bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical Leaching Near the Waiawa Shaft, Oahu, Hawaii: 2. Modeling Results
Authors: Loague Keith , Miyahira Robert N. , Green Richard E. , Oki Delwyn S. , Giambelluca Thomas W. , Schneider Randi C. 
Published: August 2005

AbstractThis paper is the second part of a two‐part series concerned with assessing the potential for organic chemical leaching to a ground‐water skimming tunnel in the Pearl Harbor Basin, Oahu, Hawaii, as a direct result of proposed urban development. The Pesticide Root Zone Model (PRZM) was used, after testing with field and laboratory data described in the companion paper, to make long‐term predictions of the movement of chlorpyrifos, diazinon, metribuzin, and nitrate under various recharge scenarios. The PRZM simulations revealed that, with the exception of chlorpyrifos, detectable levels of all the chemicals considered in this study may leach through the unsaturated zone to the water table from where they may eventually migrate to the skimming tunnel. The simulated concentrations in leachate reaching the water table were sufficiently low, considering subsequent mixing in the ground water, to suggest no adverse health effects. The reliability of the simulated results are laced with enough uncertainty, however, to suggest the need for monitoring for diazinon, metribuzin, and nitrate, if development does proceed. The methodology presented in this series is a first attempt at establishing a protocol for using numerical modeling, supported by field and laboratory measurements to aid in land‐use change consideration in Hawaii when nonpoint ground‐water contamination from organic chemicals is of concern.
A Program to Calculate Ground‐Water Mound Heights
Authors: Finnemore E. John 
Published: August 2005

AbstractMounding of the ground‐water table beneath recharge sources may be of concern where the raised water table approaches too closely to near‐surface facilities or features. Because of its high accuracy and wide range of applicability, the method of Hantush is probably the most widely used to calculate the time‐varying heights of ground‐water mounds on extensive and near‐horizontal saturated zones. Use of that method entails a number of inconveniences, however, including function evaluations and two‐dimensional interpolations between tabulated values, which must be performed iteratively. A FORTRAN computer program was developed to rapidly perform the necessary iterations and to evaluate some rather long and complex equations. These equations avoid the need for interpolation or other approximation procedures, and they provide accurate calculations for all conditions. Comparison of results from the computer program with results from approximation procedures indicates the areas and extents of the unreliability of the approximation procedures.
Program to Calculate Hydraulic Conductivity Using Dugwell Recovery Data
Authors: Lalwani Anil , Kulkarni Himanshu , Deolankar S. B. , Thomas P. Paul 
Published: August 2005

AbstractDUGREC is a computer program to estimate hydraulic conductivities for the Deccan basalts of India. Large‐diameter dugwells are still a very common source of water supply in the Deccan basaltic region of west‐central India. It is easier to conduct accurate recovery tests rather than conventional pumping tests on large‐diameter dugwells in the Deccan basalts of India. DUGREC is a program written in BASICA for IBM PC microcomputers and compatibles to calculate hydraulic conductivity values for the shallow unconfined Deccan basaltic aquifers using dugwell recovery data.
Geochemical Indicators of Intrinsic Bioremediation
Authors: Borden Robert C. , Gomez Carlos A. , Becker Mark T. 
Published: August 2005

