An Alternative Approach to Illicit Discharge Detection with Aerial Infrared Thermal Imagery. A Case Study of MS4 Dry Weather Illicit Discharge Screening.

Illicit Discharge Detection and Elimination programs are a requirement of Municipal Separate Storm Sewer System (MS4) permit programs. A key element of these programs is screening to identify non-stormwater discharges to the MS4, followed by mitigation or elimination of illicit discharges and follow-up.

Instead of conducting a traditional, labor intensive field screening of 700 miles of streams, Louisville and Jefferson County Metropolitan Sewer District (MSD) undertook an alternative approach to screen for dry weather illicit discharges with aerial thermal imagery throughout its service area, with field investigations at select thermal anomalies. This is the first application of thermal imaging on this scale for this purpose. A desktop screening was conducted to prioritize field investigations. Field investigations included rapid visual assessment, source identification, and in-field water quality analysis. This program demonstrated the use of aerial thermography as the basis for an efficient dry weather illicit discharge screening program.