Spatial assessment of the risk of consumption of contaminated (drinking) water during floods

This project will allow the development of a territorial decision support tool that can eventually be applied to the entire Quebec territory. It will also contribute to increasing the protection and resilience of communities.

Project details

Scientific program

Programmation 2020-2028

Theme(s) and priority(s)

Extreme Events

Start and duration

June 2022 • 2 years

Project Status

Completed

Linked project

Support for INFO-Crue

Principal(s) investigator(s)

Geneviève Bordeleau

INRS

Roxane Lavoie

Université Laval

Karem Chokmani

INRS

Hachem Agili

Geosapiens

Context

As climate change intensifies, the risk of flooding is an increasing concern. The impacts of floods go beyond material damage; they also affect the safety of water intended for human consumption, particularly for households that draw their water from private wells. This interdisciplinary project aims to analyze the challenges of residential groundwater contamination during flood events, using both environmental and social approaches. By combining scientific data with the analysis of the public’s perceptions and experiences, the research highlights the realities and vulnerabilities specific to riverside communities. The study focuses on the municipality of Stoneham-et-Tewkesbury, where the population depends on groundwater for its water supply. By combining physical, chemical and microbiological analyses with residents’ testimonies on their experiences, practical courses of action can be proposed to promote better collective adaptation to hydrometeorological hazards.

Objective(s)

Objective 1: Characterize changes in water quality in residential wells in relation to flooding episodes.
Objective 2: Analyze the environmental determinants associated with contamination risks and the mechanisms of surface water intrusion into wells, where applicable.
Objective 3: Examine the social representations and practices related to the use of drinking water in flood situations.
Objective 4: Collaboratively develop recommendations promoting adaptive and resilient drinking water management.

This project is part of the INFO-Crue initiative set up by the MELCCFP and one of the research axes of the Réseau Inondations interSectoriel du Québec.

INFO-CRUE RIISQ

Methodology

Water sampling from 13 private wells and 3 surface water sampling sites.
Repeated collection of samples (up to 15 samples per site) during the project to target the periods before, during and after floods.
Continuous measurements of water levels in 4 private wells, and development of a treatment protocol for time series data to eliminate the effect of domestic pumping on measured water levels.
Analysis of physico-chemical parameters (temperature, pH, electrical conductivity, redox potential, dissolved oxygen) and microbiological parameters (E. coli bacteria, total coliforms), as well as the stable isotopic composition of the water (δ¹⁸O, δ²H) in the samples.
Multivariate statistical analysis of the different measured parameters. • Semi-structured interviews with 7 well owners and 3 representatives of organizations.

Results

Literature review on water quality
Private wells in the study area exhibit widespread vulnerability to microbiological contamination, which is not limited exclusively to the immediate period of flooding. The majority of the wells studied contained total coliforms and, more sporadically, E. coli after the floods, with maximum concentrations observed within 7 days of the events.
Wells located outside the floodplain are more subject to brief but intense contamination after heavy rains, while wells in the floodplain have more continuous, but generally also more moderate, contamination.
The mechanisms of surface water intrusion into wells vary depending on the hydro-geomorphological context.
Combining isotopic, geochemical, microbiological and hydrodynamic indicators allows for a better characterization of aquifer vulnerability.
The results highlight significant health issues, and justify water monitoring and treatment protocols that must continue after the flooding recedes.
Despite this, well owners very rarely carry out water quality monitoring (analyses) and during flooding most of them do not change their water consumption habits and ignore recommended procedures, which reveals a low perception of risk.
New homeowners and households with children, however, demonstrate increased awareness and take more preventative actions.
The study highlights several barriers: lack of knowledge, the cost of testing, mistrust of institutions, and the absence of any regulatory obligation.
When water tests are carried out and reveal contamination, they provide a powerful tool for addressing the situation.
These results highlight the importance of credible scientific communication, better transfer of locally grounded information, and concerted actions by different parties to reduce the vulnerability of households that depend on a private well.

Benefits for adaptation

Unequivocally demonstrates the vulnerability of private wells to microbiological contamination during periods of flooding and heavy rain, particularly within a period of 7 to 14 days following these episodes.

The Government of Québec’s recommendations for analyzing and treating well water during flooding are adequate, but could be extended to all wells (flooded or not) during episodes of heavy rainfall. However, this project, like others before it, has demonstrated that these recommendations are neither known nor followed by well owners.

It is more important than ever to develop strategies with various stakeholders in order to reduce barriers to water analysis and treatment, and to support well owners in these processes.