AbstractA detailed field investigation has been completed at a gasoline‐contaminated aquifer near Rocky Point, NC, to examine possible indicators of intrinsic bioremediation and identify factors that may significantly influence the rate and extent of bioremediation. The dissolved plume of benzene, toluene, ethylbenzene, and xylene (BTEX) in ground water is naturally degrading. Toluene and o‐xylene are most rapidly degraded followed by m‐, p‐xylene, and benzene. Ethylbenzene appears to degrade very slowly under anaerobic conditions present in the center of the plume. The rate and extent of biodegradation appears to be strongly influenced by the type and quantity of electron acceptors present in the aquifer. At the upgradient edge of the plume, nitrate, ferric iron, and oxygen are used as terminal electron acceptors during hydrocarbon biodegradation. The equivalent of 40 to 50 mg/I of hydrocarbon is degraded based on the increase in dissolved CO2 relative to background ground water. Immediately downgradient of the source area, sulfate and iron are the dominant electron acceptors. Toluene and o‐xylene are rapidly removed in this region. Once the available oxygen, nitrate, and sulfate are consumed, biodegradation is limited and appears to be controlled by mixing and aerobic biodegradation at the plume fringes.
The Correlation Between Bedrock Uranium and Dissolved Radon in Ground Water of a Fractured Carbonate Aquifer in Southwestern Ohio
Authors: Gall Ivan K. , Ritzi Robert W. , Baldwin A. Dwight , Pushkar Paul D. , Carney Cindy K. , Talnagi Joseph F. 
Published: August 2005

AbstractTwo hypotheses have previously been proposed for the source of elevated radon in ground water of southwestern Ohio: (1) penecontemporaneous uranium at the Silurian‐Ordovician unconformity, and/or (2) parent radionuclides transported from fragments of uranium‐rich Ohio Shale within the glacial drift above the aquifer. To further test the first hypothesis, vertical profiles of dissolved radon in ground water and uranium in rock cores were obtained at two locations immediately underlain by the Silurian/Ordovician unconformity. Radon concentrations exceeding 1000 pCi/l occurred in zones where the bedrock had uranium concentrations greater than 1.5 ppm. Radon concentrations of less than 500 pCi/l occurred in zones where the rock had uranium concentrations below 0.25 ppm. A log‐linear regression model between uranium and radon had a correlation coefficient of 0.82. Three aspects of the results support the hypothesis that the source is transported, although not necessarily from fragments of Ohio Shale. First, the high uranium‐radon zones did not occur consistently or exclusively at the Silurian/Ordovician unconformity. Second, the high uranium‐radon zones are correlated to fracture zones having a higher hydraulic conductivity and thus appear to be related to the zones of greater flow and transport. Third, the amount of uranium‐radon disequilibrium increases exponentially with increasing hydraulic conductivity. The hypothesis of a penecontemporaneous source, not supported by our study, arose when previous investigators conducted regional surveys of domestic wells and springs and found a correspondence between elevated radon and the location of the Silurian‐Ordovician unconformity. The observations of the previous investigators can be explained by the fact that the basal Silurian is in some places a horizon of higher hydraulic conductivity that facilitates transport. The two most probable external sources of uranium would be uranium‐containing detritus in the glacial drift or uranium‐containing phosphate fertilizers spread on the surface. Given that the uranium was transported into the aquifer during the Holocene, it could not have generated enough radium in the time elapsed since entering the aquifer to produce the radon levels that were measured. This observation indicates that radium was cotransported with uranium into the zones of high radon.
Analytical Solutions for Gas Flow Due to Gas Injection and Extraction from Horizontal Wells
Authors: Falta Ronald W. 
Published: August 2005

AbstractAnalytical solutions are developed for modeling the transient and steady‐state gas pressure and the steady‐state streamfunction fields resulting from gas injection and extraction from a pair of parallel horizontal wells. These solutions apply to cases in which the ground surface is open to the atmosphere, and in which the porous media is anisotropic but homogeneous. By neglecting end effects due to the finite length of the wells, the three‐dimensional gas flow field is approximated as a two‐dimensional cross section perpendicular to the wells. These solutions may be used to develop estimates of the horizontal well system behavior and to analyze horizontal well gas pump tests, and are useful for numerical model verification.
Modeling of Contaminant Movement Near Pumping Wells: Saturated‐Unsaturated Flow with Particle Tracking
Authors: Akindunni Festus F. , Gillham Robert W. , Conant Brewster , Franz Thomas 
Published: August 2005

