bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Ground‐Water Flow Modeling of the Snake River Plain Aquifer Using the Superposition Technique
Authors: Hubbel J. M. , Bishop C. W. , Johnson G. S. , Lucas J. G. 
Published: August 2005

AbstractPredictive ground‐water flow modeling may be simplified by application of superposition when the governing equations are linear. The simplification allows evaluation of impacts of individual aquifer stresses and minimized model input, output, and interpretation. Modeling is performed by using (1) boundary conditions and aquifer properties provided by previous calibrations or analytical techniques, (2) setting the initial potentiometric surface and prescribed‐head boundaries to an arbitrary horizontal datum, and (3) simulating a specific recharge or discharge stress.Superposition was applied to an existing, calibrated model of the Snake River Plain aquifer to simplify prediction of changes in interaction with the Snake River. Simulations predict the temporal relationships between ground‐water use at multiple locations within the Snake River Plain and surface‐water depletion in four hydraulically connected reaches of the Snake River. Simulated aquifer water use at a location approximately five miles from a hydraulically connected river reach results in river depletions greater than 80% of the pumping rate after 10 years. Water use further than 50 miles from hydraulically connected river reaches results in depletions from 10 to 30% of the annual average pumping rate after 100 years. Results present spatial and temporal impacts of water uses on the Plain that are conceptually and quantitatively beneficial to water resources planners and water users.
A Direct Substitution Method for Multicomponent Solute Transport in Ground Water
Authors: Shen Huiying , Nikolaidis Nikolaos P. 
Published: August 2005

AbstractA numerical method was developed using a direct substitution approach for simulating one‐dimensional multicomponent solute transport in ground water. The method has the ability to treat equilibrium reactions of aqueous and surface complexation, and precipitation‐dissolution. The concentrations of aqueous component species, adsorbed component species, and precipitated species are chosen as the principal dependent variables. The substitution takes place after the transport equation is discretized. The resulting system of equations is solved using the Newton‐Raphson method and the Jacobian matrix is computed analytically. This method is computationally more efficient than sequential iteration methods due to its faster convergence rate. It is also computationally more efficient than other direct substitution methods which compute the Jacobian matrix numerically.
Incorporating Auxiliary Geophysical Data into Ground‐Water Flow Parameter Estimation
Authors: Cassiani Giorgio , Medina Miguel A. 
Published: August 2005

AbstractThe incorporation of auxiliary data into ground‐water flow parameter estimation is a challenging task which can ultimately result in a better site characterization. In this study a maximum likelihood estimation procedure has been applied to the joint identification of the parameters of the aquifer transmissivity random field, and the parameters of the linear regression between the logarithm of transmissivity and the logarithm of the electrical transverse formation factor (TF), determined from surface geoelectrical methods (Vertical Electrical Sounding or V.E.S.). This approach is basically a co‐kriging technique applied to the transmissivity and transverse formation factor random fields, but it avoids the independent estimation of the cross‐covariances and the secondary variable covariance. The procedure needs some direct well data for transmissivity and a (usually larger) number of V.E.S. measurements which have to be in part at a distance from the well locations in order to provide useful information. The algorithm determines the characteristics of the local (site dependent) transmissivity‐transverse formation factor relationship and utilizes this auxiliary information for a geostatistical transmissivity field estimation. The methodology is tested on a real field scenario: a fractured aquifer impacted by landfill leachate contamination. The use of the formation factor in place of the raw resistivity of the subsoil layers accounts for possible effects of clay and contaminant concentration on pore‐water resistivity. The information provided by the V.E.S. can add, to some extent, to the understanding of the aquifer characteristics and vulnerability. However, the specificity of each site has to be fully understood for an effective application of the present procedure. It seems unlikely that geoelectric data can differentiate between transmissivity values differing by less than two or three orders of magnitude.
Capture Zones for Passive Wells in Heterogeneous Unconfined Aquifers
Authors: Cole Bryce E. , Silliman Stephen E. 
Published: August 2005

