Advances in thermal tracers for measuring and managing groundwater resources

Global groundwater resources are being depleted, which is eliciting concern over future water and food security. The present situation is expected to be exacerbated in the coming decades due to climate change as well as population redistribution and increased groundwater demand in urban environments. Unsustainable groundwater extraction is often thought to be limited to third world countries, but regions within Canada have recently experienced groundwater shortages due to droughts. Holistic groundwater management must consider both societal and ecosystem groundwater demands because groundwater discharge to rivers is critical for modulating temperatures and sustaining flows during the dry season. Sustainable groundwater management is often challenging due to difficulties associated with measuring groundwater fluxes (flow per unit area) to and from aquifers. Standard approaches to estimate these fluxes using tracers are typically only applicable in certain environments, require expensive sampling and analyses, and are characterized by assumptions and uncertainties. Thus, there is a critical need to develop improved methods to inexpensively and accurately trace groundwater fluxes.Heat can be used to study groundwater movement because water flow induces heat advection and disturbs subsurface temperatures. Heat offers advantages over other groundwater tracers as it is always present in the subsurface, it is inexpensive to continuously monitor, and it does not require further laboratory analysis. Uptake of existing analytical techniques for using heat as a groundwater tracer has been limited in the water resources management community because most common methods are restricted to depths less than one meter. The overall objective of this research program is to develop new integrated technology and techniques for tracing groundwater from temperature in deep and shallow aquifers to inform the sustainable management of groundwater resources for both societal and ecosystem needs. This research program, which will train seven students, will include instrument design, data collection, and model development. Research focused on shallow environments will provide improved methods for monitoring aquifer-river exchanges to aid in river restoration and habitat conservation, particularly in southeastern Canada where salmon populations are in decline due to river warming and where groundwater is critical for creating fish habitat. Research focused on heat tracing to quantify flows to and from deeper aquifers will provide new tools for groundwater engineers to monitor long-term changes in groundwater recharge or assess the viability of developing well fields in new locations. Knowledge developed in this research program will be transferred to other academics as well as the broader water resources management community via journal publications, presentations, and short courses.