bluuebunny/crossref_metadata_2025_split huggingface dataset:
Uncertainty Analyses of Unsaturated Zone Travel Time at Yucca Mountain
Authors: Nichols William E. , Freshley Mark D. 
Published: August 2005

AbstractUncertainty analysis methods can be applied to numerical models of ground‐water flow to estimate the relative importance of physical and hydrologie input variables with respect to ground‐water travel time. Monte Carlo numerical simulations of unsaturated flow in the Calico Hills nonwelded zeolitic (CHnz) layer at Yucca Mountain, Nevada, indicate that variability in recharge, and to a lesser extent in matrix porosity, explains most of the variability in predictions of water travel time through the unsaturated zone. Variations in saturated hydraulic conductivity and unsaturated curve‐fitting parameters were not statistically significant in explaining variability in water travel time through the unsaturated CHnz unit. The results of this study suggest that the large uncertainty associated with recharge rate estimates for the Yucca Mountain site is of concern because the performance of the potential repository would be more sensitive to uncertainty in recharge than to any other parameter evaluated. These results are not exhaustive because of the limited site characterization data available and because of the preliminary nature of this study, which is limited to a single stratigraphie unit, one dimension, and does not account for fracture flow or other potential fast pathways at Yucca Mountain.
A Program to Analyze Aquifer Test Data and Check for Validity with the Jacob Method
Authors: Field Malcolm S. 
Published: August 2005

AbstractThe Jacob straight‐line method of aquifer analysis deals with the late‐time data and small radius of the Theis type curve which plot as a straight line if the drawdown data are plotted on an arithmetic scale and the time data on a logarithmic (base 10) scale. Correct analysis with the Jacob method normally assumes that (1) the data lie on a straight line, (2) the value of the dimensionless time factor is less than 0.01, and (3) the site's hydrogeology conforms to the method's assumptions and limiting conditions. Items 1 and 2 are usually considered for the Jacob method, but item 3 is often ignored, which can lead to incorrect calculations of aquifer parameters. A BASIC computer program was developed to analyze aquifer test data with the Jacob method to test the validity of its use. Aquifer test data are entered into the program and manipulated so that a slope and time intercept of the straight line drawn through the data (excluding early‐time and late‐time data) can be used to calculate transmissivity and storage coefficient. Late‐time data are excluded to eliminate the effects of positive and negative boundaries. The time‐drawdown data then are converted into dimensionless units to determine if the Jacob method's assumptions are valid for the hydrogeologic conditions under which the test was conducted.
Estimating Movement of Ground Water from a Pond or Large‐Radius Conduit
Authors: Brikowski T. 
Published: August 2005

AbstractEvaluation of ground‐water exchange between ponds or large‐radius conduits and surrounding aquifers is a common problem in contaminant migration studies. Analytic solutions are useful tools for this evaluation, particularly when the system is incompletely characterized. Solutions are derived below for application to ponds, lakes, and natural or artificial conduits with a known discharge/recharge flux. General features of migration in this setting are determined by the ratio of pond flux (source/sink) to regional flux crossing the pond boundary. When this ratio is large (pond dominates) the effect of the pond is indistinguishable from a well. At intermediate values, movement from the pond against the regional flow is inhibited, and discharge plumes are shifted downgradient relative to those for a well. At small ratios only a narrow plume will emerge from the downgradient side of a discharging pond, considerably narrower but longer than predicted for a well of the same strength.
Coupled Simulation‐Optimization Modeling for Municipal Ground‐Water Supply Protection
Authors: Varljen Mark D. , Shafer John M. 
Published: August 2005

