Sarah Virginia McKnight, David F Boutt, Lee Ann Munk

Despite the prevalence of density-driven flow systems in brine-rich aquifers of arid climates and coastal aquifers, the impact of realistic geologic conditions remains poorly constrained regarding interface geometry in arid regions and time-sensitive density-dependent dynamics in brine-bearing aquifers in general. Salar de Atacama provides an analog for exploring interface dynamics in arid regions. A site-specific 2D hydrostratigraphic interpretation is used to examine the dynamics of the brine-to-freshwater interface. With the same simulation framework and core data, a separate parametric series of hydraulic conductivity distributions with varying horizontal continuity provides a mechanistic explanation for observed dynamics. Comparing modeled interfaces and their sensitivity to perturbations in recharge in each realization yields insight into interface dynamics coupled with horizontal continuity in subsurface heterogeneity. Recharge fluctuation is introduced to each distribution following the interface reaching a dynamic steady state. Metrics for results evaluation include migration length, interface slope geometry, and response rate. Analyses suggest that the slope of the modeled interface shallows or decreases by 0.01 to 0.05 m $\cdot$ m\textsuperscript{-1} for every increase in continuity of highly permeable pathways by a factor. Increasing continuity also increases both the overall response times and the variability in response. Results indicate that accurate representations of transient dynamics in modeling density-driven brine-to-freshwater interface dynamics requires the consideration of heterogeneity, as saline intrusion in the highest continuity group extends over twice as far on average and the modeled interface takes over 43 percent more time on average to reach a new dynamic steady state when compared to their homogeneous counterparts.