No abstract

The relative macroporosity (w f) and the effective aggregate width (d ag) are input parameters for several dual-permeability models. As w f is geometrically related to d ag , any improvement in its determination is directly extended to d ag. The w f , as estimated by disk infiltrometers, applies only under the assumption that macropores are cylindrically shaped. We generalize the determination of w f for ring, hexagon, brick, and rectangular slab macropore-matrix shapes using a transformation factor, ξ, obtained from pore-scale modeling. The ξ was computed by dividing the relative macroporosity for noncylindrical shapes, w f_nc , over the relative macroporosity for cylindrical shapes, w f_c. The computation of ξ accounts for differences in the macropore area and macropore water flow between noncylindrical and cylindrical shapes. A total of 15 combinations of macropore width and effective aggregate width were used to construct the geometrical figures and compute both w f_nc and w f_c. For the cylindrical, ring, and rectangular slab shapes, the macropore water flow was solved using analytical solutions. For the hexagonal and brick shapes, the macropore water flow was solved numerically using COMSOL Multiphysics. Remarkably, the computed ξ was constant and equal to 1.5 for all four noncylindrical shapes under analysis. We show that the solution is exact for laminar flow under saturated conditions in the macropores with a rigid and wettable matrix. This methodology enables the derivation of a better estimate of w f and d ag from disk infiltrometer data that include different macropore geometries. This information is crucial for the setup of dual-permeability models in risk assessments and detailed studies. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Wells in groundwater aquifers are used in cyclic injection-extraction processes, otherwise named push-pull processes, in a variety of applications related to the storage of water of some particular quality (Dillon et al., 2019). Examples include fresh water supplies that are of drinking or irrigation quality, and hot or cold water to be used for indoor heating or cooling. Water that is stored in an open environment, such as within a dam or reservoir, will interact with the atmosphere and surface runoff, thereby gradually diminishing its thermal quality through heat exchange, and its chemical quality through contamination with environmental aerosols, soluble gases, and runoff of marginal quality. This has led to a pressing need for research into efficient means of large capacity seasonal thermal (Rad & Fung, 2016) and freshwater (Missimer et al., 1992) storage, amongst which geological storage exhibits the most immediate economic potential and technological feasibility (Missimer, 2012;Xu et al., 2014). Confined groundwater aquifers, which permit minimal interaction between groundwater and the external environment (e.g., the vadose zone and the atmosphere), are increasingly being used as geological storage vessels for water. Aquifer Thermal Energy Storage (ATES; Fleuchaus et al., 2018) and Aquifer Storage and Recovery (ASR; Pyne, 2017) are two aquifer storage technologies currently in widespread usage for the storage of heat and freshwater, respectively.A crucial performance metric of an aquifer storage system is the recovery efficiency of the injected solutes or thermal gradient, which is the fraction of injected solutes or heat that can be recovered at the end of a storage cycle. During the injection and extraction phases, solutes and/or heat spread around the injected water front due to hydrodynamic dispersion processes. Local hydrodynamic dispersion, which governs the rate of dispersive losses, comprises the flow velocity-dependent mechanical dispersion, and the flow velocity-independent molecular or thermal diffusion (for solutes and heat, respectively). For storage systems in homogeneous aquifers, Tang and van der Zee (2021) recently analyzed the dependence of the recovery efficiency on hydrodynamic dispersion parameters, well operational parameters, and flow field geometry. In heterogeneous aquifers, with a spatially

The vertical change in the number of macropores causes a variation of the relative macroporosity (wf) and the effective aggregate width (dag) over the soil profile. Both parameters are used in HYDRUS to represent this variation, increasing the number of parameters and making automated calibration challenging. The working hypothesis is that we can improve an analytical estimation of wf and dag developed in previous research by inverse estimation with a meta‐model for HYDRUS 2D/3D, using disk infiltrometer data of infiltration at zero pressure head. We generate a meta‐model that describes the vertical heterogeneity of the macropore number with a general function using four parameters: the relative macroporosity at the soil surface (wfs), the effective macropore radius (rm), the maximum depth of macropores (zmax) and the shape parameter of the wf curve (m). The meta‐model computes the variation of wf and dag over depth, thus reducing the parameters for automated calibration with HYDRUS. We theoretically described how to directly obtain the meta‐model parameters with disk infiltrometer data, providing an example for field conditions. A complete parametrization of matrix and macropore parameters for HYDRUS 2D/3D was generated from these data and previous studies, which were updated by automated calibration. Only wfs was calibrated, increasing by about ~3.5 times the initial measurement. We tied several macropore parameters to wfs during calibration by their physical or mathematical relations. This methodology can be utilized to estimate HYDRUS parameters for risk assessment or detailed plot studies. Highlights A meta‐model to estimate macropore parameters for HYDRUS 2D/3D is presented. The meta‐model reduces the number of macropore parameters for HYDRUS 2D/3D. Initial estimations of meta‐model parameters are obtained by disk infiltrometer. The parameters were updated through calibration with HYDRUS 2D/3D. Preferential flow is predicted by a two‐dimensional model.

Pesticide transport simulation by SWAP-PEARL (Soil-Water-Atmosphere-Plant and Pesticide Emission Assessment at Regional and Local scales) models can help to predict pesticide leaching at regional scales. For reasons of economic and time efficiency, measurement efforts should be prioritized towards critical parameters. The objective of this research is to perform a Morris screening and Sobol-Jansen sensitivity analysis to SWAP-PEARL models, using a reasonable worst-case scenario. Three pesticide compounds were analyzed:, bentazon (zero sorption), imidacloprid (moderately sorbed), and compound I (highly sorbed). Initial macropore and pesticide parameter values were varied by ±20% to generate parameter ranges. The outputs analyzed were the concentration in drainage water, the average concentration in groundwater between 1 and 2 m, and the concentration in the soil system at 100-cm depth. Influential parameters found through the Morris method were analyzed using the Sobol-Jansen method. The results for bentazon indicate that the degradation half-life (DT50), the bottom depth of the internal catchment (z ic), and the proportion of the internal catchment at the soil surface (p ic_0) are critical parameters in all the outputs analyzed. For imidacloprid and compound I, the most relevant parameters for drainage output are the Freundlich sorption exponent (F exp) and z ic ; for groundwater, the relevant parameters are F exp , the bottom depth of static macropores (z st), and p ic_0 ; and for soil concentrations at 100-cm depth, the relevant parameters are F exp , z ic , and p ic_0. The Morris and Sobol-Jansen methods produce the same results for the first position in the ranking. Measurement efforts should be performed to update national soil databases, including critical pesticide and macropore parameters.