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Abundant clay alteration, more halloysite vs. smectite, and higher electrical conductivity distinguish wet from dry canyons of the Pajarito Plateau. Gravimetric moisture analyses do not distinguish water in clay interlayers from pore water, but errors due to clay are minor. In horizons of 25 to 60% clay only 5 to 15% of gravimetric water is from clay.

Vadose Zone Journal August 01, 2005, Vol.4, 453-465. doi:

Evapotranspiration covers for waste containment were evaluated in a field study at four different slopes for 7 yr using total water balance monitoring at 6-h intervals. Increases in slope resulted in increased evaporation and decreased seepage and interflow.

Vadose Zone Journal August 01, 2005, Vol.4, 466-480. doi:

Tension infiltrometers are popular for measuring near-saturated soil hydraulic properties. We present a simple mathematical model to quantify the effects of fluctuating temperature on the pressure of the confined air space within the infiltrometer. Design modifications for future infiltrometers follow from our analysis.

Vadose Zone Journal August 01, 2005, Vol.4, 481-487. doi:

The effect of the design and installation layout of multiple equilibrium tension plate lysimeters (ETPLs) on measured leachate fluxes is evaluated with the HYDRUS-2D model. Of particular interest is the height of the ETPL, the boundary condition between the central access installation chamber and ETPL, and the required separation distances between multiple ETPLs.

Vadose Zone Journal August 01, 2005, Vol.4, 488-499. doi:

Spatial variability was measured in rainfall depth, rainfall erosivity, and soil erosion within a semiarid woodland. Rainfall erosivity was more spatially variable and a better predictor of microwatershed erosion compared with rainfall amount, thus highlighting the potential importance of within-watershed spatial variation of rainfall erosivity.

Vadose Zone Journal August 01, 2005, Vol.4, 500-504. doi:

Unsaturated zone matrix hydrologic properties have been collected for several decades at Los Alamos National Laboratory for various environmental studies. These data are analyzed using nonparametric statistics to assess the ability to merge data from different locations for estimating unsaturated zone model input parameters.

Vadose Zone Journal August 01, 2005, Vol.4, 505-521. doi:

The authors provide an overview of the hydrogeology of the Pajarito Plateau and sets the stage for discussions by other papers in this special issue. It includes overviews of the regional geographic and geologic settings, descriptions of rock units making up the vadose zone and regional zone of saturation, discussion about the relation between geologic and hydrogeologic units, and descriptions of groundwater occurrences.

Vadose Zone Journal August 01, 2005, Vol.4, 522-550. doi:

TDR soil moisture measurements are equally possible with single-rod probes as with conventional two- or multiple-rod probes. Four different single-rod probes and a conventional two-rod probe were compared for sensitivity to scattering objects in their vicinity. The volume sampled by the single-rod probes was found to be larger than for the two-rod probe.

Vadose Zone Journal August 01, 2005, Vol.4, 551-557. doi:

Water content data are used to estimate hydraulic parameters for a silty clay soil during upward water flow from a shallow groundwater table. Sensitivity analysis, response surfaces, multiple inverse solutions, and stability analysis are employed to study the uniqueness of the estimated parameters. The effect of parameter uncertainty is evaluated.

Vadose Zone Journal August 01, 2005, Vol.4, 558-572. doi:

A field plot bromide tracing experiment was conducted to assess the impact of soil structure heterogeneity created by agricultural operations on water and solute transport. Bromide, TDR, and tensiometer measurements all indicated the presence of preferential flow of water and bromide along paths immediately bordering the wheel tracks.

Vadose Zone Journal August 01, 2005, Vol.4, 573-586. doi:

A water and bromide transport field experiment in a cultivated soil was simulated with HYDRUS-2D using a fully deterministic approach to represent soil heterogeneity. Preferential flow of water and solute are shown to result from the presence of tillage-induced soil heterogeneities, especially compacted zones within the plow layer.

