bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ambiguity in Measuring Matrix Diffusion with Single‐Well Injection/Recovery Tracer Tests
Authors: Lessoff Steven C. , Konikow Leonard F. 
Published: August 2005

AbstractSingle‐well injection/recovery tracer tests are considered for use in characterizing and quantifying matrix diffusion in dual‐porosity aquifers. Numerical modeling indicates that neither regional drift in homogeneous aquifers, nor heterogeneity in aquifers having no regional drift, nor hydrodynamic dispersion significantly affects these tests. However, when drift is coupled simultaneously with heterogeneity, they can have significant confounding effects on tracer return. This synergistic effect of drift and heterogeneity may help explain irreversible flow and inconsistent results sometimes encountered in previous single‐well injection/recovery tracer tests. Numerical results indicate that in a hypothetical single‐well injection/recovery tracer test designed to demonstrate and measure dual‐porosity characteristics in a fractured dolomite, the simultaneous effects of drift and heterogeneity sometimes yields responses similar to those anticipated in a homogeneous dual‐porosity formation. In these cases, tracer recovery could provide a false indication of the occurrence of matrix diffusion. Shortening the shut‐in period between injection and recovery periods may make the test less sensitive to drift. Using multiple tracers having different diffusion characteristics, multiple tests having different pumping schedules, and testing the formation at more than one location would decrease the ambiguity in the interpretation of test data.
Inverse Models: A Necessary Next Step in Ground‐Water Modeling
Authors: Poeter Eileen P. , Hill Mary C. 
Published: August 2005

AbstractInverse models using, for example, nonlinear least‐squares regression, provide capabilities that help modelers take full advantage of the insight available from ground‐water models. However, lack of information about the requirements and benefits of inverse models is an obstacle to their widespread use. This paper presents a simple ground‐water flow problem to illustrate the requirements and benefits of the nonlinear least‐squares regression method of inverse modeling and discusses how these attributes apply to field problems. The benefits of inverse modeling include: (1) expedited determination of best fit parameter values; (2) quantification of the (a) quality of calibration, (b) data shortcomings and needs, and (c) confidence limits on parameter estimates and predictions; and (3) identification of issues that are easily overlooked during nonautomated calibration.
The Role of Bedding Fractures in the Hydrogeology of Sedimentary Bedrock—Evidence from the Newark Basin, New Jersey
Authors: Michalski Andrew , Britton Richard 
Published: August 2005

AbstractBedding‐plane partings, particularly those enlarged by stress relief, tend to provide principal ground‐water flow pathways which are often overlooked. In order to identify them, the use of a proper conceptual model of the bedrock aquifer system and appropriate methods of hydrogeologic characterization are necessary. Several pervasive bedding partings were identified at a study site located within a dipping sequence of mudstone and shales, typical of the Passaic Formation in the Newark Basin of New Jersey. These bedding fractures constitute the discrete aquifer units of a multiunit, leaky bedrock aquifer system. One such unit of exceptional transmissivity (the “Raritan unit”) was identified and selected for a detailed characterization. Results of three short‐duration pumping tests verified the continuity and relatively uniform transmissivity of the Raritan unit over distances exceeding 1,500 feet. Significant hydrochemical differences between the various aquifer units at this 100‐acre site were found to be consistent with the multiunit structure of the bedrock aquifer system. A similar pattern can be observed in regional hydrochemical data recently published by others. The principal finding, that a few bedding fractures dominate ground‐water flow at many sites in the region, has a major implication on hydrogeologic characterization requirements for the water supply, well‐head protection, and aquifer remediation projects in the Newark Basin and similar areas of sedimentary bedrock.
Fractured‐Aquifer Hydrogeology from Geophysical Logs; The Passaic Formation, New Jersey
Authors: Morin Roger H. , Carleton Glen B. , Poirier Stéphane 
Published: August 2005

