Urban Stormwater Management Strategy for the Severn Sound Remedial Action Plan

Abstract

Abstract Urban Stormwater has been identified as a significant source of phosphorus to Severn Sound and a potential source of bacterial contamination which can affect recreational bathing areas within the Sound. In order to develop an effective remedial action plan, a cooperative study of urban Stormwater impacts was initiated in the Severn Sound Area of Concern (AOC) through a joint partnership that included Environment Canada (Great Lakes 2000 Cleanup Fund), the Ontario Ministry of the Environment, the Simcoe County District Health Unit, and various municipalities in the Sound. The study objectives were (1) characterization of dry weather and runoff quantity and quality; (2) monitoring effects of Stormwater runoff on the bacterial concentrations at an urban bathing area; and (3) development of pollution control plans for the participating urban municipalities in the Severn Sound watershed with an overall goal of a 20% reduction of Stormwater phosphorus loads. In general, the event mean concentrations of most runoff pollutants lie either within the range or below ranges reported by previous storm-water studies in Canada and the U.S., while some runoff pollutant concentrations (e.g., E. coli, heavy metals and nutrients) exceed the Ontario provincial water quality objectives. The bathing area sampling program recorded E. coli concentrations exceeding 600 organisms/100 mL at an outfall right after storm events started. Based on the limited sampling, it appears that rain events of approximately 20 mm or more may result in impingement of water with elevated E. coli counts on this bathing area within 6 hours of the onset of a rain event In order to update pollution loading estimates and develop pollution control plans, a retrofit Stormwater management model was applied. The planning model estimates an annual phosphorus loading of 1083 kg/year and a 20% reduction of phosporus loading, using source controls such as downspout disconnections and oil/water interceptors, drainage system controls such as grassed ditches and exfiltration systems, and downstream control such as water quality ponds. Pollution control plans were developed for each participating municipality based on the retrofit opportunities identified through the modelling exercise. The estimated cost is about $4 million. These plans provide specific recommendations regarding the implementation of various Stormwater retrofit measures and their financial requirements. A water quality pond identified by the pollution control plan for the Town of Penetanguishene has since been implemented.