bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two‐Dimensional Sensitivity Analysis of Contaminant Transport in the Unsaturated Zone
Authors: Boateng Samuel , Cawlfield Jeffrey D. 
Published: August 2005

AbstractA two‐dimensional probabilistic transport model is developed‐by coupling a reliability algorithm to a two‐dimensional unsaturated flow and transport model. The goal is to determine the significance of the uncertainty of each variable to the probability outcome. Model input includes the mean, standard deviation, and probability distribution of each uncertain variable. The uncertain variables are assumed to be uncorrelated to each other. The uncertain variables are saturated water content, residual water content, van Genuchten model parameters alpha (α) and n, saturated hydraulic conductivity, bulk density, coefficient of distribution, molecular diffusion coefficient, and dispersivity. Coefficient of variation is used as the measure of uncertainty for each uncertain variable. Three soil samples are considered for model simulations. One half of the flow surface area is the source of a generic contaminant spill. The reliability analysis determines the probability of exceeding a specific target concentration value and also provides a sensitivity value that measures the relative significance of each uncertain transport variable to the probability outcome. Generally, saturated water content tends to be the most significant uncertain variable for transport in the unsaturated zone. Bulk density and coefficient of distribution also are significant for reactive transport. Molecular diffusion and van Genuchten model parameter n are significant in fine‐grained soils and also at locations far from the contaminant source area. The uncertainty of saturated hydraulic conductivity and dispersivity have no significant influence on the probability outcome and can be considered as deterministic input variables.
Framework for Ground Water Protection ‐ the Managua Ground Water System as an Example
Authors: Johansson P.‐O. , Scharp C. , Alveteg T. , Choza A. 
Published: August 2005

AbstractA framework for ground water protection was developed and tested in the Eastern subarea of the Managua, Nicaragua, ground water system. The framework is a planning tool aimed at identifying areas with a high need for protection to aid future land‐use decisions. The basic components of the framework are vulnerability assessment, contaminant source characterization, and assignment of a protection value. The framework is developed for a geographic information system environment. The vulnerability assessment was carried out using a modified version of the DRASTIC method. The most vulnerable parts of the study area proved to be an area with a shallow ground water table coupled with shrinking/swelling clay soils, and an area where recent porous lava flows mean high recharge and low attenuation capacity. In the contaminant sources characterization, the type of contaminant, its relative concentration, mode of deposition, duration of contaminant load, and possibility for remediation were considered. The sources characterized as emitting a high potential contamination load were concentrated in a tax‐free industrial zone and three villages. The main contaminant sources were a tannery, chemical industries, and sewage water outlets. Both the ground water vulnerability and the potential contamination load were classified as high, moderate, or low. By superimposing the potential contamination load on the vulnerability map, the ground water contamination liability was evaluated by a skewed 3x3 matrix. A relative protection value of the ground water was calculated, based on classifications of available quantities, quality, sensitivity to changes in ground water level, and present or planned use. Together, these maps form an atlas to be used for ground water protection and land‐use planning.
Relationship Between Lineaments and Ground Water Occurrence in Western Botswana
Authors: Magowe Magowe , Carr James R. 
Published: August 2005

AbstractAsemiarid region of western Botswana, the Ghanzi‐Makunda area, is the focus of a study to determine the relationship between lineaments and well yield. This relationship is inferred from geologic maps, aerial photographs, and Landsat TM (thematic mapper) images in conjunction with a well yield map produced using indicator kriging and based on 226 globally positioned wells. A composite image of Landsat TM, digital well yield, lineament trace, and well location data, formed using a raster‐based geographic information systems (GIS) technique, visually identifies a correlation between well yield, lineament density, and darker tones on Landsat TM images. Higher fracture densities correlate positively with higher well yields. Regression analysis identifies a statistically significant correlation between distance to lineament intersections and median well yield.
In‐Well Hydraulics of the Electromagnetic Borehole Flowmeter
Authors: Dinwiddie Cynthia L. , Foley Nicole A. , Molz Fred J. 
Published: August 2005

AbstractPrevious studies have suggested that head losses associated with the application of the electromagnetic borehole flowmeter (EBF) can have important and detrimental effects on the use of the instrument for measurement of hydraulic conductivity (K) profiles. Head losses associated with flow through the meter may cause bypass flow around the packer if the well is gravel packed. In any type of well, changing head losses with meter position can cause changes in flow into the well that are not related directly to the K distribution. Such flow changes, or redistribution, can cause errors in the calculation of the K profile.Numerical simulations, based on measured head losses, indicate that bypass flow in gravel packed systems increases with increasing flow rate through the meter, increasing gravel pack conductivity, and increasing gravel pack thickness. Ideally, the EBF should not be used in gravel packed wells, due to the occurrence of bypass flow.Investigations into the flow redistribution phenomenon indicate that the top portion of the aquifer is where the greatest over‐estimation of K occurs. The portion of the well below the flowmeter is isolated from the observed drawdown as measured from the surface. In this region, the well experiences a reduced drawdown, which differs from the observed drawdown by an amount equal to the head loss at that meter position. Flow redistribution causes a more pronounced effect in more highly conductive mediums and may be almost negligible in mediums of low conductivity.
Recharge Estimation by Stage‐Discharge Interpolation of Springflows from Cross‐Correlated Well Measurements
Authors: Avery William H. , Donovan Joseph J. , Ketchum J. Neil 
Published: August 2005

