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Vapor Intrusion Models for Petroleum and Chlorinated Volatile Organic Compounds: Opportunities for Future Improvements
Vapor intrusion (VI) is of major concern to society, regulators, and practitioners. Existing VI risk assessment models do not generally account for the fate of vapor as it migrates upward from a source zone. We present an overview of vapor interactions in the vadose zone and the implications of this for existing models for VI risk assessment.
A Channel Network Model as a Framework for Characterizing Variably Saturated Flow in Biofilm-Affected Soils
A channel network model is developed to study the flow in biofilm-affected soils under variably saturated conditions. The effect of the biofilm spatial distribution on the network hydraulic properties is investigated by using three synthetic scenarios. It is shown that the biofilm spatial distribution has a profound effect on the network flow.
Inferring the Location of Preferential Flow Paths of a Leachate Plume by Using a DUALEM-421 and a Quasi-Three-Dimensional Inversion Model
A single-frequency and multiple-coil electromagnetic instrument is used along with a one-dimensional spatially constrained quasi-three-dimensional inversion algorithm. The results are presented as isocontours, which allow us to infer the location of preferential leachate plume flow paths beneath a decommissioned municipal landfill.
Solute Mass Transfer Effects in Two-Dimensional Dual-Permeability Modeling of Bromide Leaching From a Tile-Drained Field
This paper analyzes effects of the mass transfer coefficients and distribution of infiltrating water and bromide among pore domains on bromide leaching in a 2D dual-permeability model concept. Soil structure-related small-scale properties and local processes were significant to the quantification of preferential flow at plot and field scales.
Simulating One-Dimensional Unsaturated Flow in Heterogeneous Soils with Water Content-Based Richards Equation
Several numerical algorithms for the water content–based Richards equation are proposed to handle the discontinuity of water content in heterogeneous soil. Cell-centered grid and vertex-centered grid are employed. The performance of various algorithms is extensively tested in terms of mass conservation, accuracy, and efficiency.
Countryside Survey: National “Soil Change” 1978–2007 for Topsoils in Great Britain—Acidity, Carbon, and Total Nitrogen Status
Understanding global environmental change is a major challenge for 21st-century science; monitoring and understanding national soil change is no exception. National scale monitoring results for soil pH, carbon, and total nitrogen status for Great Britain show that soil change is occurring on anthropogenic time scales and that environmental protection legislation is an important tool for reversing potential detrimental impacts.
Influence of Carbonation on the Microstructure and Hydraulic Properties of a Basic Oxygen Furnace Slag
Weathering impacts on transfer properties was studied for a BOF-slag used as alternative road construction material, using water infiltration experiments and geochemical analysis. Clogging affected both water retention and hydraulic conductivity curves. A physical model for pore clogging is proposed to explain the observed effects.
Prediction of Water Retention of Soils from the Humid Tropics by the Nonparametric k-Nearest Neighbor Approach
The k-nearest neighbor (k-NN) approach is very attractive for pedotransfer modeling in hydrology; however, it has not been applied so far to predict water retention in highly weathered soils of the humid tropics. In our study, the k-NN approach was found to predict water retention in such soils with high accuracy.
Sulfamethazine Transport in Agroforestry and Cropland Soils
Two soils with different vegetative management were evaluated for sorption and leaching of an antibiotic. The antibiotic was bound more tightly and leached less in soils from agroforestry than cropland management. Results will benefit managers by providing evidence in support of vegetative buffers as a practice to mitigate antibiotic transport.
Noninvasive Monitoring of Soil Water Dynamics in Mixed Cropping Systems: A Case Study in Ratchaburi Province, Thailand
Electrical resistivity tomography can be used to monitor soil moisture depletion under field conditions and with multiple plants. We showed that even though there are limitations arising from soil heterogeneity and dry measurement conditions, important knowledge about spatial and temporal patterns of water depletion can be obtained.
Sensitivity Analysis of Soil Fumigant Transport and Volatilization to the Atmosphere
We conducted a comprehensive Monte Carlo sensitivity analysis of fumigant transport and volatilization using HYDRUS. The sensitivities of fumigant flux and soil-gas concentrations varied by application scenario and are interpreted mechanistically. These data provide a reference for designing fumigation field studies and interpreting their results.
Soil Permittivity Response to Bulk Electrical Conductivity for Selected Soil Water Sensors
The dependence of measured apparent permittivity on bulk electrical conductivity was evaluated in contrasting soils using time-domain reflectometry, a time-domain transmission sensor, and a capacitance sensor during solute displacement. The magnitude and direction of the permittivity response were found to vary considerably among sensors and soils.
Effects of Near Surface Soil Moisture Profiles During Evaporation on Far-Field Ground-Penetrating Radar Data: A Numerical Study
We theoretically investigated the effect of vapor flow on the drying front that develops in soils when water evaporates from the soil surface and on GPR data. The results suggest the integration of the full-wave GPR model with a coupled water, vapor, and heat flow model to accurately estimate the soil hydraulic properties.