AbstractA transient axisymmetric saturated‐unsaturated numerical flow model was coupled with a particle tracking model to investigate the movement of contaminants when a shallow unconfined aquifer is pumped at a constant rate. The particle tracking model keeps track of locations and masses of solutes in the aquifer, and the time of capture by the well. At the end of each time‐step the flow model solves the Richard's equation for the hydraulic head distribution from which elemental velocities are calculated. Solutes are then displaced for a period equivalent to the time‐step using both the magnitude and direction of the elemental velocities. Numerical experiments were performed to investigate effluent concentrations in wells with screens of different length and in different positions relative to zones of stratified contamination. At early times of pumping the effluent concentrations were similar to the concentrations adjacent to the well screen, but at late times, the concentrations approached the vertically averaged concentration in the aquifer. Time to attain the vertically averaged concentration was determined by the well geometry, initial location of the contaminant plume in relation to the well screen, and hydraulic properties of the aquifer. The results are consistent with the hydraulics of flow to a pumping well and of particular importance, they demonstrate that short‐term pump tests could give erroneous design concentrations for pump‐and‐treat systems. The model provides a means of quantifying arrival times and mixing ratios. It could therefore provide a useful means of designing production wells in aquifers with stratified contamination and more efficient recovery systems for aquifer remediation.
Characterization of High‐K Pathways by Borehole Flowmeter and Tracer Tests
Authors: Young Steven C. 
Published: August 2005

AbstractThis paper reviews different borehole flowmeter analysis methods and evaluates their applicability to a test site composed of fluvial deposits. Results from tracer and aquifer tests indicate that the aquifer is highly heterogeneous and that low‐K skin effects exist at the wells. Borehole flowmeter tests were performed at 37 wells. An appropriate method for calculating borehole flowmeter K values was developed based on results from multiwell pumping tests, single‐well pumping tests, and slug tests. The flowmeter data produced 881 K values. The trends and the magnitude of the K values are consistent with results from geologic investigations, recirculating tracer tests, and large‐scale multiwell pumping tests. The field tests illustrate that high‐K deposits can significantly affect ground‐water flows in some heterogeneous fluvial aquifers.
Evaluation of Ground‐Water Contamination from Nonpoint Sources: A Case Study
Authors: van den Brink Cors , Zaadnoordijk Willem J. 
Published: August 2005

AbstractIn many countries a substantial part of the drinking‐water supply comes from subsurface‐water resources. During the last several decades an increasing extent of diffuse pollution has endangered these water resources. Knowledge of the changes in ground‐water quality is necessary in order to know if, and to what extent, ground‐water quality is endangered.Changes in ground‐water quality can be predicted by means of models describing both the ground‐water flow and the transport of contaminants. A Geographic Information System is an efficient tool to handle the storage and manipulation of the large amount of data needed for the description of diffuse pollution. A methodology to predict changes in ground‐water quality, which is called FLUNIT, has been built around the programs FLUZO, NITRON, ARC/INFO, dBASE, and WELCON, and the ground‐water flow package TRIWACO. The method runs on a PC (with 386 processor).The system has been applied to a well field on Csepel Sziget (near Budapest, Hungary). The purpose was not so much the prediction of the ground‐water quality, but much more the evaluation of ground‐water protection strategies based on risk analysis and effectivity of possible measures. The system has been designed in such a way that the important information can be used with the available resolution, and that new and more detailed data can be added efficiently.Change of the nitrogen concentrations in the extracted water can be predicted. The resolution is sufficient for the evaluation of alternative ground‐water protection strategies. Moreover, detailed insight into changes in ground‐water quality can be obtained quickly.
Location of Water Table by FEM and Verification by Electrical Analogy Experiments
Authors: Rao H. Suresh , Sankaranarayanan S. 
Published: August 2005