AbstractFor shallow phreatic aquifers, from which springflow is the predominant source of discharge, recharge volumes may be approximated as the time integral of springflow time series. However, field measurement of flows from numerous springs, with sufficient frequency to accurately estimate this time integral, is frequently impractical. A technique for interpolation of continuous springflow time series is presented, using cross‐correlation between flows and continuous head measurements in associated wells. Suitable wells must lie within the recharge catchment of the spring in question and display negligible phase lag between well and spring response to recharge. Brief (<1 year) periods of calibration may be sufficient to establish calibration upon which discharge interpolation from well data may be based. A 7 m thick highly heterogeneous mine‐waste aquifer, with springflows highly sensitive to recharge events, is examined as a test case. Over a 40 day recharge period, three well/spring pairs yielded acceptable cross‐correlation across four recharge events. Head from one of these wells was compared to a second nearby spring and found to show poor correlation, attributed to its location outside of that spring's catchment. Calibration statistics were found to be robust when the calibration dataset for one pair was reduced in size. Measured flows from one of the correlated springs also displayed correlation with summed discharge from the aquifer at all measured springs, based on concurrent flow measurements over time. Results suggest that continuous measurements of head from a small number of critically selected wells may allow accurate estimates of transient spring discharge rates following a relatively brief period of flow‐stage calibration. The success of the method may depend on specific characteristics of aquifers to which it is applied, such as size of spring catchments, aquifer conductance, aquifer heterogeneity, and spatial distribution of recharge.
The Channel Network Model—A Tool for Transport Simulations in Fractured Media
Authors: Gylling Björn , Moreno Luis , Neretnieks Ivars 
Published: August 2005

AbstractThe Channel Network model and its computer implementation, the code CHAN3D, are presented for simulations of fluid flow and transport of solutes. The tool may be used to simulate and interpret field experiments of flow and transport on a large or small scale. It also may also be used for performance and safety assessments of repositories for nuclear and other hazardous wastes, e.g., chemical wastes. From observations in the field it is deduced that the flow and transport take place in a three‐dimensional network of connected channels. The channels have different properties and are generated in the model from observed stochastic distributions. This allows us to represent the large heterogeneity of the flow distribution commonly observed in the field. Solute transport is modeled considering advection and rock interactions such as matrix diffusion and sorption within the interior of the rock. For repository conditions the main contributions to the dispersion of solutes come from the large variation in the flow field (channeling) and the rock interactions. Objects such as fracture zones, tunnels, and release sources can be incorporated in the model. In addition, a methodology of how data may be obtained for the model is described. Data may be obtained from borehole and laboratory measurements.
Optimal Configuration of a Wellfield
Authors: Swamee Prabhata K. , Tyagi Aditya , Shandilya Vishnu K. 
Published: August 2005

AbstractOften in urban and rural water supply, the major source of water is an aquifer. An aquifer can be fully exploited by development of a wellfield. Considering well interference, individual wells have to be located in such a manner so that adjacent wells are at a distance of radius of minimum influence. Presently, as no optimal configuration is available, the wells are located by judgment. In this paper the optimal configurations of wellfields have been obtained by considering the minimum cost and the maximum reliability aspects for transporting the water to the center of the wellfield for its onward transmission to the treatment works.
Caffeine and Pharmaceuticals as Indicators of Waste Water Contamination in Wells
Authors: Seiler Ralph L. , Zaugg Steven D. , Thomas James M. , Howcroft Darcy L. 
Published: August 2005

AbstractThe presence of caffeine or human Pharmaceuticals in ground water with elevated nitrate concentrations can provide a clear, unambiguous indication that domestic waste water is a source of some of the nitrate. Water from domestic, public supply, and monitoring wells in three communities near Reno, Nevada, was sampled to test if caffeine or Pharmaceuticals are common, persistent, and mobile enough in the environment that they can be detected in nitrate‐contaminated ground water and, thus, can be useful indicators of recharge from domestic waste water. Results of this study indicate that these compounds can be used as indicators of recharge from domestic waste water, although their usefulness is limited because caffeine is apparently nonconservative and the presence of prescription Pharmaceuticals is unpredictable. The absence of caffeine or Pharmaceuticals in ground water with elevated nitrate concentrations does not demonstrate that the aquifer is free of waste water contamination. Caffeine was detected in ground water samples at concentrations up to 0.23 μg/L. The human Pharmaceuticals chlorpropamide, phensuximide, and carbamazepine also were detected in some samples.
Cross‐Well Slug Testing in Unconfined Aquifers: A Case Study from the Sleepers River Watershed, Vermont
Authors: Belitz Kenneth , Dripps Weston 
Published: August 2005

