Metric performed Illicit Surface Water Discharge Monitoring for the Gary Sanitary District along the Grand Calumet River and Little Calumet River within Lake County, Indiana. The monitoring events included physical observation and documentation of over 70 identifiable outfalls along both rivers to detect illicit or illegal discharges from drain pipes or surface runoff contributing to water pollution. Staff sampled accessible outfalls that were discharging. In accordance with the Center for Watershed Protection’s Illicit Discharge and Elimination Guidance Manual, the collected samples were submitted for laboratory analysis. The sampled discharges were categorized by comparing the laboratory analysis results to concentrations of particular constituents commonly associated with a various potential discharge types. Additional desktop research was conducted to attempt to determine the origin points of a variety of discharges. Metric provided the Gary Sanitary District with an Illicit Surface Water Discharge Monitoring Report detailing the investigation, the findings of the investigation, and recommendations for future monitoring of the outfalls.