bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Tidal Fluctuation on a Coastal Aquifer in the UK
Authors: Erskine A. D. 
Published: August 2005

AbstractTidal fluctuation is shown to affect the piezometer readings taken in a nearshore aquifer around a working nuclear power station. Continuous monitoring of a network of 40 piezometers provided relations between the tidal cycle and the piezometer readings. These relations can be expressed in terms of a time lag and amplitude scaling factor. Using these parameters, tidal interference was filtered from the day‐to‐day piezometer readings. The early detection of ground‐water drawdown below the working station caused by construction of a new nuclear power station on an adjacent site could thus be achieved.In parallel with the field work, the theoretical relationship between the tide and piezometric response was shown to be of the same form as that observed in the field. Values of the aquifer characteristics could then be deduced and compared with those measured in conventional pumping tests. The transmission of the pressure oscillation is shown to be faster in areas of higher permeability and in the deeper parts of the aquifer. This second effect is thought to be caused by the presence of the phreatic surface.
Semianalytical Solutions for Radial Dispersion in a Three‐Layer Leaky Aquifer System
Authors: Chen Chia‐Shyun 
Published: August 2005

AbstractWaste water injected into aquifers bounded by aquitards can potentially leak into the aquitards and eventually reach other layers. Based on the mathematical framework of an earlier model, the current study deals with steady‐state and transient solutions for solute transport from an injection well into a three‐layer leaky aquifer system consisting of a pumped and an unpumped aquifer separated by an aquitard. Solutes are assumed to be transported by horizontal advection within the pumped aquifer, by advection and dispersion in a vertical flow field in the aquitard, and by molecular diffusion under hydrostatic conditions in the unpumped aquifers. Proper leaky aquifer well hydraulics are used to describe the ground‐water flow fields in the model, and radioactive (biological) decay and linear isotherm adsorption are considered. This model study shows that adsorption in the pumped aquifer has an overall retardation effect on solute movement in the whole system. Adsorption in the aquitard does not significantly affect solute movement in the pumped aquifer. Type curves are prepared to indicate whether the unpumped aquifer would be contaminated by the injection into the pumped aquifer. Pumping rate is an important hydraulic factor determining the leakage conditions of an aquifer (in addition to some hydrogeological conditions of the systems). Analytical solutions are obtained for steady‐state conditions. For transient conditions, however, only semianalytical solutions can be determined by numerically inverting the solutions of the model in the Laplace transform domain.
Some Additional Nonparametric Prediction Limits for Ground‐Water Detection Monitoring at Waste Disposal Facilities
Authors: Gibbons Robert D. 
Published: August 2005

AbstractIn a previous paper Gibbons (1990) derived nonparametric prediction limits that are applicable to ground‐water monitoring applications. The nonparametric prediction limit was defined as the maximum of n historical measurements (e.g., taken from upgradient wells), denoted X(max, n), and was designed to include one of m future measurements in each of k monitoring wells. In this way, an owner /operator who failed an initial sample but passed any one of m −1 resamples would be considered in compliance. In this paper, these limits are modified so that m −1 out of m future measurements in each of k monitoring wells are included. In this way, the owner/operator is required to pass allm −1 resamples in order to demonstrate compliance in the event of an initial failure. The paper provides a detailed tabulation of confidence levels corresponding to selections of n (4‐100), k (1‐100), and m (2‐4). Power characteristics of the nonparametric approach relative to the parametric alternative are presented for cases in which the assumed distribution is correct and incorrect.
Revisiting the Membrane Analog—A Conceptual and Communication Tool
Authors: Arnold Forest 
Published: August 2005

