Abstract

The Ohio River Sanitation Commission (ORSANCO) has undertaken a study of the sources of wet weather pollution in large rivers. The study is to be completed within two years with work in the first year concentrating on defining wet weather sources of pollution while work in the second year will concentrate on evaluating effective wet weather controls. The project includes both extensive and monitoring of water quality. At this point (March 1996), year one is nearing completion.

As part of this study, a complete XP-SWMM model of the drainage system within the greater Cincinnati area was developed. This model included interceptor sewers, trunk sewers, all combined sewer overflows (CSOs), significant overflows (SSOs), treatment plants, and receiving streams and rivers. Both flow and water quality data were modelled for the entire system. The model was calibrated using existing stream tributary flow and concentration data, and interceptor flow and concentration data.

The purpose of the modelling is to generate pollutographs from direct the Ohio River (a significant number of CSOs and three wastewater treatment plants) and tributary streams. Tributary streams within the study area receive CSO and SSO discharges during wet weather. The results of the model are to be interfaced with a WASP model of the Ohio River, currently being developed by another member of the study team.

The model was used to generate pollutographs for fecal coliform and suspended solids for a total of four wet weather events during the fall of 1995. These four events were selected due to the availability of event mean concentration data from water quality monitoring. Statistical analyses on collected data were completed to define event mean concentrations for CSO discharges. Model results were compared against data collected during an extensive water quality monitoring program. Water quality was monitored in tributary streams. A comparison of modeled results with measured results indicated good agreement between predicted concentrations of fecal coliform and measured concentrations. In the next year, the developed model will be utilized to evaluate alternatives for controlling wet weather sources of pollution into the Ohio River.

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