AbstractA technique based on numerical ground‐water flow modeling and unconstrained nonlinear optimization has been developed to provide guidance for protecting municipal ground‐water supplies from contamination through capture zone management. The technique involves conventional finite‐difference ground‐water flow modeling and numerical flowpath/travel time calculation coupled with nonlinear mathematical programming. The objective of the technique is to specify pumping rates for wells in a wellfield such that the configuration of capture zones in relation to existing potential sources of contamination minimizes the risk of contamination while maintaining the required total water output from the wellfield. An important feature of the technique is its ability to incorporate realistic boundary conditions, complicated aquifer configurations, and spatially varying aquifer properties to whatever degree site‐specific data are available. Also, the technique is implemented on a personal computer. This approach to ground‐water supply protection enhances conventional wellhead protection area delineation because a greater level of protection can be achieved if potential contaminant sources are not even included in capture zones, rather than attempting to reduce the threat of those sources. The effectiveness of the technique was verified through application to a hypothetical ground‐water system. Practical aspects were demonstrated with an application in Pékin, Illinois. These efforts demonstrate the utility of an innovative modeling technique in ground‐water quality protection.
Extension of the Method of Characteristics for Simulation of Solute Transport in Three Dimensions
Authors: Zheng C. 
Published: August 2005

AbstractThe method of characteristics (e.g., Garder et al., 1964; Konikow and Bredehoeft, 1978) has been widely used in the simulation of solute transport in ground‐water systems because of its effectiveness for handling advection‐dominated problems. However, the method requires a large amount of computer memory and execution time when it is necessary to track a large number of moving particles, especially in three dimensions. The method can also lead to large mass balance discrepancies under certain circumstances. This paper describes a number of changes which may be made in the traditional method of characteristics approach to mitigate these difficulties. These changes include a dynamic particle allocation procedure, which often reduces dramatically the total number of moving particles needed in a simulation; and a consistent velocity interpolation scheme and higher‐order particle tracking techniques, which, coupled with effective handling of particle insertion and deletion at sources and sinks, can provide improved mass balance results. The accuracy of a method‐of‐characteristics model incorporating these changes is evaluated by comparison with analytical solutions for (1) three‐dimensional advection and dispersion in a spherical flow field, and (2) concentration change in a well during an injection/pumping cycle.
Simulation of Cylindrical Flow to a Well Using the U.S. Geological Survey Modular Finite‐Difference Ground‐Water Flow Model
Authors: Reilly Thomas E. , Harbaugh Arien W. 
Published: August 2005

AbstractCylindrical (axasymmetric) flow to a well is an important specialized topic of ground‐water hydraulics and has been applied by many investigators to determine aquifer properties and determine heads and flows in the vicinity of the well. A recent modification to the U.S. Geological Survey Modular Three‐Dimensional Finite‐Difference Ground‐Water Flow Model provides the opportunity to simulate axisymmetric flow to a well. The theory involves the conceptualization of a system of concentric shells that are capable of reproducing the large variations in gradient in the vicinity of the well by decreasing their area in the direction of the well. The computer program presented serves as a preprocessor to the U.S. Geological Survey model by creating the input data file needed to implement the axisymmetric conceptualization. Data input requirements to this preprocessor are described, and a comparison with a known analytical solution indicates that the model functions appropriately.
Henry Darcy and the Fountains of Dijon
Authors: Freeze R. Allan 
Published: August 2005

AbstractThe life and career of Henry Darcy are intimately connected with the city of Dijon. He was born there; he died there; and it was there that he carried out the experiments that have brought him lasting fame. Darcy was not an obscure scientist; he was a well‐known and respected public figure. His efforts as an engineer and advocate put Dijon on the main line of the Paris‐Lyon railway, and brought a modern water‐distribution system to Dijon some 25 years before such a system was put in place in Paris. During his life he received great honors, suffered political persecution, and carried out his most productive research in his later years despite ill health. He died at the relatively young age of 55. The main square in the city of Dijon is named Place Darcy in his honor.
Correlation Between DRASTIC Vulnerabilities and Incidents of VOC Contamination of Municipal Wells in Nebraska
Authors: Kalinski Robert J. , Kelly William E. , Bogardi Istvan , Ehrman Richard L. , Yaniamoto Paul D. 
Published: August 2005