AbstractMembrane analogs were used before the advent of computers as physical models of stresses on the water‐table surface. Measurement of the membrane deflection can be related to equations representing pumping stresses. Although numerical models using computer techniques have replaced membrane analogs due to their greater accuracy and versatility, the mem brane analog remains an inexpensive way to conceptualize the effect of different boundary conditions, nearby surface‐water bodies and pumping stresses, and is useful in preparing input data sets for numerical modeling. The membrane analog is also a visual way to communicate modeling results and modeling scenarios to nonmodelers. A small office‐sized membrane analog can be constructed for less than $25.00 and can be stored on a shelf or under a desk, for ready access.
Assessing Transmissivity from Specific Capacity in a Large and Heterogeneous Alluvial Aquifer
Authors: Razack M. , Huntley David 
Published: August 2005

AbstractTransmissivity is often estimated from specific capacity data because of the expense of conducting standard aquifer tests to obtain transmissivity and the relative availability of specific capacity data. Most often, analytic expressions relating specific capacity to transmissivity derived by Thomasson and others (1960), Theis (1963), or Brown (1963) are used in this analysis. This paper focuses on a test of these relations using a large (215 pairs) data set from a heterogeneous aquifer.The analytic solutions predicting transmissivity from specific capacity do not agree well with the measured transmissivities, apparently due to turbulent well loss within the production wells, which is not taken into account by any of the analytic solutions. Empirical relations are better than the theoretical relations. Log‐log functions have greater correlation coefficients than linear functions. The best relation found for the data set chosen for this study has a correlation coefficient of 0.63, but the prediction interval was about 1.2 log cycles, indicating that the range of probable transmissivities corresponding to a single specific capacity was more than one order of magnitude. Tests with smaller subsets of data suggest that correlations based on data sets of 10 points or less are of limited value.
Coincidence of Well Fields and Tectonic Basins in the Precambrian Shield Area of Southeast Botswana
Authors: Dietvorst E.J.L. , De Vries J. J. , Gieske A. 
Published: August 2005

AbstractA compilation of ground‐water exploration data in southeastern Botswana reveals that the occurrence of ground water is not primarily controlled by large‐scale fracture systems and lithologies, but by folds in the Precambrian basement. Two sets of superimposed synforms and antiforms generate a “chess‐board” pattern of dome and basin structures. Successful boreholes and well fields appear to be preferentially situated in the areas where synforms intersect, suggesting that tectonic basins coincide with ground‐water basins. Small‐scale fractures and favorable lithologies doubtless improve the permeability within a ground‐water basin, but appear to be subordinate in determining the distribution of large‐scale aquifer characteristics.
Thermodynamic Framework for Evaluating PAH Degradation in the Subsurface
Authors: McFarland Michael J. , Sims Ronald C. 
Published: August 2005

AbstractA method is presented to evaluate the influence of redox conditions and pH on mineralization of polycyclic aromatic hydrocarbons (PAH) in subsurface environments. Microbial yields based on the free energy liberated from heterotrophic PAH metabolism are estimated under various environmental conditions using a simple bioenergetic growth model. The types and chemical forms of electron acceptors addressed in this paper include oxygen, nitrate, sulfate, carbon dioxide, iron (Fe+3and FeOOH), and manganese (Mn+4 and MnO2). PAHs addressed include naphthalene (2‐fused aromatic rings), anthracene (3‐fused aromatic rings), phenanthrene (3‐fused aromatic rings), and pyrene (4‐fused aromatic rings).Calculated free energy changes demonstrated that sequential utilization of electron acceptors will follow the order Mn+4, O2, NO3−1, Fe+3, MnO2, FeOOH, SO4−2, and CO2. The behavior in microbial growth yield predictions were found to mimic the change in free energy liberated with the use of different electron acceptors. Despite release of free energy under all conditions evaluated, the small energy liberated during PAH mineralization under sulfate‐reducing and methanogenic conditions suggests that heterotrophic degradation of PAH compounds under these conditions is unlikely to occur.The large microbial growth yields associated with reduction of free metal species (Mn+4, Fe+3) during PAH oxidation suggest a selective advantage for microbes that can tolerate acid conditions and/or participate in metal chelation processes.
Slug Tests with Storage Due to Entrapped Air
Authors: Keller C. Kent , van der Kamp G. 
Published: August 2005

