Properties Of Unsaturated Zone Research Articles

Variation of Soil Properties of Unsaturated Zone with Depth and Time at an Agricultural Site in Kuwait

Variation of Soil Properties of Unsaturated Zone with Depth and Time at an Agricultural Site in Kuwait

Transfer of water and contaminants in the Chalk unsaturated zone – underground quarry of Saint-Martin-le-Nœud

Abstract The aim of this study is to understand the water and contaminant (nitrate and atrazine) transfer in the unsaturated zone (UZ) of Chalk. For this, the underground quarry of Saint-Martin-le-Nœud is an exceptional site because it permits entry to the aquifer at the limit between the UZ and the saturated zone (SZ). It provides direct access to the water table: underground lakes and the output of the UZ (percolation water at the ceiling). The thicknesses of the UZ and the clay-with-flints (CwF) layer that overlie the Chalk, vary along the 1200 m length of the quarry. From 2012, the chemical evolution and the flow variability of groundwater are characterized for 16 sites with different UZ properties. Chalk groundwater has highly spatially variable hydrodynamic behaviour and geochemical properties. A peak of contaminants is observed in the UZ around 15–20 m depth, with differing behaviours of nitrate and atrazine. The downward matrix water velocity is estimated to be from 0.3 to over 0.72 m a −1 , and the water table is mainly composed of ‘old’ water resulting from transfer through the matrix. A thick CwF layer modifies (1) the transfer processes: surface water is stored in a sort of ‘near-surface perched groundwater’, the infiltration is concentrated by preferential pathways; and (2) water quality: pesticides degradation processes occur in the perched groundwater.

From Climate Conditions to the Numerical Slope Stability Analysis of Surface Coal Mines

A new perspective is presented for evaluating the slope stability of coal and lignite mines due to rainfall. The case of Greek lignite mining areas is employed to illustrate the methodology. Initially, past climatic records of rainfall are documented and analyzed; rainfall intensity varies from light (0.8 mm/h) to heavy (up to 9 mm/h). Few extreme phenomena are documented, with the maximum intensity being 17 mm/h. Furthermore, climatic projections of future trends are performed with open-access tools to anticipate possible deviations from the baseline conditions. Although the mean temperature is expected to increase, projections show that the past rainfall range is not expected to change. Finally, the effect of rainfall infiltration on the stability of a typical open-pit lignite mining slope is investigated by finite element analysis. The precipitation range defined by the environmental analysis is used. The SF is practically constant for the lower rainfall intensities (0.8–2.2 mm/h). For the higher intensities of 6.4 mm/h, 9 mm/h, and 17 mm/h, the SF decrease is almost the same (from 2.08 to 1.9), with reduction rates of 8.3%, 8.9%, and 9.3%, respectively. The effect of the critical geotechnical properties—groundwater table depth, unsaturated zone properties, and soil permeability—is also examined for a complete evaluation.

UZIG Research: Measurement and Characterization of Unsaturated Zone Processes under Wide‐Ranging Climates and Changing Conditions

UZIG Research: Measurement and Characterization of Unsaturated Zone Processes under Wide‐Ranging Climates and Changing Conditions

Seismic response of earth dams considering dynamic properties of unsaturated zone

It is conventionally assumed in the analysis and design of earth dams that the soil located above the phreatic line, i.e. the uppermost seepage flow line, is completely dry. However, there is often an unsaturated flow of water through an unsaturated zone above this borderline and variation in moisture content in this zone results in variation of matric suction throughout this region. Variation of matric suction, in turn, results in variation of effective stresses in this zone. In this research, the seismic response of earth dams in terms of the displacement and acceleration at the crown of the dam as well as the stress distribution in the dam body is investigated. Taking into account the effect of unsaturated zone, a comparison is made to investigate the effect of conventional simplification in ignoring the dynamic characteristics of the unsaturated zone above the phreatic line and the more complicated analysis which includes the unsaturated zone. A function for the soil-water retention curve (SWRC) was assigned to the soil in the unsaturated zone to determine the variation of matric suction in this zone and analyses were made using finite difference software (FLAC). Results are then compared to the conventional method for homogeneous dams. In these analyzes the soil shear modulus was assumed to vary with the mean effective stress both for saturated and unsaturated zones. Among various results, it was notable that the history of crest x-displacement, and acceleration show higher values in models accounting for the unsaturated region. It was attributed to the considerably lower values of damping ratio in the crest region in the unsaturated models.

