SPATIAL ASSESSMENT OF THE RISK OF CONSUMPTION OF CONTAMINATED DRINKING WATER DURING FLOODING IN SOUTHERN QUEBEC

Floods represent a significant natural hazard globally, often exacerbated by factors such as climate change and urbanization. The province of Quebec has witnessed multiple instances of severe flooding, notably during the springs of 2017, 2019, and 2023. These events, characterized by snowmelt compounded with heavy rainfall, have inflicted substantial damage and displaced numerous residents. Moreover, they have brought to light potential health hazards, particularly in regions where residential drinking water sources are vulnerable to contamination from floodwaters, especially if certain conditions are met, including: 1) the close proximity of homeowners drinking water wells to a river; 2) the presence of contaminants in the river water; and/or 3) the presence of contaminants (e.g. oil cans) on usually dry (but flood-prone) land, where these contaminants can mix with surface water if the parcel is immersed. Hence, during floods, potentially contaminated surface water can infiltrate drinking water wells, either directly from surface infiltration along the borehole or indirectly through the inversion of groundwater flow direction. There are several factors, both related to nature and human activity, that can locally increase the risk of water contamination, leading people to consume this water without proper treatment. The work presented here aims to assess the risk of contamination of water from private wells in a small watershed (Hurons River, Stoneham-et-Tewkesbury, QC). Samples were collected over 15 field campaigns and analyzed for a diverse suite of conventional geochemical parameters, isotopic tracers, and specific contaminants. Well water is generally of good chemical quality, but microbiological parameters (total coliforms and E. coli) were exceeded on many occasions. A spatio-temporal analysis is being conducted to determine: 1) the factors (well construction, lithology, etc.) leading to an increased risk of contamination, 2) the duration of contamination post-flood, and 3) the lateral extent of contamination away from the river. Results will allow formulating recommendations to enhance the protection and resilience of communities by optimizing the management of drinking water supplies exposed to floods.

Keywords: Floods, climate change, human health, contamination, drinking water, river, groundwater, spatial assessment, risks.