Vadose Zone Journal August 01, 2005, Vol.4, 587-601. doi:

We report on the effect of external applied stresses and internal hydraulic stresses on the void ratio and water retention characteristic of soils. Several models are presented for prediction of the effect of variable void ratio on the water retention curve. Models with parameters that vary with void ratio are shown to be the best predictors.

Vadose Zone Journal August 01, 2005, Vol.4, 602-613. doi:

The guest editors briefly review the unique land use history, complex hydrogeology, and research of Los Alamos National Laboratory, and situate the special section articles in the context of ongoing scientific study and remediation work at the site and beyond.

Vadose Zone Journal August 01, 2005, Vol.4, 614-619. doi:

Conceptual models for vadose zone flow and transport in the Los Alamos, NM area are presented. Field observations, data, and numerical models are used in conjunction to develop and test these conceptual models.

Vadose Zone Journal August 01, 2005, Vol.4, 620-636. doi:

This paper summarizes an extensive observational data set of deep perched water observed in multiple boreholes in the study area. General conclusions on the cause and characteristics of the perched water are discussed, and a new numerical formulation is presented that allows perched water to be simulated efficiently in vadose zone numerical models.

Vadose Zone Journal August 01, 2005, Vol.4, 637-652. doi:

This paper summarizes available data concerning the hydrogoelogy of the regional aquifer beneath the Los Alamos National Laboratory and presents new modeling analyses addressing fluxes through key portions of the aquifer. We show that fluxes through specific hydrostratigraphic units are not well quantified due to parameter uncertainty.

Vadose Zone Journal August 01, 2005, Vol.4, 653-671. doi:

This paper describes the development of a map of net infiltration for the Los Alamos area, New Mexico using GIS software and maps of topography, surface geology, and vegetation to extrapolate infiltration rates estimated from spring chemistry, borehole moisture data, and streamflow measurements to uncharacterized parts of the study area.

Vadose Zone Journal August 01, 2005, Vol.4, 672-693. doi:

Water injection in unsaturated tuff is modeled using continuum models assuming rock matrix properties, as well as models that explicitly account for fractures. For this tuff, models without fractures are sufficient to reproduce the hydrologic behavior; models with fractures can only match the data if the role of fractures is minimized.

Vadose Zone Journal August 01, 2005, Vol.4, 694-707. doi:

During construction of a sediment deposition weir in Los Alamos Canyon, fractured basalt was exposed, thereby introducing a new, potentially rapid transport pathway vertically to groundwater. A monitoring system was constructed, and two tracer tests were initiated in order to evaluate the potential for rapid vertical transport at the site.

Vadose Zone Journal August 01, 2005, Vol.4, 708-717. doi:

Field observations of bromide transport in the unsaturated zone of an important basalt unit beneath the Los Alamos National Laboratory are used to estimate bulk porosity and permeability of the formation via a numerical model. Good comparisons with solute breakthrough are obtained using an homogeneous domain with high permeability and low porosity.

Vadose Zone Journal August 01, 2005, Vol.4, 718-728. doi:

This paper presents a three-dimensional numerical model of the Los Alamos Canyon within the LANL study area. The model illustrates that a comprehensive understanding of vadose zone hydrologic and contaminant transport processes can be obtained by integrating data from geologic, hydrologic, and other site characterization sources.

Vadose Zone Journal August 01, 2005, Vol.4, 729-743. doi:

Barium and RDX have distinctive distributions in alluvial water and sediment. Barium dissolved in alluvial aquifer water precipitates as barite or witherite and is mobilized by surface fluvial processes, while RDX remains dissolved in the vadose zone pore water and is mobilized by subsurface processes into the alluvial aquifer.

Vadose Zone Journal August 01, 2005, Vol.4, 744-759. doi:

Data from a vadose zone VOC vapor plume is used to calibrate a three-dimensional numerical model that incorporates the processes identified in a conceptual model of vadose zone VOC transport. The simulations show growth of the plume is controlled by diffusive processes and is probably not affected by deep barometric pumping.

