Characterizing the Two‐Dimensional Thermal Conductivity Distribution in a Sand and Gravel Aquifer

Both hydrologic and thermal transport properties play a significant role in the movement of heat through permeable sedimentary material; however, the thermal conductivity is rarely characterized in detailed spatial resolution. As part of a study of the movement of thermal plumes through a sand and gravel aquifer, we have constructed a two‐dimensional profile of thermal conductivity. This work consisted of: (i) measuring the thermal conductivity of the soil solids, λs, for the main stratigraphic units using the steady‐state divided‐bar apparatus and estimating conductivity from mineral composition; (ii) measuring the volumetric water content and porosity using crosshole ground‐penetrating radar; (iii) evaluating four models used to predict the apparent thermal conductivity, λ, of variably saturated soils and selecting the best model using the information‐theoretic approach, (iv) calculating the λ field on a 0.25‐m square cell grid using measured data and the selected model, and (v) simulating thermal transport within the two‐dimensional domain using a finite element numerical model. The apparent thermal conductivity in the saturated aquifer ranges from 2.14 to 2.69 W m−1 K−1 with a mean of 2.42 W m−1 K−1 Numerical simulations show that the heterogeneous thermal conductivity field results in increased thermal dispersion that is most pronounced at the plume front. Our values for λ and λs may be used for glacial soils with similar mineralogy and texture. Our methods may also be used at other sites to construct the thermal conductivity distribution.