Impact of proposed Burlington and Hamilton sewage discharges in western Lake Ontario

The alternate strategy of open-lake discharge may alleviate the need for unusually stringent treatment needed to meet water quality goals of the Hamilton Harbour Remedial Action Plan (RAP). The latest update of the RAP recommended a study of the possibility of offshore discharges. A study conducted for the City of Burlington has proposed a location for outfall in Lake Ontario. This paper utilizes a combination of physical limnological data and mathematical models to predict the waste plume characteristics for the proposed outfall in the lake. Near-field dilutions obtained from a mixing zone model show that, for treated effluents with a discharge condition of 2 m(3)/s at the proposed outfall site at Burlington, the dilution ratios are in the range of 13:1 to 28:1. for weak to moderate currents during summer stratification. Winter dilution ratios increased to 21:1 to 96:1 for moderate currents. The recommended site for open-lake outfall provides acceptable near-field dilutions for treated effluents under typical lake currents and density structure. The extension of outfall to a location farther offshore is only marginally beneficial. With the proposed Burlington outfall location and discharge conditions, no far-field contamination is observed near the beaches or nearby water intakes for typical summer and winter conditions. Thus, this study indicates that by discharging the treated sewage from an outfall in Lake Ontario it is possible to achieve the Hamilton Harbour RAP goals.