AbstractAny air entrapped in the completion region of a piezometer endows that piezometer with storage due to the compressibility of the air. Such storage retards the recovery of water levels in the piezometer and leads to underestimation of formation hydraulic conductivity in the interpretation of slug tests. These effects appear to be greatest for piezometers with small‐diameter casings installed in low‐permeability formations where filter pack materials are placed dry around the piezometer intake. This paper presents (a) a method which accounts for storage due to entrapped air in slug test analysis; (b) examples illustrating the method; and (c) some recommendations for piezometer construction and slug test practice.
Difluorobenzoates as Nonreactive Tracers in Soil and Ground Water
Authors: Bowman Robert S. , Gibbens Joseph F. 
Published: August 2005

AbstractOver the past 10 years, several fluorinated derivatives of benzoic acid have proven their usefulness as nonreactive water tracers. In this study, the suitability of four previously untested isomers of difluorobenzoate (DFBA) as saturated‐ and unsaturated‐zone tracers was examined in a series of laboratory and field experiments. Experimental conditions included batch shaking tests with two different soils, laboratory soil column tests under saturated and unsaturated conditions, a three‐month aquifer tracer test, and a month‐long tracer test in a field soil. Bromide, which is considered nonreactive in most hydrological environments, was included as an index tracer in each experiment. Under every condition, each DFBA isomer snowed the same concentration distribution and mass recovery as Br. These and other previously tested fluorobenzoates were ranked according to their suitability as nonreactive soil and ground‐water tracers.
Competitive Exclusion of Sulfate Reduction by Fe(lll)‐Reducing Bacteria: A Mechanism for Producing Discrete Zones of High‐Iron Ground Water
Authors: Chapelle Francis H. , Lovley Derek R. 
Published: August 2005

AbstractThe Middendorf aquifer of South Carolina exhibits a 40‐kilometer‐wide zone where dissolved ferrous iron concentrations commonly exceed 1 mg/I. Downgradient of this zone, dissolved iron concentrations decrease to less than 0.05 mg/1. Geochemical and microbiologie evidence indicates that this zonation reflects the competitive exclusion of sulfate‐reducing activity by Fe(IH)‐reducing bacteria in the high‐iron zone and the emergence of sulfate reduction as the predominant process in the low‐iron zone. Viable Fe(III)‐ and sulfate‐reducing bacteria coexist throughout the aquifer. However, the observed linear relationship between dissolved iron and dissolved inorganic carbon as well as the lack of sulfate consumption indicates that sulfate‐reducing bacteria are much less active than Fe(III)‐reducing bacteria in the high‐iron zone. Fe(III)‐reducing bacteria appear to exclude sulfate‐reducing activity by maintaining dissolved hydrogen (˜1.0 nM), formate (˜2.0 μM), and acetate (˜1.0 μM) concentrations at levels lower than thresholds required by sulfate‐reducing bacteria. Downgradient of the high‐iron zone, Fe(III)‐reducing activity becomes limited by a lack of Fe(III) oxyhydroxides as Middendorf sediments become progressively more marine in origin. Hydrogen, formate, and acetate concentrations then increase to levels (˜3.0 nM, ˜10.9, and 2.5 μM, respectively) that allow sulfate‐reducing bacteria to become active. Increased sulfide production strips ferrous iron from solution by precipitating ferrous sulfides, and dissolved iron concentrations decrease. The observed high‐iron zonation is thus one manifestation of microbial competition for scarce substrates. The wide occurrence of similar water‐chemistry patterns implies that microbial competition mechanisms are important to the ground‐water geochemistry of many hydrologie systems.
Comparison Between Model Simulations and Field Results for In‐Situ Biorestoration of Chlorinated Aliphatics: Part 2. Cometabolic Transformations
Authors: Semprini Lewis , McCarty Perry L. 
Published: August 2005

