Heat and Chemical Transport in Aquifers at Different Geological Setting

Heat and chemical transport are two fundamental processes that are widely existed in the subsurface environments and come with natural phenomena (e.g., volcanic eruption, diurnal or seasonal temperature variation) or anthropogenic activities (e.g., well injection). A common characteristic of these two transport processes is they are both governed by the advection-dispersion equation (ADE) and both advective movements are impacted by the local heterogeneity of porous media. However, they still exhibit many different behaviors. For example, heat diffusivity in the solid matrix is usually two order of magnitude higher than the matrix diffusivity of chemicals. In addition, chemical transport usually comes with reaction and sorption. To investigate the characteristic behaviors of heat and chemical transport at different geological settings, this study focuses on three geological environments ranging from kilometer-scale to meter-scale, including volcanic hydrothermal system, shallow riverbeds where surface-water and groundwater exchange occurs and local fractured aquifer for well testing. For the volcanic hydrothermal system, a novel model that connects the heat and chemical transport is proposed to explain the over 10-year temperature and chemical data collected at the thermal springs near volcanic summit. For the shallow riverbeds, an ensemble data assimilation approach is proposed to estimate the hydraulic exchange flux between surface water and groundwater based on the heat transport observed in the riverbeds. For the local fractured aquifer, a novel fractional model for single-well push-pull test is proposed to explain the observed long tailing behavior of conservative tracer during pumping. This study demonstrates the capability of using heat and chemical as tracers to quantitatively or qualitatively estimate the flow and transport behaviors at different geological environments. Further work is needed to explore the capability of model and methods to accommodate more geological conditions