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Soil Physics

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

^a Dep. of Earth Sciences, Univ. of Western Ontario, London, ON, Canada, N6A 5B7
^b Dep. of Civil, Geological and Mining Engineering, École Polytechnique Montréal, Montréal, QC, Canada, H3C 3A7

^* Corresponding author (jmmarkle{at}uwo.ca)

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, _s, 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, , of variably saturated soils and selecting the best model using the information-theoretic approach, (iv) calculating the 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 and _s 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.

Abbreviations: AIC, Akaike's information criterion • AIC_C, Akaike's information criterion for small sample sizes • bgs, below ground surface • GPR, ground-penetrating radar • MOP, multiple-offset profile • ZOP, zero-offset profile