Krčmář D., Hodasová K., Zatlakovič M. & Ondrejková I., 2025: Thermal characterisation of groundwater systems in heterogeneous alluvial sediments: Insights from field tests in Hronsek (Slovakia). Acta Geologica Slovaca, 17, 1, 1–16.

Thermal characterisation of groundwater systems in heterogeneous alluvial sediments: Insights from field tests in Hronsek (Slovakia)

Dávid Krčmář, Kamila Hodasová, Martin Zatlakovič & Ivana Ondrejková

Department of Engineering Geology, Hydrogeology and Applied Geophysics, Faculty of Natural Sciences, Comenius University Bratislava, Ilkovičova 6, 842 15 Bratislava, Slovakia; david.krcmar@uniba.sk

Abstract

This study investigated the thermal parameters in a heterogeneous alluvial aquifer in Hronsek (Slovakia), with the aim of evaluating the suitability of analytical models for interpreting thermal response test data under groundwater flow. We conducted pumping tests and various thermal response tests in a central well and multilevel temperature monitoring in observation wells. Data were analysed by fitting observations to several analytical solutions, specifically the finite line source model, moving infinite line source with dispersion model, and moving finite line source model, using a grid search algorithm to estimate the bulk thermal conductivity and volumetric heat capacity. The results consistently showed significant subsurface heterogeneity, indicated by distinct curves in diagnostic time-over-radius squared plots derived from both hydraulic and thermal tests. The extended conduction-dominated thermal response test successfully produced a strong and detectable thermal signal. The best-fit parameters varied significantly between the analytical models. The Moving Finite Line Source model provided the best overall fit with thermal conductivity 9.4 W.m.K^-1 and volumetric heat capacity 7.0 × 10⁶ J.m^-3.K^-1. The thermal conductivity values of the Finite Line Source and Moving Finite Line Source models were notably higher than the typical literature values for saturated sandy gravels. Furthermore, non-uniqueness of parameters was observed, where different combinations of parameters produced similar model-data discrepancies. The study concludes that standard analytical models face limitations in accurately characterizing thermal properties in heterogeneous aquifers with active groundwater flow, emphasizing the need for multifaceted experimental designs and sophisticated modeling approaches for reliable thermal characterization.

Key words: thermal properties of the aquifer, thermal response test, heterogeneous medium, groundwater flow, thermal conductivity, volumetric heat capacity

Manuscript received: 2025-06-07

Revised version accepted: 2025-07-03