Modeling Reactive Solute Transport in Permafrost‐Affected Groundwater Systems. Issue 7 (21st July 2021)

• Record Type: Journal Article
• Authors: Mohammed, Aaron A.; Bense, Victor F.; Kurylyk, Barret L.; Jamieson, Rob C.; Johnston, Lindsay H.; Jackson, Amy J.
• Is Part Of: Water resources research. Volume 57:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-21
• Subjects: permafrost -- groundwater modeling -- contaminant transport -- freeze‐thaw -- coupled mass and energy transport -- cold regions; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2020WR028771
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Understanding the interactions between ground freeze‐thaw, groundwater flow, and solute transport is imperative for evaluating the fate of contaminants in permafrost regions. However, predicting solute migration in permafrost‐affected groundwater systems is challenging due to the inherent interactions and coupling between subsurface mass and energy transport processes. To this end, we developed a numerical model that considers coupled groundwater flow, subsurface heat transfer, and solute transport, including water‐ice phase change, solute‐dependent porewater freezing, and temperature‐dependent solute reaction rates. As an illustrative example, we present simulations to investigate the potential for contamination from a municipal wastewater lagoon in the Canadian sub‐arctic. Two‐dimensional groundwater models assuming varying permafrost conditions were developed to evaluate possible contaminant migration scenarios associated with groundwater flow from the lagoon to a river, including the transport of conservative, degradable, and sorbing solutes. Model results reveal important transport mechanisms controlling the behavior of aqueous contaminants in permafrost landscapes as well as the hydrogeologic factors affecting reactive transport in cold regions. Seasonal freeze‐thaw episodically restricts connectivity of transport pathways, which attenuates both transport and reaction rates. However, elevated solute concentrations can depress the freezing temperature of porewater and produce thaw‐induced solute transport. Both thermally driven and solute‐enhanced thaw can decrease ice content in permafrost, which can have significant implications for solute migration. Therefore, thermo‐hydrogeologic process controlling reactive transport in cold‐region groundwater systems must be considered when quantitatively assessing the impact of changing environmental conditions on contaminant hydrogeology. Plain Language Summary: Groundwater contamination associated with increased human and industrial activity is a growing risk in northern regions. However, current groundwater flow models generally do not simulate both permafrost dynamics and reactive solute transport. In this study we develop a hydrological model to simulate groundwater flow and dissolved contaminant transport for permafrost environments. The new model was applied at a site in the Canadian sub‐arctic to investigate the possibility of groundwater contamination associated with a wastewater lagoon. Results identified important mechanisms controlling the migration of contaminants in permafrost landscapes, including the effects of seasonal ground freezing and groundwater flow. Results show that the physical relationships describing the effects of contaminant levels on ground freezing characteristics and the influence of temperature on contaminant degradation properties strongly affect contamination movement. The new model will be useful for understanding how climate change and permafrost thaw will impact groundwater flow and associated subsurface migration of dissolved chemicals in cold regions. Key Points: Subsurface aqueous contaminant transport in permafrost regions is controlled by coupled water, energy, and reactive solute transport We developed a groundwater model to simulate reactive solute transport in permafrost landscapes Constitutive relationships describing solute‐dependent freezing and temperature‐dependent reaction rates strongly influence contaminant migration