Modeling and design of air injection-based hydraulic barriers

Hydraulic barriers are useful for manipulating groundwater flow to mitigate and contain harmful environmental effects. Injecting air into the aquifer has been suggested as a cost-efficient, sustainable, and reversible hydraulic barrier. In this, the injected air reduces the conductance of the aquifer to water flow. However, this practice is not commonly used despite its potential, probably due to a lack of a design tool and field-scale demonstrations. Evaluating the effect of air injection on the water flow is severely hindered by the ability to simulate the unstable coupled multiphase flow problem. Multiphase models are computationally expensive and unstable, require many (sometimes unattainable parameters), and generally provide poor predictive capabilities. Here, a simplified approach is suggested that decouples the phases flows, and uses analytical (fast, stable, parameters-parsimonious) solutions of the air injection problem to evaluate its effect on the water permeability field. In this manuscript, we describe the framework and the solutions of the air flow, discuss its limitations, and demonstrate its usability to evaluate the sensitivity to the media's and system design parameters in three case studies: (i) point sources in a confined aquifer, (ii) line source in a confined aquifer, and (iii) line source in an unconfined aquifer.