AbstractThe Passaic Formation consists of gradational sequences of mudstone, siltstone, and sandstone, and is a principal aquifer in central New Jersey. Ground‐water flow is primarily controlled by fractures interspersed throughout these sedimentary rocks and characterizing these fractures in terms of type, orientation, spatial distribution, frequency, and transmissivity is fundamental towards understanding local fluid‐transport processes. To obtain this information, a comprehensive suite of geophysical logs was collected in 10 wells roughly 46 m in depth and located within a .05 km2 area in Hopewell Township, New Jersey. A seemingly complex, heterogeneous network of fractures identified with an acoustic televiewer was statistically reduced to two principal subsets corresponding to two distinct fracture types: (1) bedding‐plane partings and (2) high‐angle fractures. Bedding‐plane partings are the most numerous and have an average strike of N84°W and dip of 20° N. The high‐angle fractures are oriented subparallel to these features, with an average strike of N79° E and dip of 71° S, making the two fracture types roughly orthogonal. Their intersections form linear features that also retain this approximately east‐west strike. Inspection of fluid temperature and conductance logs in conjunction with flow meter measurements obtained during pumping allows the transmissive fractures to be distinguished from the general fracture population. These results show that, within the resolution capabilities of the logging tools, approximately 51 (or 18 percent) of the 280 total fractures are water producing. The bedding‐plane partings exhibit transmissivities that average roughly 5 m2/day and that generally diminish in magnitude and frequency with depth. The high‐angle fractures have average transmissivities that are about half those of the bedding‐plane partings and show no apparent dependence upon depth. The geophysical logging results allow us to infer a distinct hydrogeologic structure within this aquifer that is defined by fracture type and orientation. Fluid flow near the surface is controlled primarily by the highly transmissive, subhorizontal bedding‐plane partings. As depth increases, the high‐angle fractures apparently become more dominant hydrologically.
Plume Distortion and Apparent Attenuation Due to Concentration Averaging in Monitoring Wells
Authors: Martin‐Hayden James M. , Robbins Gary A. 
Published: August 2005

AbstractMathematical models that simulate common monitoring well sampling demonstrate the distortions that vertical concentration averaging causes during the mapping and modeling of an idealized, three‐dimensional contaminant plume emanating from a simple source of constant solute concentration. The apparent extent of the plume, mapped using simulations of a regular grid of screened monitoring wells, ranged from a worst case of 0% of the original plume area for long screens (4 m) in a low‐permeability formation to 90% for short screens (1 m) in a high‐permeability formation. When well design and purging procedure were inconsistent among wells, the mapped plume exhibited spurious directional skewing, bifurcation, zones of low concentration, intermittent sources, or multiple sources. Although the study plume was not retarded, calibrating a transport model to the monitoring well data resulted in retardation factors of up to 23. If first‐order decay was assumed, the apparent decay constant was found to be as much as 1.8 × 10‐7 sec‐1 (T1/2= 45 days). Apparent retardation or decay was inconsistent from well to well, depending on the saturated screen length, the degree of screen desaturation during purging, and the distance from the source. The study indicates that the quantitative assessment of contaminant distributions and transport processes requires discrete vertical sampling in the common situation where concentrations vary sharply with depth, even in the most ideal hydrogeologic environment. If screened monitoring wells are used, screen lengths and placements should be appropriate to the contamination situation being assessed and inherent biases must be considered. Even so, vertical concentration averaging biases and the resulting inconsistencies can result in highly misleading evaluations of ground‐water contamination problems.
Delineating the Chemical Composition of the Salinity Source for Saline Ground Waters: An Example from East‐Central Concordia Parish, Louisiana
Authors: Stoessell Ronald K. 
Published: August 2005