AbstractMany piezometers/wells produce at such low rates and frequency that their impact on local hydraulics is negligible, e.g. monitoring piezometers or homeowner wells installed in highly permeable soils. Defining a deterministic capture zone for such wells is often of limited utility as the capture zone is effectively a single flow line directed upgradient. In order to provide more insight into the capture zone of such wells, a statistically based capture zone, termed a “percentile capture contour” (PCC), is introduced and analyzed. The capture zone is defined by quantifying, for a given travel time, the variation of the length and orientation of the flow line emanating upgradient from the well. Capture zone variation herein depends on second‐order stationary random hydraulic conductivity fields and is calculated using Monte Carlo analysis.Monte Carlo analysis yielded increases in mean travel distances as the variance and/or integral scale in log K increased, but decreases as the angle between the principal direction of the correlation structure and the regional flow increased. The average travel distance exceeded the travel distance estimated by a homogeneous solution using the geometric mean hydraulic conductivity. Transverse variation depended both on the variance and integral scale of log K, but was insensitive to the orientation of the principal correlation direction. The mean orientation of the flow path varied with the principal direction of the correlation structure, deviating up to 20° from the orientation of the hydraulic gradient. These observations are consistent with flow following preferential pathways and indicate that significant uncertainty exists for source prediction of water feeding passive wells.
Numerical Simulation of Air Sparging for Remediation of NAPL Contamination
Authors: McCray John E. , Falta Ronald W. 
Published: August 2005

AbstractA numerical simulation study of air sparging for the removal of nonaqueous phase liquids (NAPLs) from the subsurface is presented. These simulations were performed using the T2VOC integrated finite‐difference, multiphase‐flow, contaminant transport code. The code is used to model two‐dimensional air sparging experiments from Ji et al. (1993) which include both homogeneous and heterogeneous permeability distributions. The model predicts the experimental gas plume shape and behavior very well. Field‐scale simulations using a radially symmetric, cylindrical mesh are then used to model hypothetical DNAPL and LNAPL spills and air sparging remediation performance in various hydrogeologic settings. Both homogeneous and heterogeneous systems are considered. The results of the study indicate that the sparging‐induced gas pressure increase, or “positive pressure,” measured at steady state below the water table, closely corresponds to both the subsurface gas distribution and the effective zone of contaminant reduction. Because this positive pressure is easily measured in the field with a simple monitoring device, it can be used to realistically define the sparging radius of influence.
A Framework for Assessing Risk Reduction Due to DNAPL Mass Removal from Low‐Permeability Soils
Authors: Freeze R. Allan , McWhorter David B. 
Published: August 2005

AbstractMany emerging remediation technologies are designed to remove contaminant mass from source zones at DNAPL sites in response to regulatory requirements. There is often concern in the regulated community as to whether mass removal actually reduces risk, or whether the small risk reductions achieved warrant the large costs incurred. This paper sets out a proposed framework for quantifying the degree to which risk is reduced as mass is removed from DNAPL source areas in shallow, saturated, low‐permeability media. Risk is defined in terms of meeting an alternate concentration limit (ACL) at a compliance well in an aquifer underlying the source zone. The ACL is back‐calculated from a carcinogenic health‐risk characterization at a down gradient water‐supply well. Source‐zone mass‐removal efficiencies are heavily dependent on the distribution of mass between media (fractures, matrix) and phase (aqueous, sorbed, NAPL). Due to the uncertainties in currently available technology performance data, the scope of the paper is limited to developing a framework for generic technologies rather than making specific risk‐reduction calculations for individual technologies. Despite the qualitative nature of the exercise, results imply that very high total mass‐removal efficiencies are required to achieve significant long‐term risk reduction with technology applications of finite duration. This paper is not an argument for no action at contaminated sites. Rather, it provides support for the conclusions of Cherry et al. (1992) that the primary goal of current remediation should be short‐term risk reduction through containment, with the aim to pass on to future generations site conditions that are well‐suited to the future applications of emerging technologies with improved mass‐removal capabilities.
A Method for Evaluation of Artificial Recharge Through Percolation Tanks Using Environmental Chloride
Authors: Sukhija B. S. , Reddy D. V. , Nandakumar M. V. , Rama  
Published: August 2005

