Relative importance of geostatistical and transport models in describing heavily tailed breakthrough curves at the Lauswiesen site

Abstract

We analyze the relative importance of the selection of (1) the geostatistical model depicting the structural heterogeneity of an aquifer, and (2) the basic processes to be included in the conceptual model, to describe the main aspects of solute transport at an experimental site. We focus on the results of a forced-gradient tracer test performed at the "Lauswiesen" experimental site, near Tübingen, Germany. In the experiment, NaBr is injected into a well located 52 m from a pumping well. Multilevel breakthrough curves (BTCs) are measured in the latter. We conceptualize the aquifer as a three-dimensional, doubly stochastic composite medium, where distributions of geomaterials and attributes, e.g., hydraulic conductivity (K) and porosity (phi), can be uncertain. Several alternative transport processes are considered: advection, advection-dispersion and/or mass-transfer between mobile and immobile regions. Flow and transport are tackled within a stochastic Monte Carlo framework to describe key features of the experimental BTCs, such as temporal moments, peak time, and pronounced tailing. We find that, regardless the complexity of the conceptual transport model adopted, an adequate description of heterogeneity is crucial for generating alternative equally likely realizations of the system that are consistent with (a) the statistical description of the heterogeneous system, as inferred from the data, and (b) salient features of the depth-averaged breakthrough curve, including preferential paths, slow release of mass particles, and anomalous spreading. While the available geostatistical characterization of heterogeneity can explain most of the integrated behavior of transport (depth-averaged breakthrough curve), not all multilevel BTCs are described with equal success. This suggests that transport models simply based on integrated measurements may not ensure an accurate representation of many of the important features required in three-dimensional transport models.

A kriging approach based on Aitchison geometry for the characterization of particle-size curves in heterogeneous aquifers

“…Available data include PSCs, pumping and tracer tests as well as down-hole impeller flowmeter measurements. A complete description of the analyses performed at the site has been presented by Riva et al (2006Riva et al ( , 2008, to which we refer for additional details. The available data have been partially employed by Neuman et al (2007Neuman et al ( , 2008 in the context of (a) the application of a stochastic interpretation of the results of a series of cross-hole pumping tests and (b) a geostatistically-based characterization of multiscale distribution of hydraulic conductivity at the site.…”

“…These types of data are typically based on standard grain sieve analysis of soil samples, yielding a discrete representation of the curves by measuring selected particle diameters which, in turn, correspond to quantiles of the particle-size curve. The information can then be employed to classify soil types [e.g., Riva et al (2006) and references therein], to infer hydraulic parameters such as porosity and hydraulic conductivity [e.g., amongst others, Lemke and Abriola (2003); Riva et al (2006Riva et al ( , 2008Riva et al ( , 2010; Bianchi et al (2011);Tong et al (2010); Barahona-Palomo et al (2011) and references therein], or, in the presence of inorganic compounds, to provide estimates of the porous medium sorption capacity [e.g., Hu et al (2004) and references therein].…”

Toward efficiency in heterogeneous multispecies reactive transport modeling: A particle‐tracking solution for first‐order network reactions

“…In this context, Particle Tracking Methods (PTMs) offer a convenient numerical solution particularly efficient in dealing with heterogeneities [e.g., Wen and GomezHernandez, 1996;LaBolle et al, 1996;Salamon et al, 2007;Riva et al, 2008] and a large variety of complex transport processes such as non-Fickian transport [Delay and Bodin, 2001;Cvetkovic and Haggerty, 2002;Berkowitz et al, 2006;Zhang and Benson, 2008;Dentz and Castro, 2009] and multiple porosity systems [Salamon et al, 2006b;Benson and Meerschaert, 2009;Tsang and Tsang, 2001;Huang et al, 2003;Willmann et al, 2013]. Moreover, this methodology, which is always mass conservative, avoids some of the inherent numerical difficulties associated with Eulerian approaches, i.e., numerical dispersion and oscillations due to truncation errors [Salamon et al, 2007;Boso et al, 2013].…”

A random walk solution for modeling solute transport with network reactions and multi-rate mass transfer in heterogeneous systems: Impact of biofilms

“…Thus, properties such as the hydraulic conductivity and the different degradation rates can vary several orders of magnitude in an aquifer (e.g., Rubin, 2003;Fenell et al, 2001;Sandrin et al, 2004). Even though the description of the spatial variability of all these properties at high resolution is crucial for making contaminant predictions (e.g., Feehley et al, 2000;Salamon et al, 2007;Riva et al, 2008;LlopisAlbert et al, 2009), its implementation in transport models typically leads to numerical problems.…”