AbstractIn the absence of significant water‐rock interaction, the chemical composition of a saline brine polluting a ground‐water aquifer can be delineated from conservative‐mixing relations. An example is the Mississippi River Alluvium Aquifer, within Angelina Plantation in east‐central Concordia Parish, Louisiana, which has high ground‐water salinities, of unknown origin.Chloride concentrations are linearly correlated with concentrations of major cations and with bromide and iodide. These relationships are consistent with mixing of fresh water with a saline source of either a single brine or multiple brines of similar composition and with a lack of significant water‐rock interactions in the ground water during and after mixing.The saline source has the following predicted mass ratios for a brine containing 80,000 ppm CI: Na/CI, 0.58; Br/CI, 0.0013; I/CI, 0.00028; Sr/CI, 0.0026; K/CI, 0.0035; CaCI, 0.035; and Mg/CI, 0.0080. The predicted 87Sr/86Sr ratio is 0.70805. The mass ratios fall within the range of Tertiary oil‐field brines in the Louisiana Gulf Coast. The major reservoir for hydrocarbon production in the area is the Wilcox Formation; however, the “predicted” source brine is unlikely to be a “pure” Wilcox brine from Concordia Parish. Ratios of 87Sr/86 Sr are usually lower and bromide, iodide, and calcium concentrations are always lower in the Wilcox brines than predicted in the saline source.
Analyses of Slug Tests and Hydraulic Conductivity Variations in the Near Field of a Two‐Well Tracer Experiment Site
Authors: Mas‐Pla Josep , Jim Yeh T.‐C. , Williams Thomas M. , McCarthy John F. 
Published: August 2005

AbstractThree‐hundred eight slug tests were conducted in a 5 × 5 m area in a coastal, sandy aquifer at the Georgetown site in South Carolina to characterize three‐dimensional aquifer heterogeneity. Methods developed by Hvorslev, Bouwer and Rice, and Cooper et al. were employed to estimate hydraulic conductivity values from the slug test data. These three methods produced similar spatial distributions of the hydraulic conductivity but quite different values. Overall, the method of Cooper et al. produces higher conductivity values in high permeability zones but lower values in low permeability areas than the Hvorslev method. Variances of the natural log of conductivity values derived from Hvorslev's and Bouwer and Rice's methods agree with those in the other aquifers under similar depositional environments. However, the variance calculated for the data based on the method of Cooper et al. appears unreasonably large. Despite these differences, histograms of the three sets of conductivity values exhibit bimodal distributions, reflecting stratification of the aquifer. Geostatistical analyses show that correlation lengths and statistical anisotropy of the hydraulic conductivity spatial structure varies with depth.
Patterns and Age Distribution of Ground‐Water Flow to Streams
Authors: Modica Edward , Reilly Thomas E. , Pollock David W. 
Published: August 2005

AbstractSimulations of ground‐water flow in a generic aquifer system were made to characterize the topology of ground‐water flow in the stream subsystem and to evaluate its relation to deeper ground‐water flow. The flow models are patterned after hydraulic characteristics of aquifers of the Atlantic Coastal Plain and are based on numerical solutions to three‐dimensional, steady‐state, unconfined flow. The models were used to evaluate the effects of aquifer horizontal‐to‐vertical hydraulic conductivity ratios, aquifer thickness, and areal recharge rates on flow in the stream subsystem. A particle tracker was used to determine flow paths in a stream subsystem, to establish the relation between ground‐water seepage to points along a simulated stream and its source area of flow, and to determine ground‐water residence time in stream subsystems. In a geometrically simple aquifer system with accretion, the source area of flow to streams resembles an elongated ellipse that tapers in the down gradient direction. Increased recharge causes an expansion of the stream subsystem. The source area of flow to the stream expands predominantly toward the stream headwaters. Base flow gain is also increased along the reach of the stream. A thin aquifer restricts ground‐water flow and causes the source area of flow to expand near stream headwaters and also shifts the start‐of‐flow to the drainage basin divide. Increased aquifer anisotropy causes a lateral expansion of the source area of flow to streams.Ground‐water seepage to the stream channel originates both from near‐ and far‐recharge locations. The range in the lengths of flow paths that terminate at a point on a stream increase in the downstream direction. Consequently, the age distribution of ground water that seeps into the stream is skewed progressively older with distance downstream. Base flow ia an integration of ground water with varying age and potentially different water quality, depending on the source within the drainage basin. The quantitative results presented indicate that this integration can have a wide and complex residence time range and source distribution.
Study on the Contamination of Fracture‐Karst Water in Boshan District, China
Authors: Zhu Xue‐Yu , Xu Shao‐Hui , Zhu Jun‐Jie , Zhou Nian‐Qing , Wu Chun‐Yin 
Published: August 2005

