Modeling the impact of CSOs on river bacteria levels
LimnoTech provided water quality modeling and general consulting services to the Ohio River Valley Sanitation Commission for the Louisville Area Wet Weather Demonstration Study. The purpose of the study was to evaluate wet weather impacts on instream water quality, and the relative improvement in river water quality from screening-level source control scenarios. A two-dimensional water quality model was developed using the U.S. EPA’s WASP model framework to simulate E. coli and fecal coliform over a 50-mile stretch of the river. The model was calibrated and validated to data collected during four storm events. The effects of source reductions of CSO and tributary (e.g., stormwater) loads were simulated.
The simulations presented here are based on actual rain events that occurred in the Louisville area between 1998 and 2001. The animation shows how concentrations decrease in the river over time due to natural processes, but bacteria can still travel many miles downstream during large rain events. The results from the screening-level simulations indicate that stormwater is the primary source of bacteria loadings to the Ohio River. The simulations suggest that CSO controls would be more effective at reducing peak bacteria concentrations in the river than in reducing the number of days that the river exceeded the water quality standard. The modeling analysis will be refined and used to inform decision making related to CSO controls in the Louisville area.