Bacteria levels have been identified as a major cause of impairment to Ohio River water quality and its beneficial uses. Urban wet weather pollution has been identified as a major cause of impairment. A multi-agency, multi-year study was undertaken to determine the effect of urban pollutant
loadings on water quality in the Ohio River near Cincinnati, Ohio. A modeling methodology was developed to assess the water quality impacts of wet weather events on the Ohio River. A hydrodynamic model (RMA-2V) and water quality (WASP5) model were linked to provide a two-dimensional representation
of the Ohio River. The models were calibrated and validated to data collected from five wet weather events. Environmental conditions such as flow and meteorology were varied to determine the extent and severity of water quality impairments during a typical year. Finally, improvements in water
quality were evaluated by using the models to simulate simple, screening level combined sewer overflow (CSO) control alternatives. The model simulations indicated that bacteria loadings originating from CSOs have an adverse impact on water quality in the Ohio River near metropolitan Cincinnati.
Results from the CSO control alternative modeling indicated: CSO control improves water quality in some, though not all areas of the Ohio River; During the recreation season (May – October),
the single sample maximum concentration water quality standard (400 #/100 ml) is more stringent than the monthly geometric mean concentration standard; CSO control is more effective at reducing the duration that concentrations exceed the 400 #/100
ml criterion than in reducing the magnitude of maximum in-stream concentrations; The amount of rainfall influences the significance of CSO loadings on water quality and effectiveness of CSO control; In-stream concentrations
can exceed 400 #/100 ml during dry weather in some areas of the river.
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