Saturated–unsaturated flow in a compressible leaky-unconfined aquifer

An analytical solution is developed for three-dimensional flow towards a partially penetrating large-diameter well in an unconfined aquifer bounded below by a leaky aquitard of finite or semi-infinite extent. The analytical solution is derived using Laplace and Hankel transforms, then inverted numerically. Existing solutions for flow in leaky unconfined aquifers neglect the unsaturated zone following an assumption of instantaneous drainage due to Neuman. We extend the theory of leakage in unconfined aquifers by (1) including water flow and storage in the unsaturated zone above the water table, and (2) allowing the finite-diameter pumping well to partially penetrate the aquifer. The investigation of model-predicted results shows that aquitard leakage leads to significant departure from the unconfined solution without leakage. The investigation of dimensionless time-drawdown relationships shows that the aquitard drawdown also depends on unsaturated zone properties and the pumping-well wellbore storage effects.

Seepage Face Height, Water Table Position, and Well Efficiency at Steady State

When a fully penetrating well pumps an ideal unconfined aquifer at steady state, the water table usually does not join the water level in the well. There is a seepage face inside the well, which is a key element in evaluating the well performance. This problem is analyzed using the finite-element method, solving the complete equations for saturated and unsaturated flow. The seepage face position is found to be almost independent of the unsaturated zone properties. The numerical results are used to test the validity of several analytic approximations. Equations are proposed to predict the seepage face position at the pumping well for any well drawdown, and the water table position at any distance from the pumping well for any in-well drawdown. Practical hints are provided for installing monitoring wells and evaluating well efficiency.

On Leakage and Seepage from Geologic Carbon Sequestration Sites: Unsaturated Zone Attenuation

Geologic carbon sequestration is the direct injection of CO2 into deep geologic formations for permanent disposal. Although numerous trapping mechanisms exist in the subsurface, it is possible that CO2 will leak from the primary sequestration target and seep out of the ground. The unsaturated zone has the potential to attenuate leaking CO2 and decrease seepage and near‐surface CO2 concentrations. Attenuation processes include permeability trapping, ponding as dense CO2 spreads out on the water table, solubility trapping by infiltrating or residual water, and dilution through mixing with ambient soil gas. Numerical simulations of CO2 flowing upward through a thick model unsaturated zone were performed to investigate the sensitivity of various unsaturated zone properties on CO2 seepage flux and near‐surface CO2 gas concentrations. These two quantities are considered drivers for health and environmental risk due to exposure to CO2 For the conceptual model considered, seepage flux and near‐surface CO2 gas concentrations are most strongly controlled by the leakage rate at the water table, followed by the source zone radius. Permeability and permeability anisotropy, as well as porosity and infiltration rate are also important, although to a lesser degree. Barometric pumping causes local maxima in seepage flux and near‐surface CO2 concentrations, but has negligible effect in a time‐averaged sense. When the leakage source is turned off, the CO2 plume attentuates through dissolution into infiltrating water. For the case of a constant leakage rate, the unsaturated zone can attenuate low leakage fluxes but should not be expected to attenuate large CO2 leakage fluxes.

On Leakage and Seepage from Geologic Carbon Sequestration Sites: Unsaturated Zone Attenuation

