Evaluation of the percentage of septic system effluent reaching tributaries in Lake Simcoe watershed

Session: Great Lakes Tributaries: Connecting Land and Lakes (2)

Archana Tamang, The University of Western Ontario, Civil and Environmental Engineering, [email protected]
James Roy, Environment and Climate Change Canada, [email protected]
Clare Robinson, The University of Western Ontario, Civil & Environmental Eng., [email protected]

Abstract

The contribution of septic systems to nutrient loading to surface waters remains poorly quantified. Septic effluent can be delivered to surface waters via subsurface pathways for well-functioning systems, via surface pathways for failing and poorly situated systems, and via illegal direct connections. The objective of this study was to quantify the contribution of septic system effluent to tributaries in the Lake Simcoe watershed, including evaluating the importance of the various pathways via which septic effluent may reach the stream. This objective was achieved by applying a geospatial tool to automatically locate individual septic systems across the Lake Simcoe watershed and conducting stream sampling in areas with high septic system density. Stream gauging combined with analysis of stream samples for nutrients and septic tracers including artificial sweeteners and boron was conducted to identify the percentage of septic effluent in a catchment area reaching the stream. Sampling sites were located in areas with different surficial geology (e.g., sand, till, exposed bedrock) to test the hypothesis that the amount of effluent that reaches the tributaries varies depending on the surficial geology.  The study findings provide important information needed to inform septic system management strategies as well as guide effective nutrient watershed management programs.