Comparing Discrete Fracture and Continuum Models to Predict Contaminant Transport in Fractured Porous Media

Abstract

We used the FRAC3Dvs numerical model (Therrien and Sudicky 1996) to compare the dual-porosity (DP), equivalent porous medium (EPM), and discrete fracture matrix diffusion (DFMD) conceptual models to predict field-scale contaminant transport in a fractured clayey till aquitard. The simulations show that the DP, EPM, and DFMD models could be equally well calibrated to reproduce contaminant breakthrough in the till aquitard for a base case. In contrast, when groundwater velocity and degradation rates are modified with respect to the base case, the DP method simulated contaminant concentrations up to three orders of magnitude different from those calculated by the DFMD model. In previous simulations of well-characterized column experiments, the DFMD method reproduced observed changes in solute transport for a range of flow and transport conditions comparable to those of the field-scale simulations, while the DP and EPM models required extensive recalibration to avoid high magnitude errors in predicted mass transport. The lack of robustness with respect to variable flow and transport conditions suggests that DP models and effective porosity EPM models have limitations for predicting cause-effect relationships in environmental planning. The study underlines the importance of obtaining well-characterized experimental data for further studies and evaluation of model key process descriptions and model suitability.

FracKfinder: A MATLAB Toolbox for Computing Three‐Dimensional Hydraulic Conductivity Tensors for Fractured Porous Media

“…Longitudinal dispersivity (α L ) for the matrix domain was taken from Helmke et al (, ). The α L value for the fracture domain was fit using published values for fractured till (Table ; Blessent et al ). The resulting cumulative breakthrough curve from the dual‐continuum model demonstrated good agreement with the results of the column experiment, showing a modified index of agreement value ( d 1 ) of 0.97 (Willmott et al ; Helmke et al ; Figure ).…”

“…Single‐ and dual‐continuum models have been used to upscale groundwater flow in fractures (Sudicky ; Gerke and van Genuchten ; Helmke et al ; Blessent et al ). Representing fracture‐induced anisotropy requires a 3D, six‐component K tensor (symmetry assumed) for the fractures.…”

“…Fractures act as high-permeability conduits for fluid and solutes within otherwise low-permeability media (Long et al 1982;Odling et al 1999;Helmke et al 2005a). Although Single-and dual-continuum models have been used to upscale groundwater flow in fractures (Sudicky 1989;Gerke and van Genuchten 1993;Helmke et al 2005b;Blessent et al 2014). Representing fracture-induced anisotropy requires a 3D, six-component K tensor (symmetry assumed) for the fractures.…”

Experimental and Numerical Investigations of Influence on Overland Flow and Water Infiltration by Fracture Networks in Soil

“…Five 3D soil and groundwater flow and substance transport models were found that simulate preferential flow and transport, including HILLFLOW [36], TOUGH2 [37], HYDRUS-3D [38], MIKE-SHE [12,13], and a model by Laine-Kaulio et al [39]. In addition, Blessent et al [40] used the FRAC3Dvs numerical model to compare the dual porosity, equivalent porous medium, and the discrete fracture matrix diffusion conceptual model, and the study has an important role in decision-making for groundwater-related issues, while the research focus is the 2 Geofluids groundwater and the three models do not consider the surface runoff movement. Although soil swelling and shrinkage models have been included in several earlier models, most notably in FLOCR [41], MACRO [42], and SWAP [43], they are all limited to 1D or quasi 2D simulations.…”

Modelagem Numérica De Fluxo Bifásico E Transporte De Contaminantes Em Meios Porosos

“…As diferentes abordagens podem ser agrupadas em três classes: meio poroso equivalente, o modelo de dupla porosidade, e o modelo de rede de fraturas discretas (Cook, 2003) (Blessent, et al, 2014). A continuação, são apresentadas as características principais de cada modelo conceitual respeito ao fluxo e ao transporte de contaminantes em meios porosos e meios porosos fraturados.…”