The Role of Gases in Groundwater Contamination and Remediation

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Groundwater is a vital natural resource. Approximately 10 million Canadians rely on groundwater as a source of drinking water. It is also an important link between surface water and deeper regional systems, and is a source of water for Canadian industries, including agriculture and oil and gas. The quality of our groundwater is threatened by contamination. There are tens of thousands of contaminated sites in Canada, many of which are brownfield properties located in urban centres and along waterfronts. The cost to clean up these sites is substantial, and likely totals tens of billions of dollars. Gases in the subsurface play an important, but often underappreciated, role in groundwater contamination. For example, gases can be created naturally or by remediation technologies, and they affect the flow of groundwater (by reducing permeability) as well as the transport and reaction of contaminants (by mass transfer between the gas and groundwater). Gases can also be contaminants themselves. For example, the rapid increase in shale gas extraction has led to increased concern over environmental impacts, including the contamination of drinking water aquifers by methane gas.***The proposed research will consist of a coordinated program of laboratory experiments (bench-scale columns and flow cells) combined with numerical modelling to investigate fundamental mechanisms across multiple disciplines. A team of five graduate students (two Doctoral and three Master's) will develop methods to inject dissolved gas or create trapped gas bubbles using chemical reactions to enhance clean-up technologies. They will also investigate the dissolution of methane in groundwater to better understand the effects of gas leakage during shale gas extraction, and will develop novel characterization methods for the laboratory and field. This research will:***(a) Establish the scientific basis for new technologies to enhance groundwater clean-up using thermal remediation and gas emplacement;***(b) Provide the detailed data required to validate advanced numerical models of contaminant transport in groundwater where gases are present;***(c) Develop new techniques for measuring groundwater gases in the laboratory (based on high-resolution visualization) and the field (based on cryogenic coring); and***(d) Train graduate students to tackle emerging problems in groundwater contamination and remediation.***The results of this research will be used by both researchers and industry in Canada to improve the clean-up of contaminated sites, contribute to the development of best-practices for monitoring shale gas extraction, and help site investigators more accurately measure dissolved gases and gas bubbles in groundwater. Overall, these results will support the long-term research vision of improving our understanding of gas migration and mass transfer in contaminated groundwater systems.***