AbstractBecause it considers basic hydrogeologic variables believed to influence contaminant transport from surface sources to ground water, the DRASTIC method can be a valuable tool for identifying ground‐water supplies that are vulnerable to contamination. Theoretically, areas with high DRASTIC scores should have more frequent occurrences of ground‐water contamination events than areas with low scores given similar land use, well construction, and well densities. Relationships between DRASTIC scores and incidents of contamination, however, have not been extensively documented. In Nebraska, significant positive correlation appears to exist between incidents of VOC contamination of ground‐water supplied community water systems and the relative hydrogeologic vulnerability of surficial aquifers as quantified with the DRASTIC method. These results provide a means of verifying the usefulness of planning tools such as DRASTIC for identifying areas where water supplies are most vulnerable to contamination from surface sources.
Comparison of Modeled Disposal Well Plumes Using Average and Variable Injectate Densities
Authors: Larkin Randall G. , Clark James E. , Papadeas Philip W. 
Published: August 2005

Abstract“No Migration” Petitions must be submitted by operators of Class I hazardous disposal wells to apply for an exemption from the federal land ban restrictions on the disposal of hazardous waste. In many Class I disposal well operations, the injectate density can vary daily and usually has a different density than the native formation brine. The influence of the density contrast on the fluid potential must be included in a “No Migration” Petition modeling demonstration. After the model wells (s) is shut‐in, the density contrast results in a net updip (lower density injectate) or downdip (higher density injectate) component of flow near the center of mass of the calculated plume (neglecting regional flow). In many cases, two model runs are required: one using the lowest anticipated injectate density and one using the highest anticipated injectate density for the entire modeled operational period. This was intended to provide adequate plume delineation over the injectate density range and implies that buoyancy effects on the plume position are not related to the average density. Three separate cases of a two‐dimensional generic numerical model were used to examine buoyancy effects using constant and variable injectate density input values. Case 1 used a random selection of the daily variation about the mean density, and case 2 used correlated daily injectate densities over a five day period. The model calculated concentrations from cases 1 and 2 were compared to the results from a third case that used the mean density input value for the entire operational period. The calculated plume extent for all three cases is virtually identical for simulation times up to 10,000 years. The modeling results demonstrate that using a long‐term average injectate density in “No Migration” Petition modeling rather than the range of extreme values may be justifiable by operators of Class I injection well facilities.
Estimation of Residual Dense NAPL Mass by Inverse Modeling
Authors: Butcher Jonathan B. , Gauthier Thomas D. 
Published: August 2005

AbstractGround water at many sites is contaminated by chlorinated solvents which are of relatively low solubility and denser than water, as well as other contaminants of similar properties. The presence of a dense nonaqueous phase liquid (DNAPL) in an aquifer can provide continued flux to the dissolved phase long after the initial discharge. The flux may be significant even when the nonaqueous phase has dispersed to a state of residual saturation, in which little or no free product can be detected or recovered. At an industrial site we required an estimate of the magnitude of a DNAPL source without undertaking invasive exploration. In theory, the presence and magnitude of a residual DNAPL source can be inferred from observations of downgradient concentrations by (1) developing an inverse modeling solution to estimate flux, and (2) matching estimated flux to a conceptual model of NAPL dissolution, which yields an estimate of residual mass. Such a method can provide a qualitative indication of the presence of a residual DNAPL source. However, the sensitivity of the solution to assumptions regarding physical characteristics of the source medium are such that a useful quantitative estimate cannot be made without observations over long periods of time.
Ground‐Water Tracing with Injected Helium
Authors: Gupta S. K. , Lau L. Stephen , Moravcik Philip S. 
Published: August 2005