AbstractNormally, slug test measurements are limited to the well in which the water level is perturbed. Consequently, it is often difficult to obtain reliable estimates of hydraulic properties, particularly if the aquifer is anisotropic or if there is a wellbore skin. In this investigation, we use partially penetrating stress and observation wells to evaluate specific storage, radial hydraulic conductivity and anisotropy of the aquifer, and the hydraulic conductivity of the borehole skin. The study site is located in the W9 subbasin of the Sleepers River Research Watershed, Vermont. At the site, ∼3 m of saturated till are partially penetrated by a stress well located in the center of the unconfined aquifer and six observation wells located above, below, and at the depth of the stress well at radial distances of 1.2 and 2.4 m. The observation wells were shut in with inflatable packers.The semianalytical solution of Butler (1995) was used to conduct a sensitivity analysis and to interpret slug test results. The sensitivity analysis indicates that the response of the stress well is primarily sensitive to radial hydraulic conductivity, less sensitiive to anisotropy and the conductivity of the borehole skin, and nearly insensitive to specific storage. In contrast, the responses of the observation wells are sensitive to all four parameters. Interpretation of the field data was facilitated by generating type curves in a manner analogous to the method of Cooper et al. (1967). Because the value of radial hydraulic conductivty is obtained from a match point, the number of unknowns is reduced to three. The estimated values of radial hydraulic conductivity and specific storage are comparable to those derived from the methods of Bouwer and Rice (1976) and Cooper et al. (1967). The values and skin conductivity, however, could not have been obtained without the use of observation wells.
Numerical Simulation of Pumping Tests in Multilayer Wells with Non‐Darcian Flow in the Wellbore
Authors: Chen Chongxi , Jiao Jiu Jimmy 
Published: August 2005

AbstractAn important feature of pumping in a multilayer system is the dynamic interaction between the aquifers via non‐Darcian vertical flow within the wellbore. An equivalent hydraulic conductivity (EHC) approach is used to include this transient interaction as a special leakage through the confining layer in the flow system. Different flow regimes (laminar and turbulent flows, and the i transition range) are involved in a multilayer pumping test where the relation between the hydraulic gradient and flow velocity is complicated. The change of flow regimes is accommodated by varying the content of EHC as a function of the friction factor. For a particular well, the relation between friction factor and Reynolds number is unique and is obtained by interpolating Nikuradse's experimental results. A quasi‐three‐dimensional Galerkin finite‐element method is used to integrate the vertical one‐dimensional flow in the wellbore and confining layers and the two‐dimensional flow in the aquifers. This approach makes it possible to couple the aquifer and wellbore flows of different flow regimes and to solve them in a single numerical framework based on the same linear relation between gradient and velocity. A carefully designed pumping test in a multilayer aquifer system near Beihai City, Guangxi Autonomous Region, China, is used to demonstrate the performance of the approach.
Localized Sulfate‐Reducing Zones in a Coastal Plain Aquifer
Authors: Brown Craig J. , Coates John D. , Schoonen Martin A.A. 
Published: August 2005

AbstractHigh concentrations of dissolved iron in ground water of coastal plain or alluvial aquifers contribute to the biofouling of public supply wells for which treatment and remediation is costly. Many of these aquifers, however, contain zones in which microbial sulfate reduction and the associated precipitation of iron‐sulfide minerals decreases iron mobility. The principal water‐ bearing aquifer (Magothy Aquifer of Cretaceous age) hi Suffolk County, New York, contains localized sulfate‐redudng zones hi and near lignite deposits, which generally are associated with clay lenses. Microbial analyses of core samples amended with [14C]‐acetate indicate that microbial sulfate reduction is the predominant terminal‐electron‐accepting process (TEAP) in poorly permeable, lignite‐rich sediments at shallow depths and near the ground water divide. The sulfate‐reducing zones are characterized by abundant lignite and iron‐sulfide minerals, low concentrations of Fe(III) oxyhydroxides, and by proximity to clay lenses that contain pore water with relatively high concentrations of sulfate and dissolved organic carbon. The low permeability of these zones and, hence, the long residence time of ground water within them, permit the preservation and (or) allow the formation of iron‐sulfide minerals, including pyrite and marcasite. Both sulfate‐reducing bacteria (SRB) and iron‐reducing bacteria (IRB) are present beneath and beyond the shallow sulfate‐reducing zones. A unique Fe(HI)‐reducing organism, MD‐612, was found in core sediments from a depth of 187 m near the southern shore of Long Island. The distribution of poorly permeable, lignite‐rich, sulfate‐reducing zones with decreased iron concentration is varied within the principal aquifer and accounts for the observed distribution of dissolved sulfate, iron, and iron suit Ides in the aquifer. Locating such zones for the placement of production wells would be difficult, however, because these zones are of limited aerial extent.
A Mathematical Model for the Hydraulic Properties of Deforming Porous Media
Authors: Kim Jun‐Mo , Parizek Richard R. 
Published: August 2005

