Evaluation of Total Residual Chlorine (TRC) in CSO Receiving Waters

The Detroit Water and Sewerage Department (DWSD) has installed combined sewer overflow (CSO) screening and disinfection facilities to treat CSOs prior to discharge to the receiving waters. This study was conducted to determine the extent of residual chlorine in the receiving stream during and after discharges from five of DWSD's CSO treatment facilities. The current National Pollutant Discharge Elimination System (NPDES) permit has a goal of minimizing total residual chlorine (TRC) in the effluent that is discharged to the receiving water and the Michigan Department of Environmental Quality (MDEQ) is requiring the in-stream study to support evaluation of the permit requirements. The field work performed consisted of discrete sample collection at multiple locations and depths downstream of the studied CSO treatment facilities during active overflow events. Global positioning system (GPS) equipment was used to record the locations of sampling points and field analyzed TRC, specific conductivity, and pH data were merged with the geographic data.