentation on dry weather screening under the 2017 CT MS4 permit.

View Presentation                          View Slides