ASSESSING THE ROLE OF AQUIFER HETEROGENEITY ON HEAT TRANSPORT IN AN UNCONFINED AQUIFER

An extensive field investigation monitoring thermal plumes emanating from an aggregate pit in Southwestern Ontario has been carried out over the past eight years. At this site, the aquifer is a shallow unconfined aquifer formed by a glacial fluvial outwash sand and gravel deposit. One aspect of the study was the assessment of the role of spatial variability of hydraulic conductivity and thermal conductivity in the heat transport process.

The hydraulic conductivity, determined using multi-scale sampling methods (grain size, laboratory permeameter tests, insitu slug and pumping tests, and cross-hole GPR), reveals a 3 order of magnitude difference in estimates of hydraulic conductivity depending upon the scale of the investigation. We measured the thermal conductivity of the solid portion of the porous media in the laboratory. Measurements obtained on 41 samples show that the thermal conductivity ranges from 3.38 to 4.81 W m^-1 K^-1 and can be correlated to the stratigraphic units identified at the site. We estimated the effective thermal conductivity of the saturated porous media using porosities, determined from the crosshole GPR surveys, and the measured thermal conductivity values for the solid matrix. This provided an accurate estimate of the spatial variability of the aquifer thermal conductivity.

We used a numerical model, validated against field data, to investigate how the variability of porous media and heat transport parameters affect heat transport in shallow unconfined aquifers. The 3-dimensional heat transport code HEATFLOW was used to conduct the simulations. We considered the influence of aquifer hydraulic conductivity, aquifer porosity, hydraulic gradient, and aquifer thermal conductivity.