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Illicit Discharge Detection

Illicit discharge(s) from an outfall in Baltimore City

MS4 communities in the Bay watershed have permit requirements to screen their stormwater outfalls to detect illicit discharges of sewage and other pollutants, and take actions to eliminate them.

High nutrient levels have been detected in dry weather flows in a number of urban streams in the Chesapeake Bay. Subsequent outfall screening using nutrient based indicators suggest that the much of nutrients are derived from illicit discharges of sewage. Part of the reason is the interaction of flows and overflows from aging sanitary sewers and storm sewers which often run close together.

Recent studies indicate that these discharges may account for a significant fraction of the annual nutrient load of some urban streams (CWP, 2011). This suggests that an aggressive local IDDE program could achieve significant nutrient reductions. IDDE efforts are already required under municipal MS4 stormwater permits.

An Expert Panel was convened in July 2012 to review the available science on the nutrient load generated by illicit discharges in storm drain systems and to evaluate an approach for crediting such discharges that are discovered and eliminated during routine (yet advanced) outfall screening procedures.

On November 10, 2014 the Recommendations were approved by the final review committee at the Chesapeake Bay Program, the Water Quality GIT. This means this credit is now live and available to communities working to meet their Bay TMDL load allocations. Congratulations to our panelists on a job well done! 

 

U-6 Elimination of Individual Nutrient Discharges From Gray Infrastructure Fact Sheet

A 'fact sheet' on using the elimination of discovered nutrient discharges as an urban BMP in the Chesapeake Bay Watershed.

Version february 3, 2017 | Size (924 KB) | File type (.pdf) | Download

U-9 Advanced MS4 Nutrient Discovery Program Credit

A 'fact sheet' on using enhanced IDDE programs as an urban BMP in the Chesapeake Bay Watershed.

Version january 2017 | Size (460 KB) | File type (.pdf) | Download

Accounting Guidance for Meeting the Bay TMDL

Nutrient Discharges from Grey Infrastructure

This is the short version of the Final Approved Recommendations of the Expert Panel to Define Removal Rates for the Elimination of Discovered Nutrient Discharges from Grey Infrastructure - only contains Appendix A.

Version november 11, 2014 (short) | Size (1 MB) | File type (.pdf) | Download

Nutrient Discharges from Grey Infrastructure

Final Approved Recommendations of the Expert Panel to Define Removal Rates for the Elimination of Discovered Nutrient Discharges from Grey Infrastructure (w/ appendices)

Version november 11, 2014 long | Size (2 MB) | File type (.pdf) | Download

Profile Sheets for Crediting Nutrient Reductions from Grey Infrastructure

A series of profile sheets outlining each of the discharges that are eligible for a credit. Each profile sheet described the discharge, its characteristics and the crediting approach used when it is fixed and/or prevented. A design example to show how the credit is calculated is also provided.

Version november 10, 2014 | Size (1 MB) | File type (.pdf) | Download

Training Resources

[Webcast] Nutrient Discharges from Grey Infrastructure

[Webcast] Discharge Discovery Techniques

More in the Illicit Discharge Prevention section of our website here.