On the formation of multiple local peaks in breakthrough curves

Siirila‐Woodburn, Erica R.; Sánchez-Vila, Xavier; Fernàndez-García, Daniel

doi:10.1002/2014wr015840

Cited by 19 publications

(13 citation statements)

References 68 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We note also that Siirila‐Woodburn et al . [] presented 3‐D high‐resolution simulations of tracer migration in synthetic domains with geostatistically based, heterogeneous hydraulic conductivities. Particle tracking simulations were used to generate BTCs; they demonstrated the appearance of multiple (local) peaks in single realizations, and showed that the number and slopes of local peaks depend on statistical anisotropy and travel distance.…”

Section: Resultsmentioning

confidence: 99%

Structural controls on anomalous transport in fractured porous rock

Edery

Geiger

Berkowitz

2016

Water Resources Research

View full text Add to dashboard Cite

Anomalous transport is ubiquitous in a wide range of disordered systems, notably in fractured porous formations. We quantitatively identify the structural controls on anomalous tracer transport in a model of a real fractured geological formation that was mapped in an outcrop. The transport, determined by a continuum scale mathematical model, is characterized by breakthrough curves (BTCs) that document anomalous (or “non‐Fickian”) transport, which is accounted for by a power law distribution of local transition times ψ(t) within the framework of a continuous time random walk (CTRW). We show that the determination of ψ(t) is related to fractures aligned approximately with the macroscopic direction of flow. We establish the dominant role of fracture alignment and assess the statistics of these fractures by determining a concentration‐visitation weighted residence time histogram. We then convert the histogram to a probability density function (pdf) that coincides with the CTRW ψ(t) and hence anomalous transport. We show that the permeability of the geological formation hosting the fracture network has a limited effect on the anomalous nature of the transport; rather, it is the fractures transverse to the flow direction that play the major role in forming the long BTC tail associated with anomalous transport. This is a remarkable result, given the complexity of the flow field statistics as captured by concentration transitions.

show abstract

Section: Resultsmentioning

confidence: 99%

Structural controls on anomalous transport in fractured porous rock

Edery

Geiger

Berkowitz

2016

Water Resources Research

View full text Add to dashboard Cite

show abstract

“…The PT 100M BTC is considered the ''true'' transport solution, or as closely to the true solution which is numerically feasible at this time, although we acknowledge the true solution will only be achieved with an infinite number of particles. Following the approach described in Siirila-Woodburn et al [2015], the estimated 95% confidence interval of the PT 100M BTC was found to be smaller than about 10 28 for all times. To quantify how much the PT and KDE BTCs differ from the high resolution result, an integrated root-meansquare error (IRMSE) metric is calculated given the solute concentration measures {C(t 1 ),.…”

Section: Reconstruction Of Unaveraged Btcs C Versus T and Associatementioning

confidence: 93%

“…Representative BTC I (Figure 2a) is nearly Gaussian, showing somewhat ideal Fickian conditions. Representative BTCs II-IV (Figures 2d, 2g, and 2j) show some degree of anomalous behavior, displaying a number of local peaks of different duration in time [Siirila-Woodburn et al, 2015]. BTC IV (Figure 2j) resembles a power-law like curve.…”

Section: Representative Btcsmentioning

confidence: 99%

“…Rather, the U.S. EPA and other agencies propose evaluating risk from some representative Advancements in the use of kernels in reconstruction processes include obtaining optimal kernel support estimates that can lead to improved methods for reconstruction. Optimal KDE methods have been recently proposed in the PT literature to overcome oversmoothing and statistical artificial fluctuations in the BTC [Fernandez-Garcia and Sanchez-Vila, 2011;Pedretti and Fernandez-Garcia, 2013;Siirila-Woodburn et al, 2015]. Optimal KDE methods allow reconstructing an unbiased estimator of the BTC, further providing a measure of the estimation error that adapts to the number of particles used in the simulation and the smoothness of the solution.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Improving the accuracy of risk prediction from particle‐based breakthrough curves reconstructed with kernel density estimators