Geologic carbon sequestration is the direct injection of CO2 into deep geologic formations for permanent disposal. Although numerous trapping mechanisms exist in the subsurface, it is possible that CO2 will leak from the primary sequestration target and seep out of the ground. The unsaturated zone has the potential to attenuate leaking CO2 and decrease seepage and near-surface CO2 concentrations. Attenuation processes include permeability trapping, ponding as dense CO2 spreads out on the water table, solubility trapping by infiltrating or residual water, and dilution through mixing with ambient soil gas. Numerical simulations of CO2 flowing upward through a thick model unsaturated zone were performed to investigate the sensitivity of various unsaturated zone properties on CO2 seepage flux and near-surface CO2 gas concentrations. These two quantities are considered drivers for health and environmental risk due to exposure to CO2 For the conceptual model considered, seepage flux and near-surface CO2 gas concentrations are most strongly controlled by the leakage rate at the water table, followed by the source zone radius. Permeability and permeability anisotropy, as well as porosity and infiltration rate are also important, although to a lesser degree. Barometric pumping causes local maxima in seepage flux and near-surface CO2 concentrations, but has negligible effect in a time-averaged sense. When the leakage source is turned off, the CO2 plume attentuates through dissolution into infiltrating water. For the case of a constant leakage rate, the unsaturated zone can attenuate low leakage fluxes but should not be expected to attenuate large CO2 leakage fluxes.

On Leakage and Seepage from Geologic Carbon Sequestration Sites

Geologic carbon sequestration is the direct injection of CO2 into deep geologic formations for permanent disposal. Although numerous trapping mechanisms exist in the subsurface, it is possible that CO2 will leak from the primary sequestration target and seep out of the ground. The unsaturated zone has the potential to attenuate leaking CO2 and decrease seepage and near-surface CO2 concentrations. Attenuation processes include permeability trapping, ponding as dense CO2 spreads out on the water table, solubility trapping by infiltrating or residual water, and dilution through mixing with ambient soil gas. Numerical simulations of CO2 flowing upward through a thick model unsaturated zone were performed to investigate the sensitivity of various unsaturated zone properties on CO2 seepage flux and near-surface CO2 gas concentrations. These two quantities are considered drivers for health and environmental risk due to exposure to CO2 For the conceptual model considered, seepage flux and near-surface CO2 gas concentrations are most strongly controlled by the leakage rate at the water table, followed by the source zone radius. Permeability and permeability anisotropy, as well as porosity and infiltration rate are also important, although to a lesser degree. Barometric pumping causes local maxima in seepage flux and near-surface CO2 concentrations, but has negligible effect in a time-averaged sense. When the leakage source is turned off, the CO2 plume attentuates through dissolution into infiltrating water. For the case of a constant leakage rate, the unsaturated zone can attenuate low leakage fluxes but should not be expected to attenuate large CO2 leakage fluxes.

Impacts of Unsaturated Zone Properties on Oxygen Transport and Aquifer Reaeration

AbstractThis study investigated the unsaturated zone properties that affect ground water reaeration (i.e., the diffusive flux of oxygen through the unsaturated zone and into an aquifer system). Laboratory column experiments were undertaken to quantify oxygen flux into anaerobic ground water as a function of soil type, soil water content, soil oxygen demand, and unsaturated zone thickness. Soils used in these studies included coarse sand, sand, loamy fine sand, fine sandy loam, silt, silty clay loam, bentonite, kaolin, and peat. The results showed that reaeration flux rates ranging from 11,000 to 12,000 mg/m2‐day were possible under conditions typical of the natural environment. Soil water content provided the greatest resistance to oxygen transport in the unsaturated zone while the remaining factors of soil type, soil oxygen demand, and unsaturated zone thickness did not significantly inhibit reaeration flux into ground water. An unsaturated zone transport model based on Fick's second law and gas‐liquid interfacial mass transport was developed and showed good agreement with the experimental results derived from the column studies. The results of this study suggest that unsaturated zone reaeration of anaerobic ground water may be a contributing factor in controlling the steady–state size and shape of hydrocarbon plumes and incorporating reaeration into ground water models—based on unsaturated zone properties—may allow for a more accurate representation of bioattenuation reactions taking place in subsurface environments.

Modélisation d'une recharge effective de nappe alluviale en région sub-désertique: cas de l'oasis du Téloua, Niger

Local specific features of the various parameters which rule the Wadi Téloua apron water balance are described here. Although, real evapotranspiration is not well defined. A numerical modeling of the geometry of the alluvial reservoir is presented, it needs the use of electric geophysical soundings and aircraft mapping. The effective recharge is computed from year to year saturation levels changes assuming homogeneity. This results are compared to surperficial water budget. The importance of the unsaturated zone properties and the peculiar play of evaporation of