Issues

We used electromagnetic induction (EMI) geophysical imaging to map the soils of a small watershed. By comparing the gephysical signal with plant community patterns, we have discovered distinct vegetation niches corresponding to distinct zones of bulk soil electrical conductivity.

Air permeability as a function of gravimetric water content and dry bulk density is proposed as an indicator of structure formation for six porous materials including soil, peat, and compost. Air permeability and structure formation could be divided into three regions with respect to water content, and both decrease with increasing bulk density.

The low water content of the Hanford Site vadose zone is hypothesized to affect desorption/dissolution of uranium into porewater and/or groundwater. Hydraulically saturated and unsaturated column experiments were performed to evaluate the effect of water content on the advective desorption and migration of uranium from contaminated sediments.

Infiltration into a sand tank (3 by 5 m, 2 m deep) produced a constant wetting front velocity that indicates dynamic equilibrium of forces. Hence, momentum dissipation is assumed to equilibrate with gravity, while capillarity is considered a secondary force. The corresponding model satisfactorily approached the observed water content wave and drainage flow.

A new solution of the Boltzmann transform as a function of matric potential is derived to solve Richards equation for horizontal water infiltration into a sand. It also improves and provides a versatile alternative to the well-known analysis pioneered by Green and Ampt in 1911.

An introduction is given for a series of four papers that address mathematical modeling of transport phenomena in variably saturated, highly heterogeneous media.

An overview of the problem of solute transport in unsaturated heterogeneous media is presented. Field and laboratory observations that demonstrate nonclassical flow and transport behavior are reviewed. Basic factors and physical concepts to describe anomalous transport in fractured rocks are discussed.

Analysis of diffusion in heterogeneous media with sharply contrasting properties was performed. Over time, three different transport regimes were realized, resulting in a complex structure of concentration tails. The more distant tail segment was determined by the earlier time transport regime.

New elements were developed to generalize the dual-porosity model for moisture infiltration and solute transport in unsaturated rocks, taking into account fractal aspects of the percolation process. Transport regimes, a complex structure of concentration tails, and effects due to medium characteristic fluctuations were analyzed.

A stochastic random walk model of anomalous diffusion was developed to simulate solute transport in highly heterogeneous media. In the special case of isotropic space-independent parameters, the model reduces to the fractional-order advection–dispersion equation model. The model was extended to the multidimensional case with spatial anisotropy and compared with the results of field experiments.

We present a regional-scale method to predict locations of depression-focused preferential flow and chemical transport, a process that helps explain the presence of agrichemicals in recently recharged groundwater of the High Plains aquifer despite chemical transit times from diffuse recharge that exceed historical agricultural activity.

Arsenate, arsenite, selenate, and selenite adsorption as a function of the aqueous solution concentration of these constituents was determined for a set of soils near ash disposal facilities. A chemical surface complexation model was applied to quantify the adsorption of these constituents as a function of their aqueous solution concentrations.

We estimated flow parameters in the vadose zone of an ice-contact delta in Norway by inverse modeling of vadose zone flows produced by water infiltration during snowmelt. The inverse flow modeling was done by conditioning on different combinations of time-lapse GPR travel-time tomography and time series of the level of the groundwater table.

We present a simple, semianalytical approach to delineate multiple layers in partially saturated soils from resistivity and saturation measurements taken at several depths along a borehole. The proposed inversion algorithm is computationally efficient and can serve either as a stand-alone tool for layer delineation or as an autonomous module in a more comprehensive geophysical survey. We provide a detailed analysis of the algorithm's convergence and identify potential pitfalls.

The 5-yr mobility of Zn, Cu, and Pb in the vadose zone underneath an infiltration basin were modeled both with and without a colloidal phase present. Only the former model fitted profile data well. The results support the hypothesis that colloidal particles play a significant role in transport of metal species.

A simple model for predicting air permeability in natural porous media as a function of water content and dry bulk density was developed. The model is able to predict air permeability throughout the entire bulk density–water content range for a specific porous medium based on only four measurements of air permeability.

A model for the gas diffusion coefficient in unsaturated, structureless soil is presented. The model considers resistance to gas diffusion caused by air-phase reduction, solids-phase induced tortuosity, and water-phase induced blockages. The dominating resistance to gas diffusion is discussed in relation to soil texture and compaction.

Effects of surface flow and solute boundary conditions for a two-dimensional dual-permeability model on Br leaching from a tile-drained field were quantified. The conditions varied included: (i) irrigation scheme characteristics, (ii) type of the solute boundary condition, and (iii) the domain (matrix or macropores) to which solute was applied.

Dual-permeability models are sensitive to near-saturated hydraulic properties, yet little is known about how parameters can be estimated. A new closed-form model of near-saturation hydraulic properties was derived and successfully fitted to soil macropore data. Macropore size distribution was functionally related to clay content and macroporosity.