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We demonstrate a simple, cheap method for pore size characterization of porous media that generates a distribution of pore radii for improved flow and transport modeling. The new method for pore structure characterization utilizes recent theoretical developments in non-Newtonian fluids. Numerical evaluations and validations with synthetic porous media showed potential for obtaining a distribution of effective pore radii and their contribution to total flow only by complementing water with non-Newtonian fluids in saturated infiltration experiments. To demonstrate this ability on real sands, a series of one-dimensional column experiments was conducted with varying porous medium packings, including Accusands and a polydisperse sand/glass bead mixture. For each packing, distilled water and varying concentrations of guar and xanthan gum were injected over a range of flow rates and pressure gradients. The model-generated pore radii were compared with pore radius distributions measured by X-ray microcomputed tomography (μCT), with results demonstrating good agreement between the model and μCT data. Simulations of saturated water flow and drainage curves using model-generated pore radii compared favorably to experimental data, with errors typically between 2% and 10% for single-phase flow and approaching the error of the μCT measured radius distributions for the drainage curves.

This note corrects an error made in Miller et al. (2019). Modelling sediment transport in three-phase surface water systems. Journal of Hydraulic Research, 57(4), 439–463, . [ABSTRACT FROM AUTHOR]

This work advances the mathematical modeling of ion exchange treatment in completely mixed flow reactors in which there is recycle and regeneration of the ion exchange resin. The most common application of this process is magnetic ion exchange resin to remove dissolved organic carbon from raw drinking water. The motivation for this work was the complex distribution of resin particle ages and sizes that result from the recycle and regeneration processes. The newly developed model uses a single 'age-averaged' diffusion equation to represent resin particle age as compared with the previous Monte Carlo model that uses a large number of diffusion equations to represent various resin particle ages. Advantages of the age-averaged model over the Monte Carlo model include a closed-form analytical solution for the steady-state case of the model, advanced numerical techniques used for the nonsteady-state case of the model, and model simulations require much less computational time and yield more accurate results. The age-averaged model is a robust numerical tool that can be used to evaluate a range of treatment scenarios as a result of these advancements. DOI: 10.1061/(ASCE)EE.1943-7870.0000241 CE Database subject headings: Organic carbon; Drinking water; Ion exchange; Numerical models. Author keywords: Dissolved organic carbon; Drinking water; Ion exchange; Numerical models.

Concerted efforts to remediate subsurface systems contaminated with dense nonaqueous-phase liquids (DNAPLs) have met with limited success when measured by comparing solute concentrations to drinking water quality standards. One-dimensional and three-dimensional laboratory experiments and a field-scale experiment are used to investigate the effectiveness of source-zone remediation and to assess factors that contribute to the observed results. The three-dimensional laboratory experiment and the field-scale experiment used a surfactant flush followed by vapor extraction to reduce the DNAPL saturation, while vertical DNAPL mobilization was controlled using a brine barrier. DNAPL mobilization and recovery in the field-scale experiment was relatively ineffective due in part to the low saturation levels of the DNAPL. The results show essentially that complete removal of a DNAPL is required to reach typical cleanup standards and that details of the morphology and topology of a DNAPL distribution, in addition to the saturation, play an important role in determining the rate of mass transfer. The results are interpreted in terms of guidance for remediation approaches, realistic expectations for source-zone remediation, and elements needed for improved models of such systems. DOI: 10.1061/(ASCE)EE.1943-7870.0000165 CE Database subject headings: Remediation; Mass transfer; Groundwater pollution; Water quality. Author keywords: Brine-based remediation; Mass transfer; Source-zone flux.

This paper presents a new mathematical model of bacterial regrowth in distribution systems, which combines hydraulic calculations, inclusive of dispersion, with a description of the following microbial processes: free and attached growth, detachment, endogenous respiration, and inactivation by chlorine. The microbial process description has been simplified from previous models based on a sensitivity analysis. The alternating split-operator algorithm is used to solve this model. This method differs from previous approaches by decoupling the transport and reaction processes, allowing a choice among numerical algorithms that is best suited for each part of the model. The proposed solution resolves sharp fronts of a concentration profile more accurately than traditional finite difference methods. The results of the model are also compared against EPANET to show the importance of accounting for dispersion, as would occur during low water demand conditions when velocity is low. Use of the model to understand the interaction among key parameters affecting bacterial regrowth is illustrated for a simple hypothetical network. CE Database subject headings: Water quality; Water distribution; Bacteria; Simulation models.