Combination of Hydraulic and Thermal Tracer Tomography in a Heterogeneous Transient Groundwater Model

Abstract: In recent years, more and more attention has been paid to engineering projects, such as the remediation of contaminated groundwater, the restoration of water quality, and the seepage control of building foundations. For all these projects, detailed knowledge of the spatial distribution of aquifer hydraulic parameters is required. Inversion based tomography can be considered a promising subsurface investigation approach to obtain aquifer characterization with a high spatial resolution. However, single inversion cannot avoid parameter uncertainty and non-uniqueness problems. Combination of different independent inversions can help to reduce these problems. The purpose of this paper is to reconstruct cross-well hydraulic conductivity profiles by jointly using hydraulic tomography and thermal tracer tomography in a heterogeneous transient groundwater model.

In this study, based on a three-dimensional data set derived from an aquifer analogue outcrop study, a numerical ground water model is set up to simulate a number of short-term hot water injection tests in a tomographical array, and to perform 2D hydraulic tomography based on hydraulic travel time and attenuation inversions. Consequently, the hydraulic conductivity is calculated from the obtained diffusivity and specific storage values. Parallel to this, the temperature breakthrough curves of the active thermal tracers were utilized to reconstruct the cross-well hydraulic conductivity profiles by using travel-time-based thermal tracer tomography. Comparisons between the results and the “true values” of the analog have shown the satisfying accuracy of the subsurface investigation and advantages when using combined tomographical methods.