AbstractA new and relatively simple mathematical model is presented to predict the changes in porosity and saturated hydraulic conductivity that result from the skeletal deformation of porous media. A mathematical expression for the deformation‐dependent porosity is derived from the relationship between porosity and volumetric strain, assuming that the individual solid grains are relatively incompressible or less deformable compared to the solid skeleton of a porous medium. A mathematical expression for the deformation‐dependent saturated hydraulic conductivity is then obtained by substituting the deformation‐dependent porosity into the Kozeny‐Carman equation, assuming that the shape factor of the saturated hydraulic conductivity is independent of the skeletal deformation of the porous medium. To evaluate the effects of the deformation‐dependencies of the hydraulic properties on poro‐elastic consolidation, the mathematical model is applied to two different numerical experiments on fully saturated porous media. The simulation results show that the deformation‐dependencies of the hydraulic properties intrinsically induce hydraulic heterogeneity and nonlinear consolidation, and hence produce different trends than those obtained from analytical or numerical solutions with an assumption of constant hydraulic properties. Although the mathematical model presented in this paper is not applicable to all hydrogeomechanicai phenomena, the methodology should have useful application in many consolidation problems.
Uranium Removal from Ground Water Using Zero Valent Iron Media
Authors: Farrell James , Bostick William D. , Jarabek Robert J. , Fiedor Joseph N. 
Published: August 2005

AbstractRemoval of uranium from contaminated ground water using zero valent iron is currently under evaluation at several U.S. Department of Energy (DOE) facilities. Uranium removal by zero valent iron may occur via adsorption onto iron corrosion products, and by reduction to less soluble valence states by reactions with elemental iron. This research investigated the effects of water chemistry and surface precipitate buildup on the removal of soluble uranium by zero valent iron. Batch testing was performed to assess solution chemistry effects on uranium adsorption to the potential iron corrosion products, magnetite and a mixed valent amorphous iron oxide. Uranium adsorption to the simulated iron corrosion products was highly dependent on pH, and the concentration and speciation of the background electrolyte solution. Uranium removal via reduction by elemental iron closely approximated pseudo‐first‐order removal kinetics, despite the buildup of up to 40,000 monolayers of precipitated uranium on the iron surfaces. This indicates that the rate of uranium removal is not strongly dependent on the thickness of the adsorbed uranium layer. Short‐term rates of uranium reduction were similar for all solutions tested, but long‐term rates were highly dependent on water chemistry. Compared to deionized water, uranium removal rates were increased in sodium chloride containing solutions and reduced in sodium nitrate solutions. The strong influence of water chemistry on long‐term reduction rates indicates that system design will require extnded testing with the ground water of interest.
Significance of Unsaturated Flow and Seepage Faces in the Simulation of Steady‐State Subsurface Flow
Authors: Romanoa Connie G. , Frind Emil O. , Rudolph David L. 
Published: August 2005

AbstractA fully saturated, free‐surface ground water flow model and a variably saturated model are applied to the solution of the free‐surface ground water flow problem in order to determine the influence of the unsaturated flow component on the accuracy of the saturated flow solution and the water balance for homogeneous systems. The significance of the seepage face that must exist to provide a transition between a phreatic surface and a downstream surface water body is also evaluated. A series of simple generic cross‐sectional test cases are used as the basis for the numerical investigations. The fully saturated and variably saturated models used in this study are two‐dimensional Galerkin finite‐element models that incorporate exit seepage face options. The fully saturated solution is found to be almost identical to the variably saturated solution below the water table, the only significant difference being that the variably saturated model predicts a slightly lower water table due to horizontal flow components in the capillary fringe. This difference is negligible for large‐scale systems, snowing that for homogeneous systems, unsaturated flow can be neglected and steady‐state flow including seepage face discharge can be realistically simulated by a fully saturated free‐surface model. For aquifer‐scale systems where discretization limitations may prevent the explicit representation of seepage faces, the seepage face can be omitted because of its negligible influence on the overall water balance at the larger scale.