Calibration of a Novel Low-Cost Soil Water Content Sensor Based on a Ring Oscillator
We evaluated the sensor-to-sensor variability of the SPADE soil moisture sensor and found an increase in accuracy when a sensor-specific calibration was used to relate sensor response and dielectric permittivity. The effect of temperature on sensor response was accounted for by a correction function that was successfully tested on soil material.
Determination of Water Saturation Using Gas Phase Partitioning Tracers and Time-Lapse Electrical Conductivity Measurements
Time-lapse bulk electrical conductivity measurements are used with gas phase partitioning tracers to measure saturation levels and inform concerning Archie’s parameters in well characterized sands at the column scale.
Monitoring Vadose Zone Desiccation with Geophysical Methods
Neutron moisture logging, cross-hole electrical resistivity tomography, and cross-hole ground-penetrating radar approaches were evaluated with respect to their ability to provide effective spatial and temporal monitoring of moisture content changes during soil desiccation.
Modeling Increased Groundwater Recharge due to Change from Rainfed to Irrigated Cropping in a Semiarid Region
This paper deals with the application of a two-step method for quantifying changes in groundwater recharge due to an increase in irrigated areas in semiarid regions. This method was applied in the Komadugu Yobe River valley (southeastern Niger, Lake Chad Basin) and showed that irrigation development has resulted in a significant increase in recharge.
Validating the BERMS in situ Soil Water Content Data Record with a Large Scale Temporary Network
In situ soil moisture networks are expensive to operate, with costs increasing with the number of stations in the network, but more stations provide better accuracy. One method of reducing these costs is to determine how a few stations may represent a large domain with better accuracy by using temporal stability analysis. A network of stations was installed and a scaling relationship was established for the permanent stations. This research will lead to more efficient in situ network protocol, scaling sparse stations while maintaining accuracy.
U.S. Climate Reference Network Soil Moisture Observations with Triple Redundancy: Measurement Variability
NOAA U.S. Climate Reference Network Program has deployed triple redundant soil moisture and soil temperature observation instruments at 114 climate stations nationwide at 5 standard depths, providing real time insights into measurement variability. Some initial findings gathered from this unique configuration are discussed in this paper.
Evaluation of Standard Calibration Functions for Eight Electromagnetic Soil Moisture Sensors
Eight commercially available electromagnetic water content sensors were evaluated in seven well-characterized soils ranging from sand to clay textures, including an organic soil. Factory supplied calibrations were compared and sensor response to soil properties demonstrated. Soil-specific calibrations yielded measurement accuracies from 0.015 to 0.025.
Self-Potentials in Partially Saturated Media: The Importance of Explicit Modeling of Electrode Effects
Electrode effects during self-potential experiments can be as large as those related to electrokinetic and electrodiffusive sources of interest. We demonstrate through sand-filled column drainage and imbibition experiments that electrode effects can be modeled and removed before interpreting the data in terms of fluid flow or transport processes.
Characterizing Coarse-Scale Representativeness of in situ Soil Moisture Measurements from the International Soil Moisture Network
The triple collocation method is used to estimate errors in the coarse-scale representation of in situ soil moisture data sets, drawn from the International Soil Moisture Network. Relationships between the estimated errors and average soil moisture conditions, soil moisture variability, climate classes, and soil texture classes are investigated.
Accounting for Soil Spatial Variability in Soil Water Capacitance Probe Calibration
Field calibration of a capacitance probe can become a challenge in long-term studies in which spatiotemporal behavior of soil water content is investigated for field-scale crop water uptake. The small physical sphere of influence can be complemented by the spatial range of representativity in presence of considerable soil spatial variability.
Calibration of Temperature Effect on Dielectric Probes Using Time Series Field Data
A new calibration method using time series of field data that requires no laboratory experiments was proposed for temperature effect on dielectric probes. Derived calibration equations from the field data were in good agreement with those from laboratory experiment and successfully removed the effect of soil temperature on probe outputs.
A New TDR Multiplexing System for Reliable Electrical Conductivity and Soil Water Content Measurements
Commercially available time domain reflectometry (TDR) multiplexers share a common ground, which lead to inaccurate TDR measurements for closely spaced TDR probes or at sites with high electromagnetic noise. To overcome these problems a new eight-channel differential multiplexer (50C81-SDM) was developed and tested that allows communication with standard TDR equipment.
Effect of Long-Term Irrigation with Treated Wastewater on the Root Zone Environment
Long-term irrigation with treated wastewater (WW) induced higher salinity and sodicity, lower hydraulic conductivity, and higher swelling pressure in the 20- to 40-cm and 40- to 60-cm soil layers. Continuous monitoring of oxygen concentration in the root zone revealed that aeration regime at the 20-cm depth was the most affected by WW irrigation.
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Special Section: Soil Water Sensors and Measurement Technologies
In-Situ and Remote Soil Moisture Sensing Technologies for Vadose Zone Hydrology
This manuscript gives an overview of some of the current research on in situ and remote soil water sensing techniques that were presented at Hawaii’s soil moisture sensing conference. This work covers practical applications of these sensors to different land uses, data handling and processing, scaling issues, integration of in situ and remote sensing data, and limitations of these sensors.
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