AbstractFor meeting the growing demand on ground water in hard rock areas of India, man‐made percolation tanks have become important structures for augmenting ground‐water recharge. Keeping in view their increasing number and cost involved in their construction and their temporal variation in percolation due to silting or desilting operations if undertaken, it is vital to develop proper methodology to evaluate the performance of these structures. A method employing the mass balance of environmental chloride in the tank has been developed for this purpose. The results obtained using this method at one experimental site indicate that an average of 30–35% of impounded water is recharged through this structure situated in granitic gneissic terrain of a semiarid region of India. The remainder is lost through evaporation. The method developed is simple, inexpensive, and sensitive enough to observe the temporal variation in the recharge rate through such tanks.
Transient Ground‐Water Flow Simulation Using a Fuzzy Set Approacha
Authors: Dou Chunhua , Woldt Wayne , Dahab Mohamed , Bogardi Istvan 
Published: August 2005

AbstractThe expense of characterizing aquifer spatial variability often results in a lack of available or realistically obtainable direct measurement data for ground‐water system simulation. As a consequence ground‐water models that are able to utilize imprecise or “soft” information need to be developed. In this paper, a methodology based on fuzzy set theory is developed to incorporate imprecise data into transient ground‐water flow simulation. The imprecise model parameters may come from indirect measurements, expert judgment, and subjective interpretation of available information. Fuzzy numbers are used to represent imprecise parameters. They are also used as a measure of the uncertainty associated with the hydraulic head due to the imprecision of input data. A fuzzy ground‐water flow model is developed by linking the finite‐difference method with fuzzy number representations. Fuzzy number operations (α‐level cuts) are used to solve the resulting fuzzy ground‐water flow model and are extended to consider the dependencies among hydraulic head coefficients. With the fuzzy number inputs, the transient fuzzy ground‐water flow model provides a direct measure of hydraulic head uncertainties in the time domain. The model outputs can be used as the inputs for subsequent risk analysis and decision‐making processes. The fuzzy modeling technique can handle imprecise information directly without generating a large number of realizations. It is also flexible as it can handle different types of membership functions describing fuzzy input parameters. The methodology can be used to combine data with different levels of quality into ground‐water flow models and provides a realistic method to handle parameter imprecision, especially expert judgment and subjective information. A numerical model based on the methodology was tested against the Theis analytical solution for a homogeneous aquifer with pumping. The tested model was also applied to two different heterogeneous flow fields to demonstrate the methodology.
Geoelectrical and Hydrogeochemical Studies for Delineating Ground‐Water Contamination Due to Salt‐Water Intrusion in the Northern Part of the Nile Delta, Egypt
Authors: Ebraheem Abdel‐Azim M. , Senosy Mahmoud M. , Dahab Kamal A. 
Published: August 2005

AbstractA resistivity survey was conducted in the Nile Delta area to delineate ground‐water contamination caused by an improper sewage and irrigation drainage system, leaching from old lagoonal deposits, and salt‐water intrusion. Existing monitoring wells were used to measure the horizontal and vertical variations in water salinity. Vertical electrical sounding (VES) data for sounding points located near monitoring wells, together with the water salinity data of these wells, were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used together with the constructed apparent resistivity depth and geoelectric longitudinal sections to identify three zones of water‐bearing formation (fresh‐, brackish‐, and salt‐water zones). Along the studied profile, depth to the fresh‐brackish interface exceeds 150 m at Tanta City and decreases northward to 40 m or less between Qutor and Kafr El‐Sheikh. Depth to the brackish‐saline interface exceeds 180 m south of Kafr‐El‐Sheikh and decreases northward to 70 m near Hadadi village.
Potential Inaccuracies in MODFLOW Simulations Involving the SIP and SSOR Methods for Matrix Solution
Authors: Osiensky James L. , Williams Roy E. 
Published: August 2005

