Illicit Discharge

Understanding Illicit Discharge

An illicit discharge is defined in the federal regulations as:

"...any discharge to an Municipal Separate Storm Sewer Systems (MS4) that is not composed entirely of storm water..."

There are two modes of entry: direct and indirect.

Direct:

Flows in the storm drains created by illicit/improper connections between sanitary sewer and storm drain system.

Indirect: 

Flows in the storm drains created by pollutants that enter the storm drain system through an inlet or through the joints of the pipe (infiltration).

Examples of Illicit Discharge

Direct

• Sewage cross-connections with storm drains
• Straight pipe connections
• Industrial and commercial cross-connections with storm drains

Indirect

• Groundwater seepage into the storm drain pipe
• Spills that enter the storm drain system at an inlet
• Dumping liquid into a storm drain inlet
• Outdoor washing activities that create flow to a storm drain inlet
• Non-target irrigation from landscaping or lawns that reaches the storm drain system