AbstractBoshan is an industrial city in the center of Shandong Province where ground water is the only source for the urban water supply. The major water resource is fracture‐karst water in the middle Ordovician carbonate rocks. Based on the hydrogeological investigation and mapping in this area we studied the geologic and hydrogeologic settings, the major pollution sources and the pathways of contamination, the principal contaminants, and their spatial distribution in ground water. The ground‐water quality has also been estimated by the fuzzy mathematic method. The geostatistical method, such as the kriging method, was taken to simulate spatial distribution of the contaminants. The grey system method was adopted to forecast future contamination. An attempt at the remediation of Cr6+ contamination in fracture‐karst water was also discussed. Finally, some proposals for the protection of the ground‐water environment in Boshan District are offered.
Computer Determination of Aquifer Parameters Using Slope Matching
Authors: Pittenger Robert , Reichard James S. 
Published: August 2005

AbstractVarious numerical methods have been developed to solve aquifer tests and eliminate the subjectivity of traditional graphical type curve methods. The slope‐matching method, which matches the slope of the field data to the slope of the Theis type curve, can be used to numerically solve pump tests for both leaky and non leaky aquifers.The slope‐matching method was selected for implementation into a C/C++ computer program. The computerized version has the following advantages over the original hand calculator version: (1) it eliminates human error inherent in hand calculations; (2) it has the ability to quickly analyze large data sets and large numbers of data sets; and (3) it can be used on portable computers to analyze test data in the field.When performed by hand, the slope‐matching method requires the interpolation of values from tables for values of Theis curve slopes and the Bessel function Ko. For the computer implementation, an iterative “guess‐and‐correct” algorithm was developed to eliminate the need to interpolate from tables.The computer program shows a good correlation with results obtained by hand calculations for both leaky and no leaky aquifers, using the same method. Discrepancies with hand calculations are traced to rounding errors in the estimation of W (u) and elimination of the need to interpolate values from tables.
Modeling Axially Symmetric and Nonsymmetric Flow to a Well with MODFLOW, and Application to Goddard2 Well Test, Boise, Idaho
Authors: Barrash Warren , Dougherty Martin E. 
Published: August 2005

AbstractTools for analyzing aquifer test data at the pumping or injection well are limited for aquifer conditions that are not axially symmetric about the pumping well. Accurate simulations of head change at a pumping well can be generated with MODFLOW using a discretization scheme that (1) captures steep gradients adjacent to the cell(s) containing the pumping or injection well and (2) approximates radial flow despite rectangular prism well cell(s). This scheme is based on a very small incremental cell width adjacent to the pumping or injection well cell, and then a logarithmic increase in cell width outward with the expansion factor, α, in the range of 1.2 to 1.5. The validity of this scheme has been demonstrated by comparing model results with analytical solutions and RADMOD (axisymmetric adaptation of MODFLOW) for three radially symmetric confined aquifer scenarios, and with the analytical solution for a nonaxisymmetric confined aquifer scenario. Utility of this scheme is demonstrated with simulation of time‐drawdown behavior at the Goddard2 pumping well in Boise, Idaho where four observation wells did not respond during a pumping test and where 28.8 m of drawdown occurred in the pumping well during the first 2 min of the test. The hydrogeologic setting for the test is interpreted to be a partially penetrating well pumping from a sand‐stringer aquifer that receives leakage from surrounding finer grained sediments, and includes a fault (no‐flow boundary) truncating the aquifer.
Probabilistic Multiphase Flow Modeling Using the Limit‐State Method
Authors: Xiang Yanyong , Mishra Srikanta 
Published: August 2005