Siirila‐Woodburn

Fernàndez-García

Sánchez-Vila

2015

Water Resources Research

View full text Add to dashboard Cite

While particle tracking techniques are often used in risk frameworks, the number of particles needed to properly derive risk metrics such as average concentration for a given exposure duration is often unknown. If too few particles are used, error may propagate into the risk estimate. In this work, we provide a less error-prone methodology for the direct reconstruction of exposure duration averaged concentration versus time breakthrough curves from particle arrival times at a compliance surface. The approach is based on obtaining a suboptimal kernel density estimator that is applied to the sampled particle arrival times. The corresponding estimates of risk metrics obtained with this method largely outperform those by means of traditional methods (reconstruction of the breakthrough curve followed by the integration of concentration in time over the exposure duration). This is particularly true when the number of particles used in the numerical simulation is small (<10 5 ), and for small exposure times. Percent error in the peak of averaged breakthrough curves is approximately zero for all scenarios and all methods tested when the number of particles is !10 5 . Our results illustrate that obtaining a representative average exposure concentration is reliant on the information contained in each individual tracked particle, more so when the number of particles is small. They further illustrate the usefulness of defining problem-specific kernel density estimators to properly reconstruct the observables of interest in a particle tracking framework without relying on the use of an extremely large number of particles.

show abstract

“…and Tsang (1991), Siirila-Woodburn et al (2015), and Boon et al (2017). More precisely, assuming a single-pulse tracer injection signal, multimodal BTCs reflect a three-step process: 1) tracer spreading into different flowing or nonflowing aquifer subdomains characterized by different transit/residence times, 2) tracer motion within each subdomain with little or no exchange between the different subdomains, and 3) convergence (mixing) of the subtracer fluxes somewhere upstream from, 65 or at, the monitoring point.…”

mentioning

confidence: 95%

MFIT 1.0.0: Multiflow inversion of tracer breakthrough curves in fractured and karst aquifers

Bodin¹

2020

Preprint

View full text Add to dashboard Cite

Abstract. More than half of the Earth’s population depends largely or entirely on fractured or karst aquifers for their drinking water supply. Both the characterization and modeling of these groundwater reservoirs are therefore of worldwide concern. Artificial tracer testing is a widely used method for the characterization of solute (including contaminant) transport in groundwater. Tracer experiments consist of a two-step procedure: 1) introducing a conservative tracer-labeled solution into an aquifer, usually through a sinkhole or a well, and 2) measuring the concentration breakthrough curve (BTC) response(s) at one or several downstream monitoring locations, usually spring(s) or pumping well(s). However, the modeling and interpretation of tracer test responses can be a challenging task in some cases, notably when the BTCs exhibit multiple local peaks and/or extensive backward tailing. MFIT is a new open-source, Windows-based computer package for the analytical modeling of tracer BTCs. This software integrates four transport models that are all capable of simulating single- or multiple-peak and/or heavy-tailed BTCs. The four transport models are encapsulated in a general multiflow modeling framework, which assumes that the spatial heterogeneity of an aquifer can be approximated by a combination of independent one-dimensional channels. Two of the MFIT transport models are believed to be new, as they combine the multiflow approach and the double-porosity concept, which is applied at the scale of the individual channels. Another salient feature of MFIT is its compatibility and interface with the advanced optimization tools of the PEST suite of programs. Hence, MFIT is the first BTC fitting tool that allows regularized inversion and nonlinear analysis of the postcalibration uncertainty of model parameters.

show abstract

On the formation of multiple local peaks in breakthrough curves

Cited by 19 publications

References 68 publications

Structural controls on anomalous transport in fractured porous rock

Structural controls on anomalous transport in fractured porous rock

Improving the accuracy of risk prediction from particle‐based breakthrough curves reconstructed with kernel density estimators

MFIT 1.0.0: Multiflow inversion of tracer breakthrough curves in fractured and karst aquifers

Contact Info

Product

Resources

About