AbstractSheet piles are used to lower the water table that exists downstream of a sheet pile. Under certain conditions of the upstream water heads and sheet pile embedment depths, a free boundary in the form of the water table may occur on the downstream. This free boundary is not known a priori and must be determined as a part of the solution; to make this possible, additional boundary conditions need to be satisfied on the free boundary. Analytical solutions are readily available for the location of such water tables, but with the impervious bottom located at infinite depth and for rectilinear boundary geometry. In the present study, the location of the water table downstream of a sheet pile with the impervious bottom located at finite depth is obtained using Finite‐Element Method (FEM). An experimental solution using electrical analogy is attempted to validate the solution obtained using FEM. Parametric studies are also carried out to study the various parameters affecting the location of the water table.
Combining the Neuman and Boulton Models for Flow to a Well in an Unconfined Aquifer
Authors: Moench Allen F. 
Published: August 2005

AbstractA Laplace transform solution is presented for flow to a well in a homogeneous, water‐table aquifer with noninstanta‐neous drainage of water from the zone above the water table. The Boulton convolution integral is combined with Darcy's law and used as an upper boundary condition to replace the condition used by Neuman. Boulton's integral derives from the assumption that water drained from the unsaturated zone is released gradually in a manner that varies exponentially with time in response to a unit decline in hydraulic head, whereas the condition used by Newman assumes that the water is released instantaneously. The result is a solution that reduces to the solution obtained by Neuman as the rate of release of water from the zone above the water table increases. A dimensionless fitting parameter, γ, is introduced that incorporates vertical hydraulic conductivity, saturated thickness, specific yield, and an empirical constant α1, similar to Boulton's α. Results show that theoretical drawdown in water‐table piezometers is amplified by noninstantaneous drainage from the unsaturated zone to a greater extent than drawdown in piezometers located at depth in the saturated zone. This difference provides a basis for evaluating γ by type‐curve matching in addition to the other dimensionless parameters. Analysis of drawdown in selected piezometers from the published results of two aquifer tests conducted in relatively homogeneous glacial outwash deposits but with significantly different hydraulic conductivities reveals improved comparison between the theoretical type curves and the hydraulic head measured in water‐table piezometers.
Effect of Well‐Screen Placement on Recovery of Vertically Stratified Contaminants
Authors: Conant Brewster , Akindunni Festus F. , Gillham Robert W. 
Published: August 2005

AbstractField experiments and numerical modeling showed that vertical placement of a pumping‐well screen in an appropriate location could enhance the recovery of dissolved contaminants from a distinct depth interval of an unconfined aquifer. Two single‐well contaminant recovery tests were performed for 72 hours each at Borden, Ontario in a thin, fine‐grained sand aquifer. A zone 1.5 m thick at the bottom of the aquifer was contaminated by landfill leachate. One screen was located entirely within the contaminated zone and the other had only half its length placed in the zone of contamination. In both tests, concentrations in the effluent were initially high, but asymptotically declined and approached the vertically averaged concentration of the aquifer. The decline in concentration occurred because converging flow in the vertical plane caused a reduction in the thickness of the plume near the well; that in turn decreased the ratio of contaminated to clean waters entering the well screen. The field results were simulated using SUNFLOWPT, a saturated‐unsaturated flow model with particle tracking. Predictions of the model successfully matched the observed drawdown and effluent concentration data. Propagation of simulated capture zones into the overlying uncontaminated aquifer waters are consistent with the observed declines in effluent concentrations. Two‐dimensional plan‐view modeling is unable to accurately simulate observed data at early times of pumping. In aquifers having stratified contamination, only models that incorporate vertical flow should be used to interpret or predict effluent concentrations from short‐duration tests conducted for the purpose of designing pump‐and‐treat remediation schemes. The results suggest that in some cases of long‐term cleanup, two screens that separately capture the clean and contaminated waters of the aquifer could significantly reduce the volume of water requiring treatment.
Interpretation of Prematurely Terminated Air‐Pressurized Slug Tests
Authors: Shapiro Allen M. , Greene Earl A. 
Published: August 2005

