Where Does It Go

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.


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



    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


    Sewage cross-connections with storm drains

    Straight pipe connections

    Industrial and commercial cross-connections with storm drains


    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​