Abstract

The collection, transport and disposal of dry-weather and wet weather flow is an environmental problem for many U.S. cities (Roesner and Burgess, 1992). Combined sewer systems commonly service the older sections of U.S. cities and combined sewer overflows (CS0s) may be a source of bacterial, inorganic and organic pollutants to receiving water bodies (Meinholz EcolSciences, Inc., 1980; USEPA, 1984; Marsalek and Ng, 1989; Irvine et al., 1993a). There is a growing concern, particularly in the Great Lakes Basin, over pollutant loadings associated with CS0s. Many of the Areas of Concern (AOCS) around the Great Lakes have problems with CS0s and it is important under the Remedial Action Plan process to develop methodologies for the quantification and evaluation of pollutant inputs from this source.

The International Joint Commission (IJC) has identified the Buffalo River, NY as one of 43 AOCs around the Great Lakes. Among the several potential sources contributing to water quality degradation in the river, are 38 combined sewer outfalls (Figure 9.1). Other potential sources contributing pollutants to the river include direct industrial discharges, groundwater leachate from inactive hazardous waste sites, historically contaminated bed sediments and upstream (i.e. above the AOC) point and nonpoint sources (e.g. agricultural runoff, small municipal treatment plants).

One method for the determination of CSO impacts on the Buffalo River is to mathematically model the combined sewer system. Currently, a mass balance study for the Buffalo River is being conducted by a research team from the State University of New York (SUNY) at Buffalo and SLNY College at Buffalo (Loganathan et al., in prep; Atkinson et al., in prep; Irvine et al., 1993b). One of the intents of the study is to quantify pollutant inputs to the river from the different sources. This information can be used both as input to chemical transport and fate models and as a guide in the selection of appropriate remediation strategies. The objective of this chapter is to discuss the modelling approach used in the mass balance study to estimate pollutant loads from CSOs.

The impact assessment approach identified representative pollutant concentrations for the CSOs through a combination of sampling and review of past studies for the Buffalo River area. The representative pollutant concentrations were combined with estimated overflow volumes to determine pollutant loadings. The overflow volumes were estimated, at a planning level, using a personal computer (PC) version of the Stormwater Management Model, release 4 (PCSWMM4) distributed by Computational Hydraulics Int., Guelph, Ontario. Overflow volume estimates were made both for a typical year and design storms with different return intervals. Design storms were examined in the mass balance framework, in part, as a means of assessing the hydraulics of particle-bound contaminant transport and deposition in the river. For completeness, design storm estimates were done of CSO volumes. In this chapter, total PCBs, HCB, Cu and Pb, were the pollutants selected to illustrate the loading estimate approach. Total PCGs and HCB are considered an environmental concern because of their persistence and toxic effects (Loganathan et al., 1990; Wren, 1991; Williams and Giesy, 1992; and Yamashita, 1993). The heavy metals, Cu and Pb, were selected for evaluation due to the concern of impact on the river’s wildlife and available data for this study.

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