AbstractHelium has several characteristics that make it attractive for use as a tracer in hydrological studies. Two types of experiments were conducted to investigate applicability of helium as a tracer of ground‐water movement. The experiments included studies using laboratory sand and soil columns and field ground‐water tracing in a basaltic aquifer. A water helium analyzer comprised of a thin quartz glass membrane and diode ion pump (making use of the preferential permeation of helium through the quartz glass into an evacuated space) was developed and used for the experiments.Results of our studies demonstrated that breakthrough curves of specific conductance and helium were similar under saturated conditions. In the unsaturated sand/soil columns, breakthrough curves of helium were retarded relative to specific conductance reducing the usefulness of helium as a tracer.
Recovery Performance for Vertical and Horizontal Wells Using Semianalytical Simulation
Authors: Cleveland Theodore G. 
Published: August 2005

AbstractA semianalytical transient expression was used to evaluate the performance of a finite‐length horizontal well as compared to a vertical well in a hypothetical recovery scenario. Recovery was simulated in two hypothetical confined aquifers to study the effect of aquifer thickness and well orientation on recovery performance. The results show that horizontal wells can initially mobilize larger volumes of ground water (and contaminants) but that vertical wells have the same ultimate recovery ability in a homogeneous, isotropic medium.
Modeling Ground‐Water Remediation in the High Plains Aquifer
Authors: Mergia Girma , Kelly William E. 
Published: August 2005

AbstractThe Princeton Transport Code (PTC), a three‐dimensional finite‐element flow and transport model, was used to evaluate contaminant movement and recovery in the vicinity of a manufacturing facility in western Nebraska. The modeling was complicated by seasonal recharge from a nearby irrigation canal, a drainage ditch flowing across the site, municipal wells pumping at variable rates and screened at different levels in the underlying semiconfined aquifer, and the pumping of the three high‐capacity wells being used to recover contaminated ground water. The flow model was calibrated in several steps: steady‐state calibration using the unstressed (no pumping) conditions; steady‐state calibration using the prerecovery pumping conditions; and finally, transient calibration using results obtained for the early recovery pumping period–first for the nonirrigation season and then for the irrigation season. The calibrated flow model was further tested by simulating transport during the early stages of the recovery pumping.
Relation Between Hydraulic Conductivity and Texture in a Carbonate Aquifer: Regional Continuity
Authors: Rovey Charles W. , Cherkauer Douglas S. 
Published: August 2005

AbstractIn the dolomite aquifer of Milwaukee County, Wisconsin, stratigraphic units deposited as mudstones have little or no visible macroporosity and, based on injection‐pressure tests, have average horizontal hydraulic conductivities of approximately 10−6 cm/sec, controlled by jointing. Coarse‐grained units (packstones and grainstones), however, have horizontal hydraulic conductivities of 10−4 cm/sec and greater, argued to be controlled by granularity, not jointing. Using this relationship between texture and hydraulic conductivity in Milwaukee County and a sedimentary facies analysis, trends in hydraulic conductivity values are predicted for five stratigraphic units over an area of approximately 3500 km2. The predictions are tested qualitatively with sets of specific capacity values within the various stratigraphic units, and quantitatively with injection‐pressure test values from five additional locations. Seven of eight qualitative and four of six quantitative predictions are judged to be successful. Therefore, trends in hydraulic conductivity, and to some extent local values, in this carbonate aquifer are predictable over areas of thousands of square kilometers without any site‐specific data on jointing.The success rate could not have been this high if hydraulic conductivity were not controlled by the granularity of the lithologic units. It is argued, therefore, that the local bulk hydraulic conductivity of this carbonate aquifer is controlled by the granular porosity, and the aquifer will generally behave as a porous medium, even at the small scale of a typical pumping test.
Nonlinear Adsorption of Uranyi: Analytical Modeling of Liner Migration
Authors: Johnson Robert O. 
Published: August 2005

