Waterloo researchers have found that more than 30 per cent of rural groundwater samples collected in the Nottawasaga River Watershed, including those from domestic wells, show evidence for contamination by local septic system wastewater.
“We were not really surprised by the result,” said first author Dr. John Spoelstra, and adjunct professor in Earth and Environmental Sciences at the University of Waterloo. “Septic systems are designed to discharge effluent to groundwater as part of the wastewater treatment process. Therefore, contamination of the shallow groundwater is a common problem when it comes to septic systems.”
The study, which appeared this week in the Journal of Environmental Quality, describes how the researchers tested private, rural groundwater wells for four artificial sweeteners as a way to detect groundwater impacted by human wastewater being released by septic systems in the area.
Artificial sweeteners are ideal human wastewater tracers for several reasons. They enter and exit the human body essentially unchanged and are also not completely removed by treatment processes used by most septic systems or municipal wastewater treatment plants. Human wastewater contains relatively high concentrations of artificial sweeteners and represents the overwhelming source of these calorie substitutes to the environment.
More than 30 per cent of samples analyzed from 59 private wells show detectable levels of at least one of four artificial sweeteners, indicating the presence of human wastewater. Estimates reveal between 3 and 13 per cent of wells could contain at least 1 per cent septic effluent.
The team also tested groundwater seeping out of the banks of the Nottawasaga River and found 32 per cent of their samples tested positive for sweeteners. Again, this indicates that some of the groundwater entering the Nottawasaga River has been affected by septic system effluent.
“Although the four artificial sweeteners we measured are all approved for human consumption by Health Canada, it is the other septic contaminants that might also be present in the water that could pose a health risk,” said Spoelstra, also a Research Scientist with Environment and Climate Change Canada. “As for groundwater entering rivers and lakes, the effect of artificial sweeteners on most aquatic organisms is unknown.”
The Nottawasaga River Watershed in Southern Ontario is located just west of Lake Simcoe, approximately 50 km north of Toronto. The study focused on the rural areas around Alliston that are underlain by the Lake Algonquin Sand Aquifer, which is a shallow aquifer that provides water for domestic and agricultural use in the area.
Septic tank systems are commonly used in rural areas where homes are not connected to a municipal sewer system. The system provides primary treatment by removing solids before the effluent is discharged to a septic drain field where further treatment occurs. The Lake Algonquin Sand Aquifer is a relatively shallow, unconfined aquifer, meaning that contaminants untreated by the septic system can easily trickle down to the unprotected water table.
Among other contaminants, septic effluent can contain bacteria such as E. coli, viruses, pharmaceuticals, personal care products and elevated levels of nitrate and ammonium.
Previous studies by same group revealed the presence of artificial sweeteners in the Grand River as well as in treated drinking water sourced from the river.
Other authors on the paper include former Master’s student Natalie Senger and Prof. Sherry Schiff, both from the Department of Earth and Environmental Sciences at the University of Waterloo.
Environment and Climate Change Canada, the Ontario Ministry of Agriculture, Food and Rural Affairs, and the Natural Sciences and Engineering Research Council funded the study.
Soil Science Society of America: Tracking wastewater's path to wells, groundwater. January 24, 2018.
Crop Science Society of America: Tracking wastewater's path to wells, groundwater. January 24, 2018.
American Society of Agronomy: Tracking wastewater's path to wells, groundwater. January 24, 2018.