AbstractThis paper presents a study on the application of the limit‐state method for probabilistic multiphase flow modeling. The subsurface multiphase flow and heat transport simulator, TOUGH2 (Pruess, 1991), is combined with a computer shell for reliability analysis, CALREL (Liu et al., 1989). As applications of the combined code, the site at Yucca Mountain, Nevada for a potential high‐level radioactive waste repository is modeled under assumed conditions. The probability distributions of various performance functions (liquid saturation, travel time, and flux) are calculated for statistically described infiltration rate and matrix hydrogeologic parameters. Numerical experiments indicates that the limit‐state method compares fairly well with, and thus can be used as an alternative to, the Monte Carlo method for probabilistic multiphase flow simulations.
Closed‐Form Expressions for Water Retention and Conductivity Data
Authors: Leij Feike J. , Russell Walter B. , Lesch Scott M. 
Published: August 2005

AbstractClosed‐form expressions for quantifying the unsaturated soil hydraulic properties are widely used in computer programs to model subsurface flow and transport in porous media and to investigate indirect methods for estimating these properties. For example, water retention data, which relate soil‐water pressure head (h) and effective water saturation (Se), are frequently used to predict the unsaturated hydraulic conductivity (K). However, the suitability of different functions to describe unsaturated hydraulic data has rarely been investigated comprehensively. We attempted to fit 14 retention and 11 conductivity functions to 903 sets of water retention and hydraulic conductivity data measured on soil and rock samples or horizons reported in the unsaturated hydraulic database UNSODA. Some of the best mean values for r2 and MSE for fitting Se(h) data were obtained with the retention functions reported by van Genuchten (1980), Globus (1987), and Hutson and Cass (1987). A function reported by Gardner (1958) could describe K (h) data quite well whereas functions reported by Brooks and Corey (1964) and van Genuchten (1980), which are respectively based on the conductivity models by Burdine and Mualem, yielded a relatively good description of K(SC) data.
Transmissivity in the Geothermal Euganean Basin: A Geostatistical Analysis
Authors: Fabbri Paolo 
Published: August 2005

AbstractThis paper presents a geostatistical analysis of transmissivity in the Euganean geothermal field (northeast Italy). Few transmissivity values are known while specific capacity values are more common. However, transmissivity is more important than specific capacity in the characterization of aquifers. In this work, therefore, after a simple statistical analysis, an empirical relation with a high determination coefficient (r2= 0.95) is found between the above values. Subsequently, In T structural characteristics of the variable are studied by variogram analysis, identifying a second‐order pseudostationarity and two geometrical anisotropies. The second‐order pseudostationarity and the variogram fit allow a linear kriging procedure to be used to produce a map of transmissivity and kriging standard deviation of the Euganean geothermal field. The fit between geostatistical and hydrogeological analyses shows that a geostatistical approach is useful for both mapping purposes and hydrogeological interpretation.
GIBBTEQ: A MINTEQA2 Thermodynamic Data Error Detection Program
Authors: Onysko Steven J. , McNearny Richard L. 
Published: August 2005

AbstractThe U.S. Environmental Protection Agency geochemical computer code MINTEQA2 contains over 1, 500 aqueous species entries with stoichiometric, thermodynamic, and gram formula weight data. GIBBTEQ is a LOTUS 123 program that scans MINTEQA2 data base entries and directly identifies errors in stoichiometry, species charge, and formula weight. GIBBTEQ indirectly facilitates identification of errors of equilibrium and enthalpy data in MINTEQA2 data base entries by printing those entries in readable format. Anomalies of equilibrium constant, standard free energy and enthalpy of mineral species, and redox potential (for electron‐containing reactions) are amenable to user detection in the program output. MINTEQA2 errors of various types are quantified from GIBBTEQ results. Program availability inquiries can be sent via e‐mail to gibbteq@mines.utah.edu.