Hydrological events, microbes, and fugitive data: Addressing public supply well vulnerability in a changing climate

ABSTRACT: Extreme hydrological events are likely to become increasingly frequent due to climate change, and these may increase contamination threats to public supply wells. Dynamic overland flow and groundwater recharge processes may allow contaminants present in surface water to enter aquifers at rates, concentrations, or locations that would not otherwise be experienced. Groundwater recharge provides an important, unseen link between surface water event flows and the potential for contaminant arrival at a well. Data from events such as mid-winter snowmelts may represent "fugitive data" - data whose import is not realized, and which are not retained for analysis. In this study, two case studies are cited to demonstrate the potential for event-induced recharge to increase risks at public supply wells. These studies measured pathogen indicator species concentrations and monitored groundwater level and temperature to estimate recharge rates. A case study at the Thornton well field near Woodstock, ON, illustrates how fugitive data could be used to interpret sample data from the raw water at a public supply well. Research at the Woodstock site quantified localized recharge rates of up to 710 mm per two-week snowmelt event. A second study within the Mannheim West well field near Kitchener, ON, quantified depression focused recharge of up to 390 mm during extreme precipitation events. Risks to public supply wells may be more likely to increase with compound events such as heavy rainfall following snowmelt, or consecutive rainfall events. The recognition, retention, and assessment of fugitive data related to heavy rainfall or snowmelt timing could assist groundwater managers in understanding transient changes in well vulnerability as flow systems and microbial concentrations respond to events. Crowd sourcing of extreme event data may be one way to capture data related to temporary surface water and recharge processes.