AbstractThe ground‐water flow model MODFLOW is the most widely used and accepted model of its type in the world today. Several modeling runs were completed with MODFLOW for relatively simple hydrogeologic conditions to evaluate the accuracy of the strongly implicit procedure (SIP), slice successive overrelaxation (SSOR) and preconditioned conjugate‐gradient 2 (PCG2) methods for matrix solution. A series of simulations was performed with the SIP, SSOR, and PCG2 methods while adjusting the matrix solution parameters sequentially one at a time. A wide range of converged solutions was generated for identical input data. The simulation results show that MODFLOW will produce accurate results for the specific conditions simulated with PCG2, or with SIP if the proper combination of SIP matrix solution parameters is chosen by the user. Accurate results could not be obtained with SSOR for any of the combinations of matrix solution parameters used in this investigation. The simulation results confirm that model convergence for a small head change convergence criterion is not a good indicator of accurate results unless water balance error also is small.
Analytical Mass Leaching Model for Contaminated Soil and Soil Stabilized Waste
Authors: Shackelford Charles D. , Glade Michael J. 
Published: August 2005

AbstractAn analytical model for evaluating mass leaching from contaminated soil or soil stabilized waste is presented. The model is based on mass transport due to advection, dispersion, and retardation and can be used to evaluate the suitability and/or efficiency of soil washing solutions based on the results of column leaching studies. The model differs from more traditional models for column leaching studies in that the analysis is based on the cumulative mass of leachate instead of leachate concentration. A cumulative mass basis for leaching eliminates the requirement for determination of “instantaneous” effluent concentrations in the more traditional column leaching approach thereby allowing for the collection of relatively large effluent volumes. The cumulative masses of three heavy metals—Cd, Pb, and Zn—leached from two specimens of soil mixed with fly ash are analyzed with the mass leaching model to illustrate application and limitation of the model.
Influence of Viscous, Gravitational, and Capillary Forces on DNAPL Saturation
Authors: Dawson Helen E. , Roberts Paul V. 
Published: August 2005

AbstractFour dense nonaqueous phase liquids (DNAPLs)—bromoform, chlorobenzene, tetrachloroethylene, and trichloro‐ethylene—were used to investigate the influence of viscous, gravitational, and capillary forces on DNAPL saturation in a natural aquifer sand. The relative magnitudes of these forces are expressed in terms of two dimensionless groups, the Capillary Number (NCa), defined as the ratio of the viscous force to capillary force, and the Bond Number (NBo), defined as the ratio of the gravitational force to capillary force.Nondimensionalization of the equations governing two‐phase flow suggests that DNAPL saturation should be a function of a linear combination of the Capillary and Bond Numbers (NCa/krw— NBo), provided the permeability to water (krw) in the presence of discontinuous DNAPL is considered. Experimental studies in which DNAPL saturations were measured over a range of Capillary and Bond Numbers for upward, horizontal, and downward displacement of DNAPL by water corroborate the results of the nondimensionlization. DNAPL saturations generally decreased with increasing Capillary Number and with decreasing Bond Number until NCa/krw— NBo was greater than approximately 1 × 10‐5 at which point residual saturation was attained. For the DNAPLs used in this study, with adhesion tensions on the order of 26 dynes/cm and Bond Numbers ranging from 1.3 × 10‐7 to 2.4 × 10‐6, residual saturation was attained at Capillary Numbers greater than approximately 5 × 10‐5. These results provide a means of estimating the system conditions under which the DNAPLs studied achieve residual saturation in aquifer material.
Estimating Ground‐Water Recharge from Streamflow Hydrographs for a Small Mountain Watershed in a Temperate Humid Climate, New Hampshire, USA
Authors: Mau David P. , Winter Thomas C. 
Published: August 2005

