Thermal and hydrogeological aquifers characterization by coupling depth-resolved thermal response test with moving line source analysis

In this paper for the first time the Moving Line Source (MLS) model is combined with a depth-resolved Thermal Response Test (TRT). The latter was performed in a heterogeneous and groundwater rich subsoil, composed by a layering of silty sand, medium-fine sand and coarse-medium sand, with a layer of clayey silt separating a shallow aquifer from a deep one. The temperature evolution in the ground along the vertical axis was analysed with both the standard Infinite Line Source (ILS) and the MLS. The two models lead to similar estimates of the thermal conductivity in those regions of the subsoil where conduction prevails, while the MLS performs better where a significant groundwater velocity is expected. In these layers, the MLS analysis allows to derive both the thermal conductivity and the Darcy velocity. The MLS results were validated by comparison with a numerical simulation on a multiple-layers ground model developed in MODFLOW/MT3DMS using a constant energy boundary condition. The combined depth-resolved TRT/MLS approach represents an important method for an accurate design of the Ground Heat Exchangers under the presence of groundwater flow.