AbstractAir‐pressurized slug tests offer a means of estimating formation transmissivity and storativity without extensive downhole equipment and in situations where contact with formation fluids may pose a health concern. An air‐pressurized slug test, as discussed in this paper, consists of applying a constant pressure to the column of air in a well, monitoring the declining water level, and then releasing the air pressure and monitoring the recovering water level. If the maximum declining (or new equilibrium) water level is achieved for a constant applied air pressure, the slug‐test solution of Cooper et al. (1967) can be used to interpret the water‐level recovery data and estimate the formation properties. In low‐permeability terranes, the time required to achieve the equilibrium water level during the pressurized part of the test may be too long for practical purposes, and it may be necessary to terminate the applied air pressure prior to establishing a new equilibrium. To analyze data from such tests, a solution to the boundary‐value problem for the declining and recovering water level during an air‐pressurized slug test is developed for an arbitrary time‐dependent air pressure applied to the well. For the special case of applying a constant air pressure and then reducing it instantaneously to atmospheric pressure at a prescribed time, the general solution reduces to the superposition of the solution of Cooper et al. (1967) at two displaced times. Type curves are generated to estimate formation transmissivity and storativity from the recovering water level associated with prematurely terminated air‐pressurized slug tests. The application of the type curves is illustrated in tests conducted in wells completed in the Minnelusa and Madison aquifers near Rapid City and Spearfish, South Dakota.
Roberts Rift, Canyonlands, Utah, A Natural Hydraulic Fracture Caused by Comet or Asteroid Impact
Authors: Huntoon Peter W. , Shoemaker Eugene M. 
Published: August 2005

AbstractThe impact that created Upheaval crater in Canyonlands National Park, Utah, is invoked here as the source for energy that simultaneously caused Roberts rift. However, no temporal linkage has been proven between the impact and rifting events.Roberts rift lies between 22 and 32 km northeast of the Upheaval impact crater on a subradial trend. The fissure contains clasts that were carried as much as 1,000 m upward from Paleozoic sources into the Mesozoic section.A plausible model for both the rifting and clast movement involves incremental loading of overpressured fluid compartments in the Pennsylvanian Paradox section and attendant hydraulic fracturing of the overlying confining strata during the impact event. The clasts were proppants entrained in upward moving fluids that originated from overpressured aquifers in the Pennsylvanian section or materials eroded from the fissure walls.Alteration halos and mineralization along the fissure reveal that there was upward leakage of reducing fluids from the overpressured zones following opening of the fissure. The fissure infillings became cemented with time, thus reducing fissure permeabilities to negligible.
Evaluation of Simplified Stream‐Aquifer Depletion Models for Water Rights Administration
Authors: Sophocleous Marios , Koussis Antonis , Martin J. L. , Perkins S. P. 
Published: August 2005

AbstractWe assess the predictive accuracy of Glover's (1974) stream‐aquifer analytical solutions, which are commonly used in administering water rights, and evaluate the impact of the assumed idealizations on administrative and management decisions. To achieve these objectives, we evaluate the predictive capabilities of the Glover stream‐aquifer depletion model against the MODFLOW numerical standard, which, unlike the analytical model, can handle increasing hydrogeologic complexity. We rank‐order and quantify the relative importance of the various assumptions on which the analytical model is based, the three most important being: (1) streambed clogging as quantified by streambed‐aquifer hydraulic conductivity contrast; (2) degree of stream partial penetration; and (3) aquifer heterogeneity. These three factors relate directly to the multidimensional nature of the aquifer flow conditions. From these considerations, future efforts to reduce the uncertainty in stream depletion‐related administrative decisions should primarily address these three factors in characterizing the stream‐aquifer process. We also investigate the impact of progressively coarser model grid size on numerically estimating stream leakage and conclude that grid size effects are relatively minor. Therefore, when modeling is required, coarser model grids could be used thus minimizing the input data requirements.