AbstractHydrographs of stream discharge were analyzed to determine ground‐water recharge for two small basins draining into Mirror Lake, New Hampshire. Two methods of hydrograph analysis developed for determining ground‐water recharge were evaluated, the instantaneous recharge method and the constant recharge method. For the instantaneous recharge method, recharge is assumed to be instantaneous and uniform over the basin. For the constant recharge method, recharge is assumed to be constant and uniform over the basin for a period of weeks to months. Both methods require that a ground‐water recession slope be determined. The recession slope is used directly in the calculation for the instantaneous recharge method, and it is used as a base of reference for fitting a type curve in the constant recharge method. Results of the study indicated that the estimates of ground‐water recharge for both methods agree to within about 10 percent. Two approaches to the instantaneous recharge method, manual and automated, were also evaluated, and the results were statistically similar.The baseflow component of streamflow commonly is assumed to be equivalent to ground‐water recharge; therefore, two methods developed for determining the baseflow component of streamflow, graphical partitioning and digital filtering, were evaluated also. Baseflow values determined by graphical partitioning of hydrographs were about 25 percent less than the ground‐water recharge values. Baseflow values determined by two different approaches to the mathematical digital filtering method were generally less than baseflow determined by graphical partitioning. However, one of the approaches to digital filtering agreed reasonably well with graphical partitioning if an appropriate filter constant was used. The other approach to digital filtering resulted in baseflow values that were much less than the other baseflow values and was therefore deemed inappropriate for use on these small mountain watersheds.
Analytic Modeling of Impermeable and Resistant Barriers
Authors: Fitts Charles R. 
Published: August 2005

AbstractSuperpositioned analytic functions are used to efficiently and accurately model ground‐water flow fields containing thin barriers such as slurry walls and sheet‐pile walls. Barriers are modeled as a series of straight‐line segments strung together to create irregularly shaped open or closed boundaries with zero thickness. The complex analytic functions employed provide perfect continuity of flow across the boundary while approximating normal flux boundary conditions along the boundary. Along an impermeable boundary the normal flux is specified as zero, and along a resistant (leaky) barrier the normal flux is proportional to a specified resistance parameter and the potential difference across the boundary. Solution of a given flow problem requires solving a system of equations with one equation per boundary corner. These equations are linear for impermeable boundaries and for resistant boundaries in confined aquifers or single‐strata unconfined aquifers. In other cases, the boundary condition equations associated with resistant barriers can be nonlinear and a new technique for iterative solution is employed. Implementation of these techniques in a computer program is tested and it is demonstrated by modeling various configurations of flow funneled into a gap between two barriers.
Durov Plot: A Computer Program for Processing and Plotting Hydrochemical Data
Authors: Al‐Bassam Abdulaziz M. , Awad Hussein S. , Al‐Alawi Jomaah A. 
Published: August 2005

AbstractThe expanded Durov diagram has been widely used to represent the dissolved constituents of natural water and to show plausible hydrochemical processes occurring within the hydrological systems. Because of the time required to calculate Durov diagram coordinates and to plot the points, especially when dealing with large numbers of chemical analyses, the treatment of such data is often quite a tedious process. To alleviate this problem, DurovPlot program is designed to help users in calculating and plotting the diagram in a very short time. The program is written in BASIC as a special menu‐driven hydrochemical data analyses code. It was compiled using Microsoft QuickBASIC version 4.5 compiler. The utilization of this program requires the acquisition of an IBM‐PC or compatible with at least 512K bytes of memory, one disk drive (at least 360K bytes), a graphic card (EGA or VGA), and at least DOS version 5.0. DurovPlot possesses several advantages such as the ease with which the data can be entered, edited, and retrieved. The results of computation and plotting are obtained in seconds, depending on the amount of data analyzed and the speed of the computer processor.