Vadose Zone Journal August 01, 2005, Vol.4, 760-773. doi:

Techniques are presented that utilize horizontal boreholes to gather data and interpret vadose zone behavior. A flexible and retrievable liner system was air-injected into boreholes. Data were collected at volumetric water contents below 10%, and included neutron logs, liquid water and gas sample extractions, and in situ air permeability measurements.

Vadose Zone Journal August 01, 2005, Vol.4, 774-788. doi:

The performance of two waste covers is compared using neutron logging and time domain reflectometry. The studied waste site was covered with an asphalt and clay cover for 37 yr until it was replaced with an evapotranspiration cover in 1998. Data indicate that evapotranspiration from the new cover has reduced deep percolation potential.

Vadose Zone Journal August 01, 2005, Vol.4, 789-797. doi:

Landfill covers with and without an engineered barrier for mitigating lateral flow and root penetration were studied for more than a decade. The designs differed in vegetation dynamics and soil water storage, but both designs limited seepage to a small amount. Observed macropore flow associated with roots and burrows is expected to progress with time.

Vadose Zone Journal August 01, 2005, Vol.4, 798-810. doi:

A spatially distributed hydrologic model that accounts for lateral flows of surface and subsurface water was used to rank sites relative to their vulnerability for contaminant mobility. The method was applied in an area with complex topography, where improved methods for developing such rankings are particularly needed.

Vadose Zone Journal August 01, 2005, Vol.4, 811-818. doi:

A field experiment explored the use of desert plants as a general indicator and quantitative predictor of tritium contamination. Resultant contaminant distribution maps, coupled with knowledge of site features, illustrated that plants can play a role in the detection, movement, and potential remediation of subsurface tritium contamination.

Vadose Zone Journal August 01, 2005, Vol.4, 819-827. doi:

Batch and breakthrough column experiments were performed to evaluate effects of manure on E. coli transport in undisturbed soil. A decrease in E. coli attachment to soil with an increase in manure concentrations was observed in batch conditions. Retention of E. coli in soil columns was inversely affected by the flow velocity.

Vadose Zone Journal August 01, 2005, Vol.4, 828-837. doi:

Movement and spreading of water and a passive solute on a hillslope under surface drip irrigation was analyzed taking into account the slope of the terrain, the spatial heterogeneity of the soil hydraulic properties, and water extraction by plant roots. The results have implications regarding sensor placement for irrigation water management.

Vadose Zone Journal August 01, 2005, Vol.4, 838-847. doi:

A Lagrangian particle method based on smoothed particle hydrodynamics (SPH) was used to model three-dimensional unsaturated flow in fractures. Adding particle–particle interaction forces into standard SPH equations allowed numerically efficient treatment of no-flow boundary conditions, surface tension and different wettability conditions.

Vadose Zone Journal August 01, 2005, Vol.4, 848-855. doi:

A method for obtaining high-resolution solute concentration estimates using image analysis was presented and tested in four solute transport experiments with different water flux rates. Using time moment analysis, the dispersivity variations over depth could be studied at scales from 0.72 to 0.0014 m.

Vadose Zone Journal August 01, 2005, Vol.4, 856-865. doi:

The effect of suction cup size on disturbance of preferential flows during sampling is examined. Three-dimensional numerical simulations of water flow and Br transport were conducted to quantify the flow disturbance for regular and mini suction cups. It was found that caution must be applied when using cups of either size to sample preferential flows.

Vadose Zone Journal August 01, 2005, Vol.4, 866-880. doi:

Laboratory experiments were conducted to evaluate the gas-phase partitioning tracer test method for measuring water contents in unsaturated porous media. Several porous media with different mean particle diameters and particle-size distributions were used, and the results are compared to water contents measured gravimetrically.

Vadose Zone Journal August 01, 2005, Vol.4, 881-884. doi:

We improved the design of the tension infiltrometer for measuring low flow rates. The improved design is robust, with a supply disk made from stainless steel. The Mariotte and reservoir towers are now less sensitive to ambient temperature fluctuations, and the refilling operation is fully automated.

Vadose Zone Journal August 01, 2005, Vol.4, 885-890. doi:
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