Evaluation of Factors Influencing the Delivery of Septic System Wastewater Effluent to Tributaries
Abstract
There is concern that septic systems may contribute nutrients, fecal pathogens, and emerging contaminants to tributaries, and thereby impair surface water quality. The objective of this thesis was to quantify the percentage of septic effluent reaching multiple streams and to evaluate whether this percentage varies based on the stream flow conditions and the physical and socioeconomic characteristics of a subwatershed. This was addressed by broad-scale sampling in 46 subwatersheds in the Lake Erie and Lake Simcoe Basins, Ontario, with data analyzed using statistical models. It was found that the percentage of septic effluent reaching subwatershed outlets, based on acesulfame stream loads, was higher under high flow conditions and in subwatersheds with older occupied homes and lower topographic wetness index. Fecal contamination in streams, possibly associated with underperforming septic systems, was observed in smaller subwatersheds with high septic system density, small setback distances, and high topographic wetness index. The findings of this research are needed to refine estimates on the contribution of septic systems to stream contaminant loads and to inform programs for locating, constructing, and maintaining septic systems.