AbstractA nonsteady‐state model is presented and used in simulating the results of field experiments where chlorinated ethenes were cometabolically degraded by methanotrophic bacteria. In cometabolism, contaminants are degraded fortuitously by microbes growing on a primary substrate, which in this case is methane. The model includes microbial processes of microbial growth, utilization of the electron donor (methane) and the electron acceptor (oxygen), and the cometabolic transformation of the chlorinated ethenes coupled with the transport processes of advection, dispersion, and sorption onto the aquifer solids.Model simulations of the chlorinated ethenes biotransformation resulting from the biostimulation of methanotrophic bacteria agreed well with the field observations. A kinetic model for the cometabolic transformation that included the competitive inhibition by methane was required to match the field observations. The simulations duplicated the cyclic oscillations in concentration of the chlorinated ethenes that resulted from the pulse feeding of methane. Rate‐limited sorption and desorption were also required in order to match the extended tailing in the concentration response that was observed along with the pulsed oscillations in the concentration due to competitive inhibition.The kinetic parameters for the cometabolic transformation, derived from model fits to the field observations, differed for the different chlorinated ethenes tested. Vinyl chloride (VC) and trans‐dichloroethylene (t‐DCE) had the highest biotransformation rate coefficients (k/Ks), which were in the range of methane itself, the primary substrate for methanotrophic growth. Cis‐dichloroethylene (c‐DCE) and trichloroethylene (TCE) were degraded at rates one and two orders of magnitude lower than methane, respectively. The transformation rate for TCE was consistent with laboratory‐derived rates from microbes enriched and isolated from the test zone and grown under conditions that most represented those in the field. The kinetic model also permitted the activation and the deactivation of microbial mass towards the cometabolic transformation, which was based on cell growth and decay, and first‐order deactivation.
Unsteady Ground‐Water Flow Toward Extended Wells
Authors: Sen Zekâi 
Published: August 2005

AbstractGround‐water flow in naturally fractured rocks of low permeability terrain presents special problems which cannot be solved by classical radial flow techniques. Existence of fractures in these rocks increases the conductivity of the media, but the storativity does not increase significantly. Especially, a dominant vertical fracture in hydraulic connection with a well provides an extended surface for ground water to enter the well. Such a well and fracture combination is referred to as an “extended well.” The analytical approach to the ground‐water flow problem of extended wells cannot be achieved through merely radial or linear flow alone if the vertical fracture is of finite length. In fact, in practice, the fracture lengths are almost always of finite length, and the flow pattern is a mixture of radial and linear flows. This paper presents a simplified conceptual model for the ground‐water flow pattern around an extended well leading to an analytical solution with type curves which can be used in determining the aquifer parameters from the field measurements of time‐drawdown data. It is observed that for large times, extended well type curves merge with the Theis curve, and consequently the Jacob straight‐line method becomes applicable. In addition, as the vertical fracture length becomes smaller, the resulting type curve approaches the Theis type curve. The methodology has been applied for ground‐water flow in a folded and fractured limestone formation in the Conasauga Group of East Tennessee.
Simulation of Tidal Effects on Contaminant Transport in Porous Media
Authors: Yim Chan S. , Mohsen M.F.N. 
Published: August 2005

AbstractA one‐dimensional numerical model is developed with oscillating velocities and dispersions to simulate the migration process of a contaminant plume within tidally influenced aquifers. Model simulations demonstrate that a major effect the tidal fluctuation has on the migration process of a contaminant plume is the exit concentration discharging to the tidal estuary. Tidal fluctuation causes the exit concentration levels to be significantly diluted by the surface‐water body of the estuary. Sensitivity analyses demonstrate that tidal fluctuation hastens the rate of plume migration near the bank of the estuary because of the relatively high advective and dispersive fluxes induced by tides. However, tides affect the migration process only over a short distance from the tidal‐water interface (about 40 ft for the parameters used in this study). If the contaminant plume is located far beyond the interface, tidal fluctuations will not affect the rate of plume migration until an existing regional ground‐water flow velocity brings the plume to the tidally active zone. With or without tides, the rate of contaminant migration increases with higher regional hydraulic gradient. Furthermore, the effects of tidal fluctuations on the transport process become insignificant with higher regional hydraulic gradients.
Influence of Pore Pressure on Apparent Dispersivity of a Fissured Dolomitic Aquifer
Authors: Leap Darrell I. , Belmonte Pamela Mai 
Published: August 2005