AbstractThis paper is concerned with establishing the breakthrough time for leachate to migrate out of waste facilities containing large quantities of low‐level, radioactive uranium. The impoundments have clay liners which adsorb uranyl cations dissolved in the leachate. A nonlinear isotherm, derived from a consideration of the phenomenological basis and chemical kinetics of the adsorption process, is used in conjunction with a time‐dependent, one‐dimensional species transport equation to develop a mathematical expression for the retarded migration time interval. The nonlinear transport equation is identical to one occurring in theoretical gas dynamics for the description of shock waves, and whose solution is well‐known. Results indicate that large breakthrough time‐interval errors can arise if a linear isotherm is used to model the adsorption process, particularly if leachate concentrations along the floor of the pit are near saturation. Conversely, at dilute concentrations, computations based on the linear isotherm underpredict the time interval required for the onset of leakage. The underprediction is acceptable from an engineering viewpoint because environmental protection afforded by the liner is not overstated.
Analysis of In Situ Permeability Tests in Nonpenetrating Wells
Authors: Avci Cem B. 
Published: August 2005

AbstractRecent interest in ground‐water contamination problems has led to a renewed interest in the development of accurate procedures for the analysis of in situ permeability tests. The present study involves the derivation of analytical procedures for slug tests and constant head tests performed in wells with casings open at the bottom and installed flush with the upper confining boundary of a finite‐depth, anisotropic, homogeneous aquifer; the analysis takes into account the effects of a finite‐thickness skin located at the casing bottom. The Laplace transform is used on the governing ground‐water flow equations to derive the transform of time‐dependent water levels measured in the casing. The expression is numerically inverted back into the real time domain to obtain (1) a set of dimensionless type curves for analyzing slug test data, and (2) a relation between the inflow rate, the head maintained in the well, the hydraulic conductivity, and a shape factor expression for the analysis of constant head data. Existing methods of analysis are reviewed and compared with the presently derived analytical procedures.
Two‐Dimensional Dispersivity Estimation Using Tracer Experiment Data
Authors: Zou S. , Parr A. 
Published: August 2005

AbstractThis paper presents two analytical methods for estimating longitudinal and transversal dispersivities for a two‐dimensional plume generated by a slug tracer injection in a uniform ground‐water flow field. The first method requires the mapped plume area measurements at a given time after the tracer sources are injected. The second method requires concentration versus time data from one sampling well through which the plume passes. Detailed example calculations and comparisons with other procedures show that the methods presented herein represent improvements in both accuracy and ease of use over previous methods.
A Laboratory Analysis of the Effect of Macropores on Solute Transport
Authors: Wildenschild D. , Jensen K. H. , Villholth K. , Illangasekare T. H. 
Published: August 2005

AbstractMacropores play an important role in many soils in relation to ground‐water contamination by providing preferential pathways from the root zone to the water table. Surface‐applied agrochemicals may hereby be carried quickly to the shallow ground water. The reduced retention combined with a small contact area between the flowing water and the soil implies that little removal from physical, chemical, and microbiological processes may take place, thus increasing the risk of ground‐water contamination.A laboratory procedure for evaluating the effect of macropores in a given soil is proposed and tested. The procedure involves the following sequence of experiments on two undisturbed soil monoliths: (1) measurements of the distribution of outflow, (2) measurements of breakthrough curves, (3) dye application for visual observation of macropores; and (4) horizontal slicing of the monoliths to measure macropore distribution and continuity of macropores. The experimental procedure is based on well‐documented techniques that combined will provide evidence on the significance of macropores in relation to ground‐water contamination and guidance for selecting the appropriate model for simulating flow and transport at the field in question.The laboratory procedure was tested on two large, undisturbed soil monoliths (30 cm in diameter) removed from the unsaturated zone at a clayey moraine agricultural field in Denmark. This soil was known to have many macropores. The investigations documented the strong influence of these structures on flow and transport suggesting that a traditional flow and transport model would be inadequate for simulating the processes occurring in the field.