Combining 3D Hydraulic Tomography with Tracer Tests for Improved Transport Characterization

Abstract

Hydraulic tomography (HT) is a method for resolving the spatial distribution of hydraulic parameters to some extent, but many details important for solute transport usually remain unresolved. We present a methodology to improve solute transport predictions by combining data from HT with the breakthrough curve (BTC) of a single forced-gradient tracer test. We estimated the three dimensional (3D) hydraulic-conductivity field in an alluvial aquifer by inverting tomographic pumping tests performed at the Hydrogeological Research Site Lauswiesen close to Tübingen, Germany, using a regularized pilot-point method. We compared the estimated parameter field to available profiles of hydraulic-conductivity variations from direct-push injection logging (DPIL), and validated the hydraulic-conductivity field with hydraulic-head measurements of tests not used in the inversion. After validation, spatially uniform parameters for dual-domain transport were estimated by fitting tracer data collected during a forced-gradient tracer test. The dual-domain assumption was used to parameterize effects of the unresolved heterogeneity of the aquifer and deemed necessary to fit the shape of the BTC using reasonable parameter values. The estimated hydraulic-conductivity field and transport parameters were subsequently used to successfully predict a second independent tracer test. Our work provides an efficient and practical approach to predict solute transport in heterogeneous aquifers without performing elaborate field tracer tests with a tomographic layout.

Debates—Stochastic subsurface hydrology from theory to practice: Does stochastic subsurface hydrology help solving practical problems of contaminant hydrogeology?

“…so that transport is predicted by a highly resolved ADE with local transport parameters in conditional Monte‐Carlo runs as done by Bianchi and Zheng [], or whether it should be parameterized by fitting some kind of effective mass‐transfer model to the existing transport data as done by Sanchez‐León et al . []. In practice, it may not always be possible to simulate unresolved heterogeneity down to a scale where the ADE does a good job in predicting effective transport behavior.…”

Comparison of Two Ensemble Kalman-Based Methods for Estimating Aquifer Parameters from Virtual 2-D Hydraulic and Tracer Tomographic Tests

“…We define a synthetic case study based on the experimental design of Doro et al [70], but consider the injection of a solute tracer instead of heat, avoiding issues related to heat diffusivity. As a case study that resembles a real aquifer, we mimic the aquifer located at the hydrogeological research site Lauswiesen, in which previous tomographic experiments have been performed [62,70]. The numerical models and the test design consider both the hydrogeological characteristics of the aquifer and the available infrastructure for the performance of hydraulic and tracer tomographic tests, but it is restricted to two spatial dimensions to expedite the calculations.…”

Field validation of thermal tracer tomography for reconstruction of aquifer heterogeneity

“…This lack of field tests may be due to the demanding experimental design and instrumentation, the need for in situ tracer monitoring or repeated multilevel sampling, and the time and cost for carrying out a full experiment. Therefore, tracers are more commonly applied to validate or complement other hydrogeological or hydrogeophysical field tests [Sharmeen et al, 2012;Dorn et al, 2013;Jim enez et al, 2015;Sanchez-Le on et al, 2016].…”