Abstract

The City of Hamilton owns and operates an extensive combined sewer system (CSS) which discharges combined sewer overflows (CSOs) at up to 23 different locations during wet weather. To address the pollution from these discharges, the City has constructed 5 CSO storage tanks to intercept and detain overflows during periods of wet weather. During dry weather, the stored wastewater is pumped and/or drained back into the CSS and conveyed to the Woodward Avenue Wastewater Treatment Plant for treatment. The existing tanks have typically been designed to limit the frequency of CSOs to 1-3 per year, and to meet CSO control levels set out by the Ontario Ministry of the Environment’s Procedure F-5-5 (MOE, 1997).

The Greenhill CSO Storage Tank was constructed in 1988 at a cost of $5.0 million. This was the first of Hamilton’s CSO control facilities, and it was designed to control the CSO volume generated by a 15 mm design storm, which provides a significantly lower level of CSO control than the facilities constructed since. The paper discusses the historical performance of the Greenhill CSO Storage Tank in terms of the CSO frequency and volume reduction it has afforded. The actual performance of the CSO tank as indicated by the City’s Supervisory Control and Data Acquisition system is compared to the simulated performance of the facility as indicated by continuous modeling with the United States Environmental Protection Agency’s Stormwater Management Model Version 4.0. The performance of the CSO tank is also measured against the volumetric CSO control requirements of Procedure F-5-5 (i.e. the capture and treatment of all dry weather flow plus 90% of the volume resulting from wet weather flow). The limitations of the simulation models are also discussed.

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