AbstractThe U.S. Geological Survey's Amargosa Tracer Calibration Site in southern Nevada has been used for three different recirculating tracer tests using as tracers: (1) tritium, (2) sulfur‐35, and (3) tritium and bromide together. Although the physical setup, well spacings, and thus apparent scale were the same in all tests, the recirculating rates and pore pressures were different. Apparent dispersivities found in the three tests differed considerably, revealing an inverse relationship between computed dispersivity and recirculation rate. These differences are believed to be caused primarily by changes in fissureaperture widths and thus, hydraulic conductivities, with resulting changes in flow rates and directions caused by changes in pore pressure between different tests in the presence of high ambient pore pressure. The results of this study indicate that forced‐gradient tracer tests for determination of dispersivity should not be performed when ambient pore pressure and/or testing pore pressure is a significant percentage of overburden pressure. In addition, apparent dispersivity calculated by forced‐gradient tracer tests can differ considerably from that of unstressed natural situations, and consequent solute‐transport estimates are likely to be in error.
Hydrogeological Decision Analysis: 4. The Concept of Data Worth and Its Use in the Development of Site Investigation Strategies
Authors: Freeze R. Allan , James Bruce , Massmann Joel , Sperling Tony , Smith Leslie 
Published: August 2005

AbstractIn the design of new waste‐management facilities, or in the remedial design for contaminated facilities, there are economic tradeoffs possible between the resources assigned to site investigation, facility design, and site monitoring. Hydrogeological decision analysis provides a framework that allows a sequential, iterative approach to design, in which data acquisition through site investigation alternates with economic analysis of alternative design options. In this framework, the purpose of collecting hydrogeological data is to aid in the making of decisions between the alternative design options. Such decisions are made on the basis of a risk‐cost‐benefit objective function. Additional measurements have worth only if the risk reduction they provide exceeds the cost of obtaining them. The location of measurement points in a site‐investigation network should minimize economic regret with respect to design decisions. This paper provides an introduction to the concepts of data‐worth analysis for two cases: (1) the reduction of uncertainty in aquitard continuity, and (2) the reduction of uncertainty in hydraulic‐conductivity distribution in an aquifer. It is shown how the use of search theory and Bayesian updating can be applied in comparing prior and preposterior analyses to provide a stopping rule for the collection of additional data in site investigation programs at a hypothetical landfill site.
Aquifer Analysis and Modeling in a Fractured, Heterogeneous Medium
Authors: Lee R. R. , Ketelle R. H. , Bownds J. M. , Rizk T. A. 
Published: August 2005

AbstractA ground‐water flow and contaminant transport modeling study was performed at a proposed low‐level radioactive waste disposal site on the Department of Energy's Oak Ridge Reservation to assess the accuracy of a computer simulation of the flow field in the shallow water‐table aquifer. The migration of a ground‐water tracer, under controlled field conditions, was used as a comparative benchmark of solute transport simulations assuming different aquifer characteristics. A conventional approach to aquifer analysis and modeling, which assumed the domain to be homogeneous with low anisotropy, resulted in an inaccurate simulation of tracer migration. Alternative conceptual models were formulated which considered the effects of geologic heterogeneities on tracer migration which could be verified by additional data acquisition and analysis. Application of the alternative concepts in numerical modeling resulted in more accurate simulations of tracer migration. These results suggested that local geology created discrete flow pathways oriented oblique to the maximum gradient which were unresolved in conventional aquifer analysis. Results of the study showed that standard approaches to aquifer analysis and computer modeling are crudely representative of the flow field and provide nonconservative estimates of contaminant transport at the scale of a waste disposal unit. By adopting an iterative approach to site characterization, conceptual model formulation, and numerical modeling, the level of resolution provided by a ground‐water tracer was accurately simulated.